DRAFT

CLIENT

DRAFT SUMMARY REPORT

Prepared by

Mr. Sebestian Roberts (Team Leader)

Mr. Tim Pegg

Mr. Sam Billing

Mr. Nick Petousis

Mr. Iain Hughes

Mr. Danny Thomas

Mr. Carl Young

Mr. Kevin Yong

Directed by

Dr. Phil Purnell

DRAFT

TABLE OF CONTENT

1.0

INTRODUCTION......................................................................................................................1

1.1 Nirex.............................................................................................................................1

1.2 Radioactive Waste.......................................................................................................1

1.3 Nirex’s Phased Disposal Concept...............................................................................2

1.4 Multi-barrier Containment............................................................................................3

1.5 Introduction of PGRC...................................................................................................4

1.5.1 Receipt Facility...................................................................................................4

1.5.2 Inlet Cell.............................................................................................................5

1.5.3 Unshielded ILW Storage Vault...........................................................................5

2.0 PROJECT OBJECTIVES....................................................................................................6

2.1 Inspection.....................................................................................................................6

2.2 Reworking....................................................................................................................6

2.3 Unworkable Packages.................................................................................................6

2.4 General Considerations...............................................................................................6

3.0 CORROSION......................................................................................................................7

3.1 ENVIROMENTS OF EXPOSURE................................................................................7

3.2 STAINLESS STEEL.....................................................................................................7

3.3 FACTORS WHICH CAUSE CORROSION..................................................................7

3.4 CORROSION RESISTANCE.......................................................................................8

3.5 VUNERABLE AREAS..................................................................................................8

3.6 TREATMENT OF MINOR CORROSION.....................................................................8

4.0 WASTE PACKAGE MONITORING....................................................................................9

4.1 Potential Damage........................................................................................................9

4.1.1 Corrosion...........................................................................................................9

4.1.2 Swelling............................................................................................................10

4.1.3Dropping...........................................................................................................10

4.1.4 Cracking...........................................................................................................10

4.2 Monitoring in Vault.....................................................................................................10

4.2.1 ‘Parking Bay’....................................................................................................10

4.2.2 Position of ‘Dummy Packages’ & ‘Sensor Packages’......................................11

4.2.3 Electronic Sensors...........................................................................................12

4.2.4 Active RFID tags..............................................................................................13

4.2.5 Dummy Packages’ & ‘Sensor Packages’.........................................................14

4.2.6 Visual Inspection..............................................................................................14

5.0 INSPECTION CELL..........................................................................................................16

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5.1 INSPECTION PROCESSES AND METHODS..........................................................16

5.2 PARAMETERS TO BE INSPECTED.........................................................................16

5.3 METHODS AND EQUIPMENT..................................................................................17

5.3.1 Visual Inspection..............................................................................................17

5.3.2 Direct Viewing..................................................................................................17

5.3.3 Indirect Viewing...............................................................................................18

5.3.4 Radiation..........................................................................................................19

5.3.5 Weight..............................................................................................................19

5.3.6 Dimensions......................................................................................................20

5.3.7 Heat Generation..............................................................................................21

5.3.8 Chloride Levels................................................................................................21

5.3.9 Advanced Methods of Testing.........................................................................21

5.4 COMPARISON BETWEEN THE VARIOUS METHODS...........................................22

5.5 LEVEL OF INSPECTION...........................................................................................22

5.5.1 SCHEME 1.......................................................................................................23

5.5.2 SCHEME 2.......................................................................................................23

5.6 COMPARISON BETWEEN THE INSPECTION SCHEMES.....................................24

6.0 INSPECTION CELL LAYOUT...........................................................................................25

7.0 OVERPACKING CELL………………………………………………………………………….26

7.1 Functional requirements of overpacking cell.............................................................26

7.2 Overpacking cell location...........................................................................................27

7.3 Overpacking, Repackaging and Reworking...............................................................30

7.4 Overpacking damaged packages..............................................................................31

7.5 Overpacking damaged waste package......................................................................32

7.5.1 Stage 1 of overpacking damaged waste package...........................................32

7.5.2 Stage 2 of overpacking damaged waste package...........................................32

7.5.3 Stage 3 of overpacking damaged waste package...........................................33

7.6 Waste package flow diagram.....................................................................................34

7.7 Grouting stage...........................................................................................................35

7.8 Lid manipulation.........................................................................................................35

7.9 Inspection of overpack waste package......................................................................36

7.10 Overpacking cell design layout................................................................................36

8.0 LOGISTICS.......................................................................................................................37

8.1 Emplacement.............................................................................................................37

8.2 Monitoring..................................................................................................................37

8.3 Package Transport.....................................................................................................38

8.4 Maintenance..............................................................................................................39

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8.5 Transfer Tunnel..........................................................................................................39

8.6 Ventilation..................................................................................................................40

8.7 Safety features of cell designs...................................................................................41

9.0 RELIABILITY AND RISK ASSESSMENT.........................................................................42

9.1 General Package in vault...........................................................................................42

9.2 Corrosion...................................................................................................................42

9.2.1 Modelling of pit initiation..................................................................................42

9.2.2 Modelling of package failure with no inspection..............................................43

9.2.3 Probability of monitoring system failing...........................................................43

9.3 Mishandling................................................................................................................43

9.3.1 Emplacement Period.......................................................................................43

9.3.2 Monitoring Period.............................................................................................44

9.4 Inspection Cell...........................................................................................................44

9.4.1 Emplacement Period.......................................................................................44

9.4.2 Monitoring Period.............................................................................................44

9.5 Operational Risks.......................................................................................................44

9.5.1 Contaminants Release....................................................................................44

9.5.2 Shielding Malfunction.......................................................................................45

9.5.3 Fire...................................................................................................................45

9.6 Overpacking Cell........................................................................................................45

10.0 CONCLUSION................................................................................................................45

11.0 GLOSSARY....................................................................................................................46

DRAFTSUMMARY REPORT

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1 INTRODUCTION

1.1 Nirex

UK Nirex Ltd is a company jointly owned by Defra and the DTI that advises nuclear site

operators on the preparation of safety case submissions to the regulators for the

conditioning and packaging of radioactive waste.[1]

1.2 Radioactive Waste

Nirex had classified wastes into 3 main categories, which are Low Level Wastes (LLW),

Intermediate Level Wastes (ILW) and High Level Wastes (HLW).

LLW Radioactive wastes which releases radiation of not more than 4 GBq/

tonnes of alpha, or 12 GBq/ tonnes of beta/gamma activity.

ILW Radioactive wastes with radioactivity levels exceeding the upper

boundaries of LLW, but do not require heat generation to be taken into

account in the design of storage or disposal facility.

HLW Radioactive waste which generates heat as a result of radioactivity.

This factor needs to be taken into account in designing storage or

disposal facilities.

Table 1: Types of radioactive waste [1]

According to Nirex’s standard specification, ILW is mainly contained in 500L drums, 3m3

boxes, 3m3 drums and 4m3 boxes. The latter designed package incorporates radiation

shielding with thick reinforced concrete walls. This project deals with the three unshielded

ILW packages. Figures 1, 2, and 3 illustrate these waste packages.

