Hpu Question &Answer

Question Bank on HPU_1 Page 1 of 32

QUESTION BANK

ON

HEALTH PHYSICS ASPECTS

FOR

LICENSING EXAMINATIONS /

INTERVIEWS (ALL LEVELS)


1. What is dose? A measure of the radiation received or absorbed by a target. 2. What is dose rate?

Dose rate is amount of Energy absorbed per unit mass of the body per unit time (Gy/hr). The effect of radiation depends on dose and dose rate of the radiation. As the time of exposure increases, the amount of dose received increases.

3. What is absorbed dose?

The amount of radiation energy absorbed per unit mass of the material is called absorbed dose. DTR = D/M Where D TR = Absorbed dose in tissue T due to radiation R D = Energy absorbed M = Mass of the organ

4. What is equivalent dose? Equivalent dose is defined as HT = ∑WR DTR When DTR = Absorbed dose WR = Radiation weighting factor

WR (radiation weighing factor) depends on the linear energy transfer (LET) of the radiation which in turn is related to specific ionization of the radiation. The unit of equivalent dose is Sievert (Sv) (1 Sv = 100 rem).

WR for different radiation types

Radiation Type Radiation weighting factor

Gamma rays 1 Alpha particles 20 Bet particles and muons (all energies) 1 Protons other than recoil protons (all energies) 1 Neutrons with e nergy < 10 keV 5 10 keV to 100 keV 20 100 keV to 2 MeV 10 2 MeV to 20 MeV 5 > 20 MeV 10 Fission fragments (all energies) 20 Heavy nuclei (all energies) 20

5. What is effective dose and committed effective dose?

The equivalent dose when multiplied by the tissue-weighting factor (WT) for the tissue or organ T receiving the dose is called effective dose, ‘E’. E = ∑ WT ∑ WR DTR T R


Where D TR means absorbed dose in tissue or organ T delivered by radiation R. WR = radiation weighting factor The effective dose calculation is important, as the effect of radiation is different for different tissue or organs. WT = maximum for Gonads = 0.30 WT = 1 for whole body When a radionuclide is taken inside the body, it continuously keeps irradiating our body and we continue receiving the radiation dose till the radionuclide resides inside our body or in other words we commit ourselves to this particular amount of dose. This is called as committed dose and when the tissue weighting factor for the particular organ or tissue which is getting irradiated and also the radiation type being emitted by the radio -nuclide (radiation weighting factor) is taken into account it is called committed effective dose.

6. What are Stochastic and deterministic effects of radiation?

Stochastic effects Deterministic effects 1. The probability of occurring the

effects in proportional to the dose and

2. The probability of occurrence increases with the dose.

3. Occurs in exposed individual and future generations

4. Delayed effects

1. These effects occur above a threshold and

2. The severity increases with the dose

3. Occurs in exposed individuals only

4. Early effects

Example: Cancer, Genetic effects Examples: Skin erythema

7. Dose limit for occupational workers, contract workers trainees etc.?

Summary of Annual Dose Limits and Constraint

Category Radiation Workers

Apprentices trainee

Temporary worker

Member of public

Life time E (Sv)

1.0 **

Annual dose (mSv)

30 6 15 1

Equivalent dose limit (mSv) Lens of eye (mSv)

150

50

75

15

Skin mSv) 500 150 250 50 Extremities (mSv)

500 150 250 -

Intake 1 ALI 30% * E = Effective Dose ** = Medical review after 0.5 Sv


8. Explain Annual Limit of Intake (ALI) & DAC? On what factors does the

ALI value of a radionuclide depends? How DAC calculation for tritium (HTO) is different than that for I- 131

Annual limit of intake (ALI) is that quantity of a radionuclide taken inside the

body which could lead to an effective committed dose (1 50 year dose commitment) not exceeding 20 mSv and an annual equivalent dose to any single organ or tissue not exceeding 500 mSv.

The ICRP has recommended ALI values for a number of radionuclides: ALI for 1H³ (HTO form) = 1 X 109 Bq The quantity (Bq) which defines 1ALI varies widely for diffe rent radionuclides. The

ALI for a radionuclide depends on each of the following. (i) Type of radiation emitted (W R) (ii) Energy of radiation emitted. (iii) Selective deposition in the body. (iv) Presence of radioactive daughters Derived air concentration (DAC) It is the concentration of any radionuclide in air to which is a person is exposed

for 2000 hours (40 hours a week, 50 weeks a year). DAC = ALI . Annual breathing rate The annual breathing rate for a “Reference man” is 2.4 x 10³ m³.

Derived Air Concentration (DAC) for Tritium (HTO) In in the case of HTO, the DAC value has to be obtained by multiplying the above value by 2/3 for accounting 66% uptake through inhalation route. Hence for this particular radio-nuclide of tritium DAC is calculated as below :

ALI (Bq) DAC = 2/3 x ----------------- 2400 m³

9. How is tritium produced in our Reactor and why is it hazardous? Heavy water is used as Moderator and also as primary coolant in PHT system Tritium production is as per the reaction 1H² + 0n1 - 1H³ + r In the physical for tritium is present in the form of TDO (Tritiated Heavy Water).

The behavior of tritium will be same as that of water or water vapour. Whenever water is exposed to air, some of the heavy water and its contained tritium will evaporate and so we will have an air born tritium hazard.


10. Tritium is hazardous due to the following reasons: Tritium is not an external hazard duct to the following reasons. (i) Tritium emits beta particles but no γ rays. (ii) Emax (β) = 18 Kev (iii) Living cells are covered with a outer dead layer of skin (at least 0.007 mm thick). (iv) Tritium beta can penetrate only 0.05 mm. (v) Particles require at least 70 kv to penetrate the outer layer of skin. Hence, tritium is not an external hazard. Tritium is a serious internal hazards as a) The cells inside the body are not protected by a dead layer. b) When tritium is inside the body is in direct contact with live cells and even

diffuses right inside them. c) In spite of their extremely low penetrating lever, tritium beta particles can

damage the cells. Hence to minimize the amount of damage, the amount of tritium allowed in the

body is to be limited. 11. How is protection factor defined. What is the protection factor for

different clothings? Protection factor (PF) = Uptake without protection Uptake with protection PF for plastic suit = 30 (against 1H³) PF for an air respirator = 2 (a gainst 1H³) 12. What are three principles of radiation protection?

The main features of the system of dose limitation shall be the following:

Justification:

No practice shall be adopted unless its introduction produces a sufficient benefit to the exposed individual or to the society to offset the radiation harm that it might cause.

Optimization:

All exposures shall be kept As Low As Reasonably Achievable (ALARA) economic and social factors being taken into consideration.

Dose limitation:

The normal exposures of individuals resulting from all relevant practices should be subjected to dose limits to ensure that no individual is exposed to a risk that is judged to be unacceptable.


