Occupational Radiation Sources
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Occupational Radiation Sources. Sources of Contamination. Objectives. List the origins for sources in a nuclear power plant. Identify the classification of radionuclides produced in the fission process and where they are produced.

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Occupational radiation sources

Occupational Radiation Sources

Sources of Contamination


Occupational radiation sources

Objectives

  • List the origins for sources in a nuclear power plant.

  • Identify the classification of radionuclides produced in the fission process and where they are produced.

  • Provide an explanation of the fission process and its products.

  • Recognize a fission process with fission fragments and subsequent decay fission products.


Occupational radiation sources

Objectives

  • Define a ternary fission process event and its functions.

  • Provide a description of fuel rod cladding and its function.

  • List the types and origins of radiation emitted from the reactor core.

  • Identify the origins of radiation emitted from the reactor coolant.

  • Identify the importance of fission products produced.


Occupational radiation sources

Objectives

  • List the types of fission products.

  • Differentiate the types of fission products by

    their properties, isotopes, and removal

    process.

  • Name the origins of activation products

  • Name the origins of activation products.

  • Distinguish activated corrosion products by their origin, properties, isotopes, and removal process.

  • Define “crud” and describe its affect on a PWR and BWR system.


Occupational radiation sources

Objectives

  • Describe activation water oxygen products by the isotopes and radiological hazards.

  • Describe activation water air and impurities products by the isotopes and radiological hazards.

  • Describe activation water chemistry chemical products by the isotopes and radiological hazards.

  • Identify the mechanisms for tritium production, its half-life and radiological hazards.


Occupational radiation sources

Objectives

  • Compare sources of radiation outside the reactor core and coolant.

  • Define “Hot Spot” and identify potential areas for its occurrence

  • List the sources of radiation produced outside the plant and brought into the plant environment.

  • Define contamination and explain its sources.


Occupational radiation sources

Objectives

  • Identify “ hot particles” by definition and sources.

  • Explain the types of contamination, their potential for exposure and precautions utilized to limit the potential.

  • Contrast individual occupational dose and collective occupational dose and the reduction of each.


