ML23115A408

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2023 - Reew NRC Update
ML23115A408
Person / Time
Issue date: 06/28/2023
From: Steven Garry
NRC/NRR/DRA/ARCB
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NRC Update ADAMS Accession Number ML23115A408 Steve Garry, CHP Sr. Health Physicist Division of Risk Assessment Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Radiological Effluents and Environmental Workshop June 28, 2023 Knoxville, TN

Acronyms ARERR Annual Radioactive Effluent Release Report CHRM Containment High Range Monitor Equal to or greater than

< Less than FRD Facility-Related Dose GALE Gaseous and Liquid Effluents GW Ground Water GM Geiger-Mueller GPI Groundwater Protection Initiative I&C Instrument and Control LLD Lower Limit of Detection MOP Member of the Public ODCM Offsite Dose Calculation Manual RASCAL Radiological Assessment System for Consequence Analysis RG Regulatory Guide RP Radiation Protection Standard deviation SME Subject Matter Expert TS Technical Specifications 2

Topics

1. Regulatory Guide Updates
  • RG 1.21 ~ Routine Effluent Monitoring
2. Decommissioning Planning Rule
3. Accident- Monitoring Instrumentation
4. Instrument Calibrations 3

RG 1.21 Rev. 3 (September 2021)

Measuring, Evaluating, and Reporting Radioactive Material in Liquid and Gaseous Effluents and Solid Waste

  • Updated long-term, annual average /Q and D/Q values
  • Environmental monitoring for iodine - 131 in drinking water
  • ODCM - making changes to effluent and environmental programs
  • Calibration of accident-range radiation monitors 4

/Q and D/Q values

  • Long-term annual-average /Q and D/Q should be based on 5 or more years of meteorological data
  • /Q and D/Q values should be reevaluated periodically (e.g., every 3-5 years).
  • If /Q and D/Q values are substantially nonconservative (e.g., higher by 20-30 percent or more),

then revise /Q and D/Q values used in dose assessment codes 5

Environmental Monitoring I -131 in Drinking Water

  • Perform a prospective dose evaluation to determine if the likely dose from I-131 in drinking water is > 1 mrem/yr

- Review RCS to evaluate and trend I-131 concentration

- Review effluent releases for I-131 releases

- Review dose assessments (if any)

  • If dose is > 1 mrem/yr, then perform I-131 sampling &

analysis using an LLD of 1 pCi/L

  • If dose is < 1 mrem/yr, perform I-131 sampling and analysis using an LLD of 15 pCi/L 6

Offsite Dose Calculation Manual (ODCM)

  • ODCMs need to be kept current
  • Technical Specifications establish the process for changing the ODCM (not 10 CFR 50.59)

- Plant operating status (operating or decommissioning)

- Review plant changes affecting FSAR or ODCMs (e.g., radwaste processing, outdoor tank usage)

- Identify changes in principal radionuclides (e.g., failed fuel or decommissioning status - e.g., noble gas and iodine have been eliminated)

- Installation of new or out-of-service radwaste processing equipment (e.g., new outdoor holdings) 7

Environmental Dosimetry Direct Radiation Dose

  • RG 4.13, Rev. 2, Environmental Dosimetry - Performance Specifications, Testing, And Data Analysis was revised in June 2019
  • RG 4.13 provides an NRC-approved method of determining facility-related dose (FRD) from direct radiation
  • NRC endorsed ANSI/HPS N13.37, Environmental Dosimetry -

Performance Specifications, Testing, And Data Analysis

  • RG 4.13 methods can be used in the demonstration of compliance with 10 CFR 20.1302 surveys and EPAs 40 CFR 190s dose limit of 25 mrem/year 8

How to demonstrate compliance with EPA 25 mrem /yr dose limit

  • NUREG-0543 (ML081360410) says compliance with Appendix I demonstrates compliance with EPA limits, assuming no direct radiation
  • EPA annual dose limit (required by 10 CFR 20.1301(e)) is 25 mrem/yr to whole body and any organ (except thyroid = 75 mrem)
  • Assuming no inhalation dose, then demonstrate ingestion dose (mostly C-14) is < 10 mrem/yr