13. What are the basic fundamental methods to protect against external

exposures? The basic principles adopted to control external exposures are: a) Time: Time spent in radioactive work area should be optimized. b) Distance: Keep distance from the source c) Shielding: Shielding the source will reduce radiation intensity. d) Decay: allow the short lived radio nuclides to decay before entry. 14. What are the basic fundamental methods to protect against internal

exposures?

The basic principles used to protect against internal exposures are: a) Inhalation route: use suitable respiratory protection b) Ingestion route: Eatables should not be taken to radioactive areas. c) Ingestion through open wound: Not allow to work in radio active area d) Through skin absorption: Use ventilated respiratory protection 15. Why is the nuclear plant divided in four zones? What are the four zones

in a typical plant? What is the change room and what are the three fold purposes of designing a change room?

A Nuclear plant-operating island is divided into four zones called Zone – 1, Zone –

2, Zone – 3 and Zone – 4 to prevent from spread of contamination. Zone – 1 : Clean Zone. No contamination exists Zone – 2 : As such no contamination exists. Area may get contaminated due

to personnel movement. Zone – 3 : Contamination exists but contained Zone – 4 : Source of contamination Change Room: Change Room is the place where personnel clothings are removed and plant

clothes are worn by plant personnel proceeding to work in radioactive areas (Zone – 3 & 4 ).

Objectives: 1. To separate plant and personnel clothes to avoid cross contamination 2. To avoid spread of contamination to Zone – 1 areas 3. To avoid individuals getting contaminated during radioactive job. 16. What is the procedure for entering to shutdown accessible area during

reactor operation?

Entry procedure for shutdown accessible areas like pump room, moderator room, DNM room during Unit operation. Any entry to Shutdown Accessible Area during Unit operation in called on power entry. The following procedures shall be followed:

Step-1: On power entry should be justified, ON power entry should be made only

for inspection purposes.


Take approval for on power entry in on power entry form (filled in duplicate) from CS/SD.

Step-2: Conduct ALARA meeting for the entry with man-hours, manrem required &

persons entering the shutdown accessible area. All individuals should be briefed about the job. Follow three-way communication. Step-3: Collect all protective clothings, (Ventilated plastic suits), protective wear

and respiratory protection prior to the entry. The dosimeters to be collected include high range DRD, Alarming dosimeter, Neutron Badge in addition to TLD and DRD.

Step-4: Time spent in pump room shall be as minimum as possible and shall work

in batches. Step-5: Once the job is completed, assess the doses received by each individual &

fill up the ALARA planning sheet and conduct post job review. 17. While the reactor is operating, the reactor building exhaust duct shows

“very high” activity alarm. List out various causes for this alarm and the actions (manual as well as auto) to be taken after this alarm as far as radioactivity is concerned.

The causes for very high activity in Reactor Building exhaust duct may be due to the following:

1. High FPNG release 2. High argon release 3. High Iodine –131 release 4. LOCA condition

Check area radiations field of RB on RADAS. Manual actions taken during very high activity alarm: The sample cell, which is sealed at ventilation exhaust room is removed for analysis of various radionuclides present in the sample by gamma spectroscopy analysis. This will help in identifying the source of radiation and origin of the source/system. Depending on the source system, action will be taken suitably.

Auto actions:

When RB exhaust duct show very high activity alarm, the sample cell and RB will be boxed up automatically as per logic by triplicated Ventilation Duct Radiation Monitors. After the situation is assessed and controlled, the logic will be reset.

18. What are the current doses limits as applied to radiation workers and

members of public?

Dose Limits recommended by AERB

Dose Limit Application

Occupational Public

Effective Dose 30 mSv per year and 100 mSv when averaged over defined period of 5 years.

1 mSv in year and 500 averaged over 5 years.


Annual equivalent dose for:

Lens of the eye 150 mSv 15 mSv

Skin 500 mSv 50 mSv

Hands and feet 500 mSv --

19. Name five fission products and five activation products observed in your

plant and also indicate the systems in which these are found.

Fission Products: Activation Products I-131 Co-60 PHT & Mod

Cs-137 Zr-95 PHT Cs-134 Nb-95 PHT Sr-90 PHT Ar-41 AGMS, Mod & PHT Cover gas Xe-133 Fe -59 Mod Xe-135 H-3 Mod & PHT Sb-124 PHT

20. Out line the methods of contamination control in respect of surface

contamination. - Spread polythene sheets before taking up maintenance activities in the working

area. - Avoid keeping contaminated equipment on floors. Wrap all contaminated

equipment with polythene sheet - Decontaminate the floors as soon as identified as contamination is detected. - Proper rubber area / rubber change area. - Follow rubber change procedures. 21. Out line the methods of contamination control in respect of body

contamination. - Use protective clothings - Use respiratory protective equipment - Follow strictly radiation protection procedures, which include rubber station

procedures, which include Rubber Station procedures etc. - Avoid touching contaminated wall / equipment if not required. 22. What are the limits for contamination in body, personal clothes and

personal shoes?

Derived working levels for radioactive contamination Derived Working Levels (DWLs) for radioactive contamination

Surfaces Beta Emitters (Bq/cm2) Alpha Emitters (Bq/cm2) Skin 1.5 1.0

Hands 350* 250*

Clothes: Plant

Personnel

6 2

2

0.5 Shoes: Plant

Personnel

37

0.37

3.7

0.037 Floor/Equipment 3.7

0.37


* Total contamination on either side. * No loose contamination is permitted on hands and skin. 23. What is natural background radiation? On what factors does it depend?

Name the isotopes causing natural background radiation.

The radiation due to presence of naturally occurring radionuclides in atmosphere, earth crust, etc. gives to natural background radiation. The sources of natural background radiation include Radon (Uranium series), Thoron (Thorium series), K-40, Cs-137 (Nuclear fall out), cosmic rays, etc. The natural back background radiation in a place depends on

a. Intensity of cosmic radiation b. K-40 c. Nuclear fall out d. Presence of Uranium or Thorium materials in the earth crust e. The elevation of a place with reference to sea level 24. A failed fuel bundle was being transported from your station to Bombay.

On the way it met an accident what actions you will undertake as the leader of the convoy?