Figure 1: 4 500L drums in a stillage [1]

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Figure 2: 3m3 box [1]

Figure 3: 3m3 drum [1]

1.3 Nirex’s Phased Disposal Concept

Nirex’s Phased Disposal Concept envisages the following phases.

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The latter step would constitute deep disposal of radioactive waste, which is intended to

provide long-term isolation. Each phase will be reversible, and sufficient time will be

available to build confidence at each stage before moving to the next. [1]

1.4 Multi-barrier Containment

Figure 4: Multi-barrier containment system [1]

The multi-barrier containment system is designed so that, after closure, it does not rely on

the actions of future generations to ensure safety. The multi-barrier containment system

is comprises engineered barriers and a natural barrier. [1]

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Immobilisation and packaging of waste

Interim surface storage

Transport to a repository

Backfilling of the repository

Monitoring of packages

Emplacement in vault

Sealing and closure of the repository

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1.5 Introduction of PGRC

Figure 5: Concept drawings of the Phased Geological Repository Concept (PGRC) [1]

Phased Geological Repository Concept (PGRC) envisages emplacement of radioactive

wastes in a facility constructed at depth within suitable host geology. The concept is

assumed to be generic, rather than site specific. It is envisaged that the PGRC facility will

to be operated as a store initially, where waste would be monitored and readily

retrievable. The concept will undergo a 300 years monitoring period, where waste

packages will be monitored, reworked and overpacked if necessary. The decision of

backfilling, sealing and closure will be left to future generations. [1]

1.5.1 Receipt Facility

Repository receipt facilities would accept packages transported by road and rail. On

arrival, waste packages will be inspected, monitored and decontaminated if necessary.

[1]

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1.5.2 Inlet Cell

Figure 6: Concept drawings of the inlet cell [1]

The inlet cell has the function of removing packages from the Reusable Shielded

Transport Container (RSTC) and checking waste packages prior being transferred to the

storage vault. Empty transport containers will be monitored and decontaminated before

returning to the surface facility for reuse.

1.5.3 Unshielded ILW Storage Vault

Figure 7: Concept drawings of an unshielded ILW storage vault [1]

The storage vault will be shielded from radiation to provide safety for both employees and

the general public. The conditions within the storage vault will be monitored and

controlled, in order to prolong the life expectancy of the packages. Every activity within

the vault will be conducted remotely.

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2 PROJECT OBJECTIVES

The design brief received from Nirex was to create a concept for the Inspection and

Waste Repackaging Cells for the PGRC. Considering the aforementioned information

concerning the PGRC, and the details in the design brief, the following objectives were

drawn up.

2.1 Inspection

To formulate methods of inspection for the waste packages. The waste packages

themselves would be examined for structural integrity, corrosion, degradation of the

packaged wasteform and any change in the dimensions of the waste package.

2.2 Reworking

If a package were deemed faulty following inspection, it could be ‘reworked’. This would

be affecting slight repairs to the waste package, primarily polishing out pit corrosion and

covering with a protective coating.

2.3 Unworkable Packages

Solutions for damaged packages which are not workable were being devised. This is to

ensure packages are deemed safe to the public and could be managed by the PGRC.

2.4 General Considerations

Whilst working to provide solutions in these three areas, proven technology and simplicity

were to be used where possible. Health and safety of both the public and workers should

also be considered.

The design of the inspection cell and Overpacking cell should also be able to allow

packages to be inspected and overpacked in a satisfactory rate.

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3 CORROSION

Waste packages which will be used in the PGRC will be made out of stainless steel.

Stainless steels are iron alloys that have a minimum chromium content of 10.5% which

leads to the formation of the chromium-rich oxide on the surface. This provides the high

corrosion resistance and that is why it is named ‘stainless’ [2].

3.1 ENVIROMENTS OF EXPOSURE

The waste packages will be subjected to various environments from their manufacture to

their placement in the vaults. They will be subjected to atmospheric conditions during

their storage and they will experience alkaline environment during their manufacture and

over-packing stage. In addition, during storage, packages are expected to come in

contact with water coming from ground water flows. Therefore, the packages must be

highly resistant to atmospheric, aqueous and alkaline environments [2].

3.2 STAINLESS STEEL

The reason why stainless steel has such a high resistance to corrosion is because the

high chromium content creates a thin oxide film on exposure to air or water. This film acts

as a shield to the underlying material against further reaction with the surrounding

environment. When this film is damaged it reforms itself and therefore provides long term

protection. However, the stainless steel is vulnerable to localised corrosion when the film

breaks down in small areas. Localised corrosion usually takes the form of small pits (pit

corrosion) which penetrate perpendicularly into the metal or crevices between the mated

surfaces (crevice corrosion) [2].

3.3 FACTORS WHICH CAUSE CORROSION

The main factor which causes corrosion is the presence of aqueous chloride ions. These

ions tend to break the thin protection film and prevent it from reforming. The more

chloride ions are present the higher the risk of corrosion will be. The relationship between

the number of chloride ions and corrosion level follows an exponential relationship [3].

Another factor that causes corrosion is the, surface roughness. The more homogenous

the surface is the lower the active sites for pit initiation are. Therefore, the lower the risk

for corrosion will be [4].

Finally, sulphur tend to cause pitting corrosion. This is due to the fact that the chromium

concentration in the vicinity of the sulphate inclusions is reduced [5].

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3.4 CORROSION RESISTANCE

The type of stainless steel which will be mainly used for the container packages will be

304L and 316L. For these types of alloys there is a large amount of previously collected

data [6]. According to this data the lifetime of the packages will be as follow:

Table 2: Estimated lifetime of a package from previous data. [6]

3.5 VUNERABLE AREAS

3.6 TREATMENT OF MINOR CORROSION

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4 WASTE PACKAGE MONITORING

The purpose of monitoring waste packages in the vault is to provide a periodic

observations and measurements to determine changes in the physical condition of the

packages over time [7]. By monitoring packages in the vault, the condition of the vault

could also be predicted.

Monitoring of waste packages also had the advantage of increasing the efficiency of

waste package inspection, by identifying damaged packages before being transferred

into the inspection cell.

4.1 Potential Damage

Although the condition of the vault is being monitored and controlled, packages are still

prone to be damaged. The following are types of damages that were predicted to occur to

the packages stored in the vault.

4.1.1 Corrosion

Figure 8: A typical corrosion sensor used in gas pipes [8]

There are mainly two types of corrosion which are pit corrosion and stress corrosion.

Corrosion is difficult to be detected because the sensors only detect corrosion locally.

Pit corrosion is mainly caused when corrosive agents are being deposited in a pit surface.

Pit corrosion happens locally on the package’s surface, and corrodes the package

progressively.

Stress corrosion occurs when a material experienced both tension and corrosion attacks.

Stress corrosion could be detected by measuring strain instead.

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4.1.2 Swelling

Figure 9: A typical strain gauge mounted on the wall [9]

Swelling are mainly caused when the venting filter of the package are clogged. Building

up of gasses within the package could cause packages to swell. Swelling of packages will

be detected by a metallic strap around the package together with a strain gauge.

4.1.3 Dropping

Dropping of packages are assumed mainly due to mishandling of packages. Dropping of

packages could be detected by placing a load cell on the crane. An unpredictable

decrease in the load on the crane could indicate a drop from happening.