Occupational radiation sources

Origins of Sources of Radiation

  • Produced within the plant

  • Produced outside plant and received into plant


Occupational radiation sources

Types of Radionuclide Products

FISSION PRODUCTS

ACTIVATION PRODUCTS


Occupational radiation sources

Fission Process


Occupational radiation sources

Fission Process

  • Releases ~200 MeV Energy

  • Energy heats water

  • Initiates the production of Power


Occupational radiation sources

Binary Fission Process

Produces2 heavy nuclei -

Fission Fragment

Fission Fragment


Occupational radiation sources

Fission Fragments

  • Light fragment –

  • 72-100

  • Heavy fragment -

  • 110-162

  • ~80 different fragments


Occupational radiation sources

Fission Process & Fission Fragments

14156Ba

9236Kr

23592U + 10n -> 14156Ba + 9236Kr + 3 10n + γ


Occupational radiation sources

Fission Process &

Fission Fragments

23592U + 10n ->

14054Xe + 9438Sr + 2 10n + γ


Occupational radiation sources

Fission Process & Fission Fragments

23592U + 10n -> 14256Ba + 9236Kr + 2 10n + γ


Occupational radiation sources

Fission Process & Fission Fragments

13853I

23592U

9539Y

23592U + 10n -> 13853I + 9539Y + 3 10n + γ


Occupational radiation sources

Fission Process & Fission Fragments

23592U + 10n -> 14456Ba + 8936Kr + 3 10n + γ


Occupational radiation sources

Fission Products

Fission fragments and their decay products

~250 different isotopes are known as fission products


Occupational radiation sources

Fission Process & Fission Products

neutron

13552Te

13554Xe

13553I

13555Cs

23592U

b

g

13556Ba

g

b

9742Mo

9740Zr

9741Nb


Occupational radiation sources

Fuel Rod

  • Contains 235U Fuel Pellets

  • Made of thin metal sheath –

  • Cladding

  • Provide mechanical support

  • Uniform heat transfer

  • Protect fuel

  • Contain products


Occupational radiation sources

Radiation in the Core

n– Fission Process

γ- Fission Process

γ

γ – Fission Product Decay

n

γ – Activation Product Creation

γ– Activation Product Decay


Occupational radiation sources

Radiation from the Coolant

γ- Release of fission product

γ

n

γ

γ

γ

n

n

n

γ

γ


Occupational radiation sources

Fission Product Release Rate

  • Chemical nature of fission product

  • Pressure across cladding

  • Fuel temperature

  • Size of cladding crack

  • thermal stresses

  • corrosive action by coolant

  • mechanical forces

  • internal gas pressures


Occupational radiation sources

Radiation from the Coolant

γ- Release of fission product

nγ – fission product from tramp uranium outside cladding

γ

nγ – fission product from tramp uranium in cladding material

n

γ

γ

γ

n

γ

γ– Activation of corrosion

n

n

γ

γ


Occupational radiation sources

Reactor Coolant Loop Structure Material

  • Stainless steel

  • Zircaloy

  • Inconel

  • Carbon steel

  • Steel & Copper Alloys

nickel

chromium

cobalt


Occupational radiation sources

Radiation from the Coolant

γ- Release of fission product

nγ – fission product from tramp uranium outside cladding

γ

nγ – fission product from tramp uranium in cladding material

n

γ

γ

γ

n

γ

γ– Activation of corrosion

n

n

γ

γ

γ– Activation of coolant & impurities

γ-Transuranic elements


Occupational radiation sources

Fission Products

  • Oxygen availability

  • Different volume

  • Increase pressure

  • Thermal conductivity

  • Melting point

  • Radiation source

  • Chemical properties

  • Physical properties

  • Radiological properties

  • Chemical change

  • Physical change

  • Radiological change


Occupational radiation sources

Fission Process – Fission Products

Noble gases

Very volatile – disperse

Insoluble – build pressure, diffuse quickly

Normally short half-lives

Kr-85, Kr-88, Xe-133, Xe-135

PWR – waste decay system

BWR – air ejector, gland seal system

Noble gases

Particulates

Chemical state – nuclide dependent

Soluble – degree nuclide dependent

Aerosol – volatile

Various half-lives most <2 months

Diffuse slowly

Removed demineralizer

Halogens- Iodines

Volatility form dependent

Isotopes – I-131, I-133, I-135

Removal form dependent

Halogens

Particulates


Occupational radiation sources

Fuel Defect Operation

  • A reactivity maneuver restriction was imposed, limiting power changes to 3%/hr between 80-100%.

  • Chemistry verified that increased coolant Xenon activity was not caused by cross-contamination between units.

  • Letdown purification flow was raised and additional sampling for fission product trends was started.

  • A second Xenon/Iodine spike occurred 72 days into the operating cycle.

  • A significant increase in Iodine 131 occurred 400 days into the cycle, indicating that the cladding crack had opened up.


Occupational radiation sources

Fuel Defect Operation

  • Off gas activity increased from 2 micro curies/second to 480 micro curies/second and peaked at 1000 micro curies/second.

  • Reactor coolant Iodine levels increased by more than a factor of 10.

  • End cap weld failure can result in hydriding and cladding perforation.

  • Chemistry samples confirmed that a fuel defect was present.

  • The station increased sampling of the off gas release.

  • Conservative limits were placed on power ramp rates to mitigate additional cladding damage.

  • A control rod was fully inserted to suppress local power around the suspected fuel rod.