Actions to be taken by CIC during level 3 emergencies are:

a. Attend to the injured and if necessary arrange for medical aid b. Monitor the cask for radiation and contamination levels. Also monitor the

wagon/conveyance and adjoining areas for possible contamination. Monitor the radiation levels around the cask.

c. Inform the local / concerned railway/police/district authorities and seek their assistance.

d. In case of fire, get assistance of local fire brigade. Fire fighting personnel should make use of the standard respiratory protective equipment

e. Cordon off the area as specified in the TREMCARD. f. Inform the consignor and the CMG, DAE about the emergency situation in the

prescribed format and seek any assistance that may require. g. Keep a watch over the controlled area until the Emergency Response team (ERT)

arrives. h. Assist in the efforts of the emergency response personnel sent by the railways,

police or local fire brigade. i. Assist the Emergency Response Team (ERT) j. Decontaminate the affected area, if any, and arrange for improvised

shielding, tie -down, etc, for the cask, if require as recommended by the Emergency Response Team (ERT)

k. Inform the consignor and the CMG, DAE upon completion of the emergency response work.

l. Resume the shipment in accordance with the advice of the ERT. 25. What are the different categories of radioactive shipments? Give their

dose limits

Categories of the Radioactive Shipments All shipments shall be in any one of the following four categories:


Conditions Category Maximum radiation level at any point on

external surface Transport Index (TI)

1- White Not more than 0.005 mSv/h (0.5 mR/h) 0

2- Yellow

More than 0.005 mSv/h (0.5 mR/h ) but not more than 0.5 mSv/h (50 mR/h )

More than 0 but not more than 1

3- Yellow

More than 0.5 mSv/h (50 mR/h) but not more than 2 mSv/h (200 mR/h)

More than 1 but not more than 10

3- Yellow

(for exclusive use)

More than 2 mSv/h (200 mR/h ) but not more than 10 mSv/h (1000 mR/h )

More than 10

26. A Heat transport pump is to be transported to Bombay. The radiation

field on contact of the package is 150 mrem/h. Write down its category and the documents required to be filled up and required to accompany?

Radiation field on contact of the package in 1.5 mSv/h. Since on contact radiation field is less than 2 mSv/h, the radioactive shipment comes under category III yellow.

Documents required for category III yellow package:

1. Radioactive shipment advice (for the consignee and station records) 2. Normal Release Permit (for station security) 3. Instructions to vehicle drivers ( for emergency conditions) 4. Tremcard 5. Tremdata

The above documents shall be filled up and accompany the consignment. 27. What is plant emergency? Give a few examples. Who is Plant Emergency

Director?

This involves excessive release of radioactive materials or high radiation fields in a section of the plant requiring immediate operator action and /or automatic operation of safety systems. Although positive isolations or restrictions on occupancy of the affected areas might be enforced, evacuation of personnel might be required if it is suspected that the doses to personnel are likely to exceed the intervention levels

1. Actual or suspected occurrences of loss of core cooling both during operation and

shutdown. 2. Closure of RB isolation damper on high activity release or high pressure in reactor

building or emergency core cooling system. 3. Major fire in Reactor Building. 4. Earthquake measuring more than 6.0 Richter's scale or major damage observed

due to earthquake.


5. Failure of a structure inside reactor building which may incapacitate the core cooling or reactor protection system or regulating system.

Plant Emergency Director: Station Director

28. Give a sketch for possible escape routes for radioactive materials from

fuel to the environment. What are the likely isotopes to escape?

Fuel Fuel cladding Fuel cladding Primary Heat Transport System Primary Containment Secondary Containment Secondary containment Environment

Isotopes likely to escape from fuel: I-131, Xe-133, Xe-135 etc.

29. What is an emergency? What are different types of emergency? Explain

with one example each. What and where is he various counter measures to be taken in each type of emergency?

Emergency:

Emergency is an incident in a nuclear power plant, which may lead to release of radioactivity into the environment above the technical specifications in an uncontrolled manner.

There are three types of emergencies encountered at Nuclear Power Plants:

Plant Emergency:

This involves excessive release of radioactive materials or high radiation fields in a section of the plant requiring immediate operator action and /or automatic operation of safety systems. Although positive isolations or restrictions on occupancy of the affected areas might be enforced, evacuation of personnel might be required if it is suspected that the doses to personnel are likely to exceed the intervention levels.

Counter measures implemented:

a) Assembly of personnel in Assembly areas for mutual counting. b) Sheltering c) Access control

Examples: 1. Actual or suspected occurrences of loss of core cooling both during operation and

shutdown. 2. Closure of RB isolation damper on high activity release or high pressure in reactor

building or emergency core co oling system. 3. Major fire in Reactor Building. 4. Earthquake measuring more than 6.0 Richter's scale or major damage observed

due to earthquake. 5. Failure of a structure inside reactor building which may incapacitate the core

cooling or reactor protection system or regulating system.


Site Emergency:

This class of emergency arises due to situation, which seriously affects plant operations involving high radiation fields in accessible areas and release of radioactive materials extending beyond the plant up to the site environment. The protective measures such as incorporation of stable Iodine, sheltering and evacuation of personnel from plant areas other than control room to areas designated to be habitable under the site emergency conditions and evacuation of non-essential persons from the site may be considered.

Counter measures implemented:

a) Access control b) Sheltering c) Evacuation

Examples: 1. Known loss of coolant greater than make up pump capacity. 2. Actual or suspected core melting. 3. Fire affecting safety systems. 4. Primary steam line breaks outside containment without isolation. 5. Severe natural phenomena being experienced or projected with plant not in cold

shutdown condition.

Off-site Emergency:

An Off-site emergency situation results when the release of radioactive materials from the plant is of a magnitude necessitating protective action to be taken for members of the public in the neighborhood of the plant.

Counter measure implemented:

a) Access control b) Administration of stable Iodine c) Sheltering d) Evacuation e) Control on food stuff

Examples: 1. Known loss of coolant greater than make up pump capacity. 2. Actual or suspected core melting. 3. Fire affecting safety systems. 4. Primary steam line breaks outside containment without isolation. 5. Severe natural phenomena being experienced or projected with plant not in cold

shutdown condition. 30. How is area around a nuclear power plant is divided? What is the

significance of each zone?

Emergency planning zone, defined around the plant up to 16 KM radius, provides a basic geographic framework for decision making on implementing measures as part of a graded response in the event of an emergency. The area around the RAPS site is divided into the following zones up to 16 KM radius.


Exclusion Zone:

The exclusion zone extends up to a distance of 1.6 KM around the central plant zone of 0.7 KM where no public habitation is permitted. This zone is physically isolated from outside areas by plant fencing and is under the control of RAPS.

Sterilized Zone:

Sterilized zone is an area where no new growth of population is permitted. Natural growth is however allowed in this zone. This area extends up to a radius of 5 Kms from the central plant zone. This zone is defined to restrict the population to an easily transportable number in case of an Emergency.

Primary Zone:

The primary zone extends up to 8 Kms from central plant zone where protective measures like evacuation and sheltering are required against possible plume exposures during an Emergency.

Secondary Zone:

The secondary zone extends up to 16 Kms from Central Plant Zone protective measures like sheltering control on foodstuff are required against possible exposures from ingestion of radioactivity.

Sectional Division of EPZ:

The Emergency-planning zone around the RAPS-3&4 is further divided into 16 sectors radially (designated by letter codes 'A' to 'P' marked clockwise) to implement protective measures to areas actually affected during an emergency. Each sector covers 22.5 and the centerlines of sector 'A', 'E', 'I' and 'M' coincide with the North, East, South and West directions respectively.