- If effluent dose < 10 mrem

- If direct radiation dose < 10 mrem

- Then < 20 mrem is less than the 25 mrem EPA 40 CFR 190 limit 9

Calculating Direct Radiation Dose Using Environmental Dosimetry

  • Environmental dosimetry can measure facility-related dose (FRD) dose at ~

5 mrem/quarter, and ~ 10 mrem/year

  • Do not use Ring-averaging, averaging masks a single sectors dose
  • Using historical data, determine the baseline background dose rate and the baseline standard deviation () at each location
  • Then, on a quarterly basis, perform a 2-step data analysis:

- At each location, determine if there is a detectable increase greater than 3? (this is a yes/no question)

  • If potential increase 3, then no facility-related dose (FRD)
  • If potential increase > 3, determine the facility-related dose
  • FRD is calculated by subtracting the current quarterly reading from baseline background dose rate
  • Do not subtract the 3 value 10

Reporting Abnormal Discharges (leaks and spills)

  • RG 1.21, Section 9.5, Supplemental Information

- Provides guidance on reporting abnormal releases from plant equipment into onsite groundwater

- RG 1.21, Section 9.5 reporting thresholds include:

  • Voluntary reports under NEI 07-07, Industry Groundwater Protection Initiative - Final Guidance Document, Rev. 1
  • Abnormal discharges to the unrestricted area
  • Information submitted should include:
  • Date, duration, volume, etc.
  • Doses to public 11

12 RG 4.25 Groundwater Discharges to Offsite Areas

  • A common question is the tritium leak getting off-site?
  • Leaks to offsite areas are detected by boundary sentinel wells
  • RG 4.25 - provides guidance on calculating groundwater discharges to off-site groundwater 13

Return/Reuse of Previously Discharged Radioactive Effluents

  • Regulatory Issue Summary (RIS) 2008-03 (ML072120368) discusses return/reuse of RAM (e.g., rainout of tritium or a water intake from lakes or rivers)
  • RIS 2008-03 states radioactive material (with less than exempt concentrations) that once properly released in gaseous or liquid effluent is no longer considered licensed material (this does not apply to solid waste)
  • Therefore, unlicensed material returned to the site can be discharged without being considered a new radioactive material release
  • However, licensees are responsible for evaluating any new exposure pathways contributing to more than 10% of total effluent dose (per RG 1.109) 14

List of Leaks and Spills (L&S)

  • 54 currently licensed and operating nuclear sites
  • 37 of those sites historically have had L&S of H-3 20,000 pCi/L reported
  • 8 sites currently have residual radioactive ground water with H-3 20,000 pCi/L 15

Remediation of Leaks and Spills

  • SRM-SECY-13-108, Remediation of Residual Radioactivity During Operations
  • Evaluate feasibility of prompt remediation
  • However, prompt remediation is not a requirement 16

Decommissioning Planning Rule* (DPR)

  • During operations, licensees are required to plan for decommissioning
  • The DPR (2012) made changes to 10 CFR 20.1501(a) to require radiological surveys in the subsurface (i.e., ground water)
  • 10 CFR 20.1406(c) - Licensees shall minimize residual radioactivity (contamination), including subsurface (ground water) 17

10 CFR 20.1501 Radiological Surveys and Monitoring for Groundwater

  • Industry guidance documents:

- NEI 07-07, Industry Groundwater Protection Initiative - Final Guidance Document, Rev. 1

- NEI 08-08, Generic FSAR Template Guidance for Life Cycle Minimization of Contamination

- NEI 09-14, Guideline For The Management Of Underground Piping And Tank Integrity 18

Decommissioning Programs

  • Licensees must maintain and update 10 CFR 50.75(g) record-keeping files to include leaks and spills
  • In support of license termination, groundwater monitoring may need to be increased
  • Decommissioning-related RGs

- RG 4.22, Decommissioning Planning During Operations

- RG 1.185, Standard Format and Content for Post-Shutdown Decommissioning Activities Report

- NUREG-1757, Consolidated Decommissioning Guidance (Vol. 2 was updated in 2022) 19

