ML18171A035

Reew Accident-Range Rms Calibration Process

ML18171A035
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Issue date:	06/27/2018
From:	Steven Garry Office of Nuclear Reactor Regulation
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Accident-Range Gaseous Effluent Monitoring Calibration and Time-Dependent Instrument Response Factors Steve Garry, CHP Sr. Health Physicist Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Radiological Effluents and Environmental Workshop June 27, 2018 New Orleans, LA 1

• This presentation:

- provides basic information on calibration of accident-range gaseous effluent monitors

- is based on proposed guidance for calibration of accident-range effluent monitors given in HPPOS-001 and HPPOS-040

• Other calibration methods may be acceptable 2

TMI Accident Wednesday, March 28, 1979 3

TMI Lessons Learned Task Force Status Report and Short-Term Recommendations NUREG-0578

• March 28, 1979, TMI Accident occurred

• July, 1979, NUREG-0578, TMI Short Term Report, was issued 3 months later, in

• May, 1980, NUREG-0660, NRC Action Plan, was issued in and submitted to Commission for approval

• Nov, 1980, NUREG-0737, TMI Action Plan Requirements, was approved by Commission, & issued in

• RG 1.97, Rev. 2, Instrumentation for Emergencies, was revised in Dec, 1980 4

NUREG-0737 (November, 1980)

(NUREG-0660) 5

NRR Calibration Guidance HPPOS-001

• August 16, 1982, memo from NRR to Regional Administrators

- NRR proposed calibration guidance

- Now known as Health Physics Position HPPOS-001 6

7 RG 1.97 Instrumentation for Nuclear Power Plants to Assess During an Accident

• Rev 0 (1975) provided general guidance

• Rev 1 (1977) provided general guidance

• Rev 2 (1980) & Rev 3 (1983) provided specific guidance for radiation monitoring design and performance specifications

• Rev 4 (2006) provides guidance on new digital instrumentation systems 8

Noble Gases RG 1.97, Rev. 2 & Rev. 3

• Footnote 9: Monitors should be capable of detecting and measuring radioactive effluent concentrations with compositions ranging from fresh equilibrium noble gas fission product mixtures to 10-day-old mixtures, with overall system accuracies within a factor of 2.

• Effluent concentrations may be expressed in terms of Xe-133 equivalents, in terms of noble gas nuclides, or in terms of integrated gamma MeV per unit time.

9

NEI 99-01 [Revision 6]

10

• Unusual Event = 2x ODCM release rate limit

• Alert (1% EPA PAG)

- 10 mrem TEDE, or

- 50 mrem CDE (thyroid)

• Site Area Emergency (10% EPA PAG)

- 100 mrem TEDE

- 500 mrem CDE (thyroid)

• General Emergency (100% EPA PAG)

- 1 rem TEDE

- 5 rem CDE 11

• Establish EALs based on pre-calculated effluent monitor values corresponding to EPA PAG doses for a 1 hr exposure

• X/Qs based on ODCM annual average meteorological data 12

Instrument Manufacturers

• Older Models

- Victoreen (GM and Ion Chambers)

- Eberline (GM and Ion Chambers)

- Kaman (GM and Ion Chambers)

- General Atomics (Cd/Te)

• Newer Models

- Mirion flow-through ion chambers 13

Instrument Response Factors (IRFs)

Monitor Outputs and Dose Code Inputs

• Noble gas effluent monitor outputs are in:

- cpm, or mR/hr, and converted to Ci/sec, or µCi/cc

• Dose Assessment Computer code inputs are:

- Ci/sec (of a mix of radionuclides), or

- µCi/cc (mix) and stack flow rate (CFM) 14

Dose Assessment Computer Codes

• URI, MIDAS, RADDOSE-V, RASCAL, others

• Dose code input is in units of µCi/cc or Ci/sec of a mix of noble gases

• The dose assessment computer codes calculates the adjusted radionuclide mix based on decay of the T = 0 source term

• So the input needs to be Ci/sec or µCi/cc of the total MIX of noble gas radionuclides at each time step 15