31. With unit operating at full power “Stack Iodine Activity high”

annunciates. What could be the causes and what actions will you take? Stack iodine activity high annunciates when unit is operating at full power

The reasons for above can be

a) Discharge of failed fuel bundles to SFSB b) Loss of coolant accident in RB

Actions to be taken: a) Put into service the Iodine filter beds in spent fuel storage bay area for removal of

iodine during failed fuel discharge. b) Put into service, the primary containment filtration & pump back system, and

secondary containment of iodine during LOCA condition. 32. What are the radionuclides that are significant at later stage in the event

of accident? How do they affect the population?

The radionuclides likely to be released to the environment during an off site emerg ency are Cuss-137, I-131, Xe-133, Xe-135, Sr-90, Co-60 etc. Different radionuclides will be absorbed in different ranges of the body.


Example Cs-137 Muscle

I-131 Thyroid Sr-90 Bones 33. In a hypothetical radiation accident in the plant, automatic closure of

R/B dampers isolates the Reactor Building. Explain the basic principles or bases or methods for:

a) How would an assessment of the activity released be made b) Declaring Plant and Off-site emergency c) Deciding on evacuation and sheltering measures d) Treatment of contamination injuries

The Reactor Building gets boxed up by automatic closure of Reactor Building dampers in a hypothetical accident

a) The assessment of activity released through the stack is estimated by counting

the 5-liter sample cell kept at Ventilation Duct Radiation Monitoring room. The radionuclides present and quantitative estimation of releases is estimated.

b) Declaring Plant and Off-site emergency

Plant Emergency is declared based on the following conditions:

Whole body dose: 5 mSv or committed equivalent dose to thyroid : 50 mSv to many persons in the plant.

Off-site Emergency:

When the radiation level at 1 m above the ground level is more than 0.01 mSv/h or food samples containing activity more than allowed limits for consumption.

c) Deciding on evacuation and sheltering measures

Sheltering:

The radiation level is more than 0.01 mSv/h in domain 2 and more than 0.1 mSv/h in domain 1 and persistent for 10 hours, sheltering of the public shall be done to avoid inhalation dose and plume dose.

Evacuation:

Evacuation is implemented, if the radiation level is more than 1.0 mSv/h and persistent for 4 hours in domain 1, within 12 hours.

d) Treatment of contamination injuries

Treatment of contaminated injuries: The contaminated injuries are treated at Radiation Emergency Medical Center (REMC) prior to decontamination of injured persons, first aid and medical treatment will be given to save the life. Later, decontamination of the injured person will be carried out at Radiation Emergency Medical Center.


34. Which are the samples to be collected from an affected area? What will

be the follow up actions, if required?

The following samples are collected during a radiation emergency in an affected area:

a) Air samples for estimation air borne radioactivity present in the affected area.

These samples include for particulate and iodine b) To estimate the contamination level in food materials, the following food samples

are collected for analysis: (i) Water samples (ii) Paddy rice (iii) Milk (iv) Milk products (v) Goat’s thyroid (vi) Soil samples etc.,

Follow up actions required during emergency:

The frequency of sample collection shall be increased if the radioactivity levels are in increasing trend in all food samples as mentioned above. If the activity levels are more than the allowed limits, the countermeasure of control on foodstuff shall be implemented. Sheltering and Administration of stable Iodine shall be done based on radiation levels at 1m above the ground level in the affected area/village.

35. Classify the off-site emergency on space domain basis; specify the dose

limits for counter-measures in the domain. Time space domains are defined to appraise the implementation of countermeasures.

Domain Concepts Domain – 3 Domain - 2 Domain - 1

Radiation level (mSv/h)

<0.01 0.01-0.1 >0.1

Objective To reduce collective dose and thus to minimize the overall incidence of stochastic effects

To limit the stochastic risk to individual members of the public

To avoid individual doses so as to avoid serious deterministic effects (0.5 Gy & 5 Gy)

Exposure pathways

Ingestion route predominant

Ingestion route (major) a . Inhalation route of exposure to thyroid b. External gamma dose

from plume c. External gamma dose

from ground deposition

Counter measures

Control of food stuff

a. Administration of stable iodine

b. Sheltering and c. Control of food stuff

a . Administration of stable iodine

b. Sheltering and / or c. Evacuation


36. What are intervention levels for various counter measures in off-site emergency?

Intervention levels for various counter measures in different domains during an Off-site emergency are given below:

Intervention levels for implementation of countermeasures

Intervention level (mSv) Whole body Thyroid

Domain Countermeasure

Lower Upper Lower Upper Domain –1 Administration of

stable iodine Sheltering Evacuation

--

20

100

--

100

500

500 -- --

2500 -- --

Domain – 2

Administration of stable iodine Sheltering Control on food stuff

-- 5 5

--

20

20

50 --

50

500 --

500

Domain – 3

Control on food stuff

1

5

Not anticipated

Note: The Ils for Doma ins 1 and 2 are CED / CEED from intakes during the first year following the accident

37. What are the different protective measures suggested in the off-site

emergency? When and how will these be implemented? The protective measures implemented during an Off-site Emergency are: a) Administration of Stable Iodine: KIO3 Tablets are administered at the earliest

by district medical authorities b) Sheltering: Sheltering of all public in the affected village is implemented within

24 hours if the radiation level at 1 m above the ground level is more than 0.1 mSv/h by police personnel.

c) Evacuation: Evacuation of all public in the affected village is done within 12

hours of the radiation level at 1 m above the ground level is more than 1.0 mSv/h by police personnel.

d) Access Control: Entry and Exit of vehicles from affected villages are diverted

and traffic in controlled by police personnel. e) Control on foodstuff: Consumption of contaminated food is restricted by district

authorities.


38. What are the different design features provided at your station to handle emergency in order to ensure releases are within technical specifications?

The design features provided to handle emergency in order to ensure releases are within technical specifications are as follows:

a) Pressure Suppression System:

The suppression pool system is designed to remove undissolved gases and reduce the pressure of primary contaminant by dissolving certain gases in a water column of 2.1 meters. Most of the soluble radioactivity may also be contained in the system.

b) Primary Containment Filtration and pump back system:

This system is designed to remove iodine released during emergency conditions. c) Secondary Containment recirculation and purge system:

This system is derived to remove iodine & particulate activities of any leakage from primary containment and to avoid ground releases.

e) Primary Containment Control Discharge:

This system is designed to discharge the gaseous effluents in a controlled manner during post accident situation based on suitable meteorological conditions.

f) Double containment:

The secondary containment avoids the ground releases if any leakage & from primary containment by keeping at negative pressure and starting of secondary containment recirculation and purge system.