4.1.4 Cracking

Cracking could occur either by corrosive attack or mechanical damage. Cracking is

difficult to be detected as it occurs locally. Cracking is only feasible to be detected by 3D

mapping within the Inspection Cell.

4.2 Monitoring in Vault

Monitoring of packages is being conducted by remote electronic sensors mounted on

‘Dummy Packages’ and ‘Sensor Packages’. These packages will take measurements

periodically and signals will be transferred back to the inspection cell by active RFID tags.

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The strain gauge on the wall gives a rough estimation of the size of a strain gauge that could be adopted.

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4.2.1 ‘Parking Bay’

‘Parking Bay’ is empty space in a storage vault. Its purpose is to allow extraction of

bottom packages without having to move packages on top of a stack to the end of the

vault.

Figure 10: A drawing of a ‘Parking Bay’ in a vault

4.2.2 Position of ‘Dummy Packages’ & ‘Sensor Packages’

Figure 11: A box in a box layout [10]

The arrangement for unshielded ILW packages within the vault will be 7 stillages across

and 7 stillages in a stack. Assume 7 stillages across by 7 stillages high by 7 stillages

along the vault to be named as a block.

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Distance = 3 stillages packages apartDistance = 7 stillages

packages apart

Position of ‘Dummy Packages’

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‘Dummy Packages’ will be placed in all 8 corners of each cube, while ‘Sensor Packages’

will be placed at the centre of every face of each cube. Hence, a total of 16 ‘Dummy

Packages’ and 12 ‘Sensor Packages’ in each block.

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The following table summarises the statistics of packages in a storage vault.

Type of

Package

‘Real

Packages’

‘Sensor

Packages’

‘Dummy

Packages’

‘Parking

Bay’ (1

every 2

blocks)

Total Space

500L Drums 29464 276 304 336 30380

3m3

drums/boxes

6520 265 292 77 7154

By introducing ‘Dummy Packages’ and ‘Parking Bays’, the effective storage capacity of

the vault is only reduced by 2% for 500L drums and 5% for 3m3 packages. It is also found

that 2% of the 500L drums will be monitored directly and 9% of the 3m3 packages will be

monitored directly. It is arguably that the quality of the sampling methods is the same,

because the distances between ‘Dummy Packages’ and ‘Sensor Packages’ are the

same.

4.2.3 Electronic Sensors

Electronic sensors and active RFID tags require batteries to be replaced. It is assumed

that ‘Dummy Packages’ will have a battery life of 10 years, while ‘Sensor Packages’ will

have a battery life of 5 years.

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Figure 12: A typical ‘Sensor Package’

Electronic sensors which are attached in the ‘Sensor Packages’ include corrosion

sensors, strain gauge, humidity and thermometer. It should be noted that strain gauge will

not be equipped in ‘Dummy Packages’ because swelling is not likely to occur.

4.2.4 Active RFID tags

Figure 13: A typical active RFID tag [11]

An active RFID tag will be used to transmit signals to the receiver placed on the crane. By

performing and ‘RFID Sweep’, one could collect readings from ‘Dummy Packages’ and

‘Sensor Packages’ easily and quickly. [12]

Active RFID tag has the advantage of longer range and faster data transfer, compared to

passive RFID tag which only has a range of 3 to 4 feet.

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Corrosion Sensors

Strain Gauge on metallic strap

Humidity Sensors

Battery, active RFID tag and electronic components

DRAFTSUMMARY REPORT

4.2.5 ‘Dummy Packages’ & ‘Sensor Packages’

‘Dummy Packages’ are packages which contain inert materials. They are being

introduced for easy handling purposes and been used to obtain information of the

condition of a typical ‘Real Package’.

‘Sensor Packages’ are however ‘Real Packages’ which are equipped with electronic

sensors. These packages contain active wastes and hence require strain gauges to

measure swelling of packages.

4.2.6 Visual Inspection

Figure 14: A typical radiation resistant robotic crawler [13]

Visual inspection is only feasible to be carried out by remote CCTVs. Visual inspection

will be the main monitoring method for packages within the vault. It has the advantage of

being reliable, cheap, fast and provide and independent judgement from electronic

sensors.

Figure 15: Corrosion in welded regions [14]

In order to aid visual inspection of corrosion, welded metal coupons will be attached in

every stillages or 3m3 packages. Metal coupons are two metals of the same material

welded together and being attached to the packages. Since welded regions are most

susceptible to be corroded, by just viewing these coupons, one could justify if other

welded regions are corroded.

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The following illustrates the sequence of visual inspection to be carried out.

4.3 Waste Package Monitoring Sequence

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Filter (whether it’s corroded or clogged)

Corrosion in welded areas

Other visible areas

Check for significant deformation

Welded Coupon

RFID

Sweep

Extract + transfer to Inspection Cell

Problem package assessed with mobile CCTV

4 real packages randomly selected. These are taken to Inspection Cell

Real packages randomly selected. These are inspected by mobile CCTV.

All packages confirmed safe.

Problem package(s) identified

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5 INSPECTION CELL

5.1 INSPECTION PROCESSES AND METHODS

5.2 PARAMETERS TO BE INSPECTED

The inspection of a container will consist of two parts.

Part 1: inspection for contamination and structural integrity of the package.

Part 2: inspection of degradation and condition of waste stream.

For both parts of inspection individual data should be saved for each package. This will

give information about the behaviour and degradation of the package. In addition, it will

help to identify packages which show unexpected and dangerous behaviour for more

frequent future inspection

The 1st part of inspection will primarily not include measurement of any parameters since

direct and indirect viewing of the package will be available. Contamination on the

package will be in form of corrosion which will probably occur in the corrosion susceptible

area. [See corrosion technical report]

Inspection for structural integrity will consist of check for swelling, cracks or deformation

of the package which could be caused by dropping or chemical reactions within the

package’s waste stream.

The 2nd part of inspection requires more indirect inspection methods and measurement of

various parameters will be necessary. The parameters that can be measured to indicate

degradation and condition of the waste stream are:

Radiation of the package

Weight

Dimensions

Heat generation

Chloride levels

For more specific information on the density change and degradation of the package

more advanced methods of testing should be provided. These methods of testing should

provide:

Image of the waste stream within the package.

Identification and quantification of the radionuclide within the waste stream.

Check on the fissile content of the waste packages.

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5.3 METHODS AND EQUIPMENT

This section presents and discusses various methods and equipment which can be used

to measure each of the parameters introduced in section 1.2.

5.3.1 Visual Inspection

Visual Inspection may be direct, that is, looking at the package through an oil filled

shielded window, or indirect, using cameras. It has been decided that this direct method,

and a further indirect technique will be used. The latter will use a through-wall Endoscope

with built in camera.

Please refer to the Technical Report ‘Visual Inspection and 3D Mapping’ for more details.

Furthermore, ‘Inspection Processes and Methods ’ considers all the methods of

inspection and discusses the preferred processes for an overall inspection routine.

Visual inspection is one of the inspection methods proposed for use in the Inspection

Cell. The pros and cons of the different methods are discussed below.