Occupational radiation sources

Activation Products

  • Corrosion Products

  • Chemicals

  • Air

  • Water

  • Impurities


Occupational radiation sources

Activation

Corrosion Products

Cr-51

Mn-54

Corrosion from

Core & Coolant System

Mn-56

  • Coolant System

  • Nickel

  • Cobalt

  • Iron

  • Manganese

Ni-63

Fe-59

Zirconium – Cladding

Copper – Condenser

Silicon/organic material –

Water Purification

Co-60

Fe-55

Zn-65

Co-58


Occupational radiation sources

Activation Corrosion Products

Iron

58Fe + 10n -> 59Fe

Stainless steel

Inconel

x

Stellite

Ni58(n,p)Co58

Co59(n,g)60Co


Occupational radiation sources

Corrosion Products

Forms

of

Soluble cationic

Soluble anionic

Insoluble

Co58

Mn54

Cr51

Co60

Fe55

Fe59


Occupational radiation sources

CRUD

Insoluble

voluminous

colloid-like

corrosion products

Leads to cladding defects

Blocks cooling canals

Poor thermal conductivity


Occupational radiation sources

CRUD -BWR

Main “crud” – Co60 from stellite

Deposits on bottom of fuel

Accumulates in vessel –

requires special cleaning circuit


Occupational radiation sources

CRUD - PWR

Main “crud” – Co58 from Inconel

Throughout coolant system -

removal purification system

  • “Crud” mobile

  • Transport affect –

  • Coolant pH

  • Hydrogen Concentration


Occupational radiation sources

CRUD

Chemistry

control

Removal

from system

Creates serious radiation hazard

Filtrate to radwaste

Proper pH

Corrosion inhibitors use

Develop & select corrosion-resistant material

Mechanical cleaning of chemical washing


Occupational radiation sources

Crud Bursts During Station Outages

Important Points

  • A crud burst was in progress at the time the vessel head was removed because hydrogen peroxide addition was delayed for two hours.

  • Letdown flow was maintained at too low a value to effectively clean up the reactor coolant system before the head lift began

  • The recirculation pumps were tested with their discharge valves fully open.

  • The crud in solution following the shutdown plated out in the reactor coolant system because of the prolonged time the reactor coolant system was maintained at 340 degrees Fahrenheit.


Occupational radiation sources

Crud Bursts During Station Outages

Contributors

  • Operations personnel were mot responsive to chemistry requests to increase letdown flow rate.

  • Chemistry procedures did not incorporate EPRI guidance on the concentration of soluble Cobalt 58 that would have minimized radiological hazards.

  • Station personnel did not recognize the radiological implications of starting the recirculation pumps.

  • There were no restrictions on the number of recirculation pumps that could be started at the same time.

  • The intermediate range compensating voltage should have been adjusted within 20 to 60 minutes following shutdown.

  • Upper and lower limits on source range count rate were not established to ensure the intermediate range detectors were adjusted during periods of low gamma radiation levels.


Occupational radiation sources

Activation Water Products

2H(n,g)3H

x

18O(n,g)19O

16O(n,g)17N

26.8 sec

4.14 sec


Occupational radiation sources

Activation of Oxygen in Water

Nitrogen Produced

n

β

Major source in steam lines

7.2 sec half-life – so source on shutdown

Shielding requirements due to gamma

PWR reactor coolant

BWR reactor coolant and steam lines

16O

16O

167N

p

16O(n,p)16N

γ

167N -> 166C + β + γ

16N

166C


Occupational radiation sources

Activation of Oxygen in Water

Nitrogen Produced

p

β+

16O

16O

BWR masked by N-13

PWR minimal significance

9.9 min Half-life

BWR discharge as effluent

N-13 also produced by –

14N(n,2n)13N

137N

a

16O(p,a)13N

137N -> 136C + β+

13N

136C


Occupational radiation sources

Activation of Oxygen in Water

Fluorine Produced

n

β+

18O

18O

Very soluble

110 min half-life

PWR liquid activity

BWR feedwater activity

189F

p

18O(n,p)18F

189F -> 188O + β+

18F

188O


Occupational radiation sources

Activation of Air - Argon Produced

Ar-41 half-life 1.38 hrs

High Ar-41 content indicates air in coolant

40Ar(n,g)41Ar

40Ar

41Ar

41K

n

b

g

~1% air Argon

Air impurity in water

Deaerated water low Ar-40 content

4118Ar -> 4119K + b + γ


Occupational radiation sources

Activation

of

Impurities

34S

35Cl

35S

13C

14C

Half-life

2730 yrs

14N

Ternary

fission


Occupational radiation sources

Activation of Chemicals

Tritium produced by:

Fission process

Reaction on

lithium & boron

Activation water


Occupational radiation sources

Activation of Chemicals

Boric Acid

Chemical shim

Burnable poison

Control reactor level

Lithium and Boron

Additive

Neutron absorbers

Impurities

Boron Activation

Lithium Activation

PWR’s

105B

63Li

73Li

31H

n

Fast neutron

a

Thermal neutron

Lithium and Boron

Contribute to H3

tritium production

Lithium

pH control

B-10 activation

Low or high energy neutrons


Occupational radiation sources

Activation of Chemicals

Tritium

Half-life 12.3 yrs

Decays by beta only

Hard to detect

Part of coolant

T2 or HT exchanges with Hydrogen in H2O

HT = H2O -> HTO + H2

Difficult to separate

Discharged to environment in condenser water

Major source of activity in effluents


Occupational radiation sources

Sources of Radiation

Operational Reactor

Access

limited

Activation products

gdecay

Fission process

ng

g

g

n

g

g

g

Fission products

gdecay

BWR source in Turbine Bldg also.