39. a. What is the source term? Mention the inventory of I-131 and Noble gases in PHWRs.

b) Outline the system of measuring radioactivity discharge from NPP under building box up conditions during accidents.

a) Source Term

Source Term denotes “information about the actual or potential release of radioactive material from a given source, which may include a sp ecification of the amount, the composition, the rate and the mode of release. The following characteristics of the source term have an important bearing on the accident consequences:

(i) The rate and the total amount of radioactive material released: This is determined by the reactor inventory (which in turn depends on the design and operating power of the reactor), and by the nature and severity of the accident.

(ii) The relative mixture of radio -nuclides released:


This may be different from the composition existing in the core before the accident. It is determined by the chemical, physical and radiological properties of the nuclides concerned.

(iii) The relative mixture of gases, volatiles and particulates released: The physical form of the activity released determines primarily its escape potential from the plant.

(iv) The environment of release and the accompanying energy: Atmospheric releases at high level, accompanied by high energy, ensure a wide dispersal of radioactivity.

Inventory of I-131 and Noble gases at RAPS-3&4 For LOCA: I-131: 1.06 × 106 curies Noble gases: 1.56 × 106 curies For LOCA+ ECCS failure: I-131: 22.6 × 106 curies Noble gases: 201.7 × 106 curies

b. Sample Cells are used to analyse air activity of Reactor Building (RB) quantitatively and qualitatively during accidental conditions when reactor gets boxed up. Sample cell is located at Ventilation Duct Radiation Monitoring (VDRM) room at 106m.El. of Service building. The air from RB continuously flows through the cells. When the reactor is boxed up, the cell will be sealed and the air gets trapped in the cell. The sample is removed and analysed on MCA for various radionuclides.

- The sample cell is connected with quick disconnect couplings. - Shift Charg e Engineer will inform Shift Health Physicist about reactor box-up. - Immediately after Reactor box up, disconnect the sample cell. - Note the time of removal of sample cell. - Analyse the cell on Multi Channel Analyser system as per standard procedure. - Note the activity of each radionuclide. - Inform the values to control room and Station Health Physicist. - Connect the sample cell back in the system. - Reset the flow through the sample cell. 40. Give the bases, on which the limits of releases of radioactive effluents

are stipulated. Give the limits of, releases of the following radionuclides in your reactor

a) Tritium in air route b) Iodine in air route c) Gross beta activity in water route

The limits on release of radioactive effluents are derived based on the following factors:

a) Site dispersion factor b) Critical path of exposure


c) Critical group for a given path of exposure d) Food habits & consumption rate e) Transfer coefficients f) Relative humidity g) Atmospheric stability class h) Deposition velocity of Radionuclide

Release limits for RAPS-3&4 (annual average rate of discharge) a) Tritium in air route (as oxide)

7.4 TBq/d (200 Ci/d). Ten times maximum discharge from both the units in a single day can be the average daily discharge limit provided annual average is not exceeded.

b. Iodine in air route 0.74 GBq/d (20 Ci/d). Ten times in a day provided annual average is not

exceeded. c) Gross beta activity in water route

Total release not to exceed 1.48 GBq/d for R-1 to 4 (total 40 mCi/d, 20 mCi/d, each for RAPS-1&2 & RAPS-3&4) and concentration in water shall not exceed 7.4 x 10-4 MBq/ml. Ten times in a day provided annual average is not exceeded.

41. What are the factors that determine the radioactive releases to the environment? What are specifications of these releases for your station? Your answer should include both air and water routes? The factors that determine the radioactive rele ases to the environment are:

a) Site dispersion factor b) Critical path of exposure c) Critical group for a given path of exposure d) Food habits & consumption rate e) Atmospheric stability f) Radio nuclides released g) Deposition velocity of radio nuclides h) Transfer coefficient of radioactivity from Grass to Animals etc., i) Relative humidity of atmosphere

Liquid Effluents

Tritium Gross Beta-gamma activity

Release limit 35 Ci/d (for RAPS-3&4) 20 mCi/d (for RAPS-3&4)

Concentration in water

30 PCi/ml 2.0 x 10-8 µCi/ml

Gaseous Effluents

Radionuclide Release limit

Tritium (as oxide) 7.4 TBq/d (200 Ci/d)

FPNG 23.68 TBq (640 Ci/d)


Ar-41 2.96 TBq (80 Ci/d) I-131 0.74 TBq/d (20 mCi/d)

Particulate 0.56 TBq/d (15 mCi/d)

The releases can be ten times in a day provided the annual average is not exceeded.

42. What do you mean by target dose, manrem budgeting and manpower

control? a) Target Dose:

Target dose in the limit of collective dose approved by SARCOP derived from source control techniques at design, construction and operation of nuclear power plants and experience. This dose limit should not be crossed by adopting appropriate ALARA practices.

Manrem Budgeting:

A manrem budget is a plan expressed in quantitative terms of dose for a particular group/job. It includes;

a) Quantification of tasks to be performed b) Quantification of manpower required and c) Scheduling the works in active areas

The manrem budget provides a set of guidelines for use in controlling the operation and maintenance activities in the organization.

Manpower control:

Manpower control means the availability of manpower and man-hours for executing the planned jobs during the years. The employment of temporary workers may increase the collective dose due to less efficiency while working in radioactive areas.

43. How can source control technique help in reducing the total manrem

consumption? The above can be achieved by reducing the inventory or eliminating the following.

Activation products

The major activation products observed in PHT and moderator system are Co-60 and Fe -59. The selection of components shall be such that the impurities of these will be minimum so that source control can be achieved.

Examples: Selection of colomony for adjuster rod ball bearings.

System inventories of radionuclides

The major radionuclides observed in PHT and Moderator system are: Zr-95, Zr-97, Mn-56, Co-60, Cu-64, Fe-59 and Mn -65.


The equilibrium system activity of various radionuclides is ava ilable in design manual on shielding for RAPS-3&4. These inventories can be minimized by increasing the current time and reducing the corrosion rate by maintaining good system chemistry.

44. Which are the important factors, important role in the achieving of low

annual occupational exposure at NPP’s? The important factors to achieve low annual occupational exposures at NPPs are: a) Manrem Budgeting

A manrem budget is a plan expressed in quantitative terms of dose for a particu lar group/job. It includes;

- Quantification of tasks to be performed - Quantification of manpower required and - Scheduling the works in active areas

The manrem budget provides a set of guidelines for use in controlling the operation and maintenance a ctivities in the organization.

b) Monitoring of working conditions

RP group monitors the radiological conditions in the work area routinely and/or before carrying out any special jobs. A database of radiological conditions is created by HPU in specific areas to study any increase/change in such conditions and necessary action will be taken by the management to reduce the dose-rates/contamination levels in the work environment. The radiological survey in general includes:

- Assessment of radiation levels - Identification of hot spots - Assessment of air borne contamination levels - Assessment of surface contamination levels c) Work process steering and control

Work process steering and control can be achieved by adopting the following procedures:

- Radiological work permit for all radioactive jobs for dose accounting. - Work area supervision by a Green qualified person - Dose follow-up and review for jobs with radiation exposure - Job co -ordination by supervisors and Engineers in the work area to avoid rework. d) Training on “ALARA Principles and practices”:

Education and Training are one of the pre-requisites for worker's involvement to achieve ALARA exposures. To implement and follow an ALARA approach, all personnel shall be trained and ALARA principles & practices. An Operating Manual is prepared on "ALARA Principles and Practices" to train all personnel and it is necessary to write examination on this topic to be Green qualified. The training programme will be repeated as a refresher course before outages to inform workers of the important aspects of radiation protection and special aspects of dose reduction in work.