Visual inspection could be conducted using a variety of methods:

‘Direct Viewing’ - workers looking at packages through shielded windows

‘Indirect Viewing’ – crawler-cam – cameras mounted on robotic crawlers that

move within the ‘hot’ area

‘Indirect Viewing’ with fixed CCTV within the ‘hot’ area

‘Indirect Viewing’ with an through-wall Endoscope

‘Indirect Viewing’ with Master/slave Manipulator held CCTV

5.3.2 Direct Viewing

Workers would view a package through an oil filled shielded window of thickness

approximately 1.2m [15]. needs to be referenced !!!!!!!!!!! Direct Viewing is carried out

by humans so only the maintenance of the window would be required. This would include

cleaning, a monthly inspection of oil reservoir levels and annual light transmissibility

checks. It is felt that a strong point of direct viewing is that independent inspectors would

have the chance to physically see the package which would enhance public confidence in

the PGRC. However, this method would not provide a record with which future

inspections could be compared. Thus, the experience of the viewer would be a critical

factor in the accuracy of this method.

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5.3.3 Indirect Viewing

Four methods of indirect viewing are put forward. The two stationary techniques would

use either fixed CCTV cameras located in the ‘hot’ area, or an Endoscope with built in

camera that would be routed from the ‘cold’ to ‘hot’ side through the Inspection Cell wall.

The CCTV cameras are cheaper and can have built in lighting [16]. The more expensive

Endoscope would need external lighting but its internal mechanisms and camera are

always ‘cold’ side. This ensures ease of maintenance as ‘hot’ side equipment would

need to be maintained in the ‘hot’ area using the Master/Slave Manipulators, or, the

equipment would need decontaminating before being repaired/replaced in a ‘cold’

environment.

The two further options for indirect viewing are ‘Crawler-Cams’ and ‘Master/Slave

Manipulator held CCTV’. Crawler-Cams are cameras mounted on radio controlled robotic

crawlers that move around the ‘hot’ cell, sending images to a remote monitor.

Master/Slave Manipulators are mechanical arms that reach into the ‘hot’ area. Workers

on the ‘cold’ side will operate these MSMs. They are already used with great success at

the current waste retrieval facility at Nirex UK, although it is not known whether MSMs

have been used to hold cameras for inspecting a package before.

Through-wall Endoscopes are a proven technology and combined with their

straightforward maintenance make a sensible choice for the indirect Visual Inspection

method.

Figure 16: Schematic of Endoscope [17]

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5.3.4 Radiation

Measuring radiation is a relatively straight forward simple process. There is a wide variety

of radiation sensors available in the market. Some radiation sensors are designed and

manufactured to produce data corresponding to radioactive materials therefore a number

of different radiation sensors may be used to measure radiation according to package’s

content. [18]

5.3.5 Weight

The weight of package is also a simple process since it will only consist of a scale of high

accuracy. However, the accuracy level must be very high since it will measure the water

loss from the package surface. Assuming that an average 3m2 box will hold up to 100

grams of water then a reasonable accuracy level would be to measure to the nearest

gram (see Appendix calculations).

The weighting of the packages can either be carried out on the crane during

transportation or on the rump where the package will be place for visual inspection.

Figure 17: Position of the weight scale in the Inspection Cell.

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Figure 18: Crane with adjacent weight scale.

5.3.6 Dimensions

Dimensions of the packages can either be measured directly or with the use of more

advanced methods such as three dimensional mapping. High accuracy tapes can be

used to measure the height of the package and adjustable rings to measure the diameter.

This procedure can be carried out on the visual inspection ramp within twenty minutes but

will provide only a limited amount of accuracy.

Three dimensional mapping consist laser scanning which uses the time of flight to record

direct distance. This results in producing a high accuracy image of the scanned package

within a period of seconds. [19] This method can also be carried out on the visual

inspection ramp.

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Figure 19: Three Dimensional Mapping in the Inspection Cell.

5.3.7 Heat Generation

Heat generation can be measured in many ways. The most popular ways are using

computer imaging, calorimeters and temperature gauges. [20] Heat generation is an easy

to perform procedure and it will take only a few seconds.

5.3.8 Chloride Levels

Explain briefly the process.

5.3.9 Advanced Methods of Testing

Advanced methods of testing include the use of Real time Radiography, High resolution

segment gamma scanning and Passive Neutron Multiplicity Counting. Real Time

Radiography is an advanced method of X-Ray which can produce images of the waste

stream of the package. [21]High Resolution Segment Gamma will provide information on

the amount of active radionuclide within the waste stream and its elevation within the

package. In addition, it can detect density variations within the waste stream. Passive

Neutron Multiplicity Counting can measure the fissile content within the waste stream for

both encapsulated and un-capsulated waste. [3]

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5.4 COMPARISON BETWEEN THE VARIOUS METHODS

Radiation measurement is one of the main parameters that will indicate straight forward

the condition of the waste stream. It is therefore suggested to be included as an

inspection process since it is easy to perform and it is not time consuming.

Weighting of the packages is also an easy and cheap method to measure the water

content change but it will be fairly difficult to obtain accurate results. Frequent calibrations

of the weight scale will be required to obtain reliable results therefore it is decided to

place the weighting scale onto the crane. In this way access for calibration will be easy

and weighting will be included as an inspection process.

Measuring the dimensions of the package is considered as an essential process since it

will indicate whether both the risk for corrosion and will provide information about the

state of the content of the package. Direct measuring with the use of an adjustable ring

and high accuracy tapes will be cheap but will be neither easy to perform nor accurate. It

is therefore decided to use the three dimensional mapping method which provides

accuracy to the nearest millimetre [22].

Chloride level is an important parameter in identifying the risk for corrosion. However,

chloride levels are expected to be controlled and sensors will be provided inside the

vaults. Therefore, it is considered non essential to have a chloride test in the inspection

cell.

For the more advanced methods of testing it is suggested to use only the High Resolution

Segment Gamma. High Resolution Segment Gamma provides higher accuracy than the

Passive Neutron Multiplicity Counting and provides information both on the density

variation and the number of active radionuclide. Real Time Radiography and Passive

Neutron Multiplicity Counting are also useful techniques but the opportunity to over-pack

the defective packages limits the amount of tests that need to be performed

5.5 LEVEL OF INSPECTION

The inspection level of the packages can be carried out in different levels since some of

the packages will be more suspicious due to their content or history record. Two possible

schemes are considered.

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5.5.1 SCHEME 1

5.5.2 SCHEME 2

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Flow Chart of package for Scheme 1

Inspection Cell

Level 1:

Documentation validationWeightVisual Inspection

Level 2:

RadiationHeat generation3D MappingHigh ResolutionSegment Gamma

Level 3

Destructive test

Vault

Duration: 90 min

Duration: 65 min.

Flow chart for Scheme 2

Inspection Cell

Level 1:

Documentation validationWeightVisual Inspection

Level 2:

RadiationHeat generation3D Mapping

Level 3

High ResolutionSegment Gamma

Vault

Duration: 5 minDuration: 90 min

Duration: 60 min

DRAFTSUMMARY REPORT

5.6 COMPARISON BETWEEN THE INSPECTION SCHEMES

As it can be seen from the flow diagrams the two schemes will take the same time to

perform a full inspection for a package. However, for the main inspection part (Level 1

+Level 2) Scheme 1 requires a total of 135 minutes while Scheme 2 requires only 95

minutes. This is because for Scheme 2 no High Resolution Segment Gamma testing is

included which is one of the most time consuming procedures. In this way less

information and accuracy is achieved for the main inspection part but more packages can

be inspected in the same amount of time. This is preferable because accurate inspection

will be required only to some certain packages and the main aim of the inspection cell is

to investigate whether things go wrong rather than why

In addition, Scheme 2 is preferable because no destructive test is included. Destructive

test would be of use if detailed information about the package degradation was required.

