ML23143A306
| ML23143A306 | |
| Person / Time | |
|---|---|
| Site: | Nuclear Energy Institute, 99902028 |
| Issue date: | 05/23/2023 |
| From: | Mccullum R Nuclear Energy Institute |
| To: | Lois James Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| EPID L-2022-NTR-0002 | |
| Download: ML23143A306 (1) | |
Text
ROD MCCULLUM Sr. Director, Decommissioning and Used Fuel 1201 F Street, NW, Suite 1100 Washington, DC 20004 P: 202.739.8082 rxm@nei.org nei.org May 23, 2023 Ms. Lois M. James Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
Subject:
Response to NRC Request for Additional Information Supporting the Review of NEI 16-03, Rev. 1, Guidance for Monitoring of Fixed Neutron Absorbers in Spent Fuel Pools (EPID L-2022-NTR-0002)
Project Number: 689
Dear Ms. James:
By letter dated August 19, 2022, as supplemented by letters dated October 12 and December 15, 2022 (ADAMS Accession Nos. ML22231B041, ML22298A281, and ML22349A656, respectively), the Nuclear Energy Institute (NEI)1 submitted NEI 16-03, Guidance for Monitoring of Fixed Neutron Absorbers in Spent Fuel Pools, Revision 1, for U.S. Nuclear Regulatory Commission (NRC) staff for review and endorsement. The staff reviewed and accepted the guidance for review on January 11, 2023 (ADAMS Accession No. ML23005A144).
Subsequently, via your e-mail dated April 24, 2023, nine requests for additional information (RAIs) identified during NRC staffs review were transmitted to NEI.
This letter transmits industrys response to these RAIs in the attached document. This response has been coordinated with industry through EPRIs Neutron Absorber Users Group.
1 The Nuclear Energy Institute (NEI) is the organization responsible for establishing unified industry policy on matters affecting the nuclear energy industry, including the regulatory aspects of generic operational and technical issues. NEI's members include entities licensed to operate commercial nuclear power plants in the United States, nuclear plant designers, major architect/engineering firms, fuel cycle facilities, nuclear materials licensees, and other organizations and entities involved in the nuclear energy industry.
Lois M. James May 23, 2023 Page 2 Please let me know if you have any questions.
Sincerely, Rod McCullum Attachment c:
Mr. Steven Bloom, NRC/NRR Mr. Matthew Yoder, NRC/NRR Ms. Leslie Fields, NRC/NRR NRC Document Control Desk
RAI #1 Issue/Request:
Section 1.2, Background, on page 1 states that, In some cases, sufficient operating experience was acquired over several decades to allow individual licensees not to need coupons or in-situ examinations, but to rely on the collective industry experience. The staff is unaware of any licensees that have cited collective industry experience in lieu of in-situ or coupon testing for any neutron absorbing material. In addition, this is not consistent with the guidance in NUREG-1801, Revision 2. Please provide the plants and associated NAMs that are relying on collective industry experience instead of in-situ examinations/coupons or modify the background language. The staff recognizes that this statement was also included in Revision 0 of NEI 16-03 (ADAMS Accession No. ML16265A248).
NEI Response:
As indicated in the RAI, this statement was included in NEI 16-03, Revision 0 and left unchanged as part of the Background information. This was the practice in the past, as plants were following industry experience, via EPRIs Neutron Absorber User Group (NAUG), in combination with water chemistry monitoring.
However, based on the RAI, this statement will be removed from revised NEI 16-03, Revision 1.
RAI #2 Issue/Request:
The foreword and background state that i-LAMP is intended to replace a water chemistry monitoring approach from Revision 0 that was not accepted by the NRC to be considered as a stand-alone monitoring approach. It is unclear to the NRC staff what the purpose of this statement is. If the intention of this revision is to make i-LAMP an acceptable stand-alone monitoring approach, why would the current revision reference an approach that was previously rejected and does not appear in the approved Revision 0?
NEI Response:
This statement was included in NEI 16-03 Revision 1 to provide background information and clearly state the differences between NEI 16-03 Revision 0 and Revision 1.
However, based on the RAI, this statement will be removed from the foreword and background sections of the revised NEI 16-03 Revision 1.
RAI #3 Issue/Request:
The last paragraph of the Background section discusses options for licensees to modify their current licensing basis with respect to neutron absorbing material surveillance programs. This paragraph seems insufficient to address the wide variety of individual plant licensing scenarios.
The previously approved revision of this guidance focused on the material surveillance program and did not address plant-specific licensing scenarios. Please clarify that the Revision 1 guidance is not intended to address individual licensing scenarios.
