ML16280A369
| ML16280A369 | |
| Person / Time | |
|---|---|
| Site: | Nuclear Energy Institute |
| Issue date: | 11/09/2016 |
| From: | Kevin Hsueh Licensing Processes Branch (DPR) |
| To: | Cummings K Nuclear Energy Institute |
| Benney B, NRR/DPR, 301-415-2767 | |
| References | |
| CAC MF8122 | |
| Download: ML16280A369 (10) | |
Text
November 9, 2016 Mr. Kristopher Cummings Senior Project Manager, Used Fuel Programs Nuclear Energy Institute 1201 F Street, NW, Suite 1100 Washington, D.C. 20004
SUBJECT:
DRAFT SAFETY EVALUATION FOR NUCLEAR ENERGY INSTITUTE TOPICAL REPORT NEI 16 GUIDANCE FOR MONITORING OF FIXED NEUTRON ABSORBERS IN SPENT FUEL POOLS (CAC NO. MF8122)
Dear Mr. Cummings:
By letter dated May 10, 2016 (Agencywide Documents Access Management System (ADAMS)
Accession No. ML16147A078), as supplemented by letter dated August 30, 2016 (ADAMS Accession No. ML16265A248), the Nuclear Energy Institute (NEI), on behalf of the nuclear industry, submitted NEI 16-03, Guidance for Monitoring of Fixed Neutron Absorbers in Spent Fuel Pools, Revision 0. The NEI submittal provides guidance for monitoring programs for fixed neutron absorbers in spent fuel pools as a means to demonstrate compliance with the applicable requirements in Title 10 of the Code of Federal Regulations Part 50.68, Criticality Accident Requirements, with respect to the neutron absorbing materials.
Twenty working days are provided for you to comment on any factual errors or clarity concerns contained in the safety evaluation (SE). The final SE will be issued after making any necessary changes. The NRC staff's disposition of your comments on the draft SE will be discussed in the final SE. To facilitate the NRC staff's review of your comments, please provide a marked-up copy of the draft SE showing proposed changes and provide a summary table of the proposed changes.
If you have any questions, please contact Brian Benney at 301-415-2767.
Sincerely,
/RA/
Kevin Hsueh, Chief Licensing Processes Branch Division of Policy and Rulemaking Office of Nuclear Reactor Regulation Project No. 689
Enclosure:
Draft SE
Draft SE ML16280A369;
- concurred via e-mail NRR-1043 OFFICE NRR/PLPB/PM NRR/PLPB/LA*
NRR/ESGB/BC*
NRR/PLPB/BC NAME BBenney DHarrison PKlein KHsueh DATE 11/2/16 10/27/16 11/2/16 11/9/16
Enclosure DRAFT SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION 1
2 NUCLEAR ENERGY INSTITUTE TOPICAL REPORT 16-03 3
4 GUIDANCE FOR MONITORING OF FIXED NEUTRON ABSORBERS 5
6 IN SPENT FUEL POOLS 7
8 PROJECT NO. 689 9
10
1.0 INTRODUCTION
11 12 By letter dated May 10, 2016 (Agencywide Documents Access Management System (ADAMS) 13 Accession No. ML16147A078), as supplemented by letter dated August 30, 2016 (ADAMS 14 Accession No. ML16265A248), the Nuclear Energy Institute (NEI), on behalf of the nuclear 15 industry, submitted NEI 16-03, Guidance for Monitoring of Fixed Neutron Absorbers in Spent 16 Fuel Pools, Revision 0. The purpose of the document is to provide guidance for licensees to 17 develop an acceptable fixed neutron absorber monitoring program in spent fuel pools (SFPs) as 18 a means to demonstrate compliance with applicable regulations in Section 50.68 of Title 10 of 19 the Code of Federal Regulations (10 CFR), Criticality Accident Requirements, 10 CFR Part 50, 20 Appendix A, General Design Criterion (GDC) 61, Fuel Storage and Handling and Radioactivity 21 Control, and 10 CFR Part 50, Appendix A, GDC 62 Prevention of Criticality in Fuel Storage 22 and Handling, with respect to neutron absorbing materials (NAMs).
