Occupational Radiation Sources

1
Occupational Radiation Sources
Sources of Contamination
2
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.

3
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.

4
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.

5
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.

6
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.

7
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.

8
Origins of Sources of Radiation

• Produced within the plant

• Produced outside plant and received into plant

9
Types of Radionuclide Products
FISSION PRODUCTS
ACTIVATION PRODUCTS
10
Fission Process
11
Fission Process

• Releases 200 MeV Energy
• Energy heats water
• Initiates the production of Power

12
Binary Fission Process
Produces 2 heavy nuclei -
Fission Fragment
Fission Fragment
13
Fission Fragments

• Light fragment
• 72-100
• Heavy fragment -
• 110-162
• 80 different fragments

14
Fission Process Fission Fragments
14156Ba
9236Kr
23592U 10n -gt 14156Ba 9236Kr 3 10n ?
15
Fission Process Fission Fragments
23592U 10n -gt 14054Xe 9438Sr 2 10n ?
16
Fission Process Fission Fragments
23592U 10n -gt 14256Ba 9236Kr 2 10n ?
17
Fission Process Fission Fragments
13853I
23592U
9539Y
23592U 10n -gt 13853I 9539Y 3 10n ?
18
Fission Process Fission Fragments
23592U 10n -gt 14456Ba 8936Kr 3 10n ?
19
Fission Products
Fission fragments and their decay products
250 different isotopes are known as fission
products
20
Fission Process Fission Products
neutron
13552Te
13554Xe
13553I
13555Cs
23592U
b
g
13556Ba
g
b
9742Mo
9740Zr
9741Nb
21
Fuel Rod

• Contains 235U Fuel Pellets
• Made of thin metal sheath

• Cladding
• Provide mechanical support
• Uniform heat transfer
• Protect fuel
• Contain products

22
Radiation in the Core

n Fission Process
? - Fission Process
?
? Fission Product Decay
n
? Activation Product Creation
? Activation Product Decay
23
Radiation from the Coolant
? - Release of fission product
?
n
?
?
?
n
?
n
n
?
24
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

25
Radiation from the Coolant
? - Release of fission product
n ? fission product from tramp uranium outside
cladding
?
n ? fission product from tramp uranium in
cladding material
n
?
?
?
n
?
? Activation of corrosion
?
n
n
?
26
Reactor Coolant Loop Structure Material

• Stainless steel
• Zircaloy
• Inconel
• Carbon steel
• Steel Copper Alloys

nickel chromium cobalt
27
Radiation from the Coolant
? - Release of fission product
n ? fission product from tramp uranium outside
cladding
?
n ? fission product from tramp uranium in
cladding material
n
?
?
?
n
?
? Activation of corrosion
?
n
n
?
? Activation of coolant impurities
? -Transuranic elements
28
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

29
Fission Process Fission Products
Noble gases
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
Particulates Chemical state nuclide
dependent Soluble degree nuclide
dependent Aerosol volatile Various half-lives
most lt2 months Diffuse slowly Removed
demineralizer
Halogens- Iodines Volatility form
dependent Isotopes I-131, I-133, I-135 Removal
form dependent
Halogens
Particulates
30
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.

31
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.

32
Activation Products

• Corrosion Products

• Chemicals

• Water

• Air

• Impurities

33
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
34
Activation Corrosion Products
Iron
58Fe 10n -gt 59Fe
Stainless steel Inconel
x
Stellite
Ni58(n,p)Co58
Co59(n,g)60Co
35
Corrosion Products
Forms of
Soluble cationic
Soluble anionic
Insoluble
Co58
Mn54
Cr51
Fe55
Fe59
Co60
36
CRUD
Insoluble voluminous colloid-like corrosion
products
Leads to cladding defects
Blocks cooling canals
Poor thermal conductivity
37
CRUD -BWR
Main crud Co60 from stellite
Deposits on bottom of fuel
Accumulates in vessel requires special
cleaning circuit
38
CRUD - PWR
Main crud Co58 from Inconel
Throughout coolant system - removal purification
system

• Crud mobile
• Transport affect
• Coolant pH
• Hydrogen Concentration

39
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
40
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.

