ML18340A028

Response to Request for Additional Information for Proposed Technical Specifications Changes for Spent Fuel Pool Storage and New Fuel Storage

ML18340A028
Person / Time
Site:	Millstone
Issue date:	11/29/2018
From:	Gerald Bichof Dominion Energy Nuclear Connecticut
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
18-403
Download: ML18340A028 (7)

Text

Dominion Energy Nuclear Connecticut, Inc.

5000 Dominion Boulevard, Glen Allen, VA 23060 ~ Dominion Dominion Energy.com

. November 29, 2018 P' Energy U.S. Nuclear Regulatory Commission Serial No.18-403 Attention: Document Control Desk NRA/SS RO Washington, DC 20555 Docket No. 50-423 License No. NPF-49 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 3 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION FOR PROPOSED TECHNICAL SPECIFICATIONS CHANGES FOR SPENT FUEL POOL STORAGE AND NEW FUEL STORAGE By letter dated May 3, 2018, Dominion Energy Nuclear Connecticut, Inc. (DENC) requested Nuclear Regulatory Commission (NRC) approval of the proposed Technical Specifications (TS) changes for Millstone Power Station Unit 3 for spent fuel pool storage and new fuel storage. In an email dated October 18, 2018, the NRC transmitted a request for additional information (RAI) related to the TS change request.

The attachment to this letter provides DENC's response to the NRC's RAI.

If you have any questions regarding this submittal, please contact Shayan Sinha at (804) 273-4687.

Sincerely,

,/

/ .' 7

'J:t k~

Gerald T. Bischof Senior Vice President - clear Operations & Fleet Performance COMMONWEALTH OF VIRGINIA COUNTY OF HENRICO The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by Gerald T. Bischof, who is Senior Vice President - Nuclear Operations & Fleet Performance of Dominion Energy Nuclear Connecticut, Inc. He has affirmed before me that he is duly authorized to execute and file the foregoing document in behalf of that company, and that the statements in the document are true to the best of his knowledge and belief.

• Acknowledged before me this ~ y otA/oVcmhc .. ,2018.

My Commission Expires: S -- 3, - a.:a . Uc.1w.: Xi2/IA/;t....

Notary Public VICKI L. HULL NOTARY PUBLIC REG. # 140542 COMMONWEALTH OF VIRGINIA MY COMMISSlON EXPIRES 5131/2022 I

Serial No.18-403 Docket No. 50-423 Page 2 of 2

Attachment:

Response to Request for Additional Information for Proposed Technical Specification Changes for Spent Fuel Pool Storage and New Fuel Storage Commitments made in this letter: DENG will revise the Updated FSAR to follow the Baral coupon testing schedule requirements in NEI 16-03 following end of Cycle (EOG) 21.

cc: U.S. Nuclear Regulatory Commission Region I 2100 Renaissance Blvd Suite 100 King of Prussia, PA 19406-2713 Richard V. Guzman Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 08 C 2 11555 Rockville Pike Rockville, MD 20852-2738 NRG Senior Resident Inspector Millstone Power Station

Serial No.18-403 Docket No. 50-423 ATTACHMENT RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION FOR PROPOSED TECHNICAL SPECIFICATION CHANGE FOR SPENT FUEL STORAGE AND NEW FUEL STORAGE MILLSTONE POWER STATION 3 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

Serial No.18-403 Docket No. 50-423 Attachment, Page 1 of 4 By letter dated May 3, 2018, Dominion Energy Nuclear Connecticut, Inc. (DENC) requested Nuclear Regulatory Commission (NRC) approval of the proposed TS changes for Millstone Power Station Unit 3 for spent fuel storage and new fuel storage.

In an email dated October 18, 2018, the NRC transmitted a request for additional information (RAI) related to the request. This attachment provides DENC's response to the RAI.