NEI Response:
The Revision 1 guidance is not intended to address individual licensing scenarios. The intent of the portion of the Revision 1 guidance alluded to in the RAI is to recognize the various individual licensing scenarios at plants around the country. These scenarios fall under several categories depending on how the commitment to NAM monitoring is captured in the licensing basis (e.g.,
technical specification, FSAR, licensing commitment, etc.). This guidance paragraph recognizes that each facility adopting the endorsed guidance will need to implement it in accordance with their plant-specific processes. This will likely involve review under the plant commitment control process and/or 10 CFR 50.59. Either of these processes could result in the need for a license amendment request. Each licensee will need to make its own evaluation in this regard under its site-specific change control program.
Based on the above response, no change is proposed to revise this statement in NEI 16-03.
RAI #4 Issue/Request:
Section 2.2.3 states that the 2-bin approach will eliminate regulatory submissions and the need for plant-specific review by the regulator. It is unclear to the NRC staff how the proposed binning approach would absolve a plant from the regulatory process and licensing requirements. Any licensee seeking to adopt an i-LAMP monitoring approach would need to modify their current monitoring program and associated licensing commitments. Please discuss why the proposed binning method would eliminate regulatory submissions and plant-specific reviews by the NRC?
NEI Response:
The intent of the statement is to emphasize the simplicity of the two-bin approach both for the licensee and the regulator.
Proposing to revise NEI 16-03 Revision 1 for this sentence to read:
The two-bin approach will simplify implementation as it would not require identification of siblings for every licensee without coupons unless future NAM monitoring data indicates there is a need for identification of specific siblings or further binning refinement in the future.
RAI #5 Issue/Request:
Section 2.2.3 states that the 2-bin approach is applicable until loss of 10B is identified by global operating experience. However, this does not account for the potential scenario where a plant or plants with the oldest Boral runs out of coupons or ceases operation without transferring their remaining coupons to another operating plant. In this scenario there will be a subset of plants that relied on the data from the plant with the oldest Boral that will no longer be bounded by the collective data set. If a plant is not monitoring a specific sibling plants data but relies on the generic i-LAMP program, as a whole, they may be unaware that they are no longer bounded by the program. How does NEI propose to account for this scenario?
NEI Response:
This RAI is answered in multiple parts to address each question/scenario.
- 1. Unlike previous practice, when it is possible, it is now recommended to return the coupons to their pools after the analysis. The primary objective of this approach was to make sure plants do not run out of coupons during their operating time.
- 2. When a plant with coupons ceases operation, when possible, their coupons will be transferred to a sibling pool after all spent fuel is removed from the pool. This will be coordinated via the NAUG.
- 3. EPRI will be performing continuous data collection and analysis. If a loss of 10B is identified and considered significant enough to impact the assumptions in the criticality analysis, further binning will be performed and communicated to the industry via the NAUG.
Once i-LAMP is endorsed, coupons from the oldest Boral material in service will reside in two pools. It is recommended to re-insert coupons, when possible, after periodic removal and evaluation. These actions reduce the likelihood of not having Boral age coverage. Section 2.2.1.3 addresses another possible response: If a particular characteristic is unbounded, i-LAMP data may still be applicable for surrogate coupon monitoring provided analysis shows that there is no degradation trend related to that characteristic.
Finally, in Section 2.2.4:
Periodic review of i-LAMP data performed at 5-year intervals maintains this consistency with the coupon testing program interval (performed at 5-year or 10 -year intervals, as discussed in Section 2.1). Results are acceptable if:
The sibling pool Boral material is represented in the i-LAMP database. Representation is determined using the characteristics described in Section 2.2.2 and Appendix A, including material age, areal density, and SFP water chemistry.
Applicable surrogate data has been updated with new operating experience within the last 10 years, unless older data remains bounding for the sibling pool.
Section 2.2.4 processes ensure that if the proposed situation does occur, it will be identified within the normal surveillance interval time frame and dealt with using the plant corrective action process.
Based on the above response, no change is proposed to revise this statement in NEI 16-03.
RAI #6 Issue/Request:
There is a potential scenario where a Boral degradation mechanism that results in loss of 10B is identified in the future. If this occurs all plants relying on i-LAMP for their neutron absorber monitoring programs face regulatory uncertainty. Plants relying on a generic 2-bin approach would not have the plant-specific analysis available to rule out the degradation mechanism for their site based on material age or other applicable parameters. How would i-LAMP participating plants demonstrate their material condition and continued criticality safety without plant-specific
analysis or the analysis of a sibling plant with closely related material and spent fuel pool conditions? Specifically, how does the degradation feedback loop from other boral plants work or apply.