g

n

g

g


Occupational radiation sources

No longer produced

Fission process n,g

Fission product decayg

Activation product decayg

Source from

Long-livedg

Fission Products

Activation Products

Sources of Radiation

Shutdown Reactor

g

g

g

g

g


Occupational radiation sources

Sources of Radiation

Outside Core or Coolant

System clean-up

  • Designed to remove fission & activation products

  • Uses filters & ion exchangers

  • High exposure potential with components & piping

  • Filters & ion exchange media - High exposure potential Radwaste

Process control

Exposure from

Fission Product decayg

Activation Product decayg

Percentage of coolant piped to

outside systems for

Safety design

Reactor water control


Occupational radiation sources

ID#__________

ID#__________

ID#__________

ID#__________

ID#__________

ID#__________

HOT

HOT

HOT

HOT

HOT

HOT

SPOT

SPOT

SPOT

SPOT

SPOT

SPOT

______mrem/hr

______mrem/hr

______mrem/hr

______mrem/hr

______mrem/hr

______mrem/hr

Sources of High Radiation

Piping bends

Piping reducers

Areas of build-up

High exposure potential

Fission & activation products

Flow through system

Deposit in low flow areas

Create build-up of radiation levels

Hot Spots

Valves

Piping welds or joints


Occupational radiation sources

Sources of Radiation

Produced Outside the Plant Brought into the Plant Environment

Radioactive Sources

X-ray devices

Radioactive Shipments


Occupational radiation sources

Sources of Radiation

Produced Outside and Brought into the Plant Environment

Radioactive Sources

Special Nuclear Material (SNM)

Examines Materials

Emit g radiation

Co-60, Cs-137, Ir-192

Electronic x-rays

By-product Material

Purposes:

Measuring, Checking, Calibrating, Controlling processes – quantitatively or qualitatively

Known Isotopes

Known Activity

Manufactured

Radiography sources

Contains Uranium/Plutonium

Surveyed on receipt/routinely

Controlled by SNM Custodian

Exposure potential based upon isotope/content

Surveyed on receipt

Strict use requirements

Radcon coverage

High potential for exposure

Made radioactive outside plant

Surveyed on receipt/routinely

Controlled by By-product Material Custodian

Exposure potential based upon isotope/content


Occupational radiation sources

Radiography – Important Points

  • The trainee left his TLD and alarming dosimeter in his truck.

  • The trainee did not use a survey meter to verify the source was locked before handling the end of the guide tube with the radiographic source in it.

  • The radiographers did not survey the camera as required by procedure to verify the source was fully retracted.

  • The radiographers did not attempt to lock the source in the stored position between radiographs as required by procedure.


Occupational radiation sources

Radiography – Important Points

  • The two workers disregarded radiological postings and entered a controlled area.

  • Licensed personnel did not realize that radiation from the radiography activities would cause the radiation monitors to activate the engineered safety features.

  • Licensed personnel were unaware of the proximity of the radiography to the radiation monitors.


Occupational radiation sources

Radiography – Contributor

  • The qualified radiographer assumed the trainee was qualified, and the trainee assumed the trainee was qualified, and the trainee assumed the radiographer knew he was a trainee.

  • The radiographers did not use alarming rate meters.

  • The survey meter being used had not been checked for response on all scales, and it was not working properly.

  • Misaligned and bowed parts in the camera prevented the source from being fully retracted.


Occupational radiation sources

Radiography – Contributor

  • The radiographers and radiation protection technician did not verify the radiologically controlled area was free of personnel prior to starting work after a break.

  • The radiography was performed approximately 50 feet from the radiation monitors.