45. Proper dose management system helps to take correct actions and

enforce radiation protection standards a) What is the dose management system followed at your station? b) Give five important examples of administrative factor achieve ALARA

doses. a. Individual and collective dose control is a requirement in nuclear power plants.

Atomic Energy Regulatory Board in tune with the recommendations of International Commission on Radiological Protection stipulates individual dose limits. Several inputs such as Training of personnel in radiation safety aspects, work-planning methodology, assessment of radiological conditions in plant areas and techniques to achieve ALARA measures form part of overall dose management in the power station.

i) Organization on Radiation Safety ii) Training on Radiation Safety iii) ALARA Committee iv) Job planning and ALARA Techniques

a) Manrem Budget b) Manhours of working conditions c) Work process status and control d) Training on ALARA principles and practices

v) Use of computers in Dose Management

a) Computerization of dose records b) On-line dosimeter issue c) Display of radiation levels in charts

vi) Quality circle b) Administrative factors to achieve ALARA doses are: - Access Gates to shutdown Accessible areas - No entry to Zone-2 onwards without TLD - No exit to Zone-1 without monitoring at Exit Portal Monitor - No work is allowed in radioactive area without Radiological work permit - No entry to radioactive areas without Direct Reading Dosimeter. 46. What is ALARA? Why no numerical value is given for ALARA?

ALARA is an abbreviation for As Low As Reasonably Achievable. This principle is used for optimization of radiation protection and is defined as follows:

"In relation to any particular source within a practice, the magnitude of individual doses, the number of people exposed, and the likelihood of incurring exposures where these are not certain to be received should all be kept as low as reasonably achievable (ALARA), economic and social factors being taken into account. This procedure should be constrained by restrictions on the dose s to individuals (Dose Constraints) or the risks to individuals in the case of potential exposures (Risk Constraints), so as to limit the inequity likely to result from the inherent economic and social judgments (The optimization of Protection)".

No nume rical value is given for ALARA, as it is a qualitative term used to indicate the reduction in dose by various optimization processes.


47. What are the different characteristics of the stack release needed for

evaluation of dose due to gaseous discharge from NPPs. Four general elements necessary for performing dose assessments are: Characterization of the radionuclide or the radiation source – including the chemical form and the type of radiation emitted. Determination of radionuclide distributions in cluding where and how the radionuclides are being released (e.g. stacks, water discharges, etc.) Determination of radiation incident on the population and / or its radionuclide accumulation. Determination of the subsequent radiation dose to the population.

48. a. What are the data Meteorological Laboratory attached to NPP are

collecting? b. What is X/Q? On what does it depend? c. How does X/Q value influence release limit for a given apportioned dose

at fence post? Is a lower or higher value of X/Q desirable? a. The data collected by meteorological laboratory and the application of data is

given below:

Description of data Application 1. Wind direction To know the affected section 2. Wind speed To know the extent up to which the sector is

affected 3. Rain fall To take into accent wash down factors etc. 4. Atmospheric stability class To make decision for release of gaseous effluents

during accidental conditions

5. Horizontal and vertical dispersion coefficients

To identify suitable atmospheric conditions for effluent releases during accidental conditions.

b. X/Q is the ratio of ground concentration to the release rate of gaseous effluents

through the stack. It is called Site dispersion factor. The site dispersion factor depends on atmo spheric stability class, terrain and height of the stack, etc.,

c. For a given apportioned dose at fence post, the release limit decreases with

increase in X/Q value. The lower X/Q is desirable to increase release limits. 49. What are the basic meteorological parameters needed in evaluation of

the dose due to gaseous releases?

The basic meteorological parameters needed for evaluation of the dose due to gaseous releases are:

- Wind direction - Wind speed - Affected sector - Stability class - Site dispersion faction - Maximum temperature - Relative Humidity - Rainfall etc.,


50. Explain the following terms: a) Inversion b) Fumigation c) wake effect d) deposition velocity e) critical pathway f) Fanning g) Lofting h) Coning i) Looping

Inversion:

The reversal of the usual variation of an atmospheric property (Temperature) with height is called Inversion and the layer through which the reversal takes place is called Inversion layer.

Fumigation:

The transport to the ground of radioactive effluent plume when there is an adiabatic lapse rate in the lower layer topped by an inversion. Downward mixing goes on readily but the inversion limits the upward mixing. This configuration arises when there is an inversion at the ground at sunrise, which arises above the stack plume level due to heating from solar radiation. After this level is reached, the effluents mix downward rapidly fumigating the ground, which has until this time been protected from the plume by the inversion. This process may result in an abrupt increase of the effluent concentration at the ground to a high level.

Wake effect:

Radioactive materials released through leaks in the buildings or from short stacks will be mixed in the turbulent wake created by the ambient air flow around these buildings. This effect creates a volume source, called Wake effect.

Deposition velocity:

Deposition velocity is a parameter used to apply correction for impaction or adsorption on surfaces along the Plume downwind direction. The Deposition velocity is defined as:

Rate of deposition (Bq cm-² sec -1) Vg ( m sec -1 ) = Concentration near the surface (Bq cm -3) For Iodine -131, Vg = For Particulate, Vg =

Critical pathway:

Radionuclides released into the environment can irradiate the population through many pathways. But some pathway may result in substantially higher dose to public than others. Such pathways which cause maximum dose to public for a given release / concentration are called critical pathways. For eg. I-131 released into the environment, the air-grass-cow-milk pathway is the critical pathway of exposure.


Fanning:

When the radioactive effluents are emitted into an inversion layer, the stability prevents diffusion up and down, so that the only spreading of the effluents is sideways. Since the plume is thin in the vertical and is V -shaped in the horizontal, the phenomena are fanning.

Lofting:

The spreading in upward arcs of a radioactive plume emitted into air with an inversion below the stack exit and an unstable lapse rate at and above it. The radioactive effluents are emitted at the top of an inversion layer, where it is kept from mixing downward but spreads upward. This tendency to be carried aloft but to the ground has been termed as lofting.