The fact that there is an over packing cell, diminishes the need to understand deeply the

degradation of the packages

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6 INSPECTION CELL LAYOUT

7 [WORK IN PROGRESS]

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8 OVERPACKING CELL

8.1 Functional requirements of overpacking cell

The primary function of the overpacking cell is to overpack packages that are deemed

unsafe for handling, recovery for inspection, and storage within the PGRC. The damaged

waste packages will come directly from the inspection cell, which through rigorous

inspection techniques has determined the packages to require overpacked. The waste

packages will remain radioactive and hazardous for possibly hundreds and thousands of

years. It is therefore necessary that appropriate measures are put in place for long term

management of these waste packages [23].

There is the potential that the waste packages might not conform to the Nirex waste

package standards [24]. As a consequence small numbers may not adhere to these

specifications either through manufacturing errors, dropping of packages, corrosion, and

degradation of package waste form. If the problems are too extensive to be reworked and

rectified in the inspection cell they will be sent to the overpacking cell to be overpacked.

Multiple corrosion locations to critical parts of the package (Reference waste monitoring

technical report) could have made reworking of the package an unviable option.

Packages could have incurred damage that was deemed unsafe during handling resulting

in overpacking being the only course of action. The package, depending on the size and

nature of the drop, may have undergone deformation that is deemed unsafe to store.

Once the packages are deemed safe for transportation and storage they will be returned

to their respective vaults. Figure 20 show the movement of packages around PGRC.

Figure 20: Movement of damaged waste packages around the PGRC

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8.2 Overpacking cell location

Many locations were considered for the overpacking cell (see overpacking cell technical

report for more details). The locations included:

An overpacking cell in each vault

An overpacking cell in every other vault

An centrally located overpacking cell

An overpacking cell at the end of each block of vaults

These locations were scored in a decision matrix against a set of criteria. This set of

criteria comprised of;

Cost – this includes the operational, maintenance, and the initial capital costs

Logistics – this includes how quickly the damaged waste package can be

transferred to the overpacking cell and how quickly the possible congestion this

may cause

Risk – this includes the associated risk of handling the damaged waste package

through to the overpacking cell

Flexibility of design – This includes the ability to upgrade the overpacking cell in

the future and the possibility of adding additional cell if the situation requires

The afore mentioned criteria were marked against the following scale;

The decision matrix is as follows;

Locations Logistics Cost Risk Flexibility Total

Each vault 1 4 4 1 10

Every other vault 2 3 3 1 9

Central 4 2 1 4 11

End of transfer

tunnel

3 2 1 3 9

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It was decided that including an overpacking cell in the vaults would cause issues with

the lack of space and the costs involved. It was however decided that a central

overpacking cell will be the preferred location that will service all the overpacking needs

for the PGRC. Figure 21 shows a more detailed location of the overpacking cell drawn on

a schematic plan drawing of the PGRC [25].

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Figure 21: Plan view of the PGRC

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8.3 Overpacking, Repackaging and Reworking

As noted before, there is the potential that waste packages may need remedial action to

render them safe for handling, recovery for inspection, and storage within the PGRC.

There are certain factors that could attribute to the packages being deemed unsafe.

These factors are [26];

Packages not manufactured with the waste product specification

Inappropriate handling resulting in the package becoming damaged

Certain package components may degrade

Storage conditions may result in package corrosion

All of these deleterious factors could result in remedial action taking place to restore the

package to safe limits. The remedial action taken not only depends on the factors above

but additional factors. The benefits of the remediation process need to be weighed up

against the environmental impact caused, and the associated risks and costs. The three

ways considered as remedial actions are;

Reworking

Repackaging

Overpacking

The first level of action to restore the package to safe limits is by reworking the package.

This will be in the case of minor corrosion and aliments that are able to be rectified within

a 6 hour period in the inspection cell.

If reworking can not make the package safe then another course of action will need to be

undertaken to ensure the package integrity. Repackaging the waste package involves

taking the encapsulated waste out of its damaged package and placing it in new waste

package. This would be a difficult and messy process to undertake remotely and will still

require the damaged package to be disposed. This process is not deemed to be a

practical measure within the PGRC. This method will therefore not be used.

Overpacking of the damaged package is a process in which the damaged waste package

is placed inside a larger waste package and encapsulated in cement. This process is

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relatively simple and quick and leaves no mess behind. The damaged container is fully

immobilised in cement and the new package can be transported safely and stored back in

its respective vault. The only disadvantage with this process is the fact the packages will

be larger than they originally were and may be problematic to store within the vault.

8.4 Overpacking damaged packages

The Idea behind the overpacking cell is to encapsulate the damaged package in a larger

package to give sufficient protection and to allow the damaged package to be

manipulated. The package will be encapsulated in cementitious grout.

The packages will be overpacked according to their size;

The larger package will allow a 150mm envelope around the package to allow for a

suitable grout encapsulation layer. Due to this encapsulation layer the overpack

packages will be larger that the standard Nirex waste packages. The new package

dimensions are as follows;

Waste

containerExternal dimensions (m)

Overpack dimensions

(m)

3m3 Box1.72 x 1.72 plan x 1.225

high

2.02 x 2.02 plan x 1.525

high

3m3 Drum 1.72 dia x 1.225 high 2.02 dia x 1.525 high

8.5 Overpacking damaged waste package

8.5.1 Stage 1 of overpacking damaged waste package

The required package will then need to be retrieved from the storage room and be

positioned ready for the damaged package to be placed inside. In order for there to be a

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Damaged package

3m3 Box 3m3 Drum

Overpacked package

3m3 Box + 150mm Envelope 3m3 Drum + 150mm Envelope

Damaged package

5oo litres drum x 2

Overpacked package

3m3 Box

Figure 22: Overpacking the damaged packages

DRAFTSUMMARY REPORT

150mm grout cover to the bottom, a pre-cast grout unit will first need to be placed on the

bottom of the new package, with the old package then situated on top. This will then allow

sufficient cover to the bottom of the package to the required grout envelope of 150mm.

Figure 23 shows a cross section of the overpack waste package with the pre-cast grout

unit in place.

8.5.2 Stage 2 of overpacking damaged waste package

The next stage is for the damaged package to be placed inside the overpack. For the 500

litre package two damaged packages will be required for the overpack. With the

package(s) in place it is now possible for the encapsulation grout to be pumped into the

overpack waste package. The package will be vibrated as the grout is pumped into the

overpack waste package to ensure the grout is compacted. With the encapsulation

process complete the overpack waste package is left to set of a period of 24 hours.

Figure 24 illustrates the cross-section of the overpack waste package with grout

encapsulent.