23 24
2.0 REGULATORY EVALUATION
25 26 The credited neutron absorber monitor (NAM) installed in SFP storage racks ensures that the 27 effective multiplication factor (keff) does not exceed the values and assumptions used in the 28 criticality analysis of record (AOR) and other licensing basis documents. The AOR is the basis, 29 in part, for demonstrating compliance with plant technical specifications and with applicable 30 NRC regulations. Degradation or deformation of the credited NAM may reduce safety margin 31 and potentially challenge the subcriticality requirement. NAMs utilized in SFP racks exposed to 32 treated water or treated borated water may be susceptible to reduction of neutron absorbing 33 capacity, changes in dimension that increase keff, and loss of material. A monitoring program is 34 implemented to ensure that degradation of the NAM used in SFPs, which could compromise the 35 ability of the NAM to perform its safety function as assumed in the AOR, will be detected. The 36 U.S. Nuclear Regulatory Commissions (NRCs) regulatory requirements and corresponding 37 staff review criteria and guidance for NAM monitoring programs are contained in the following 38 documents:
39 40 10 CFR 50.68(b)(4), Criticality accident requirements, states that if the licensee does 41 not credit soluble boron in the SFP criticality AOR, the k-effective (keff) of the SFP 42 storage racks must not exceed 0.95 at a 95 percent probability, 95 percent confidence 43 level. If the licensee does take credit for soluble boron, the keff of the SFP storage racks 44 must not exceed 0.95 at a 95 percent probability, 95 percent confidence level, if flooded 45 with borated water, and if flooded with unborated water, the keff must remain below 1.0 at 46 a 95 percent probability, 95 percent confidence level. The keff is defined as the effective 47 neutron multiplication factor.
48 GDC 61, Fuel storage and handling and radioactivity control, states that The fuel 1
storage and handling, radioactive waste, and other systems which may contain 2
radioactivity shall be designed to assure adequate safety under normal and postulated 3
accident conditions. These systems shall be designed (1) with a capability to permit 4
appropriate periodic inspection and testing of components important to safety 5
6 GDC 62, Prevention of Criticality in Fuel Storage and Handling, states that Criticality in 7
the fuel storage and handling system shall be prevented by physical systems or 8
processes, preferably by use of geometrically safe configurations.
9 10 NUREG-0800, Standard Review Plan [(SRP)], Section 9.1.1, Revision 3, Criticality 11 Safety of Fresh and Spent Fuel Storage and Handling (ADAMS Accession 12 No. ML070570006) provides guidance regarding the acceptance criteria and review 13 procedures to ensure that the proposed changes satisfy the requirements in 14 10 CFR 50.68.
15 16 NUREG-0800, Standard Review Plan, Section 9.1.2, Revision 4, New and Spent Fuel 17 Storage (ADAMS Accession No. ML07055057) (ML103490041) provides guidance 18 regarding the acceptance criteria and review procedures to ensure that the proposed 19 changes satisfy the requirements in 10 CFR 50.68.
20 21 NUREG-1801, Generic Aging Lessons Learned (GALL) Report, Revision 2 (ADAMS 22 Accession No. ML103490041) provides guidance on what constitutes an acceptable 23 monitoring program for NAM credited for criticality control in the SFP.
24 25
3.0 TECHNICAL EVALUATION
26 27 Guidance for developing a NAM monitoring program for the SFP is provided in NEI 16-03. The 28 purpose of a NAM monitoring program is to verify that the NAM installed in SFPs continues to 29 perform its safety function (i.e., criticality control) as assumed in the AOR. The guidance 30 provided in NEI 16-03 for a NAM monitoring program, relies on periodic inspection, testing, 31 monitoring, and analysis of the NAM to ensure that the required subcriticality margin is 32 maintained in accordance with 10 CFR 50.68 requirements. To accomplish this purpose, the 33 guidance document states that a monitoring program must be capable of identifying 34 unanticipated changes in the absorber material and determining whether anticipated changes 35 can be verified. The guidance recommends a combination of coupon testing, in-situ 36 measurement, and SFP water chemistry monitoring as a means to monitor potential changes in 37 characteristics of the NAM. The NRC staff reviewed the proposed guidance for what constitutes 38 an acceptable monitoring program and its ability to ensure that potential degradation of SFP 39 NAM will be detected, monitored, and mitigated. The staff determined that an appropriate 40 combination of the three methods listed above (coupon testing, in-situ measurement, and SFP 41 water chemistry monitoring) can comprise an effective NAM monitoring program. During the 42 course of the NRC staffs review, there were several topics identified in the guidance that 43 required clarification. A Category 2 public meeting was held with NEI on August 10, 2016, to 44 seek clarification on these topics. The NRC staff and NEI representatives discussed these 45 topics and NEI subsequently submitted a revision to NEI 16-03. A meeting summary is included 46 as a reference (ADAMS Accession No. ML16209A375) in this safety evaluation (SE) that 47 describes the topics that were discussed at the public meeting, as well as the changes that were 1
made to the guidance document as a result of the discussion.