Coning:

The radioactive effluents released from a stack into a deep adiabatic layer allow spreading of plume uniformly in all cross wind directions. viz., lateral & vertical ) The turbulent motions that are induced by irregularities of the ground and shearing of the wind are not amplified by instability. The vertical spreading and lateral spreading are about equal and the effluent plume resembles a cone

Looping:

When there is a super adiabatic lapse rate through a deep layer the radioactive effluents are carried up-and-down by convection currents forming a looping pattern and are rapidly diluted by the intense vertical mixing.

51. Explain the following terms:

a) Lapse rate b) Adiabatic Lapse rate c) Sub Adiabatic Lapse rate d) Super Adiabatic Lapse rate e) Stable condition f) Unstable condition g) Neutral condition Lapse rate: The rate of decrease of temperature with height is known as lapse rate.

Adiabatic Lapse rate

A process in which no heat exchange between an air parcel and its surroundings occur is called adiabatic process. The motions of the air are approximately adiabatic near the ground.

The rate of decrease of temperature with height as one goes upward in air

column is different from the adiabatic rate of cooling . ∆ T - = γ ∆ h observed


∆ T - = Γ ∆ h Adiabatic process

If the lapse rate in an air column (γ ) is equal to the rate of adiabatic cooling Γ, the air column is said to have an adiabatic lapse rate.

γ = Γ

Sub Adiabatic Lapse rate: If the lapse rate in an air column (γ) is less than the rate of adiabatic cooling Γ,

the air column is said to have super adiabatic lapse rate. γ < Γ

Super Adiabatic Lapse rate: If the lapse rate in an air column ( γ ) is greater than the rate of adiabatic cooling

Γ, the air column is said to have super adiabatic lapse rate. γ > Γ

Stable condition:

If the displacement of the object gives rise to forces that tend to bring it back to its original equilibrium position is said to be stable.

The lapse rate γ (sub adiabatic) is less than the adiabatic rate of cooling Γ, the system is said to be under stable equilibrium.

Unstable condition:

If the displacement of the object leads to forces that tend to increase the displacement from the equilibrium position, the equilibrium is called Unstable.

The lapse rate γ (super adiabatic lapse rate) is greater than the adiabatic rate of cooling Γ. The system is said to be under unstable equilibrium

Neutral condition:

If no forces arise from the displacement of the object, the equilibrium is neutral. The lapse rate γ is equal to the adiabatic rate of cooling Γ. The system is said to be under Neutra l equilibrium

52. Explain the classification of Pasquill atmospheric stability.

Classification of Pasquill atmospheric stability: Class A - Strongly unstable Class B - Moderately unstable Class C - Slightly unstable Class D - Neutral Class E - Slightly stable Class F - - Moderately stable


The above classification depends on wind speed, horizontal and vertical dispersion coefficients in the atmosphere.

53. What do you understand by: (a) Windrose

Wind rose is the graphical display of wind speed and wind direction by magnitude. Wind rose indicates the predominant wind direction and magnitudes of wind direction in percentage at different elevations.

54. What are the limits in the following cases: a) Monthly dose to a radiation worker b) Annual dose to a casual radiation worker c) Annual dose to skin d) Annual dose to eye lens e) Emergency planned dose - Monthly dose to a radiation worker : 10 mSv - Annual dose to casual radiation worker : 15 mSv - Annual dose to skin : 500 mSv - Annual dose to eye lens : 150 mSv - Emergency planned dose : 250 mSv 55. Why are the ALI values of different radioisotopes different?

The committed effective dose due to unit uptake of a radionuclide is different for different radionuclides. ALI is derived from annual effective dose of 20 mSv. Hence, ALI values are different for different radionuclides.

56. What is the maximum unplanned dose for one month? What action is required if it is planned to exceed this limit? The maximum unplanned monthly dose limit is 5 mSv for department persons and 2.5 mSv for contractor persons. Notification of planned exposure (NOPE) is required for the persons who planned to exceed the limits. NOPE shall be authorized by section Head in case of department personnel and CS in case of contractors.

57. Outline the procedure for disposal of the following types of radioactive

wastes - Ion exchange Resin (field is less then 10 R/h) - Wet filter cartridge (field: 50 R/h) - Organic liquid wastes a. Ion exchange Resin (field is less then 10 R/h)

Ion-exchange resin ejected from SS hopper of PHT/Mod system at Waste Management Centralized Facility (WMCF) into MS hoppers for disposal purposes. If the field is less than 50 R/h, these MS hoppers are disposed into RCC trenches or RCC vaults.


b. Wet filter cartridge (field: 50 R/h)

The wet filter cartridges removed from various systems are shielded after removal and transported to Waste Management Centralized Facility for treatment and disposal. The systems, which generate wet filters as a waste, are PHT Gland Filters, SFSB, Filters, PHT Filters, Resin transfer system filters, liquid effluent treatment process filters etc.

The wet filters are fixed with cement and vermiculate soil in a 200 l drum and allowed for curing.

The wet filter fixed in a drum will be disposed off at Solid Waste Management Facility (SWMF) based on the radiation levels.

c. Organic liquid wastes

Procedure for disposal of organic liquid waste: The organic liquid waste is collected in carboys at the source mainly from tritium counting laboratory and chemical control laboratories. Then, the organic waste is transferred to Waste Management Centralized Facility (WMCF) for treatment and disposal purpose. At WMCF, the organic waste is transferred to a 200 l drum and vermiculate powder is sprinkled to soak in organic waste. The solidified organic waste is disposed off into RCC trenches in resp ective of radiation levels.

58. What are the basic principles of waste management? How are high active

liquid wastes disposed of?

Basic principles of waste management: - Dilute and Disperse (Low active Liquid effluents) - Concentration and contain (High active liquid effluents) - Delay and Decay (Short live radio nuclides)

Disposal of high active Liquid wastes:

High active liquid waste is fixed in vermiculate glass matrix. The disposal of conditional high active liquid waste is depends on the nature of radionuclides and disposed into suitable various Engineered safety disposal facility based on the radiation levels.

59. What is over-exposure? How can it be avoided? How and why it is

investigated?

Over exposure: Dose limits are specified for occupational and temporary workers for a block period of 5 years. In house limits are provided by the station, to ensure that these dose limits are not exceeded. These limits are specified for monthly, quarterly, yearly and internal uptake of tritium & iodine. Any person exceeding these in house limits are said to be received over exposure.

Over exposure shall be investigated to know the genuineness of the dose received by an individual.

Over exposure cases shall be investigated within 72 hours of the report of the exposure, if the quarterly or annual limits are exceeded. In other cases, investigation shall be carried out within 15 days of the report. Investigation


report shall be issued with 48 hours of investigation. A copy of the report shall be sent to SARCOP.

