L-MT-13-048, License Amendment Request for Fuel Storage Changes Supplement to Respond to NRC Staff Requests for Additional Information
| ML13158A269 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 06/07/2013 |
| From: | Schimmel M Xcel Energy, Northern States Power Co |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| L-MT-13-048, TAC ME9893 | |
| Download: ML13158A269 (7) | |
Text
Xcel Energy@ Monticello Nuclear Generating Plant 2807 W County Rd 75 Monticello, MN 55362 June 7,2013 L-MT-13-048 10 CFR 50.90 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Monticello Nuclear Generating Plant Docket 50-263 Renewed License No. DPR-22 License Amendment Request for Fuel Storage Changes Supplement to Respond to NRC Staff Requests for Additional Information (TAC ME9893)
References:
- 1) Letter from M A Schimmel (NSPM) to Document Control Desk (NRC),
"License Amendment Request For Fuel Storage Changes," L-MT 076, dated October 30,2012 (ADAMS Accession No. ML12307A433).
- 2) Email from T A Beltz (NRC) to G D Adams (NSPM), "Monticello Nuclear Generating Plant - Requests for Additional Information (SRXB) re: License Amendment Request to Support Fuel Storage Changes (TAC No. ME9893)", dated April 30, 2013 (ADAMS Accession No. ML13121A269).
Pursuant to 10 CFR 50.90, the Northern States Power Company, a Minnesota corporation (NSPM), doing business as Xcel Energy, requested in Reference 1 an amendment to the Monticello Nuclear Generating Plant (MNGP) Renewed Operating License (OL) and Technical Specifications (TS) to reflect fuel storage system changes and a revised criticality safetx analysis that addresses the legacy fuel types in addition to the new AREVA ATRIUM M 10XM fuel design.
In Reference 2, the NRC sent a request for additional information (RAI) concerning the letter sent by NSPM in Reference 1.
The enclosure to this letter provides the NSPM response to the NRC RAls.
Document Control Desk Page 2 The supplemental information provided herein does not change the conclusions of the No Significant Hazards Consideration and the Environmental Consideration evaluations provided in Reference 1.
In accordance with 10 CFR 50.91 (b), a copy of this application supplement (without enclosure) is being provided to the designated Minnesota Official.
Summary of Commitments This letter makes no new commitments and no revisions to existing commitments.
I declare under penalty of perjury that the foregoing is true and correct.
Executed on: June 07 ,2013 dfJdJU Mark A. Schimmel Site Vice-President Monticello Nuclear Generating Plant Northern States Power Company-Minnesota Enclosure cc: Administrator, Region III, USNRC (w/o enclosure)
Project Manager, Monticello Nuclear Generating Plant, USNRC Resident Inspector, Monticello Nuclear Generating Plant, USNRC (w/o enclosure)
Minnesota Department of Commerce (w/o enclosure)
L-MT-13-048 NSPM Page 1 of 5 ENCLOSURE MONTICELLO NUCLEAR GENERATING PLANT RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION FROM THE REACTOR SYSTEMS BRANCH (SRXB)
This enclosure provides responses from the Northern States Power Company, a Minnesota corporation (NSPM), doing business as Xcel Energy, to a request for additional information (RAI) provided by the Nuclear Regulatory Commission (NRC) on April 30, 2013.
The NRC questions are provided below in italic font and the NSPM response is provided in the normal font.
In the spent fuel pool (SFP), the spent fuel stored in the racks must comply with the regulations to remain sub critical. In the case of Monticello, they are licensed under 10 CFR 50.68, "Criticality Accident Requirements. This regulation states that:
JJ If no credit for soluble boron is taken, the k-effective of the spent fuel storage racks loaded with fuel of the maximum fuel assembly reactivity must not exceed 0.95, at a 95 percent probability, 95 percent confidence level, if flooded with unborated water.
To demonstrate compliance with the regulation, the licensee has performed a nuclear criticality safety (NCS) analysis of record (AOR). In this NCS AOR, Monticello has credited Boral in the analysis to help maintain sub criticality. With respect to Boral, the NCS AOR assumes that the minimum B-10 areal density is 0.013 glcm 2 and that a uniform 0.055 inch void region is used as a model for potential blistering.
