Occupational Radiation Sources

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.

Provide an explanation of the fission process and its products.

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

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.

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.

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.

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.

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.

Origins of Sources of Radiation

Produced outside plant and received into plant

Produced within the plant

Types of Radionuclide Products

ACTIVATION PRODUCTS

FISSION PRODUCTS

Fission Process

Fission Process

•Releases ~200 MeV Energy

•Energy heats water

•Initiates the production of Power

Binary Fission Process

Produces 2 heavy nuclei -

Fission Fragment

Fission Fragment

Fission Fragments

1.Light fragment – 72-100

1.Heavy fragment - 110-162

~80 different fragments

14156Ba

9236Kr

23592U + 1

0n -> 14156Ba + 92

36Kr + 3 10n + γ

Fission Process & Fission Fragments


23592U + 1

0n ->

14054Xe + 94

38Sr + 2 10n + γ

23592U + 1

0n -> 14256Ba + 92

36Kr + 2 10n + γ


23592U


9539Y

13853I

23592U + 1

0n -> 13853I + 95

39Y + 3 10n + γ


23592U + 1

0n -> 14456Ba + 89

36Kr + 3 10n + γ

Fission ProductsFission fragments and their decay products

~250 different isotopes are known as fission products

23592U

neutron

13552Te

9740Zr

9741Nb

9742Mo

13553I

13554Xe135

55Cs

13556Ba

Fission Process & Fission Products

Fuel Rod

CContains 235U Fuel Pellets

CMade of thin metal sheath –

Cladding

Provide mechanical supportUniform heat transferProtect fuelContain products

γ

γ - Fission Process

n

n– Fission Process

γ – Fission Product Decay

γ – Activation Product Creation

γ – Activation Product Decay

Radiation in the Core

Radiation from the Coolant

γ

γ

γ

γγ

γ

γ - Release of fission product

nn

n

n

Fission Product Release RateChemical nature of fission product

Pressure across cladding

Fuel temperature

Size of cladding crack

thermal stressescorrosive action by coolantmechanical forcesinternal gas pressures


γγ

γ

γ

γγ

γ


n γ – fission product from tramp uranium outside cladding

nn

n

n n γ – fission product from tramp uranium in cladding material

γ – Activation of corrosion

Reactor Coolant Loop Structure Material

Stainless steel

Zircaloy

Inconel

Carbon steel

Steel & Copper Alloys

nickelchromiumcobalt


γγ

γ

γ

γγ

γ


n γ – fission product from tramp uranium outside cladding

nn

n

n n γ – fission product from tramp uranium in cladding material

γ – Activation of corrosion

γ – Activation of coolant & impurities

γ -Transuranic elements

Fission Products

Oxygen availability

Different volume

Increase pressure

Thermal conductivity

Melting point

Radiation source

Chemical propertiesPhysical propertiesRadiological propertiesChemical changePhysical changeRadiological change

Fission Process – Fission Products

Noble gases

HalogensParticulates

Halogens- IodinesVolatility form dependent

Isotopes – I-131, I-133, I-135Removal form dependent

Noble gasesVery volatile – disperse

Insoluble – build pressure, diffuse quicklyNormally short half-lives

Kr-85, Kr-88, Xe-133, Xe-135PWR – waste decay system

BWR – air ejector, gland seal system

ParticulatesChemical state – nuclide dependentSoluble – degree nuclide dependent

Aerosol – volatileVarious half-lives most <2 months

Diffuse slowlyRemoved demineralizer

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.

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.

Activation Products

●Chemicals●Corrosion Products

●Water●Air●Impurities

Activation Corrosion Products

Corrosion fromCore & Coolant System

Coolant System•Nickel•Cobalt•Iron•ManganeseZirconium – Cladding

Copper – Condenser

Silicon/organic material – Water Purification

Cr-51 Mn-54

Mn-56

Fe-55

Fe-59

Co-58

Co-60

Zn-65

Ni-63

Activation Corrosion Products

xNi58(n,p)Co58Co59(n,g)60Co

58Fe + 10n -> 59Fe

Stainless steelInconel Stellite

Iron

Corrosion Products

Insoluble

Fe55 Fe59

Soluble anionic

Cr51

Formsof

Soluble cationic

Co58Co60

Mn54

CRUD

Insoluble voluminous colloid-like

corrosion products

Blocks cooling canalsPoor thermal conductivity

Leads to cladding defects

Deposits on bottom of fuel

CRUD -BWR

Accumulates in vessel – requires special cleaning circuit

Main “crud” – Co60 from stellite

CRUD - PWR

“Crud” mobileTransport affect –

Coolant pHHydrogen Concentration

Throughout coolant system - removal purification system

Main “crud” – Co58 from Inconel

CRUDCreates serious

radiation hazard

Proper pH Corrosion inhibitors use

Mechanical cleaning of chemical washing

Chemistry control

Removal from system

Filtrate to radwaste

Develop & select corrosion-resistant material

Crud Bursts During Station Outages

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.