RAI-MCCB-1 Part 50.68(b)(4) of Title 10 of the Code of Federal Regulations (10 CFR) states, in part, that ".. .the k-effective (kerr) of the spent fuel storage racks loaded with fuel of the maximum fuel assembly reactivity must not exceed 0. 95 ... " In order to demonstrate that kerr doesn't exceed 0. 95, the licensee submitted its SFP criticality analysis, for MPS3, as part of its LAR dated May 3, 2018. This analysis, in part, takes credit for the neutron absorbing properties of the Bora/ material installed in the SFP racks.

In its LAR, the licensee referenced 'its response to request for additional information (RAJ) Jetter dated November 22, 2017, related to Generic Letter 2016, "Monitoring of Neutron-Absorbing Materials in Spent Fuel Pools", (ADAMS Accession No. ML17338A057), to provide information regarding the Bora/ monitoring program at MPS3. In the RAJ response, the licensee noted that it had discovered weight 'Joss with an unknown cause in its Bora/ coupons since their installation in 2000. In addition, the licensee stated thatit did not discover any degradation that would impact SFP criticalitf In order to have reasonable assurance that the weight loss has not impacted the SFP criticality, the NRG staff has the following questions:

a) Has the weight loss caused any dimensional changes (e.g. length, width, or thickness) in the Bora/ coupons?

b) Has there been any decrease in Boron 10 (B-10) areal density (AD) in the coupons?

c) Provide any corrective actions taken to mitigate the degradation of the Bora/

material, and describe how these actions are meant to mitigate, or account for any impacts to the SFP criticality analysis* due to the *weight loss of the Bora/

coupons.

Serial No.18-403.

,\

Docket No. 50-423 Attachment, Page 2 of 4 DENC Response a) There have been no significant changes to the length or width of the coupons. The thickness has decreased to varying degrees. Table 1 below shows the average dimensional changes of the coupon measurements to date relative to the as-built measurements for each coupon.

Table 1: Percent Change to the Dimensions of the BORAL Coupons Year of Measurement Weight Length*1 Width*1 Thickness.:

2003 -1.4% -0.1% -0.1% -0.7%

2004 -1.9% -0.1% -0.2% 0.3%

2005 -2.7% -0.2% -0.2% -0.2%

2008 -4.4% -0.1% -0.1% -3.3%

2013 -6.1% -0.2% -0.2% -3.0%

2017 -5.8% --0.2% -0.2% -1.3%

1 Average of three measurement locations along the coupon.

2 Average of five measurement locations on the coupon.

b) The coupons have shown no indication that the B-10 areal density (AD) has decreased. Table 2 shows the measured B-10 AD.

Table 2: Percent Change to the 8-10 AD of the BORAL Coupons Year of Measurement B-10 AD 2003 1.6%

2004 0.9%

2005 -4.1 %*

2008 -2.8%*

2013 -5.6%*

2013 1.6%*

Reevaluation 2017 1.1%

• As previously discussed in DENC's response to the RAls for Generic Letter 2016-01 (ADAMS Accession No. ML17338A057), the 2013 coupon's areal density was reevaluated based on the vendor's newer and more accurate chemical analysis of the BORAL standards. This reevaluation changed the B-10 AD from 0.0302 g/cm 2 to 0.0325 g/cm 2 compared to* an as-built value of 0.0320 g/cm 2 . The 2005 and 2008 measurements used the same chemical analysis of the standards as the 2013 measurement and thus, had the same issue. With the more accurate calibrations, these coupon measurements do not indicate that B-10 AD is being lost.

Serial No.18-403 Docket No. 50-423 Attachment, Page 3 of 4 c) DENC does not currently consider that the weight loss in the BORAL coupons is of immediate concern based on three factors:

(1) The weight loss is occurring slowly in comparison to the measurement interval.

(2) It is unclear whether the weight loss phenomenon is also occurring to the BORAL in the SFP racks.

(3) The effect of losing the aluminum clad is small and already quantified in the submitted criticality analysis.

These factors are further explained as follows:

1. The 2017 coupon measurement leveled off the weight loss trend. However, conservatively ignoring the 2017 measurement, the trend shows a weight loss of about 0.5% per year. The aluminum clad surrounding the B4C cermet accounts for about 22% of the BORAL mass. If the pre-2017 trend continued, it would take 32 more years until the B4C cermet is exposed to the SFP water environment.