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Figure 23: Cross-section of overpack waste package with pre-cast grout unit

Figure 24: Cross-section of overpack waste package with grout encapsulent

DRAFTSUMMARY REPORT

8.5.3 Stage 3 of overpacking damaged waste package

After the 24 hour period has elapsed the package is now in the position to be bolted up

and sent to be inspected. All the lids will be bolted rather than welded. Figure 25

illustrates the finished overpack process for a 3m3 box waste package.

The overpack waste package will comply with Nirex’s waste package specification and

will be manipulated in the same way as the other waste packages. The overpack waste

packages will be heavier than the original packages due to the additional weight caused

by the encapsulent material and the overpack container.

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Figure 25: Overpacking of 3m3 box package

DRAFTSUMMARY REPORT

8.6 Waste package flow diagram

The flow of the damaged waste packages through the overpacking cell is illustrated by

the flow diagram below.

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Package arrives from inspection cell & placed in buffer store

Sort which package is required for overpack

New package retrieved from storage and placed into position

Cementitious grout mixed and prepared ready to be pumped

New package filled with pre-cast units and damaged package placed on top

Grout pumped into the package and vibrated

Curing takes place to allow the concrete to set and develop early strength

The drum is then lidded and bolted shut

Package is inspected to ensure overpack is satisfactory

DRAFTSUMMARY REPORT

9

9.1 Grouting stage

The encapsulation material must be able to render the radioactive waste package as

passively safe and not affect the performance of other barriers to radionuclide

contamination. Cement based encapsulent materials are easily and quickly formed and

can be designed to resist the expected conditions of intermediate level waste (ILW) forms

[27]. The encapsulent material will be OPC (ordinary Portland cement) based and will

contain cement replacement materials (used to substitute some of the OPC).

To achieve acceptability of the quality of the grout, the following properties are required of

the grout [28];

Sufficient fluidity for up to 2.5 hours from mixing to enable infilling of package

Capable of being pumped and vibrated without segregation

Controlled heat generation during hydration to ensure product temperatures are

within acceptable limits

Setting to occur within 24 hours

9.2 Lid manipulation

There is a need for the packages to be sealed shut after the damaged packages have

been encapsulated in the overpack waste package. There are two possible way in which

this could be achieved;

Welding the lid shut

Bolting the lid shut

It has been decided that the lid will be bolted shut. Welding could present a fire hazard.

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New identification marks are applied to the package and 3-D mapping of package

Return to respective vault location via transfer tunnel

DRAFTSUMMARY REPORT

9.3 Inspection of overpack waste package

After the overpack waste package has been bolted shut it will come to the inspection

process. This will ensure that the package meets the generic waste package specification

and can be safely transported and stored within its respective vault.

New identification marks are applied to the package at this stage. This will act as the

unique identification mark that will document the history of this package.

In keeping with the process of 3-D mapping of all the packages within the PGRC the new

overpack waste package will undergo this process. This scan will act as the reference

scan of the package and further scans will be compared to the dimensions obtained here

(Waste monitoring technical report).

9.4 Overpacking cell design layout

Will include the final design layout with explanations.

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10 LOGISTICS

This document demonstrates the logistics of the integration of inspection cell and

overpacking cell into the PGRC.

Package traffic throughout the whole system is illustrated, and the logistics are broken

down into two key phases. Phase 1 is the emplacement period during which packages

are located in the vaults. Phase 2 is the monitoring period in which the packages are

monitored and cyclic inspection processes are performed.

10.1 Emplacement

Packages initially enter the repository through the inlet cell. Here the package is prepared

for storage in the vault. It is between here and the vault that the first stage of inspection is

performed. The package will be transferred into its designated vault via the transfer

tunnel, however before emplacement it will be transferred from the transfer tunnel to the

inspection cell assigned to that vault via the emplacement crane. Here the package will

be examined, and data of that particular package will be stored for future inspection

comparison (see …). The package will then be transferred into the vault for long term

storage and further monitoring.

Due to the process in which the vaults are filled (one at a time), each inspection cell must

have the capability to deal with 16 packages per day in the case of 4 stillages, or 13

packages per day in the case of 3 stillages and one larger container (it is assumed a

larger container will present greater handling/inspection difficulties) during the

emplacement phase.

During this emplacement phase the inspection cell is unlikely to be used to its full

capabilities (reworking etc). Furthermore the reworking element is likely only to be used in

the case of dropped packages.

10.2 Monitoring

During its time in storage the package will undergo further inspection. This will be carried

out due to scheduled inspection or requested inspection which can arise from vault

monitoring or external party demands. The package will be transferred to the inspection

cell via the emplacement crane. The package is then inspected for defects; if defects are

present the package will require either minor reworking (performed in the inspection cell)

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or transfer to the repacking cell. If the defects are easily reparable reworking will be

performed in the inspection cell, the package will then be re-inspected and transferred

back to the vault via the emplacement crane. If the defect is too severe for the rework

capabilities of the inspection cell, it will be transferred to the repacking cell via the

emplacement crane and the transfer tunnel. Once the package is repaired or over-packed

it is returned to the vault via the transfer tunnel and the emplacement crane.

The inspection selection will be a scheduled, cyclic process where the first into the vault

is first inspected. This however is open to review as it is suggested ‘higher threat’

containers should be inspected more frequently.

Figure 26: Flow of packages

10.3 Package Transport

The role of proven technology in the designs of the transport systems is highlighted, with

emphasis on using existing operational designs. Improvements to the transfer tunnel

design are demonstrated to cope with the increased package flow. Existing proven

technology designs will be used for all cranes in the repository. In the vault the overhead

crane has the facility to lift stillages, 3m3 boxes and 3m3 drums. Accurate crane

positioning is of high importance. This is achieved using high precision crane winding and

traversing carriage along with an optical encoding system.

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vault from inlet

vault from inspection

vault from repacking

repacking from inspection

inspection from vault

DRAFTSUMMARY REPORT

Figure 27: Overhead crane at Sellafield

10.4 Maintenance

Maintenance procedures and frequency for cells and transfer tunnel is considered with

reference to existing Nirex specifications. Maintenance of the following areas will be

required throughout the life of the repository;

- Vaults

- Transfer tunnel

- Inspection cell

- Overpacking cell

Nirex reference case states that vaults will need to be refurbished every 100 years. This

value is used as a rough guide for cell maintenance.

10.5 Transfer Tunnel

The transfer tunnel cannot be replaced without significant construction in all areas;

therefore it is important it is maintained frequently. The current concept design

incorporates two transfer tunnels.

Between transfer tunnels 1 and 2 there is a shield wall. The tunnels are also separately

shielded from the inlet cell and repacking cell. This allows an individual tunnel, or section

of tunnel to be maintained whilst other sections remain in use. Transfer tunnel will be

used most frequently as it is the primary transfer route for packages travelling to the

vaults from the inlet cell. In the case of maintenance of this tunnel, transfer tunnel 2,

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which is primarily used for transport of defected packages to the repacking cell, will be

used for inlet – vault transfer.

Figure 28: Transfer tunnel bogie at Sellafiend

10.6 Ventilation

Integration of the inspection cell and overpacking cell with this system is fairly complex.