Important Points

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.

Crud Bursts During Station OutagesContributors

Activation Water Products

x18O(n,g)19O16O(n,g)17N

2H(n,g)3H

26.8 sec

4.14 sec

β16O 16O

16N

n

p16

7N

γ

16O(n,p)16N

167N -> 16

6C + β + γ

166C

Activation of Oxygen in WaterNitrogen Produced

Major source in steam lines7.2 sec half-life – so source on shutdownShielding requirements due to gammaPWR reactor coolantBWR reactor coolant and steam lines

β+

16O 16O

13N

p

a13

7N16O(p,a)13N

137N -> 13

6C + β+

136C

Activation of Oxygen in WaterNitrogen Produced

BWR masked by N-13PWR minimal significance9.9 min Half-lifeBWR discharge as effluentN-13 also produced by – 14N(n,2n)13N

β+

18O 18O

18F

n

p18

9F18O(n,p)18F

189F -> 18

8O + β+

188O

Activation of Oxygen in WaterFluorine Produced

Very soluble110 min half-lifePWR liquid activityBWR feedwater activity

Activation of Air - Argon Produced

40Arng41Arb41K

40Ar(n,g)41Ar

4118Ar -> 41

19K + b + γ

~1% air Argon

Air impurity in water

Deaerated water low Ar-40 content

Ar-41 half-life 1.38 hrs

High Ar-41 content indicates air in coolant

Ternary fission

Activation of Impurities34S

35S 35Cl

14C

13C

14NHalf-life2730 yrs

Activation of Chemicals

Tritium produced by:

Fission processActivation water

Reaction on lithium & boron

Boron Activation10

5Bn73Lia

31H

Lithium and BoronAdditive

Neutron absorbersImpurities

Lithium and BoronContribute to H3

tritium production

Boric Acid

Chemical shimBurnable poison

Control reactor level

PWR’s

LithiumpH control

B-10 activation

Lithium Activation6

3LiFast neutron Thermal neutron

Low or high energy neutrons

Activation of Chemicals

Activation of ChemicalsTritium

Half-life 12.3 yrsDecays by beta only Hard to detect

Part of coolant

T2 or HT exchanges with Hydrogen in H2O

HT = H2O -> HTO + H2

Discharged to environment in condenser waterMajor source of activity in effluents

Difficult to separate

Fission process

n

Fission products

decay

Activation products

decay

n

n

BWR source in Turbine

Bldg also.

Sources of Radiation

Operational Reactor

Access limited

Sources of RadiationShutdown Reactor

No longer producedFission process n,

Fission product decay Activation product decay

Source from

Long-lived Fission Products

Activation Products

Reactor water control

Safety design

Process control

System clean-up

Exposure from Fission Product decay

Activation Product decay

Designed to remove fission & activation products

Uses filters & ion exchangersHigh exposure potential with

components & pipingFilters & ion exchange media -

High exposure potential Radwaste

Sources of RadiationOutside Core or Coolant

Percentage of coolant piped to outside systems for

Sources of High Radiation

Fission & activation products Flow through system

Deposit in low flow areasCreate build-up of radiation levels

Areas of build-upHigh exposure potential

Hot Spots

ID#__________

HOTSPOT

______mrem/hr

ID#__________

HOTSPOT

______mrem/hr

Piping bendsID#__________

HOTSPOT

______mrem/hr

Piping reducers

ID#__________

HOTSPOT

______mrem/hr

Piping welds or joints

ID#__________

HOTSPOT

______mrem/hr

Valves

ID#__________

HOTSPOT

______mrem/hr


Produced Outside the Plant Brought into the Plant Environment

Radioactive SourcesX-ray devices

Radioactive Shipments

Sources of Radiation Produced Outside and Brought into the Plant

EnvironmentRadioactive Sources

By-product Material

Special Nuclear Material (SNM)

Contains Uranium/PlutoniumSurveyed on receipt/routinelyControlled by SNM CustodianExposure potential based upon isotope/contentMade radioactive outside plantSurveyed on receipt/routinely

Controlled by By-product Material CustodianExposure potential based upon isotope/content

Radiography sources

Examines MaterialsEmit g radiation

Co-60, Cs-137, Ir-192Electronic x-rays

Surveyed on receiptStrict use requirementsRadcon coverageHigh potential for exposure

Purposes:Measuring, Checking, Calibrating,

Controlling processes – quantitatively or qualitatively

Known IsotopesKnown ActivityManufactured

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.