2 3
3.1 Coupon Testing Program 4
5 3.1.1 Description of NEI 16-03 6
7 The guidance document states that the use of a coupon testing program is the preferred method 8
for a neutron absorber monitoring program. This program consists of small sections (coupons) 9 of the same NAM installed in the SFP, which are attached to a structure (coupon tree) in the 10 SFP. The coupon tree is placed near freshly discharged fuel assemblies in an attempt to 11 accelerate potential degradation mechanisms. The document provides the following criteria for 12 an acceptable coupon program:
13 14 The number of coupons needs to be adequate to allow for sampling at interval for the 15 intended life of the absorbers.
16 The sampling intervals are based on the expected rate of material change.
17 Performance of coupon testing 18 19 o Basic testing: visual observations, dimensional measurements, and weight 20 o Full testing: density measurements, Boron-10 (10B) areal density (AD) 21 measurements, microscopic analysis, and characterization of changes, in 22 addition to the basic testing parameters 23 24 The guidance document states that the coupons will be located in the SFP such that their 25 exposure to parameters controlling change mechanisms is conservative or similar to the 26 in-service neutron absorbers. For neutron attenuation testing, NEI 16-03 provides acceptance 27 criteria for the NAM depending on if there is, or is not, an anticipated loss of 10B AD. The 28 acceptable result for NAMs with expected 10B AD loss is the 10B AD of the test coupon is greater 29 than the 10B AD assumed in the licensees SFP criticality AOR. For NAM without an expected 30 loss of 10B AD, the acceptable result is the 10B AD of the test coupon is equal to the original 31 10B AD of the coupon (within measurement uncertainty). Furthermore, the guidance states that 32 the acceptable initial sampling interval for testing of new material (i.e., with a limited, or no, 33 operating history) is 5 years, with subsequent intervals up to 10 years. For those materials that 34 have well documented operating experience, do not have a history of degradation or 35 degradation mechanisms, and information on stability of the material condition is well 36 developed, the document states initial and subsequent test intervals up to 10 years are 37 acceptable. The document states that for materials with known degradation mechanisms, or a 38 history of known degradation (e.g., Boraflex, Carborundum, Tetrabor, etc.), the acceptable 39 interval for neutron attenuation testing is at least once every five years. In addition, NEI 16-03 40 includes neutron attenuation testing in the full testing approach for any NAMs used, as a 41 component of a satisfactory NAM monitoring program.
42 43 3.1.2 NRC Staff Evaluation 44 45 The NRC staff has evaluated the guidance for the basic and full portions of a coupon testing 46 program. The basic portion of the testing includes methods to monitor the physical condition of 47 the NAM so that signs of potential degradation may be observed. The full portion of the testing 48 includes neutron attenuation testing for all NAMs that are credited in the SFP criticality analysis 1
that will allow the licensee to detect a potential loss in 10B AD. The staff finds the coupon testing 2
program to be acceptable because it includes measurements of 10B AD and of geometric 3
changes in the material that can impact the ability of the NAM to perform its function as 4
assumed in the licensees SFP criticality AOR.