In order to ensure that the Boral will remain within the assumptions used in the NCS AOR, a Surveillance Program to identify and monitor any degradation is in place. This program will confirm that the material will perform as designed for in the NCS A OR.
The NRC staff questions the amount of information described in Monticello's proposed Technical Specifications (TSs) in regard to the neutron absorbing material, Boral, and its Surveillance Program. In particular:
- 1. Please justify why a minimum areal density limit of the Boral, a material of construction with a significant effect on safety, in the Spent Fuel Pool, is not specified in the Limited Condition for Operation section of the TS. Note: in 10 CFR 50.36(c)(2)(ii)(B), it states:
L-MT-13-048 NSPM Enclosure Page 2 of 5 Criterion 2. A process variable, design feature, or operating restriction that is an initial condition of a design basis accident or transient analysis that either assumes the failure of or presents a challenge to the integrity of a fission product barrier.
Furthermore 10 CFR 50.36(c)(2)(ii)(C) states:
Criterion 3. A structure, system, or component that is part of the primary success path and which functions or actuates to mitigate a design basis accident or transient that either assumes the failure of or presents a challenge to the integrity of a fission product barrier.
NSPM Reply:
NSPM recognizes the NRC Staff initiative to address spent fuel pool neutron absorber integrity on a generic basis in the Improved Standard Technical Specifications. Accordingly, NSPM would prefer to address this particular RAI question with the full regulatory review and evaluation that the industry review process can assure. In the interim, NSPM can justify the acceptability of the current MNGP TS based on the following discussion.
After more than 32 years of exceptional performance of in-service Boral, and no adverse results or trends in coupon surveillance, there is no basis for reversing the results of previous licensing activities that excluded B-10 areal density from the MNGP TS. A lifetime of favorable operating history is discussed extensively in the regulatory correspondence of MNGP license renewal (References 1-1 through 1-3);
concluding that there has been no degradation of representative Boral coupons and no negative trend that would indicate Boral degradation is credible over the period of extended operation. Accordingly, the minimum boron-10 areal density parameter for Spent Fuel Pool rack Boral has never been considered to cross a threshold for inclusion as a Technical Specification (TS) Limiting Condition for Operation (LCO).
NSPM and NRC have considered this areal density parameter to be a design feature that is important to spent fuel storage safety. This parameter, along with the geometry of the storage racks are passive features that ensure the subcriticality margins of the regulation are preserved such that a criticality event is considered non-credible. Although this parameter is important, it does not fall within the two criteria cited above because it is not associated with "a design basis accident or transient analysis that either assumes the failure of or presents a challenge to the integrity of a fission product barrier." Neither the MNGP Updated Safety Analysis Report (USAR) nor the Standard Review Plan (NUREG-0800, Chapter 15) includes discussion of a spent fuel pool criticality accident. There is no discussion of initial conditions, accident mitigation, or consequences of such an accident. In other words, there is no design basis criticality accident that has been postulated to present a challenge to a fission product barrier. Therefore, NSPM has determined
L-MT-13-048 NSPM Enclosure Page 3 of 5 that the two cited 10 CFR 50.36 criteria do not apply, and it is not appropriate for NSPM to request an LCO for this parameter.
References:
1-1 Nuclear Management Company (NMC) letter L-MT-05-014, Application for Renewed Operating License, March 16, 2005 [ADAMS Accession No. ML050880241 ].
1-2 NMC letter L-MT-05-099, Response to Three Requests for Additional Information Regarding the Monticello License Renewal Application (TAC No.
MC6440), September 16, 2005 [ADAMS Accession No. ML052630320].
1-3 NMC letter L-MT-05-114, Supplement to Responses to Requests for Additional Information Regarding the Monticello Nuclear Generating Plant License Renewal Application (TAC No. MC6440), November 17, 2005 [ADAMS Accession No. ML053250099].