NEI Response:
Based on historical trends over decades of operation and observation, a new or different Boral degradation mechanism is unlikely to be discovered. However, should such a scenario unfold, that information would be both addressed at the plant of discovery in the corrective action program and shared with the industry via the NAUG. Since i-LAMP is proposed as a learning aging management program, when this scenario happens, i-LAMP will move to the next level of binning (finer binning as needed). Each plant receiving this information would evaluate it within its operating experience program and/or corrective action program.
Additionally, if i-LAMP is no longer applicable, the issue will be addressed under the corrective action program, including possible use of other NEI 16-03 options - develop a coupon monitoring program, or alternatively use in-situ monitoring.
NEI proposes to make a clarification to the guidance by adding the paragraph below to the end of NEI 16-03, Section 2.2.3:
Should a new or different degradation mechanism that causes a loss of 10B in the NAM be discovered, that information would be entered into that sites corrective action program and shared with the industry via the NAUG. Each plant receiving this information would evaluate it within its operating experience program and/or corrective action program as circumstances dictate.
RAI #7 Issue/Request:
Temperature and cumulative dose (gamma and neutron) are listed in Section 2.2.1 as parameters affecting neutron absorber aging. Why are these parameters not included in the list of sibling pool criteria discussed in Section 2.2.2?
NEI Response:
Section 2.2.1 of NEI 16-03 describes general parameters that affect aging mechanisms.
Temperature and cumulative dose are parameters of interest more applicable for NAM materials other than Boral (i.e., Boraflex, Carborundum), which are not part of i-LAMP. The evaluations of axial 10B areal density distribution from the Boral NAM panels removed from Zion and an operating plant with over 40 years of service time (see NEI 16-03, Section A.2) confirm that dependence on temperature and cumulative dose for Boral is negligible. If the radiation and temperature were factors in degradation, it would have been evident in the areal density values, provided in Figures A.14 and A. 15, as a function of axial height given temperature and radiation dose profiles vary significantly as a function of axial height for a given panel.
Additionally, coupon data comes from operating pools with coupons, in which NAM age and NAM cumulative dose are correlated. Coupons are placed in lead locations, with highest exposures; no trending is observed to date and i-LAMP will continue to analyze and trend the data.
Based on the above response, no change is proposed to revise this statement in NEI 16-03.
RAI #8 Issue/Request:
Appendix A Section A.3.1.4 proposes actions that the pilot plant may make pending regulatory approval. The NRC staff does not intend to perform any regulatory assessment of plant-specific neutron absorber programs as part of its review of NEI 16-03, Rev. 1. Please clarify the intent of this section of Appendix A.
NEI Response:
This section was retained to provide background information regarding the i-LAMP program planned actions intended to maintain the broadest possible coupon coverage for the industry.
The actions listed in this section were referring to pending regulatory approval of i-LAMP as part of NEI 16-03 Revision 1. They were not referring to regulatory assessment of a plant-specific neutron absorber program.
This sentence will be revised in NEI 16-03 Revision 1 as following (by adding bolded i-LAMP is to avoid misunderstanding for plant specific review/approval):
If i-LAMP is approved by the regulator as a replacement for Pilot-1s current commitments, instead of simply proposing to use Sibling-1 as surrogate for Pilot-1, proposing the following:
RAI #9 Issue/Request:
Section 2.2.1.1 states that water chemistry is used as a monitoring tool for early indications of anomalies. In the case of Boraflex, water chemistry programs identified excess silica in the spent fuel pool water. For Boral, the primary material composition is aluminum (Al). However, Appendix A Section A1.2 states that very few pools also measure Al and the majority of utilities discontinued this practice. For pools that do not have their own Boral coupons, plant specific data such as dissolved Al is essential for ensuring the integrity of the Boral. This is exemplified by the other industry programs (reactor vessel integrity and steam generator integrity) that are cited in NEI 16-03 as examples of industrywide monitoring programs that rely on water chemistry measurements. How can water chemistry readings identify early signs of Boral degradation if pools are not testing for the primary element comprising the Boral material (Al)?
NEI Response:
As discussed in the document, plants have been following EPRI water chemistry guidelines to minimize corrosion. As indicated, these water chemistry guidelines are used by other programs as well. EPRI water chemistry guidelines have mandatory and recommended measurements. However, the current EPRI water chemistry guidelines do not require measuring Al levels - they are more focused on measurement of Cl, F, Sulfate as they are known corrosion accelerants as well as B level (PWR), and pH and conductivity.
Because no correlation between dissolved Al and Boral effectiveness has been developed to date, industry does not view Al monitoring as essential for this purpose. Measured coupon data provides more direct confirmation of Boral performance. Monitoring water chemistry for other elements or compounds is intended to enable identification of the cause and extent of
condition of any degradation that may be identified in the future. While Al monitoring may be useful it is not currently actionable for confirming the B-10 content of the Boral.
Based on the above response, no change is proposed to revise this statement in NEI 16-03.