Status on support for RPrS

– Plant worker occupational radiation exposure (ORE) estimates

Started February 2007

• Maintenance scenario…hardware arrangement…time and motion study

• Worker dose estimate

• Impacts from PbLi

RPrS: Report on preliminary safety

B. Merrill, M. Dagher, M. Youssef and M. SawanReported by C. Wong

US-TBM Meeting, UCLA, February 14-15, 2007

Input Required for RPrS

• The RPrS input includes the US TBM and ancillary systems:– Technical description - completed – Source terms (radioactive, energy, and chemical) - completed– Operational releases - completed– Plant worker occupational radiation exposure (ORE) estimates

Started February 2007– Failure modes and effects analysis (FMEA) study

Started November 2006, to be completed by March 2007

– Consequence analysis for selected accident scenariosFMEA must be completed before this activity can start, but some accident analyses have been completed

– Waste disposal analysis – not yet started, due by June 2007.

• There will be a TBM Safety Workshop in Aix en Provence on March 19th , just in front of TBWG-18, where the status of these tasks will be discussed.

Port Cell Area: replacement of TBM

TBM removal from machine:Step 1: Disconnect port plug and ancillary equipment and

move the ancillary equipment unit (AEU) to its maintenance area.

Step 2: Bring in the transfer cask, extract the port plug to the transfer cask and move them to hot cell area.

Step 3: Move and insert the port plug into the hot cell “red zone” area.

Step 4: Maintain or replace the TBM in the hot cell and maintain or refurbish the AEU in its maintenance area.

TBM return to machine:Step 5: Test the TBM and AEU with the testing utilities.Step 6: Insert the port plug to the transfer cask and return

them to the port cell.Step 7: Insert port plug, move the transfer cask away,

move in the AEU and reconnect TBM with the AEU

AEU & transport TBM transfer cask

Cutting and re-weldingof PbLi pipes on the AEUwill be done in a temporary tent

Hot cell area

AEU Transporter

AEU Components

Bio-Shield Plug

Equatorial Port Inner Space Area

Vacuum Vessel

TBM Assembly

TBM frame Assembly

Shielding

Equatorial Port DCLL TBM General Arrangement

Ancillary Equipment Unit (AEU)

All Dimensions mm

Ancillary Equipment Assembly

Pb-Li Concentric

Pipe

Primary He Coolant Line

AEU Center Point

X

YZ

Center point coordinates relative to ITER Center point

X= 20400 mmY= -1300 mmZ= 0

DCLL Ancillary System Components General Arrangement

1

3

2

1

4

6

2

5

Pb-Li/He Tritium Extraction6

Cold Trap5

Pb-Li Expansion Tank4

Pb-Li Pump3

Pb-Li /He Heat Exchanger2

Pb-Li Tank1

Item No. Description Size (mm) Position*,**X,Y,Z

1 Pb-Li Tank 2000x1000x300 -2380,270,-680

2 Pb-Li /He Heat Exchanger 245 Dia, 1200 L -1422,870,-362

3 Pb-Li Pump 254 Dia, 1266 L -2078,1800,-1042

4 Pb-Li Expansion Tank 254 Dia, 1066 L -1578,1700,-1042

5 Cold Trap 600x300x550 -620,1750,-900

6 Pb-Li/He Tritium Extraction 400 Dia, 1250 L -3100,1760,-962

•* Position coordinates are measured at the center of each component

•** All coordinate points are relative to AEU center point shown on slide no. 5

Occupation Radiation Exposure Shielding codes available for this analysis are MicroShield and QADMOD

– MicroShield, commercially available from Grove Software• Deterministic code – ray tracing• Only simple source geometry (sphere, cube, wall)• Only one radioactive source but can include multiple

radionuclides that emit gamma rays (data base included)

• Possible use of multi-shields (with simple geometries)• GUI user interface with flexibility in defining gamma

energy distribution for attenuation– QADMOD-GP, obtained for the ORNL RSICC –contributed by

TU Electric• Point kernel gamma-ray shielding code with geometric

progression buildup factors• Allows for up to 1000 point sources• Cartesian, cylindrical, or spherical geometries for

defining shield and regions being modeled

Output results: Equivalent dose rate (mSv/hr)

Occupation Radiation Exposure (cont.) • Issues that makes this analysis a problem for these

codes

– MicroShield only allows for a single source which make it difficult to model the radiation field from a complex piping system

– QADMOD-GP, only has point source definition. This makes it difficult to accurately model cylindrical or planar sources. The commentarial geometry input makes complex models difficult to specify. Code will not allow cylindrical shields that do not lie on the x, y, or z axis – problem for modeling shield of cylindrical AEU components

• Solution, model the AEU with QADMOD but adjust source strengths for QADMOD to match MicroShieldresults

MicroShield Results for a Single Pipe • Based on TRITEX results, after draining their loop they found PbLi

films on the pipe walls that were about 45 mg/cm2. (TRITEX – A ferritic Steel Loop with Pb-15.8Li Facility and Operation, FZHA 6286, 1999)

• According to M, Youssef’s activation calculations this film will be radioactive with the activity after one week dominated by Pb-203

MicroShield model

MicroShield Results for a Single Pipe • Maintenance issue is that 30 cm from this pipe the dose is about 0.5

mSv/hr.• Because the ITER goal for worker dose is 500 person-mSv/y (ITER

activities estimated at 178 p-mSv/y), and ITER will only allow 1% of total or ~2 p-mSv/yr for maintaining the AEU, then at 0.5 mSv/hr this dose would be exceeded in 4 hours. Even worse, the dose rate from the drain tank will be 10 times higher.

Bottom line: AEU components will have to be shielded

• Comparison of Microshield and QADMOD results for the single pipe

0.3921.09e-30.24160

0.5041.31e-30.30250

0.6721.62e-30.39040

0.9442.08e-30.52730

1.4492.88e-30.76620

2.6644.63e-31.29410

No Shield(mSv/hr)

1 cm Pb shield(mSv/hr)

No shield(mSv/hr)

Distance(cm)

QADMODMicroShield

Generation of Po-210 from PbLi

1. Bi impurity: Bi-209 (n,γ) Bi-210 (β) Po-210. Bi-210 T1/2 ~5 days so its concentration saturates and Po-210 is produced at constant rate and builds up roughly linearly with time.

2. Starts from Pb:

Pb-208(n,γ)Pb-209(beta)Bi-209(n,γ) Bi-210 (β) Po-210. Pb-209 T1/2 ~3h so its concentration reaches equilibrium and Bi-209 is produced at constant rate and its concentration increases linearly with time.

As a result Po-210 concentration from this reaction builds up roughly t2.

(Notice that we start with (n,γ) reaction, so even in DD phase, but total accumulation is small due to low fluence.)

Dose calculation continuing, activation results from M. Youssef is being used inthe dose calculations

Projection: getting down to < 10 microSv/hr can be a problem, presently tents during maintenance are recommended to minimize contamination from Po-210

Occupation Radiation Exposure (cont.)

Assessment is continuing and the status of these tasks willbe discussed at the TBM Safety Workshop in Aix en Provenceon March 19th before TBWG-18

Time and motion study being generated by M. Dagher