Detector measurements

• Detectors DO NOT measure the concentration of the mix, instead, they measure ionizations in cpm, or mR/hr

• Dose assessment codes input is the concentration of the mix (and flow rate);

e.g., uCi/cc or Ci/sec

• So we need an Instrument Response Factor to convert from cpm or mR/hr into concentration uCi/cc or Ci/sec 16

Time Dependent Instrument Response Factors

• Detector signal (cpm or amps) is converted by microprocessor to Ci/cc or Ci/sec

• Vendor Detector Calibration

- Primary calibration is based on Xe-133 gas; e.g., cpm // µCi/cc of Xe-133 (81 keV with 36.5% yield)

• Instrument Response Factors should be based on the calculated isotopic mix

• Isotopic mix changes as a function of time after Rx shutdown 17

Isotopic Mix

• The isotopic mix has a significant effect on the instrument response factors (conventional detectors)

• Use of only Xe-133 calibrations will generally over-estimate the total µCi/cc of a mix

• Use of Xe-133 calibration w/o correction could lead to premature EAL and ECLs declarations

• Can lead to unnecessary protective actions such as sheltering or, more importantly, or unnecessary evacuation 18

GM Detectors

• GMs are energy compensated (e.g., lead shield)

Regular size paper clip

• Energy compensated GMs have a strong energy dependency, under-responding at low energy 19

Ion Chambers

• Measures electrical current (amps) caused by radiation exposure

• Detector output is electrical current (e.g. milliAmps);

- current is directly proportional to exposure rate

• Programmable microprocessor converts milliAmps to mR/hr or µCi/cc or Ci/sec 20

Instrument Response Factors

• Detectors based solely on a Xe-133 calibration (81 keV gamma), at T = 0

• Exposed to a core melt mix of noble gas:

- GM detectors could over-respond by a factor ~30

- Ion Chambers could over-respond by a factor of ~ 10

- Cd/Te detectors could over-respond by a factor of ~ 5

- Flow-through ion chambers may be within factor of ~ 2 21

Mid-Range and High Range Monitors

• Main Issues with GM or Ion Chambers:

- GM response factors that are based only on Xe-133 will over-estimate the release: e.g.,

• 0 to 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />

- Gas Gap - T = 0 high estimate by a factor of ~ 5

- Core Melt - T = 0 high estimate by a factor of ~ 30

• 8 - 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />

- Gas Gap - much better estimate

- Core Melt - much better estimate

• > 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> - under estimate 22

Potential for Unnecessary Evacuations

• Fukishima

- the estimated number of directly-related evacuation caused deaths were more than 50

- includes hospital patients and elderly people at nursing facilities who died from causes such as hypothermia, deterioration of underlying medical problems, and dehydration.

- for long-term displacement, many people (mostly sick and elderly) died at an increased rate while in temporary housing and shelters.

23

Calibration & Surveillances (HPPOS-001)

NUREG 0737, Item II.F.1 Additional Accident-Monitoring Instrumentation (pdf pg 6,7)

ANSI N323 - 1978 calibration methods are NOT applicable

- ANSI N323 applies to portable instrument calibration only and requires portable instruments be:

• Calibrated to the radiation type, geometry, intensity and energy spectrum of intended use

• Un-calibrated scales or ranges should be identified on instrument as not being verified

• Periodic performance tests 24

Calibration Process Step 1. Vendor Calibrations

- Step 1.1 Gas calibration

- Step 1.2 Linearity check

- Step 1.3 Transfer calibration

- Step 1.4 Energy response characterization Step 2. Secondary Calibrations at Plant Step 3. Energy Response Factors Step 4. Instrument Response Factors 25

Xe-133 and Kr-85 HPPOS-001, pdf pg 9

• In general, only 2 gas calibration sources that can be purchased

- Xe-133 with 81 keV gamma (yield = 36.5%)

- Kr-85 beta source (0.5% gamma emission)

• Kr-85 not useful for gamma detection because of low gamma yield, and the sample is in a sample chamber and beta radiation is stopped by the sample chamber wall 26

cpm & mR/hr (HPPOS-001, pdf 17)