41
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.

42
Activation Water Products
2H(n,g)3H
x
18O(n,g)19O
16O(n,g)17N
26.8 sec
4.14 sec
43
Activation of Oxygen in Water Nitrogen Produced
n
ß
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
?
167N -gt 166C ß ?
16N
166C
44
Activation of Oxygen in Water Nitrogen Produced
p
ß
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 -gt 136C ß
13N
136C
45
Activation of Oxygen in Water Fluorine Produced
n
ß
18O
18O
Very soluble 110 min half-life PWR liquid
activity BWR feedwater activity
189F
p
18O(n,p)18F
189F -gt 188O ß
18F
188O
46
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 -gt 4119K b ?
47
Activation
of
Impurities
34S
35Cl
35S
13C
14C
Half-life 2730 yrs
14N
Ternary fission
48
Activation of Chemicals
Tritium produced by
Fission process
Reaction on lithium boron
Activation water
49
Activation of Chemicals
Boric Acid Chemical shim Burnable poison Control
reactor level
Lithium and Boron Additive Neutron
absorbers Impurities
Boron Activation
Lithium Activation
105B
PWRs
n
73Li
31H
63Li
a
Fast neutron
Thermal neutron
Lithium and Boron Contribute to H3 tritium
production
Lithium pH control B-10 activation
Low or high energy neutrons
50
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 -gt HTO H2
Difficult to separate
Discharged to environment in condenser
water Major source of activity in effluents
51
Sources of Radiation Operational Reactor
Access limited
Activation products g decay
Fission process n g
g
g
n
g
g
g
Fission products g decay
BWR source in Turbine Bldg also.
g
n
g
g
52
No longer produced Fission process n, g Fission
product decay g Activation product decay g
Source from Long-lived g Fission
Products Activation Products
Sources of Radiation Shutdown Reactor
g
g
g
g
g
53
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 decay g
Activation Product decay g
Percentage of coolant piped to outside systems
for
Safety design
Reactor water control
54
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
55
Sources of Radiation Produced Outside the Plant
Brought into the Plant Environment
Radioactive Sources
X-ray devices
Radioactive Shipments
56
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
Contains Uranium/Plutonium Surveyed on
receipt/routinely Controlled by SNM
Custodian Exposure potential based upon
isotope/content
Radiography sources
Made radioactive outside plant Surveyed on
receipt/routinely Controlled by By-product
Material Custodian Exposure potential based upon
isotope/content
Surveyed on receipt Strict use requirements Radcon
coverage High potential for exposure
57
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.

58
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.

59
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.

60
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.

61
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
62
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
63
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
64
Loose Contamination
HOT PARTICLES
Single discrete particle difficult to see gt0.1
mCi
Activated corrosion product (stellite) Fuel
fragment
65
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.

66
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.

67
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.

68
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.

69
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.

70
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.

71
Onto Body ?, 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
72
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 Sandin
g



UNITS OF MEASURE CPM
73
AIRBORNE Radioactive material in air
GASES
PARTICLES
VAPORS




74
Noble Gases
Emits b
Skin dose
Inert - evenly disperse
75
Vapors - Iodines
Form dependent Volatility vaporization
Exposure potential dependent on Iodine
isotope Iodine form radioactivity
Enters body through inhalation or
ingestion Travels to thyroid
76
Vapors - Iodines
Pollutant iodines removed by activated charcoal
Organic iodine Not bound on charcoals Less
effective high humidity Impregnated with chemical
Trietheylemidiamine(TEDA) Converts radioiodine to
quaternaryiodone absorbed R3N CH3I131 -gt R3N
CH3I131- Effective in high moisture
Elemental iodine Coconut charcoal Physical
attractive forces
Potassium iodine (KI) Isotopic exchange CH3I131
KI127 -gt CH3I127 KI131
77
Particulates
Degradation of fixed contamination
Release of fission or activation products in
aerosol form
Movement of loose contamination particles
78
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





79
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.

80
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.

81
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.

82
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.

83
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