The coupon measurement interval is much shorter than 32 years (See DENC's response to RAI-MCCB-2 below). Therefore, the weight loss phenomenon is occurring slowly enough that DENC will be able to detect the weight loss trend if it recommences and enact mitigating corrective actions before the B4 C cermet is exposed to the SFP environment.

2. Prior to the 2017 measurement, the BORAL coupons were not encased in stainless steel wrappers whereas the BORAL panels in the SFP racks are encased. A Condition Report was written regarding the coupon weight loss trend. One of the Corrective Actions to address the cause of the weight loss is to investigate whether storing BORAL coupons fully exposed to the SFP environment on the coupon* tree is contributing to the weight loss, possibly by allowing physical interaction with the tree structure or storage cell. To determine whether the absence of wrappers contributes to the coupon weight loss trend, the remaining coupons were encased in stainless steel sheaths in April 2018.

Future measurements will determine if the stainless steel wrapper has an effect on the BORAL weight loss.

3. The possible weight loss and thinning of the BORAL in the SFP racks is evaluated in the criticality analysis. Table 9.6, 9.14, and 9.20 of Attachment 5 to the LAR (ML18128A049) shows the uncertainty cases for BORAL thickness. The uncertainty cases remove al_l of the clad from one side of the BORAL plate for all panels in the pool. Proportionally this is roughly double the amount of weight loss observed to date in the coupons. The SFP k-eff sensitivity to the BORAL thickness is small. For Region 1, the sensitivity is 0.0010 delta k (dk, including statistical uncertainties) compared to the minimum margin to the limit of 0.0079 dk. For Region 2, the sensitivity is 0.0003 dk compared to the minimum margin to the limit of 0.0052 dk. Note that the minimum margin to the limit of the whole LAR is in Region 3 with 0.0049 delta k.

Serial No.18-403 Docket No. 50-423 Attachment, Page 4 of 4 Based on the information presented above, there are no planned corrective actions at this time. It should be noted that if future information challenges the assertions outlined above, then the situation will be reevaluated to determine if corrective actions are needed to mitigate the Baral weight loss.

RAI-MCCB-2 10 CFR 50.68(b)(4) states, in part, that " ... the kerr of the spent fuel storage racks loaded with fuel of the maximum fuel assembly reactivity must not exceed 0.95 ... ". The MPS3 TS 5. 6. 1. 1, "Fuel Storage - Criticality," ensures the sub-criticality requirements of 10 CFR 50.68(b)(4) are met. The kerr found in the SFP criticality analysis is used to demonstrate compliance with TS 5. 6. 1. 1. Certain assumptions in the SFP criticality analysis rely on the condition of the Bora/ neutron-absorbing material. In order to verify the assumed values for certain properties of Bora/ (Boron-10 areal density, length, width, etc.), the licensee has previously implemented a Bora/ coupon monitoring program.

Because the Bora/ coupon monitoring program provides assurance, in part, that TS

5. 6. 1. 1 will continue to be met, the NRC staff requires assurance that the coupon monitoring program will not be subject to changes which reduce the effectiveness of the program. Describe how the Bora/ coupon monitoring program will be controlled (e.g.

UFSAR/TS update) to provide assurance that changes reducing the effectiveness of the program will not be made.

• DENC Response The MPS3 Updated FSAR, Section 9.1.2.3 provides the required BORAL coupon testing schedule which at present extends through the end of Cycle (EOC) 21 (spring 2022). Dominion Energy Nuclear Connecticut has committed to revising the Updated FSAR to follow the Baral coupon testing schedule requirements in NEI 16-03, "Guidance for Monitoring of Fixed Neutron* Absorbers in Spent Fuel Pools" following EOC 21. In accordance with NEI 16-03, until the weight loss trend has been arrested, Millstone Unit 3 will test the BORAL coupons approximately every 5 years in accordance with the Millstone procedure for Baral Test Coupons. Revisions to the Updated FSAR are subject to the requirements of 10 CFR Part 50.59.