• cpm, or mR/hr, is not a good measure of activity or concentration because of detector energy dependence; i.e.,

different gamma energies and different gamma yields

• Example:

- 1 µCi of Xe-135 (250 keV) produces 7.6 times the dose as Xe-133

- 1 µCi of Kr-88 (~2 MeV) produces 48 times the dose as Xe-133 27

GM Detectors

• GM detectors measure gamma flux in cpm (or mR/hr derived from cpm)

• Unshielded GM detectors over-respond to low energy gammas

• Energy compensated, (e.g., lead shielded) GM detectors under-respond to low energy gammas

• Energy compensated GM detectors were designed as a dose-rate monitor for gamma energies > 100 keV 28

Energy-Compensated GM Detectors

• Characteristics:

- Shielding over-compensates for low energy gammas

- Significantly decreases GM response to our primary calibration gas (81 keV gamma from Xe-133)

- Results in inaccurate scaling off the 81 keV response to high energies gammas 29

Ion Chambers

• Ion chambers measure dose & exposure, not activity

- A dose rate instrument (i.e., ion chamber) is being used to measure activity concentrations (µCi/cc of a mix of nuclides)

- Ion chambers are great for dose-rate measurements, but are not a good tool to measure activity

- Mass energy absorption coefficients (i.e., probability of gamma interaction) are about the same for 100 keV as 1 MeV

- However, 10 times the energy is absorbed, so the ion chamber response is 10X higher for 1 MeV vs. 100 keV

- Difficult to measure concentrations of a mix of nuclides

- Requires knowledge of gamma flux (gamma #s and energies) and the detectors response to different gamma energies 30

Cd/Te Solid State Detectors

• General Atomics sold Cd/Te solid state detectors to ~ 20+ sites

• Calibration Report No. E-255-0961, (1984)

RD-72, Wide-Range Gas Monitor, High and Mid-Range Detectors 31

Detector Terminology HPPOS-001

• Prototype - hereafter referred to as a Golden detector; e.g., a Model (V) 847 ion chamber

• Production Unit - A detector identical to the Golden detector sold to power plants 32

Primary Calibration HPPOS-001, pdf pg 8

• Radioactive gas of a NIST traceable concentration is injected into the system to determine detector response:

• At low, medium, & high concentrations

• Measure instrument response factors (cpm // µCi/cc) or (mR/h//µCi/cc) of Xe-133

• Note: re-calibrations at plant, using Xe-133 gas at the plant are not practical, because too much gas would be released: e.g., 1E4 uCi/cc ~ 100 curies 33

Step 1. Primary Calibration HPPOS-001, pdf pg 8 - 11

• Do a rigorous and comprehensive calibration

• Golden (Prototype) detector calibration:

- Step 1.1 GAS CAL: Xe-133 gas at low, medium, and high concentrations

- Step 1.2 LINEARITY Check: Low, medium and high doses

- Step 1.3 TRANSFER Calibration (check):

• Use a reference Cs-137 source

• Use a secondary transfer Cs-137 source (for plants to use for in Secondary Calibration)

- Step 1.4 ENERGY Characterization: To solid sources in a wide energy range from 81 keV to ~ 2 MeV 34

Geometries

• We have two calibration geometries:

- Gas geometry for Xe-133 in the sample chamber/detector geometry

- Solid source geometry in a calibration jig 35

Step 1.1 Primary Calibration Determine the detectors response to a NIST traceable gas source, e.g.,

Xe-133 gas source:

- GM detectors # of cpm // µCi/cc of Xe-133; or

- Ion Chambers # of mR/hr // µCi/cc of Xe-133 Why Xe-133? Its the only readily-available gamma emitting gas source!