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.

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.

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.


Produced Outside the Plant Brought into the Plant Environment

X-ray devicesRadioactive Shipments

Used for processes such as searchesDesigned with shielding to limit exposureRoutine surveys to ensure limited potentialHigher potential with design change or operational error

Non-source items received on siteSurvey required upon receipt

Exposure potential with opening unknown items

RWP REQUIRED FORENTRY

“RADIATION AREA”

“CONTAMINATION AREA”

RWP FOR ENTRY

REMOVE ALL ANTI-C ZONE

CLOTHING BEFORESTEPPING HERE

Spills Of Reactor Coolant

Spills Of Reactor Coolant

Reactor CoolantLeaks

Reactor CoolantLeaks

Maintenance Activities

Performed On A System

Maintenance Activities

Performed On A System

SOURCES OF CONTAMINATION

Contamination Is Radioactive Material In An Unwanted Place!MAJOR SOURCES

Fission ProductsActivation Products

Activated Corrosion Products

Escape piping or components Reactor CoolantCoolant Gases

Activation ProductsFission Products

Boric Acid Corrosion

Boric Acid Corrosion

Defective Welds

Defective Welds

Defective Pump

Gaskets

Defective Pump

Gaskets Flanged Connections

Flanged Connections

ValvesValves

FIXEDContamination Embedded In

Object Cannot Be Removed Through Normal Cleaning

AIRBORNE

RADIOACTIVE

PARTICLES OR GASES

SUSPENDED IN THE AIR

LOOSERADIOACTIVE

MATERIALTRANSFERRABLE

SMEARABLE

Units Of MeasureDPM/100 CM2

UNITS OF MEASURE

CPM

TYPES OF CONTAMINATION

Loose Contamination

HOT PARTICLES

Single discrete particle difficult to see

>0.1 mCi

Activated corrosion product(stellite)

Fuel fragment

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.

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.

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.

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.


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.


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.


LOOSERADIOACTIVE

MATERIALTRANSFERABLE

SMEARABLE


Onto Bodyγ, b

Exposure –IsotopeActivity


Into bodyg, b, a

Exposure –IsotopeActivity


Loose to Fixed

Embedded In Object

UNITS OF MEASURE

CPM

Loose to airborne

Movement to air

FIXED

Contamination Embedded In Object Cannot

Be readily Removed

UNITS OF MEASURE

CPM

FIXED

Exposure – IsotopeActivity

Fixed to Loose or AirborneWeldingGrindingSanding

Fixed to loose or airborneCutting

Abrasive activities

AIRBORNE

Radioactive material

in air PARTICLES

GASES

VAPORS

Noble Gases

Inert - evenly disperse

Emits –

Skin dose

Vapors - Iodines

Form dependentVolatility

vaporization

Exposure potential dependent onIodine isotopeIodine formradioactivity

Enters body through inhalation or ingestionTravels to thyroid

Vapors - Iodines

Pollutant iodines removed by activated charcoal

Elemental iodine Coconut charcoal

Physical attractive forces

Organic iodineNot bound on charcoals

Less effective high humidityImpregnated with chemical

Potassium iodine (KI)Isotopic exchange

CH3I131 + KI127 -> CH3I127 + KI131

Trietheylemidiamine(TEDA)Converts radioiodine to quaternaryiodone – absorbed

R3N + CH3I131 -> R3N + CH3I131-

Effective in high moisture

ParticulatesParticulates

Release of fission or activation products

in aerosol form

Movement of loose

contamination particles

Degradation of fixed

contamination

AIRBORNE

Radioactive particles,

vapors, or gases

suspended in air

Onto body b, g

Exposure potential isotope

radioactivity

Into Bodyb, g, a

Exposure potential isotope

radioactivity

Airborne to loose

Plate-out

Airborne to fixed

Plate-out and embedded in

object

Removal with filtration

Radioactive Filter Handling - Important Points

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

o 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.

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

o 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.

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.

Radioactive Filter Handling - Contributor

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

o 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.

• 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.

Radioactive Filter Handling - Contributor

Occupational exposure from sources of radiation and contamination

Individuals - ALARARadcon – assist individuals

Collective dose – all individualsPlant procedures/work instructions

Source term reduction

Average all monitored – 110 mrem/yr or 1.1 mSv/yr

Average all monitored measurable –220 mrem/yr or 2.2 mSv/yr

Total collective in U. S. all plants12126 Rem/yr or 121.26 Sv/yr

Average total collective per reactor – 117 rem/yr or 1.17 Sv/yr

Documents

Occupational Radiation Sources