- 2. Justify why the Surveillance Program, which is related to a test or inspection to assure that the necessary quality of the component (Boral) is maintained so that the facility (Monticello SFP) is within its safety limits, is not included in the Surveillance Requirements Section of the Monticello TSs. Note: in 10 CFR 50.36 (c)(3) it states:
Surveillance requirements are requirements relating to test, calibration, or inspection to assure that the necessary quality of systems and components is maintained, that facility operation will be within safety limits, and that the limiting conditions for operation will be met.
NSPM Reply:
As discussed in the reply to question 1, NSPM would prefer to address this particular question with the full regulatory review and evaluation that the industry review process can assure. In the interim, NSPM can justify the acceptability of the current MNGP TS based on the following discussion.
A monitoring program can be an effective defense-in-depth means to assure that any adverse trend in Boral performance is discovered early. Accordingly, commitments were made in previous correspondence (Reference 2-1) to enhance the Boral program, including performance of neutron attenuation testing at an interval not to exceed ten years.
Nevertheless, NSPM does not assert that a monitoring program is needed to "assure that the necessary quality" of MNGP Boral is maintained. It is NSPM's position that the following processes assure the necessary quality of the SFP rack Boral panels:
L-MT-13-048 NSPM Enclosure Page 4 of 5
- 1. The Boral manufacturing process was originally qualified to provide the required level of boron-1 0 distribution in the panel. Specifications required: (1)
Certification of all boron carbide (B4C) indicating boron content and B-10 isotopic content, (2) a sampling plan for isotopic analysis consistent to provide a minimum 95% confidence that each Boral panel exceeded the specified B-10 loading, and (3) the actual B-10 content per unit area was determined by chemical or transmission analyses of each sheet of Bora!.
- 2. Other post-manufacturing tests are performed on random samples to confirm at a 95% confidence level that the B-10 is uniformly distributed.
- 3. Six intervals of coupon examination and neutron attenuation testing (over a 32-year service history) have indicated no degradation of representative Boral coupons and no negative trend that would indicate that significant Boral degradation is credible over the period of extended operation. Each of the recorded areal density tests demonstrated no loss of neutron attenuation capability.
- 4. Before any loss of B-10 areal density can be expected at MNGP, very significant rack deformation would first be manifest. Industry experience indicates that even with significant deformation in some Boral racks, there has been no associated loss of B-10 areal density reported (Reference 2-2).
- 5. Following more than 32 years of operating history, a review of corrective action program (CAP) records indicates that MNGP has experienced no in-situ bulging or blistering of rack cells (beyond that discovered during initial installation and recorded in USAR Section 10.2). A review of Reactivity Management Performance Indicator and CAP records indicates that, in recent history (following the original SFP rack installation campaign) no SFP rack cells have been taken out-of-service due to blistering or bulging. Thereby, the surveillance program is shown to be not necessary to ensuring Boral integrity.
- 6. Recognizing that no amount of blistering is expected for Boral in the MNGP storage racks, the criticality analysis nonetheless conservatively models a very extensive blister and shows that criticality criteria can still be met. Thereby, a Technical Specification Surveillance Requirement for B-1 0 areal density is not necessary because the criticality analysis does not require unblemished Bora!.
It accommodates significant deformation.
Inherent to the 50.36 criterion is the concept that the surveillance would be "necessary" (i.e., the only means) to ascertain that Boral meets the design criterion.
As illustrated by the evidence above, quality is assured by the manufacturing process controls, favorable operating history, in-service monitoring for adverse effects, and with conservative assumptions in the criticality safety analysis that accommodate extensive deformation. A Boral monitoring program including neutron attenuation testing will improve confidence in the material's integrity, but it is not necessary to assure that Boral meets the areal density design criterion.
L-MT-13-048 NSPM Enclosure Page 5 of 5
References:
2-1 Xcel Energy letter L-MT-13-046, License Amendment Request for Fuel Storage Changes Supplement to Respond to NRC Staff Requests for Additional Information (TAC ME9893), dated May 16, 2013.
2-2 Electric Power Research Institute (EPRI) Report 1019110, Handbook of Neutron Absorber Materials for Spent Nuclear Fuel Transportation and Storage Applications, 2009 Edition.