36

Xe-133 Primary Gas Calibration 37

Xe-133 Primary Gas Calibration repeat gas calibration 38

Summary of Calibration Data:

GM (V) Detector, Response to Xe-133 Remember this number 39

Xe-133 Gas Calibration (Example)

• The instrument response factor to Xe-133

- 7,193 cpm // µCi/cc of Xe-133

- 0.54 cpm / gps of Xe-133

• The dose assessment code conversion factor

- 1.39E-4 µCi/cc (Xe-133) // cpm 40

Step 1.2 Linearity Check (Cs-137)

Detector Measurements 500 mR/h measurement Source Source dose rates 500 mR/h 41

Step 1.3 Vendor Transfer Calibration

• Vendor does a transfer calibration

- A Reference source is used to validate that each Production detectors response matches the prototype (Golden) detectors primary calibration

- A Secondary transfer source calibration is performed for later use at the plant 42

6.585E3 cpm // 49.7 uCi = 132.3 cpm // uCi 43

Step 1.4 Golden Detector Energy Characterization (at vendor)

• The accident source term is composed of various 60 gamma energies from ~0 keV to ~2 MeV

• We need to know how the detector responds to each of those different gamma energies

• In a solid source geometry, determine the Golden detectors response to various energy gammas 44

Step 1.4 Energy Characterization

• Factory builds a solid-source calibration jig so that they have a fixed geometry

- Calibration jig holds the Golden detector

- Calibration jig has a solid source holder 45

Solid Source Cal Jig

• Place the Golden detector in the jig at a fixed distance (e.g., 6 inches) from the source holder

• Expose the detector to various gamma energies in a solid source geometry 46

GM (V) Energy Characterization end on 47

end-on geometry 48

GM (V) Energy Characterization Side on 49

Outlier 50

51 52 53 Transfer to Plant

• The vendor is finished with Calibration Step 1

- Step 1.1 Gas calibration

- Step 1.2 Linearity check

- Step 1.3 Transfer Calibration

- Step 1.4 Solid source energy characterization

• The equipment and primary calibration data are sent to the plant

• Likely without further instruction on what to do with the energy characterization data 54

Step 2. Plant Secondary Calibration (check)

• Basic Method:

- Use the calibration jig

- Use the transfer source

- Set the detector in the calibration jig

- Mount the transfer source in the calibration jig

- Measure the detectors response

- Compare the results to the factory transfer source results

- Tweak as needed 55

• Repeat periodically

Calibration Step 3 Energy Response Factors

• Objective: calculate the detectors energy response factors (ERF) to each of 60 different gamma energies in a gas geometry

• Analogous to doing an energy efficiency calibration on a gamma spectroscopy system 56

Source Term: 13 Noble Gases 6 Kryptons 7 Xenons

• 1. Kr-83m 7. Xe-131m

• 2. Kr-85m 8. Xe-133m

• 3. Kr-85 9. Xe-133

• 4. Kr-87 10. Xe-135m

• 5. Kr-88 11. Xe-135

• 6. Kr-89 12. Xe-137

13. Xe-138 There are 60 different gamma energies from 13 noble gas nuclides 57

60 Gamma Energies Half keV Half keV Half keV Life Life Life 58

Step 3. Energy Response Factors

• What is an Energy Response Factor (ERF)?

• At each specific energy, the ERF is the detectors response in a gas geometry to a gamma flux; i.e.,

(# of cpm // gps // cc)

• ERFs are gamma energy dependent

• Acronyms

- ERF - Energy response factor

- gps = gammas per second 59

Energy Response Factors (ERFs)

• Objective:

- Calculate ERFs in a gas geometry

(# of cpm // gps / cc )

-For each of 60 different gamma energies 60

Basic Method

1. In a Gas Geometry

• Measure the detectors response to the Xe-133s 81 keV gamma (# of cpm // µCi/cc)

• Normalize (convert) from uCi to gps (# of cpm // gps // cc)

2. In a Solid Geometry

• Measure the detectors response to a wide range of gamma energies (# of cpm // gps) at each solid source energy

• Calculate the relative ratios of the solid source ERFs

3. In a Gas Geometry

• Multiply the Xe-133s 81 keV ERF by the solid source ratios

• Calculate the ERFs for 60 gamma energies 61

Detector Response Depends on the Gamma Energy (HPPOS-001, pdf pg 17 )

Detector response ( cpm or amps ) // µCi/cc depends on each gamma energy and nuclides yield at each gamma energy For example, compare 1 µCi/cc (Xe-133) to 1 µCi/cc (Xe-138)