5 6
The NRC staff also determined the acceptance criteria for the coupon testing program provided 7
in NEI 16-03 is acceptable. The acceptance criteria provide reasonable assurance that the 8
assumptions in the licensees SFP criticality AOR will be maintained, because the acceptance 9
criteria show that the material is either not losing 10B AD (for materials not expected to lose 10 10B AD), or the 10B AD is still above the 10B AD assumed in the licensees SFP criticality AOR 11 (for NAM anticipated to lose 10B AD). The NRC staff also finds that it is not acceptable for the 12 measurement uncertainty to result in a 10B AD value that is lower than the assumed value in the 13 SFP criticality AOR. In addition, the NRC staff recognizes that if a coupon being tested 14 approaches the 10B AD limit as stated in the licensees SFP criticality AOR, the licensee would 15 likely need to perform further evaluations and/or take additional corrective actions to provide 16 reasonable assurance that the in-service NAM will not exceed the stated 10B AD limit, given the 17 active degradation of the NAM. Guidance on additional corrective actions that may be 18 necessary is given in Section 2.3, Evaluating Neutron Absorber Test Results, of NEI 16-03, 19 and this guidance is evaluated in Section 3.3 of this SE.
20 21 3.2 In-Situ Measurement Program 22 23 3.2.1 Description of NEI 16-03 24 25 The NEI guidance document states that in-situ measurement is another method that can be 26 used to confirm 10B AD of NAM. It further states that this method can be used to supplement 27 coupon monitoring to extend the coupon testing interval, permit greater reliance on basic 28 testing, or in lieu of coupon testing for plants that may no longer have coupons in the SFP. It 29 also states that in-situ measurement can be used instead of coupon testing if coupons do not 30 exist.
31 32 The guidance states that all in-situ measurement campaigns are to be performed at an 33 acceptable interval and on an adequate number of panels. The guidance gives two options for 34 determining what constitutes an adequate number of panels. The first option uses the 35 methodology of NUREG-6698 (ADAMS Accession No. ML050250061) to measure a minimum 36 of 59 panels to provide 95/95 confidence limits. The second option selects the panels with the 37 greatest exposure (top 5%) to parameters that influence degradation (e.g., neutron fluence, 38 temperature, time). The amount of panels will be no less than one percent of the total panels in 39 the SFP, although more panels can be tested from other areas of the SFP to gain a more 40 representative sampling. The guidance also states sources of uncertainty in the in-situ 41 measurement will be identified and quantified.
42 43 The sampling interval will be based upon the NAM credited in the SFP. New materials with 44 minimal operating experience will have an initial test interval that does not exceed 5 years, with 45 subsequent intervals up to 10 years (with appropriate operating experience). For materials with 46 known histories of degradation and known degradation mechanisms, test intervals do not 47 exceed 5 years. For other materials that do not have known histories of degradation or known 48 degradation mechanisms test intervals will not exceed 10 years. The guidance also states that 1
if used in conjunction with a coupon monitoring program, the in-situ sampling interval can be 2
longer.
3 4
The NEI document also provides acceptance criteria for in-situ measurements. It states that for 5
NAMs that do not have potential degradation mechanisms for loss of 10B AD, results of the 6
in-situ measurements are acceptable if the nominal measured 10B AD is greater than or equal 7
to the value assumed in the licensees criticality AOR (within measurement uncertainties). For 8
materials that have potential degradation mechanisms that result in loss of 10B AD, results are 9
considered acceptable if the nominal measured 10B AD minus measurement uncertainty is 10 greater than the 10B AD in the licensees criticality AOR.
11 12 3.2.2 NRC Staff Evaluation 13 14 The NRC staff has reviewed the guidance for performing in-situ measurement testing and finds 15 it to be acceptable, because it allows for detection of degradation mechanisms, potential loss of 16 neutron absorption capacity (e.g. loss of 10B), and ensure the NAM will continue to perform its 17 safety function. The NRC staff reviewed the methodology recommended for determining the 18 number of panels that may be selected for in-situ inspection and finds it to be acceptable 19 because it is based in part on guidance provided in NUREG-6698, Guide for Validation of 20 Nuclear Criticality Safety Calculational Methodology, and on selecting panels that have 21 experienced the greatest exposure to the SFP environment. The NRC staff also finds that 22 depending on the population of NAM panels in the SFP, a licensee may need to measure more 23 than the minimum of 59 panels in order to produce 95/95 confidence limits. The method used 24 for selecting the panels for in-situ testing is used to obtain data that is bounding or 25 representative of the entire NAM in the SFP.