Occupational radiation sources

Sources of Radiation

Produced Outside the Plant Brought into the Plant Environment

Non-source items received on site

Survey required upon receipt

Exposure potential with opening unknown items

Radioactive Shipments

X-ray devices

Used for processes such as searches

Designed with shielding to limit exposure

Routine surveys to ensure limited potential

Higher potential with design change or operational error


Occupational radiation sources

SOURCES OF CONTAMINATION

Valves

Maintenance Activities Performed On A System

Defective Pump Gaskets

Defective Welds

Flanged Connections

Boric Acid Corrosion

Escape piping or components

Reactor Coolant

Coolant Gases

Activation Products

Fission Products

MAJOR SOURCES

Fission Products

Activation Products

Activated Corrosion Products

Reactor Coolant

Leaks

Contamination Is Radioactive Material In An Unwanted Place!

Spills Of Reactor Coolant


Occupational radiation sources

TYPES OF CONTAMINATION

LOOSE

RADIOACTIVE MATERIAL

TRANSFERRABLE

SMEARABLE

FIXED

Contamination Embedded In Object Cannot Be Removed Through Normal Cleaning

AIRBORNE

RADIOACTIVE PARTICLES OR GASES SUSPENDED IN THE AIR

Units Of Measure

DPM/100 CM2

UNITS OF MEASURE

CPM


Occupational radiation sources

Loose Contamination

HOT PARTICLES

Single discrete particle

difficult to see

>0.1 mCi

Activated corrosion product

(stellite)

Fuel fragment


Occupational radiation sources

Hot Particle Work Area – Important Points

  • Radiation Protection work planning and work practice were inadequate.

  • Managers were aware of the potential fro DRPs to be present; however, the magnitude of the dose rates that were encountered was not anticipated.

  • There was previous plant experience with DRPs in excess of 100 rem per hour when this evolution was performed in 1991, but theirs information was not widely known, nor was it incorporated into planning for this evolution.


Occupational radiation sources

Hot Particle Work Area – Important Points

  • The increase in hot particle contamination was attributed to the reduced scope of containment and scaffold decontamination.

  • Relevant information about hot particles had been omitted from previous post work ALARA reviews therefore, this information was not incorporated into the incore instrumentation work.


Occupational radiation sources

Hot Particle Work Area – Contributors

  • A radiation protection supervisor determined that the requirements of the hot particle program were not applicable because the definition of a hot particle area was not met, even though it was known that a hot particle existed within the valve for several years.

  • The assigned radiation protection supervisor did not immediately stop work or urge the workers to leave the area when indication of general radiation levels increased from 15 mrem per hour to 250 mrem per hour.


Occupational radiation sources

Hot Particle Work Area – Contributors

  • Contingency plans or actions to be taken if DRPs were encountered in other than controlled areas were not developed.

  • Turnover to the evening shift occurred while work continued,potentially distracting individuals from receiving needed information.

  • Clear expectations regarding DRP controls for the travel path during the transfer of the ACS were not established.

  • Although workers believed DRPs might be present, a DRP check of the unit was not required by the work package nor was one completed before the transfer of the ACS began.


Occupational radiation sources

Hot Particle Work Area – Contributors

  • Because of the ACS design, and the inability to hydrolaze in an upward direction, portions of the unit could not be effectively cleaned.

  • The ACS was not rinsed with demineralized water as it was raised from the fuel pool as had been the practice in the past to help remove potential DRPs.

  • The personnel contamination monitors at the RCA exit were relatively insensitive to the higher energy cobalt-60 gamma radiation and may not detect beta radiation if shielded by clothing or in a location of poor geometry relative to the monitor.


Occupational radiation sources

Hot Particle Work Area – Contributors

  • Sticky pads were not used as prescribed by procedure.

  • Less than adequate radiological work practices were identified.

  • Lack of proper labeling existed at the job site.

  • Less than adequate planning regarding communication methods when wearing certain protective equipment.

  • Less than adequate training for identifying the location of special tags and equipment used for hot particles.