Both cells have facilities involving the use of particulates which could contaminate waste

packages, causing defects. Therefore airflow from these cells should not meet other flows

before the return side, and in the case of the vaults, after the outlet. The inspection cell is

located at the front of each vault; this proves difficult to integrate from a view to optimising

ventilation, therefore it is proposed the inspection cells require a separate ventilation

outlet which bypasses the vault and rejoins the airflow at the end of the vault. This would

be very simple to engineer; ventilation pipes along the vault wall would suffice.

The overpacking cell is located adjacent to the inlet cell. This is very close to the

construction return therefore it is suggested the overpacking return should feed into the

construction return before leaving the repository.

In both cells pressure differentials would be maintained to ensure that any air transfer

was from the inactive to active areas (N/079)

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10.7 Safety features of cell designs

Safety features specific to the inspection cell / repacking cell design include;

- Transfer tunnel running through mid section of vault minimising aggressive

features and dropping distances.

- Ventilation systems with pressure differentials to prevent personnel exposure or

vault contamination.

- Use of proven technology in both cells.

1 N/074: Generic Repository Studies: The Nirex Phased Disposal Concept, July 2003

2 Nirex report N/110, “Corrosion Resistance of Stainless Steel Radioactive Waste Packages”, March 2004

3 Henshal, Modelling Pitting Degradation of Corrosion Resistant Alloys (1996)

4 Z. Szklarska-Smialowska, Pitting Corrosion of Metals, NACE, 1986

5 M.P. Ryan, D.E. Williams, R.J. Chater, B.M. Hutton and D.S. McPhail,”Why

Stainless Steel Corrodes”, Nature 415, 770, 2002

6 “Options for Monitoring During Phased Development of a Repository for Radioactive Waste”, Contractor Report to United Kingdom Nirex Limited, June 2002.www.nirex.co.uk Access date: 09/02/07

7 WPS/640: Guidance on monitoring waste packages during storage, September 2005

12 RFID Journal at www.rfidjournal.com/article/articleview/208#Anchor-33869, January 2007

15 What is this reference ???????????

16 Personal correspondence with Peter Gregory. IST Corp. (March 2007).

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11 RELIABILITY AND RISK ASSESSMENT

11.1 General Package in vault

Whilst in vault storage the package is subjected to certain risks which are detrimental to

package life. These risks include mishandling and corrosion (localised and uniform).

These risks are minimised by good operating procedures to minimise mechanical

damage, and a monitoring and inspection system to minimise corrosive defects. There is

the possibility of risks being raised if systematic monitoring failure occurs leading to

missed inspection, or if the monitoring system goes offline.

11.2 Corrosion

Package corrosion given no inspection is to be modelled. The mean time to package

failure is 200years [29] under poor conditions (high levels of airborne salts). This value will

18 “Radiation Detectors”, Electronics Manufactures Directoryhttp://www.electronics-manufacturers.com/Safety_and_surveillance_electronics/Radiation_detectors/

Access date: 15/03/07

19 “3D Laser Mapping Technology”, Fujikura Europe Ltdhttp://www.fujikura.co.uk/pdf/spec%20-%203D%20LASER%20MAPPING%20TECHNOLOGY_A4_APRIL06%20_2_.pdf

Access date: 15/03/07

20 “Options for Monitoring During Phased Development of a Repository for Radioactive Waste”, Contractor Report to United Kingdom Nirex Limited, June 2002.www.nirex.co.uk Access date: 09/02/07

21 “Real Time Radiography”, BNFLhttp://www.bilsolutions.co.uk/products_real_time_radiography.php

Access date: 12/02/07

22 “Optical Shape Measurement With Structured light”, Skothei Qystein, March 2006http://www.sintef.no/upload/IKT/OpticalMeasurementSystems/Fact%20sheets/Structured_Light_Factsheet.pdf

Access date: 12/02/07

23 Nirex technical note, Summary note for CoRWN on repackaging of waste, number: 484085, September 2005, pg 2

24 Nirex report N/104, Generic waste package specification: volume 1 – specification, June 2005

25 Nirex Report N/077 – Generic Repository Studies, Generic Repository Design – Volumes 1 & 2

26 Nirex technical note, Summary note for CoRWN on repackaging of waste, number: 484085, September 2005, pg 9

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be taken as a reference worst case scenario for modelling purposes. It should be noted

that under controlled environmental conditions as would be present in the repository,

perforation due to pitting would not occur for some 2500 years.

11.2.1 Modelling of pit initiation

Experimental research has shown that the instigation of corrosion pits is a stochastic

process. Shibata and Takeyamad were the first to show that the critical potential

necessary to induce pitting and the “induction” time elapsed before pits become

observable are both statistically distributed quantities.

For example, the graph below presents their data showing the distribution of induction

times for 72 ostensibly identical Type 304 stainless steel specimens subjected to identical

conditions. The data exhibit a wide distribution of induction times, suggesting that pit

initiation occurs stochastically [30].

Graph 1: Distribution of induction time

Therefore pit initiation cannot be accurately predicted as it is a random process; however

the distribution, over time, follows a predictable pattern.

27 Nirex report N/034, why a cementitious repository, 2001, cited in Nirex technical note, Summary note for CoRWN on repackaging of waste, number: 484085, September 2005, pg 6

28 Fairhall & Palmer, The encapsulation of Magnox swarf in cement in the United Kingdom, Cement & Concrete Research, Volume 22, Pg 293-298, 1992

30 Henshal Modelling Pitting Degradation of Corrosion Resistant Alloys (1996)

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11.2.2 Modelling of package failure with no inspection

- exponential distribution

- lognormal distribution

- Weibull distribution

Question to Phil: unsure which distribution to use

11.2.3 Probability of monitoring system failing

Unsure if modelling is possible, numerous variables – RFID, power, component, log

computer failure.

Any suggestions Phil??

11.3 Mishandling

General package mishandling frequency in the vault is estimated by Nirex [31];

Reference case - 6.8 dropped packages per year

11.3.1 Emplacement Period

With the integrated design of the inspection cell, the emplacement crane will make twice

as many transportations during the emplacement; hence the risk is effectively doubled.

13.6 dropped packages per year

11.3.2 Monitoring Period

During the monitoring and inspection period all vaults will be operational and movement

of packages will be at a rate of 11 per day (1 per day, 11 vaults). This gives a higher

probability of package damage due to increased risk.

19.2 dropped packages per year

The rate of mishandling is significantly increased due to inspection procedures. This rate,

however, still remains very low. Mechanical damage to packages will be sufficiently

covered by overpacking facilities.

11.4 Inspection Cell

Handling procedures within the inspection cell are comparable with that of the inlet cell.

The Nirex reference case for the inlet cell is;

Reference case - 1.5 dropped packages per year

31 N/079 Part 2: Generic Repository Studies, Generic Operational Safety Assessment Part 2: Fault and Hazard Schedule, July 2003

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11.4.1 Emplacement Period

During the emplacement period the inspection cell will handle 16 * 500 litre drums (4

units) per day in a worst case scenario;

6.2 dropped packages (drums) per year

11.4.2 Monitoring Period

During the monitoring period each inspection cell will handle 4 * 500 litre drums (1 unit)

per day in a worst case scenario;

16.9 dropped packages (drums) per year

Dropped packages in the inspection cell are not deemed to be as much of a problem as

in the vault due to reduced dropping distances. Package damage will be minimal under

normal circumstances and package retrieval will be conducted remotely using master

slave manipulators.