Liquid Effluents Disposed Into On-site Ponds

  • Some licensees dispose of liquid effluents to on-site ponds, reporting as though releases were to the unrestricted area
  • There is an important footnote in RG 4.25 that provides an exclusion for reporting leakage from on-site ponds into GW if the release has been previously accounted for

- Leakage from bottom of lake or pond to groundwater does not need to be reported (again)

  • However, if the off-site dose from leakage from onsite ponds is greater than 10% of all exposure pathways combined (per RG 1.109*), then the potential dose through the new groundwater pathway must be assessed
  • *RG 1.109, Calculation of Annual Doses to Man from Routine Releases of Reactor Effluents for the Purpose of Evaluating Compliance with 10 CFR part 50, Appendix I 20

Regulatory History:

Post-Accident Radiation Monitoring

  • March 28, 1979, TMI accident occurred

- Noble Gas effluent monitoring range to be increased

- Iodine and Particulate sampling to be provided

- Containment high range monitors must be increased

  • Sept 13, 1979, Generic Letter 1979-040:

NRC Short Term Recommendations (ML031320328)

- Operating reactors should begin to implement the actions in NUREG-0578

- Within 30 days, licensees are requested to submit a commitment to meet the short-term recommendations in NUREG-0578 21

Regulatory History:

Post-Accident Radiation Monitoring

  • October 30, 1979, Generic Letter 79-56: Lessons Learned on TMI Short Term Requirements (ML031320403)

- Requesting licensees to submit within 15 days a description and justification of any differences with NRC staff recommendations described in NUREG-0578

- The NRC staff action plan was issued and submitted to the Commission for approval

- The NRC staff Action Plan identified discrete, scheduled tasks, including Item II.F.1 Additional accident monitoring instrumentation 22

Regulatory History:

Post-Accident Radiation Monitoring

- 1980, NUREG-0737 - TMI Action Plan (ML051400209)

- Item II.F.1 & Table II.F.1-1

- Calibrate effluent monitoring instruments to Xe-133

- Describe procedures for converting instrument readings to release rates, considering radionuclide spectrum distribution as a function of time after shutdown

- 1982 - Generic Letter 82 Post-TMI Requirements

- Requested licensees to furnish information within 30 days of completion of TMI action items that were scheduled for implementation between July 1, 1981, and March 1, 1982.

- 1982 - Generic Letter 82 Post-TMI Requirements

- 50.54(f) letter - NRC sent a letter requiring licensees to furnish information within 30 days of completion of TMI action items and if not completed, a proposed schedule for completion 23

Accident Monitoring Instrumentation

  • Item II.F.1 is Additional Accident-Monitoring Instrumentation

- Item II.F.1 Noble gas effluent monitoring

- Item II.F.1 Iodine and particulate sampling and analysis

- Item II.F.1 Containment high range radiation monitoring

  • Tables II.F.1-1, II.F.1-2, and II.F.1-3 establish specifications for radiation monitoring equipment 24

NUREG-0737, Item II.F.1-1 Noble Gas Effluent Monitoring

  • Calibrate effluent monitoring instruments to Xe-133
  • Describe procedures for converting instrument readings to release rates, considering radionuclide spectrum distribution as a function of time after shutdown 25

NUREG-0737, Item II.F.1-2 Iodine and Particulate Monitoring

  • Real time monitoring is not required
  • Capability for effluent monitoring by sampling is required
  • Use adsorption on charcoal or other media
  • Licensees must develop procedures for collection and analysis of onsite samples
  • Note: Iodine releases can be calculated based on partitioning (scaling) factors to noble gas (RG 1.21) 26

NUREG-0737, Item II.F.1-3 Containment High Range Monitors (CHRMs) 27 27

Instrument Criteria

  • Three different instrument criteria:

- Design criteria - how good is the instrument?

- Calibration criteria - what tolerance?

- Measurement criteria - how accurate?