Xe-133 (127 hour0.00147 days <br />0.0353 hours <br />2.099868e-4 weeks <br />4.83235e-5 months <br /> half-life) 81 keV 36.5% yield Xe-138 (18 min half-life) 1.77 MeV energies with 17% yield 2.02 MeV with 12% yield (29% combined yield) 62 On a uCi //cc basis, Xe-138 produces 80 times more dose rate than Xe-133

If Xe-133 was the only effluent

• In a gas geometry, we could calibrate to Xe-133 and be finished

• Example: 7,193 cpm // µCi/cc Xe-133

= 7,193 cpm // µCi/cc = 1.39E-4 µCi/cc // cpm

- RMS output reads 14,000 cpm

- We then multiply 14,000 cpm x 1.39E-4 µCi/cc // cpm

• = 1.95 µCi/cc of Xe-133

• We input the value 1.95 µCi/cc into the dose code (e.g., RASCAL, MIDAS, RADDOSE) 63

Only 1 gamma emitting calibration gas is available HPPOS-001 (pdf pg 9)

• Xe-133 (81 keV with a 36.5% yield)

- Exception: Kr-85 (beta emitter) (0.5% gamma)

• Our best calibration method:

- Characterize detector energy response using solid sources

- Calculate ERFs in a solid source geometry

- Convert ERFs from a solid source geometry to gas source geometry 64

Xe-133 and Solid Sources

• What we have:

- We have the vendor calibration to Xe-133 in a gas geometry (# of cpm // µCi/cc)

- We have the vendor detector energy characterizations in a solid geometry for 9 gamma energies 65

Example:

• A GM effluent detector is calibrated to Xe-133 gas (81 keV)

• The detector read-out is 7,193 cpm // µCi/cc of Xe-133

• The gamma yield is 0.365 gammas per disintegration

• 1 µCi = 3.7E4 dps

• Gamma emission rate (gps // µCi) =

= (3.7E4 dps // µCi of Xe-133) x 0.365 gamma/dis

= 13,320 gps // µCi of Xe-133 (81 keV)

• ERF (81 keV) = (7,193 cpm // µCi/cc) // 13,320 gps // µCi Xe-133

• ERF (81 keV) = 0.54 cpm //gps //cc of Xe-133 66

Example Assume the plant has received from the factory:

• 1) a rad monitor,

• 2) a transfer source,

• 3) a calibration jig, and

• 4) calibration data as follows:

- Xe-133 gas calibration (# of cpm // µCi of Xe-133)

- A solid source transfer calibration factor

- Energy characterization data for 9 gamma energies in a solid source geometry 67

Primary Gas Calibration - Response to Xe-133 GM (V) Mid-Range Detector, Remember this number 68

Convert ERFs from solid geometry to gas geometry

• We have the solid source gamma energy calibration data from the factory

• Assumption: The ratios of ERFs in a solid geometry is the same as the ERF ratios in a gas geometry 69

Example Energy Calibration

• There are 7 solid calibration sources that were purchased, with 9 gamma energies

• In a solid source geometry, the vendor measured the detectors response to each of 7 solid sources

• Vendor provided the solid source activity in gps and detector response in cpm to each source

• Plant staff calculates the # of cpm // gps for each gamma energy (in a solid source geometry) 70

Solid Source Energy Response GM (V) orientation end-on

• Steel plate simulates sample chamber wall 71

GM Solid Source Energy Calibration Detector Orientation is End-On 72

Solid Source Energy Response GM (V) - orientation side on

• Steel plate simulates sample chamber wall 73

Solid Source Energy Calibration GM (V) Orientation side on OUTLIER 74

Average Solid Geometry ERF Ratios Outlier 75

Relative

Response

Solid Source GM (V) Average ERFs 60.0 50.0 40.0 30.0 20.0 10.0 gamma energy (keV) 0.0 0 200 400 600 800 1000 1200 1400 1600 1800 2000 76

GM (E) Energy Dependence 77

Convert Solid Source ERFs to Gas Geometry ERFs

- From the primary gas calibration, the ERF for Xe-133s 81 keV gamma in a gas geometry is 0.54 cpm // gps/cc

- The ratios of the solid source gamma energies to 81 keV are known.