11.5 Operational Risks

11.5.1 Contaminants Release

Many of the processes in the inspection cell create particulates which are potentially

harmful to the packages within the vault. For a release of contaminants into the vault one

of the following would be necessary;

- damage to the ventilation system

- damage to the airlock door

To be concluded with probabilistic analysis.

11.5.2 Shielding Malfunction

The shielding between the inspection cell and personnel area is essential to operations.

Inadequate shielding could be as a result of shield damage due to processes within the

inspection cell or the personnel area.

To be concluded with probabilistic analysis.

11.5.3 Fire

The probability of a fire, hence thermal damage will be of higher probability than that of

the vault due to the type of operations, and close proximity of operations.

To be concluded with probabilistic analysis.

11.6 Overpacking Cell

The frequency of use for the overpacking cell is far lower than the inspection cell or the

vault, therefore rate of dropped packages in the overpacking cell is considered to be

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negligible. As is the case with the inspection cell dropped packages will present low risk

due to reduced lifting heights in comparison to the vault. Operational risks will be identical

to that of the inspection cell, with the addition of risk of grout system malfunction – to be

concluded with probabilistic analysis

12 CONCLUSION

It was concluded that the inspection cells and an overpacking cell is feasible to be integrated with the existing PGRC design. The inspection cells and Overpacking cell also proved to operate in an adequate capacity where unshielded ILW waste packages are confident to be safe.

Waste package monitoring in the vault is also feasible to be conducted, and is able to provide a satisfactory sampling result, with the usage of electronic equipments mounted on ‘Dummy Packages’ and ‘Sensor Packages’.

Visual inspection is the prime inspection method, and is being used in monitoring of packages, inspecting packages and also during Overpacking processes.

Overpacking damaged packages is concluded to be easier and more robust compared to repackaging packages.

Health and safety of both workers and the public were also ensured to be safe, by providing adequate shielding and remote handling of packages.

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GLOSSARY

500L drum Unshielded cylindrical waste package which has a volume of 500L.

Normally contains ILW.

3m3 drum Unshielded cylindrical waste package which has a volume of 3m3.

Normally contains immobilised radioactive ILW sludge.

3m3 box Unshielded waste package which has a volume of 3m3. Normally contains

solid radioactive ILW waste.

3D Mapping A Non Destructive Testing method which emits waves and receives the

reflected waves. Such method could detect surface cracks and dimensions

of an object

Backfilling Filling the PGRC with concrete. This is envisaged to occur at the end

of the 300 year monitoring period.

Concrete A cementitious based composite which consists of cement, water, coarse

aggregate and fine aggregate.

Cold An environment that contains levels of radiation that are suitable for

humans to work in.

Container An empty stainless steel package which has no grout or any waste forms

in it.

Decontamination The complete or partial removal of contamination by a deliberate

physical, chemical or biological process.

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Direct Workers visually inspecting a package with the naked eye. Primarily

Viewing through an oil filled shielded window which provides protection from

radiation.

DPI Dye Penetrant Inspection method is a Non Destructive Testing method. By

allowing dye to seep into cracks, and cleaning the surface, one could

identify the presence of a crack easily.

Encapsulation Immobilisation of solid waste by mixing it with a matrix material

within a container in order to produce a more stable waste form.

GPR Ground Penetrating Radar is a Non Destructive Testing method. By

transmitting radio wave and receiving it, one could determine the

attenuation of concrete. It is being used to monitor the curing of concrete

structures.

Grab Three armed lifting crane to lift/move a 500L drum.

Grout A cementitious based composite used to immobilise waste. It mainly

consists of cement, water and fine aggregate. This will be used in the

Overpacking procedure.

Half-life The time required for half the number of nuclei of a specific radionuclide to

undergo radioactive decay.

Hot An environment that contains levels of radiation that are too high for

humans to work in.

Harwell Current (February 2007) home of Nirex, UK where ILW stored just below

surface’ is being removed, inspected, and stored. This waste will be

transferred to the PGRC when built.

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Indirect Visual inspection of a package using indirect means such as cameras.

Viewing

ILW Intermediate Level Waste; wastes with radioactivity levels exceeding the

upper boundaries for Low Level Waste but which do not require heating to

be taken into account in the design of storage or disposal.

Immobilisation Conversion of waste into a less mobile or non-mobile form by, for

example grouting or encapsulating.

Magnox Gas cooled fission reactor using un-enriched uranium as fuel, with

magnesium alloy as cladding, the reactor type used in the UK’s first

generation nuclear power plants.

Master/Slave Tools currently used to inspect and rework waste drums that are being

Manipulator extracted from ‘just below surface’ storage at Harwell.

Nirex UK Nirex Ltd. A company jointly owned by DEFRA and the DTI that

advises nuclear site operators on the preparation of safety case

submissions to the regulator for the conditioning and packaging of

radioactive waste.

Oil filled Allows direct viewing into hot areas of the Inspection and

shielded Overpacking Cells whilst providing protection from the dangerously

window high levels of radiation within the cells.

Overpack- A process which encapsulates damaged packages in a larger package.

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PGRC Phased Geological Repository Concept is the concept facility which will

manage radioactive waste in the long term, which includes storage,

monitoring and backfilling in a phased geological disposal method.

Radionuclide A nucleus of an atom that possesses properties of spontaneous

disintegration. Nuclei are distinguished by their mass and atomic number.

Reworking Minor repair work on damaged packages and to prevent further minimise

further degradation from occurring.

Sievert (Sv) The SI unit of radiation dose.

Stillage A container for holding four 500L drums. The drums are only extracted

from a stillage when being individually inspected in the Inspection Cell or

overpacked in the Overpacking Cell.

Storage Vault A facility within the PGRC which is used to store the waste packages.

Transfer Tunnel The tunnel which connects all inspection cells together and with the

overpacking cell. A rack and pinion system will be adopted.

Twist Lock A crane locks into this feature to move/lift a package. A T-Lock is

(T-Lock) used on a 3m3 box, 3m3 drum and stillage.

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DRAFTSUMMARY REPORT

8 Images from National Energy Technology Laboratory, U.S.A. http://www.netl.doe.gov/publications/press/2003/tl_conformablearray.html, 29th Oct 2003

9 Photographs from Duncan Heron from Duke University , www.env.duke.edu/eos/geo41/mmo.htm, April 1984

10 Images from Donald Bren School of Information and Computer Sciences http://www.ics.uci.edu/~eppstein/junkyard/box-in-box.gif

11 Images from Fujitsu http://www.fujitsu.com/global/news/pr/archives/month/2004/20040927-01.html , September 2004

13 Images from Inuktun, www.inuktun.com, January 2007

14 Images from Corrosion Technology Testbed, Kennedy Space Centre http://corrosion.ksc.nasa.gov/filicor.htm, January 2007

17 IST Corp. (unknown) ONLINE “Radiation Tolerant Thru-Wall/Roof Viewing

System”. [Online]. Last viewed 2007 March 11. Available:

http://www.istcorp.com/documents/ThruWall.pdf

29 N/094, Nirex Document

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