28

Three Different Criteria

  • Design Criteria:
  • RG 1.97, Instrumentation For Light-Water-Cooled Nuclear Power Plants to Assess Plant and Environs Conditions During And Following an Accident,
  • Establishes a design accuracy criterion of a factor of 2 over an energy range of 60 keV to 3 MeV
  • Note: These are design criteria, not calibration criteria 29

RG 1.97 Design Criteria

  • Effluent monitors should be capable of detecting and measuring fresh noble gas mixtures (0 - 10 days) within overall system accuracy factor of 2 (Table 1, footnote 9)
  • Iodine and particulate sampling and analysis

- Capability of removing samples and analyzing without exceeding 5 rem

  • Containment High Range Monitors (CHRMs) should respond to gamma radiation photons:

- from 100 keV to 3 MeV within +/- 20%, and

- from 60 keV to 3 MeV within a factor of 2 (Table 1, footnote 7)

- Note: That is essentially the specifications of an ion chamber 30

Accuracy Criteria

  • NUREG-0737, Rev. 1, Clarification of TMI Action Plan Requirements states that the accuracy requirement is that accuracy is sufficient to perform intended function (no numerical guidance)
  • ANSI N320-1979, Performance Specifications for Reactor Emergency Radiological Monitoring Instrumentation provides an overall system accuracy criteria for logarithmic instruments of +/- 40%
  • IEEE-497, Accident Monitoring Instrumentation for Nuclear Power Generating Stations specifies required accuracy within +/- 50%

31

Design, Calibration & Measurement

  • Design criteria is prescribed in RG 1.97 within a factor of 2 (this is not a calibration criteria)
  • Calibration criteria is prescribed in NUREG-0737 as sufficiently accurate to perform the intended function

- ANSI N320-1978 says overall accuracy should be +/- 40%

- IEEE-497 - required accuracy should be +/- 50%

  • Measurement criteria is prescribed in NUREG-0737 is per RG 1.97 (i.e., within a factor of 2) 32

NUREG-0737 Item II.F.1-1 Noble Gas Effluent Monitoring

  • Ion chamber, GM detector, scintillator or CdTe(Cl) solid-state detector output is in mR/hr or cpm
  • Vendor provides energy response characterization from low (~81 keV) to high (~3 MeV) gamma energy
  • Vendor provides instrument response factor (efficiency factors) for Xe-133 (and Kr-85 for scintillators and CdTe(Cl) detectors) 33

NUREG-0737 Item II.F.1-1 Noble Gas Effluent Monitoring

  • Licensees perform periodic calibration checks with a solid source to ensure proper operation
  • Licensees should account for time-dependent, changing radionuclide mix 34 34

Basic Calibration Process 35

Accident Range Effluent Monitors

  • Vendors perform initial calibrations, the vendor:

- Performs dose-rate linearity check

- Determines the detectors energy response characteristics

- Determines the instrument response factor for a standard gas (Xe-133 or Kr-85)

- (µCi/cc) / (cpm) or (µCi/cc) / (mR/hr)

- Provide a field calibration check method (e.g., a field calibrator with a Cs-137 source)

- Provide a calibration summary report with a certificate for a check source value 36

In-plant Calibration Checks

  • Licensees decay correct the check source dose rate
  • I&C/RP/ Chem conduct a one-point radiological calibration check
  • I&C conduct an electronic calibration check for all scales above first decade
  • Instrument adjustments are normally NOT made based on the radiological calibration check 37

Instrument Response Factors (effluent monitors)

  • Normally, noble gas effluent monitoring instruments are GM detectors, ion chambers, plastic scintillators, or CdTe(Cl) solid-state detectors
  • GM and ion chambers are typically calibrated to Xe-133; i.e., to low energy, 81 keV photons with low yield (~36%)
  • Plastic scintillators and solid-state detectors are calibrated to Xe-133 (gamma) and/or Kr-85 (beta)
  • Energy response curves are provided in the vendor calibration summary report 38

Instrument Response Factors (Contd)

  • Instrument output is a count rate or a dose rate
  • Output is converted to a Xe-133 concentration, µCi/cc
  • Concentration (µCi/cc) times flow rate (cubic feet per sec) = release rate (µCi/sec)
  • µCi/cc x flow rate = release rate (µCi/sec) of Xe-133 39