- The ERFs for 9 gamma energies in a gas geometry (based on scaling to solid source ratios) are calculated

- In order to calculate the ERFs for the other 60 gamma energies,

• Plot the 9 ERFs, do a curve fit and get equation

• Calculate the 60 ERFs for the noble gas gammas 78

Convert ERFs from a Solid Geometry to Gas Geometry 79

Plot the ERFs in Gas Geometry 80

Excel Method

• Let Excel do the work

• Plot the 9 response factors, and do a Trendline

• Get an equation for energy response factors 81

Add Trendline &

Curve Fit Equation 82

Next step:

• Calculate energy response factors for 60 gamma energies

• Use the Excel equation to calculate the 60 different gamma energy response factors 83

13 Noble Gases 6 Kryptons 7 Xenons

• 1. Kr-83m 7. Xe-131m

• 2. Kr-85m 8. Xe-133m

• 3. Kr-85 9. Xe-133

• 4. Kr-87 10. Xe-135m

• 5. Kr-88 11. Xe-135

• 6. Kr-89 12. Xe-137

13. Xe-138 84

Apply Excel equation to calculate 60 Gamma ERFs 85

Apply Excel equation to calculate 60 Gamma ERFs ERF = 0.017* E - 0.2528 86

Apply Excel equation to calculate 60 Gamma ERFs ERF = 0.017* E - 0.2528 87

Apply Excel equation to calculate 60 Gamma ERFs ERF = 0.017* E - 0.2528 88

Apply Excel equation to calculate 60 Gamma ERFs ERF = 0.017* E - 0.2528 89

End of ERF Calculations

• It is now known how the detector will respond to various gamma energies in a gas geometry; i.e.,

• # of cpm // gps/cc for each of 60 gamma energies in a gas geometry 90

Step 4. Calibration Process Instrument Response Factors 91

Dose Code Input URI, MIDAS, RADDOSE-V, others

• Most dose assessment code input is based on a total (combined) radionuclide mix (µCi/cc of a total mix) or Ci/sec of a time-dependent mix of noble gases 92

Two Types of Response Factors

• Energy Response Factors (ERFs) (for each gamma energy)

- cpm or mR/hr // gps/cc

- different ERFs for each gamma energy

• Instrument Response Factors (IRFs) (for a mix of gases)

- cpm // µCi/cc of mix of noble gas nuclides

- mR/hr // µCi/cc of a mix of noble gas nuclides

- IRF values change as the time-dependent mix changes 93

Gamma Flux

• Detectors respond to gamma flux

• Gamma flux:

- Number of gammas per second (gps)

- Energy of the gammas

• The gamma flux of a mix change as gases undergo radioactive decay

• So we need to know, as function of time:

• Gamma flux (numbers of gammas and their energies) 94

Gammas per second (gps)/cc

• Calculate the number of gps/cc in 1 µCi/cc of each isotope, at each energy

- We start by taking 1 µCi/cc of each isotope

- We identify each gamma energy

- We identify the yield of each gamma energy

- Then we calculate the # gps/cc in 1 µCi/cc of each gamma energy 95

Calculate # of gps/cc in 1 Ci/cc of each isotope gps/cc // uCi/cc = 1 µCi x 3.7E4 gps//µCi x Yield 96

Calculate # of gps/cc in 1 µCi/cc of each isotope 97

Calculate # of gps/cc in 1 µCi/cc of each isotope 98

Calculate # of gps/cc in 1 µCi/cc of each isotope 99

Calculate the isotopic fractions

• We just calculated the (# of gpsge/cc) // (µCii /cc) of each isotope (i) at each of 60 energies (ge)

• Next step, we calculate the

(# of gpsge / cc) // (µCi/cc) of the mix

• = isotope fraction of mix * # of gpsge/cc // µCi/cc 100

Isotopic Fractions

• The isotopic fractions change at each time step

• Time steps; e.g., T = 0 hr, T= 1 hr, T = 2 hr, T = 4 hr, T = 8 hr, T=

12 hr, T = 24 hr, T= 7 days, T = 30 days

• For each time step, calculate each isotopes fraction of the mix

• This takes several Excel calculations!