Over exposure can be avoided by following radiation protection procedures, ALARA practices during normal operation of the plant and by following radiation emergency procedures during emergency conditions. These procedures mainly includes the following:

- Adhering to Radiation protection procedures. - Use of Alarming dosimeters - Monitoring individual doses during the job 60. What are the objectives of stack monitoring (sampling)? What are the

technical specifications for releases through stack at your station?

- To estimate the amount of radionuclides released through the stalk to the environment

- To ensure that the effluents released to the environment are within technical specifications of the station approved by Atomic Energy Regulatory Board

- To control the consequences which lead to release of effluents in excess of technical specifications.

Technical Specifications for Gaseous effluents:

H-3 (as oxide) 7.4 TBq/d 200Ci/d

Ar-41 2.96 TBq/d 80Ci/d FPNG 23.68 TBq/d 640 Ci/d

Radioactive Particulate 0.56 GBq/d 15 m Ci/d Iodine-131 0.74 GBq/d 20 mCi/d 61. ALI values are different for different radioisotopes

ALI values are different for different radioisotopes. The committed effective dose due to each radionuclide is different. This is due to type of radiations emitted from a radionuclide, its energies and fields are different. Hence, the dose received by one Bq of different radionuclides is different and thus ALI values are different.

Tritium : 3 × 109 Bq

Iodine-131: 1× 106 Bq 62. Tritiated water is more hazardous than tritium

Tritiated water is more hazardous than tritium. Human body consists of water 60% weight. Hence, tritiated water is easily miscible with body water and thus gives exposure to whole body. Whereas tritium can only replace hydrogen atoms present in body water and gives dose locally. Hence tritiated water is more hazardous than tritium.

63. What hazards do neutrons and X-ray present to the eye?

Neutron posses high Linear Energy Transfer (LET) per a given distance traveled. Hence, exposure of neutrons to eye may cause cataract of the lens. Similarly, X-rays are monoenergetic in nature, may lead to cataract of the eye.


64. Name two changes that occur to atom / molecule when radiation passes

through matter The radiation effects the atom/molecule in two different ways: - Excitation - Ionization

In excitation, the irradiated atom/ molecule goes to high energy level and comes to ground level by emitting excess release in the form of energy. For this process, the atom/molecules rearranges its electrons.

In Ionization, the irradiated atom/molecules divided into positive and negative and which further react with other biological chemical molecules thus changing the chemistry of the body.

65. How is internal exposure of your plant is measured and how it can be

minimized?

Internal Exposure: The internal exposure of plant personnel is estimated by urine analysis. All plant personnel are advised to submit urine samples two hours after completion of the job. The frequency of submission of urine samples shall be once in a week or as and when tritium uptake is suspected.

The internal dose is estimated using the formula: D (mSv) = 0.0583 Q T (for weekly sample submission) = 0.5 Q (Committed dose assuming Tb= 6 d) Where Q=(Q1+Q2)/2 - average tritium uptake in the body in MBq/l. Q1 - tritium uptake on date t1 in MBq/l Q2 - tritium uptake on date t2 in MBq/l T - the time period between two sample submission in days. Control of internal dose: Internal exposure due to tritium can be minimized by

the following methods: a) Use of appropriate respiratory protection b) Avoiding skin wetting c) Providing local ventilation in high tritiated atmospheres. d) Use of remotely operating vacuum mopping systems for recovery of heavy water. 66. Tritium dose contributes a significant % of the collective dose. Give a

comprehensive recommendation and an action plan for minimizing tritium exposure in the operating units.

Tritium dose contributes to about 20% of the collective dose in Pressurized Heavy Water Reactors (PHWRs). The tritium dose can be minimized in PHWRs by the following:

a) Minimizing leaks from PHT System in all areas of reactor building b) Ensuring the availability of all dryers for heavy water collection and with high

efficiency. c) Ensure proper ventilation balance in all reactor-building areas.


d) Provide remotely operable vacuum mopping systems like vacuum for heavy water

recovery. e) Use of appropriate respiratory protection f) Avoiding Skin wetting during heavy water recovery g) Proper isolation of the system, which has high potential for heavy water spillage

prior to taking up the maintenance jobs. 67. What is the importance of Radiation Work Permit (RWP)? How is it

issued?

RWP issue procedures: - RWP Shall be applied by a Green qualified person for all radioactive jobs - Person applying RWP shall fill up all the columns like Reactor Status, Job details,

Job code; persons involved in the job with TLD Nos. and planned doses. - The Shift Health Physicist shall fill up the current month, annual dose details,

uptake details and category details in the permit - He also mention the radiological conditions - He also shall recommend appropriate protective wear and respiratory protective

equipment depending on the radiological conditions. - He also should mention any special precautions to be taken in the work area. - The permit shall be signed by Shift Health Physicist and permit holder

The Radiological Work Permit is valid for a shift, a day depending on the nature of the job

68. Name three dosimetry devices and explain when they are used to

maximum advantage. a) Thermo luminescent dosimeter (TLD):

Used for assessment of gamma and beta dose of station personnel on monthly basis. It is mandatory to use this dosimeter regularly and treated as official dosimeter.

b) Direct Reading Dosimeter (DRD):

Used for assessment of gamma dose on day to day basis for accounting of dose to ensure that monthly, quarterly or yearly doses are not exceeded. It is mandatory to use this dosimeter regularly along with TLD during worker in a radioactive area.

c) Fast Neutron Foils (Cr-39)

Used for assessment of fast neutron dose during on power entry to moderator room or pump room where fast neutron fields exist. It is mandatory to use this dosimeter during on power entry for neutron dose assessment.

69. State the factors on which the tritium concentration in PHT & Moderator

System depends?

The tritium concentration in PHT and Moderator System depends on the following factors:


? Average thermal neutron flux in the system ? Activate cross section of deuteron. ? Disintegrate constant/half-life of tritium ? Total circuit time ? Core transit or influx time ? Total time of reactor operation (full power days) 70. What are the isotopes monitored during whole body counting. What is

the type of detector? The isotopes monitored during while body counting are I131, Co60, Cs137. Gamma detector is used for measuring the γ activity due to the above isotopes

during the whole body counting. Additional Questions (asked during the licensing interviews) 71. What is year’s budgeted Station dose and what percentage of it has already been

consumed? 72. What is Operation section’s budgeted dose and what percentage of it has been

consumed? 73. What kind of filter is used for preventing Iodine escape to environment? Which

are the systems that employ such filters? 74. What will be the actions at our end if any other facility of RAPS site declares site

emergency? 75. What kind of emergency will it be in case of LOCA? 76. What are in -house dose limits for individuals? 77. What are the investigations levels for radiation dose for monthly, quarterly, &

yearly exposure? 78. What are the different parameters available on RADAS? How would you know the

radiation levels incase of failure of RADAS? 79. What is radioactivity?

***** ***** *****

Date post:	04-Apr-2015
Category:	Documents
Upload:	amitsonunitj8131
View:	77 times
Download:	0 times