Time-Dependent Instrument Response Factors

  • Gaseous effluent is not just Xe-133
  • Gaseous effluent is a mix of noble gases, and is very energy dependent and time dependent
  • Generally, short-lived noble gas nuclides have higher energy gammas than long-lived nuclides
  • Detector efficiency is higher for high energy gammas
  • A time-dependent instrument response factor is needed for a mix of noble gases 40

Accident Source Term: ~ 13 Noble Gases 6 Kryptons 7 Xenons

  • 1. Kr-83m 7. Xe-131m
  • 2. Kr-85m 8. Xe-133m
  • 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 and gamma yields from ~13 noble gas nuclides 41

~ 60 Gamma Energies Half keV Half keV Half keV Life Life Life 42

Isotope Specific Efficiency Factors

  • Effluent monitor output is based on a Xe-133 calibration
  • Dose assessment code input is based on a mix of gases
  • Need to converting rad monitor output to dose assessment code input
  • Each noble gas has its own efficiency factor, uCi/cc / mR/hr (or cpm)
  • Calculate each noble gass efficiency factor; e.g.,

- Xe-133 has 81 keV photon with 36% yield, and efficiency is 7.5 mR/hr / uCi/cc

- Xe-138 has 1.8 MeV photon with 17% yield and efficiency is 30 mR/hr / uCi/cc

  • For each time step, determine the isotopic fractions of each noble gas
  • The isotopic mix is time dependent because short-lived nuclides decay
  • Example:

- at T = 0, Xe-133 (T1/2 = 127 hr) is 32% of mix; at T = 8 hr, Xe-133 is 80% of mix

- at T = 0, Xe-138 (T1/2 = 0.3 hr) is 27% of mix; at T= 8 hr, Xe-138 is 0.0% of mix 43

Weighted Efficiency Factors

  • Determine the weighted efficiency factors at each time step
  • Multiply the fraction of each isotope in the mix by each isotopes efficiency factor
  • To obtain the time-dependent instrument response factor, sum the weighted efficiency factors over all nuclides; e.g.,
  • From slide 43, obtain each isotopes efficiency factor and multiply by the isotopes fraction of the mix; e.g.,

T = 0 hr: Xe-133 (32% x 7.5) + Xe-138 (27% x 30)

= 10.5 gross uCi/cc / mR/hr T = 8 hr: Xe-133 (80% x 7.5) + Xe-138 (0.0% x 30)

= 6 uCi/cc gross / mR/hr 44

Dose Assessment

  • Rad monitor output is then multiplied by this time dependent conversion factor to get gross uCi/cc for entry into the dose assessment code
  • Dose assessment codes then re-fractionate the gross mix back into isotopic activity concentrations
  • Dose assessment codes then calculate the dose rate from each isotope and add them together to get total dose rate to MOP 45

Relative Instrument Response Factors for GM detector (based on calibration to 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 Hours after shutdown 46

Plant Staff Responsibilities

  • Plant staff should:

- know which department is in charge and who is the SME

- know what equipment is installed and how equipment works

- have vendor manuals and calibration summary reports available

- how calibration checks are performed and whether checks meet calibration tolerances

- the basis for instrument response factors

- how monitor output interfaces with dose assessment codes 47

Iodine and Particulate (I&P)

Monitoring

  • Real-time iodine and particulate monitoring is not required
  • However, licensees should have procedures for sample collection and analysis of hot samples
  • Real-time dose assessment for iodine and particulate can be performed using scaling factors to noble gas 48

Containment High Range Monitors (CHRMs)

  • CHRMs readings are used in Emergency Action Levels (EALs) thresholds and for assessing core damage
  • Licensee staff perform a one-point radiological calibration check below 10 R/hr
  • Licensee staff perform an electronic calibration check for each decade above 10 R/hr
  • Several recent NRC violations for calibration checks not meeting acceptance criteria for calibration tolerances 49

NRC Staff Training CHRMs

  • NRC gave training to NRC inspection staff on CHRMs in 2021
  • Training material is publicly available at ML21327A271 50

Questions & Discussion 51

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