101

Calculating Isotopic Fractions Core Melt

• We need to calculate noble gas isotopic fractions

• For example:

- At T = 0 hrs, we have higher fractions of shorter-lived, with higher energy gamma isotopes

- At T = 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />, we have higher fractions of longer-lived isotopes, with medium energy photons, and lower fractions of short-lived isotopes

- At T = 30 days, we expect mostly Xe-133 and Kr-85 102

Example: Calculate Isotopic Fraction of Mix Core Melt 103

Calculate Isotopic Fraction of Mix Core Melt 104

Calculate Isotopic Fraction of Mix Core Melt 105 105

Calculate Isotopic Fraction of Mix Core Melt 106 106

Mix Fractions (%)

(Core Melt) 107

Calculating gps/cc //µCi/cc of mix for each energy for each isotope (Core melt)

• We now know (for each time step):

Each isotopes fraction of a 1 µCi mix of isotopes The number of gpsge/cc in a 1 µCi/cc of each isotope

• For a 1 µCi/cc mix of isotopes, we can now calculate the number of gps/cc at each energy

= isotopes fraction * # gpsge/cc //1 µCi/cc of each isotope 108

gps/cc // Ci/ccmix at T = 0 (Core melt) 109

gps/cc // Ci/cc at T = 0 (Core melt) 110

(Core melt) 111

(Core melt) 112

(Core melt) 113

Calculate Each Gamma Energys Contribution to the IRFs We started with 1 µCi/cc of a total mix of nuclides At each of the 60 gamma energies, we calculated the

1. of gps/cc at each gamma energy in a 1 µCi/cc mix of isotopes

• For each gamma energy, we now we multiply the # gps/cc //

µCi/cc mix by their ERFs (cpm //gps/cc)

• = (# gps/cc // µCi/cc of a mix) X (# cpm // gps/cc)

= # of cpm // µCi/cc of a mix 114

IRF Contributions @ T = 0 Kr-83m, Kr-85m, Kr-85, Kr-87 115

Kr-88 116

Xe-131m, Xe-133m, Xe-133, Xe-135m, Xe-135, Xe-137 117

Xe-138 118

IRF @ T = 1 hr 119

120 IFRs GM (V) 121

Core Melt IRFs Core melt at 30 days, Kr-85 is 23% of mix Xe-133 is 73% of mix Xe-133 is the primary contributor to the IRF Gas Gap at 30 days Kr-85 is 69% of mix Xe-133 is 29% of mix Xe-133 is the primary Hours after Rx trip contributor to the IRF 122

GM Instrument Relative Response Factors compared to calibration based on Xe-133 Relative Response to Xe-133 Instrument Over-Response Factors 36.0 31.0 Core Melt 26.0 21.0 16.0 11.0 6.0 Gas Gap 1.0 0.1 1 2 4 8 12 24 48 168 720 123

Assumptions & Limitations

• Assumed ideal conditions

• There is no impact from loss of AC power, degraded voltage, high temp & humidity, monitor saturation

• There is no iodine spiking

• No background interference from adjacent sample lines or filter banks Note: for a PWR Reactor Building with 100% NG and 25%

iodine release into containment, at T=0 , the shine through containment 3 walls is 30 R/h 124

• There is:

- no contamination of sample lines or chambers

• Important contaminants are

- Kr-88 decays to daughter Rb-88 particulate (18 min half life)

- Xe-138 decay to Cs-138 particulate (32 min half life)

- no dose rate from HEPA/Charcoal filter banks

- no impact from changes in temperature, humidity,

- A/C power is available or stable voltage 125

Conclusions

• Detector response (in cpm or mR/hr) is highly dependent on incoming photon energy

• The incoming photon energy spectrum decreases rapidly after an accident

• Time-dependent instrument response factors are needed to convert detector response from cpm to uCi/cc of the mix 126

Questions 12 7