26 27 In addition, the NRC staff has determined that the proposed testing intervals (10 year intervals 28 for materials with no known history of degradation/degradation mechanisms, and 5 year 29 intervals for materials with a known history of degradation/degradation mechanisms or for new 30 materials (i.e., no operating history)) are acceptable and consistent with NRC guidance in the 31 GALL report, Revision 2. The neutron attenuation testing must be performed on the intervals as 32 described in the document, regardless of how the licensee uses the in-situ monitoring program 33 (e.g., in conjunction with coupons, without coupon program, or other reasons as described in 34 NEI 16-03). The statement in the guidance that the in-situ sampling interval can be longer if 35 used in conjunction with a coupon program does not obviate the need to perform neutron 36 attenuation testing on the 5 or 10 year intervals.
37 38 In addition, the NRC staff finds it to be acceptable to identify and evaluate sources of 39 uncertainty in order to assess the reliability of the instruments and methodology used to the 40 collect the data. Sources of uncertainty can greatly impact results and confidence in the data 41 collected, especially as it relates to the subcriticality margin.
42 43 3.3 Evaluating Neutron Absorber Test Results 1
2 3.3.1 Description of NEI 16-03 3
4 The guidance document states that the test results from neutron absorber monitoring may fall 5
within the following categories:
6 7
- 1)
Confirmation that no material changes are occurring 8
- 2)
Confirmation that anticipated changes are occurring, and/or 9
- 3)
Identification that unanticipated changes are occurring.
10 11 Furthermore, the guidance document states that the testing results will be compared to the AOR 12 input (i.e., 10B AD assumed in criticality AOR). If no changes, or if anticipated changes are 13 occurring, then the guidance assumes that the material continues to be adequately represented 14 in the AOR.
15 16 The guidance document also describes the additional actions that may be necessary when 17 unanticipated changes in the NAM are identified. It states that there are certain technical 18 evaluations that may be necessary in addition to any required regulatory or licensing processes.
19 The technical evaluations include a determination if these changes may result in a loss of 20 10B AD. Any potential impacts of a loss of 10B AD on the SFP criticality AOR will be evaluated 21 and addressed through licensee procedures. In addition, the results of monitoring and testing 22 are to be evaluated and trended, regardless of potential impact on the SFP criticality AOR. If 23 the unanticipated changes do not appear to result in the loss of 10B AD, the changes will still be 24 evaluated for impacts on the SFP criticality AOR. The effects on the SFP criticality AOR due to 25 potential dimensional changes of the NAM, or other material in the SFP, are evaluated and 26 addressed in accordance with licensee procedures.
27 28 3.3.2 NRC Staff Evaluation 29 30 The NRC staff has reviewed the actions described in the guidance for when potential 31 degradation is detected in the neutron absorbing material as potential degradation of the NAM 32 may impact 10B AD assumptions in the SFP criticality AOR. The NRC staff finds the actions 33 described in the guidance acceptable because they will be able to identify anticipated, and 34 unanticipated changes in order to provide information that will allow a licensee to determine 35 whether or not the neutron absorbing material is performing its safety function (i.e., whether or 36 not there is a loss of 10B AD).
37 38 The NRC staff has also determined that it is necessary to evaluate and trend the results of 39 10B AD measurements from neutron attenuation testing in the NAM as described in NEI 16-03.
40 The NRC staff finds the methods, and requirement, to trend data acceptable because it will 41 provide information regarding the potential degradation mechanism(s) and rate for the NAM in 42 the SFP. This information will also help to provide reasonable assurance that the 10B AD of the 43 NAM will not decrease below the value assumed in the SFP criticality AOR between the 44 specified test intervals for neutron attenuation testing. In addition, this data can identify 45 previously un-evaluated degradation mechanisms that may have an impact on the SFP 46 criticality AOR.
47 The actions described above ensure, in part, that the ability of the NAM to perform its safety 1
function as assumed in the AOR, is maintained.
2 3
3.4 Technical Evaluation Conclusion
4 5
The NRC staff has determined that in order for a NAM monitoring program to be acceptable, 6
the licensee must perform neutron attenuation testing at the intervals stated in NEI 16-03. The 7
NRC staff finds the interval for inspection and testing acceptable because the frequency is 8
determined based on the neutron absorbing material credited, and operating experience of that 9
material. Depending on the material used, the interval for neutron attenuation testing will not 10 exceed 5 years (for materials with a history of known degradation or a known degradation 11 mechanism, and new materials), or 10 years (for other materials that do not have a history of 12 degradation, or a known degradation mechanism). Periodic neutron attenuation testing, and the 13 intervals described in NEI 16-03, are consistent with staff guidance (i.e., the GALL Report, 14 Revision 2). Licensees must request site-specific NRC review and approval to extend the 15 interval of any neutron attenuation testing past the 5 year and 10 year intervals, as described in 16 NEI 16-03.