Occupational radiation sources

Onto Body

γ, b

Exposure –

Isotope

Activity

LOOSE

RADIOACTIVE MATERIAL

TRANSFERABLE

SMEARABLE

Loose to Fixed

Embedded In Object

Loose to airborne

Movement

to air

Into body

g, b, a

Exposure –

Isotope

Activity

Units Of Measure

DPM/100 CM2

Units Of Measure

DPM/100 CM2

UNITS OF MEASURE

CPM

Units Of Measure

DPM/100 CM2


Occupational radiation sources

FIXED

Contamination Embedded In Object Cannot Be readily Removed

FIXED

Exposure –

Isotope

Activity

Fixed to loose or airborne

Cutting

Abrasive activities

Fixed to Loose or Airborne

Welding

Grinding

Sanding

UNITS OF MEASURE

CPM


Occupational radiation sources

AIRBORNE

Radioactive material in air

GASES

PARTICLES

VAPORS


Occupational radiation sources

Noble Gases

Emits –b

Skin dose

Inert - evenly disperse


Occupational radiation sources

Vapors - Iodines

Form dependent

Volatility

vaporization

Exposure potential dependent on

Iodine isotope

Iodine form

radioactivity

Enters body through inhalation or ingestion

Travels to thyroid


Occupational radiation sources

Vapors - Iodines

Pollutant iodines removed by activated charcoal

Trietheylemidiamine(TEDA)

Converts radioiodine to quaternaryiodone – absorbed

R3N + CH3I131 -> R3N + CH3I131-

Effective in high moisture

Organic iodine

Not bound on charcoals

Less effective high humidity

Impregnated with chemical

Elemental iodine

Coconut charcoal

Physical attractive forces

Potassium iodine (KI)

Isotopic exchange

CH3I131 + KI127 -> CH3I127 + KI131


Occupational radiation sources

Particulates

Degradation of fixed contamination

Release of fission or activation products in aerosol form

Movement of loose contamination particles


Occupational radiation sources

Removal with filtration

Airborne to loose

Plate-out

AIRBORNE

Radioactive particles, vapors, or gases suspended in air

Onto body

b, g

Exposure potential isotope

radioactivity

Into Body

b, g, a

Exposure potential isotope radioactivity

Airborne to fixed

Plate-out and embedded in object


Occupational radiation sources

Radioactive Filter Handling - Important Points

  • The operator did not recognize that draining the filter had the potential to change radiological conditions in the room.

  • The pre-job brief did not include a discussion of the likelihood that draining the reactor coolant filter could produce high dose rates in the room or a specified sequence of how the activity was to be performed.

  • The radiation work permit did not address the aspect of handling dry filters, filter mishandling incidents, airborne radioactive material control or prevention.

  • The pre-job brief did not consider filter dryness during contingency actions. A hold point that was discussed regarded a dropped filter, but the technicians did not recognize that a filter not dropping completely into the HIC would have the same potential for producing airborne contamination.


Occupational radiation sources

Radioactive Filter Handling - Important Points

  • It was not recognized that the extended drying of the filter over a four-day period, between filter removal and transfer to a temporary storage cask, increased the potential for spreading contamination from the filter.

  • The personnel transferring the radioactive filter did not adequately use ventilation or containment controls to prevent the spread of loose contamination.


Occupational radiation sources

Radioactive Filter Handling - Contributor

  • The work authorization guideline did not recognize that draining the filter had the potential to change radiological conditions in the room.

  • The HP technician did not inquire as to why the operator briefly left the room, assuming that the filter had previously been drained and vented. The operator did not tell the HP technician what he was planning to do.


Occupational radiation sources

Radioactive Filter Handling - Contributor

  • There was a lack of adequate supervisory oversight. One of the technicians was assigned the lead, but was also required to operate the crane ad perform surveys of the filters.

  • The HIC was expected to contain approximately 100 filters, but the problem occurred with filters 68 and 69. If the filling of the HIC had been adequately monitored to observe the remaining free capacity, the technician could have rearranged the filters in the HIC prior to trying to load these filters.

  • The filter was left in service after it exceeded the change-out dose rate limit, which resulted in higher than normal activity level during change-out.

  • The work controls addressed routine conditions. They were not adequate for handling the dry, highly contaminated filter.


Occupational radiation sources

Occupational exposure

from sources of radiation and contamination

Average all monitored –

110 mrem/yr or 1.1 mSv/yr

Individuals - ALARA

Radcon – assist individuals

Total collective in U. S. all plants

12126 Rem/yr or 121.26 Sv/yr

Average all monitored measurable –

220 mrem/yr or 2.2 mSv/yr

Collective dose – all individuals

Plant procedures/work instructions

Source term reduction

Average total collective per reactor –

117 rem/yr or 1.17 Sv/yr


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