17 18 Based on its review of NEI 16-03, the NRC staff has determined that a NAM monitoring program 19 meeting the provisions in NEI 16-03 will allow a licensee to reasonably ensure that the ability of 20 the NAM to perform its safety function, as assumed in the AOR, is maintained, thus 21 demonstrating compliance with the subcriticality requirements of 10 CFR 50.68.
22 23
4.0 CONCLUSION
24 25 The NRC staff has reviewed NEI 16-03, and the proposed methods for developing a NAM 26 monitoring program. A NAM monitoring program implanting the proposed guidance provides 27 reasonable assurance that such program will be able to detect degradation of neutron absorbing 28 material, and provides assurance that the ability of the NAM to perform its safety function as 29 assumed in the AOR, is maintained. The NRC staff finds that the requirements of 30 10 CFR 50.68(b)(4), GDC 61, and GDC 62, as well as the guidance provided in SRP 9.1.1, 31 SRP 9.1.2, and the GALL, Revision 2, with respect to NAMs and the NAM monitoring program, 32 are satisfied. Therefore, the NRC staff finds the proposed guidance in NEI 16-03 acceptable for 33 developing a NAM monitoring program.
34 35
5.0 REFERENCES
36 37
- 1. Letter from Kristopher W. Cummings to Timothy J. McGinty, Submittal of NEI 16-03, 38 Guidance for Monitoring of Fixed Neutron Absorbers in Spent Fuel Pools, Draft A, dated 39 May 2016, May 10, 2016 (ADAMS Accession No. ML16147A078).
40 41
- 2. Letter from Kristopher W. Cummings to Brian J. Benney, Submittal of NEI 16-03, 42 Guidance for Monitoring of Fixed Neutron Absorbers in Spent Fuel Pools, Revision 0, 43 dated August 2016, August 30, 2016 (ADAMS Accession No. ML16265A248).
44 45
- 3. Federal Regulation, U.S. Code of Federal Regulations, Criticality accident 46 requirements, Title 10 of the Code of Federal Regulations Part 50, Section 50.68(b)(4).
47 48
- 4. U.S. Code of Federal Regulations, "Domestic Licensing of Production and Utilization 1
Facilities - Proposed General Design Criteria for Nuclear Power Plants," Part 50, 2
Appendix A (10 CFR Part 50, Appendix A).
3 4
- 5. U.S. Nuclear Regulatory Commission, Standard Review Plan, Section 9.1.1, Criticality 5
Safety of Fresh and Spent Fuel Storage and Handling, NUREG-0800, Revision 3, 6
March 2007 (ADAMS Accession No. ML070570006) 7 8
- 6. U.S. Nuclear Regulatory Commission, Standard Review Plan, Section 9.1.1, New and 9
Spent Fuel Storage, NUREG-0800, Revision 4, March 2007 (ADAMS Accession 10 No. ML070550057) 11 12
- 7. U.S. Nuclear Regulatory Commission, Generic Aging Lessons Learned (GALL) Report, 13 NUREG-1801, Revision 2, December 2010 (ADAMS Accession No. ML103490041) 14 15
- 8. U.S. Nuclear Regulatory Commission Category 2 Public Meeting, Summary of 16 August 10, 2016, Meeting with the Nuclear Energy Institute to Discuss NEI 16-03, 17 Guidance for Monitoring of Fixed Neutron Absorbers in Spent Fuel Pools, 18 September 27, 2016 (ADAMS Accession No. ML16209A375) 19 20
- 9. U.S. Nuclear Regulatory Commission, Guide for Validation of Nuclear Criticality Safe 21 Calculation Methodology, NUREG/CR-6698, January 2001 (ADAMS Accession 22 No. ML050250061) 23 24 Principle Contributor: Alex Chereskin, NRR 25 26 Date:
27 28