ML19224A052

(Lgs), Units 1 and 2 - Response to Requested Supplemental Information for a One Time Alternative Request Pertaining to Dry Shield Canisters Equipped with Boral Neutron Absorber Plates

ML19224A052
Person / Time
Site:	Limerick, 07201004
Issue date:	08/08/2019
From:	Sturniolo F Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Material Safety and Safeguards, Office of Nuclear Reactor Regulation
References
LG-19-068
Download: ML19224A052 (5)

Text

CoC 1004, Amendment 14 LG-19-068 August 8, 2019 ATTN: Document Control Desk Director, Division of Spent Fuel Management Office of Nuclear Material Safety and Safeguards U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Limerick Generating Station (LGS), Units 1 and 2 Renewed Facility Operating License Nos. NPF-39 and NFP-85 Docket Nos. 50-352, 50-353, and 72-65

Subject:

Response to Requested Supplemental Information for a One Time Alternative Request Pertaining to Dry Shield Canisters Equipped with BORAL Neutron Absorber Plates Reference 1: Exelon Generation Company letter to the NRC, ALTERNATIVE REQUEST PERTAINING TO DRY SHIELDED CANISTERS EQUIPPED WITH BORAL NEUTRON ABSORBER PLATES, DATED April 8, 2019 Reference 2: NRC letter to Richard Libra, ALTERNATIVE REQUEST PERTAINING TO DRY SHIELDED CANISTERS EQUIPPED WITH BORAL NEUTRON ABSORBER PLATES - SUPPLEMENTAL INFORMATION NEEDED, dated June 17, 2019.

In Reference 1 Exelon Generation Company, LLC (EGC) is requesting NRC approval of a one-time alternative for the Limerick Generating Station (LGS), Units 1 and 2 Independent Spent Fuel Storage Installation (ISFSI) pursuant to Standardized NUHOMS CoC 1004 Renewed Amendment 14, Technical Specification (TS) 4.1.

Specifically, the alternative request addresses use of two Dry Shielded Canisters (DSCs) equipped with BORAL neutron absorber plates that were subject to different acceptance testing requirements than those specified in CoC 1004 Renewed, Amendment 14.

In Reference 2 the U.S. Nuclear Regulatory Commission requested supplemental information. The Attachment to this letter provides the response to the requested information.

There are no regulatory commitments contained in this letter.

LG-19-068 August 8, 2019 Page 2 If you have any questions or need additional information, please contact Mr. Joe Dougherty at (61 O) 718-2630.

Respectfully, Frank Sturniolo Acting Vice President - Limerick Generating Station Exelon Generation Co., LLC Attachment Response to Requested Supplemental Information for a One Time Alternative Request Pertaining to Dry Shield Canisters Equipped with BORAL Neutron Absorber Plates cc: W. Allen J. McKirgan S. Rutenkroger

LG-19-068 Attachment Page 1 of 3

Attachment:

Response to Requested Supplemental Information for a One Time Alternative Request Pertaining to Dry Shield Canisters Equipped with BORAL Neutron Absorber Plates

1. Provide justification for 95% confidence level that 95% of the Boral material in the subject DSCs complies with the required Boron-10 content for Amendment 14 of the CoC 72-1004 and supports the conclusions in Section 3.0 of Enclosure 6, Appendix A, of the application.

The applicant made conclusions regarding the adequacy of the Boral material in the two (2) subject dry shielded canisters (DSCs) upon considering the non-compliance with some of the requirements per the Technical Specifications of Amendment 14 of CoC 72-1004.

The applicant justified these conclusions by citing the reduced design-basis credit for the assumed Boron-10 concentration in the criticality safety analyses. Therefore, the staff considers that these conclusions are solely based on engineering judgement without presenting an appropriate statistical analysis based on operating experience. This approach is insufficient for the staff to make conclusions on adequate performance of the Boral material in the subject DSCs.

The applicant is asked to provide justification, such as an operating experience assessment with a rigorous statistical analysis, that:

a) identifies any non-conformances on the Boron-10 content per measurements on the approved sampling rate of every 2000 square inches of product. The assessment should justify that decreasing the sample rate (to every 3200 square inches of product) does not reasonably increase the risk of non-conformance; and,

Response

There are no non-conformances identified on the Boron-10 content in the final document packages of these fabricated DSCs. Section 6.0 and Appendix F of the Boral In-process and Final Inspection procedure (Reference 1) describe and justify the following process for demonstrating 95% confidence that 95% of the Boral inspected complies with the specified Boron-10 areal density. 100% of the sheets produced from the first 100 ingots were tested at the beginning of a production run. Individual sheets that failed the minimum areal density specification were rejected. If the average areal density minus two standard deviations (2) of the first 100 ingots met the specification, subsequent sheets in the production run were subject to reduced inspection. If not, inspection continued at 100%. Reduced inspection started with twenty sheets out of one hundred. The sampling rate was increased until (average areal density) - K minimum specified B10 areal density, where K is a factor that decreases with the increase of the sample size, taken from Natrellas Experimental Statistics, Table A-7, Factors for One-Sided Tolerance Limits for Normal Distributions at P = 0.95 and = 0.95.

An excerpt of Table A-7 from Experimental Statistics is shown below for reference.

LG-19-068 Attachment Page 2 of 3 TABLES OROP 20-114 TABLE A-1 (Continued). FACTORS FOR ONE-SIDED TOLERANCE LIMITS FOR NORMAL DISTRIBUTIONS

• 'J'he two starred values have boon corrected to the vaJues given by D. B. Owen in "Factors /or One-Sided Toleranoo r.tmil.S and for Variables Sampling Plans", Sandia Corporation Monograph SCR-607, available from the Clearing R ou.c:efor Federal Sclcntlnc a.nd Tccbnieal Informo.tion, U.S. Department of Commerce, Sptinglield, Vu. 221~1. Tbo Owen Tables lndicate othr.r error!'! In the ta.blc below, not exceeding -4 io tbo last digit.

l x

"l' = 0.95 "l' = 0.99 I I 1----...,..-- -...,----I 0.75

__._ _ _,_ _ _ \

0.90 *~*95 0.99 0.999 I 0.75 0.90

_ _ _ _ , _ _ _,_ _ _ _,_ _ _ l'- - - - 1

\I 0.95 I 0.99 0.999 3 3.804 2.619 6.158 7. 655 , 10. 552 13 .857 II 4 4 .163 5.1:45 7 .042 9.215 11 5 2.149 3.407 4.202 5.741 7.501 11 6 1.895 3.006 3.707 5.062 6.612 11 2.849 4.408 5.409 7 .334 9.550*

7 1. 732 2.755 3.399 4.641 6.061 ' 2.490 3.856 4.730 6.411 8.348 B 1.617 2.582 3.188 4 .353 5 .686 11 2.252 3.496 4.287 5.811 7.566 9 1.532 2.454 3.031 4.143 5.414 I 2 .085 3.242 3.971 5.389 7.014 10 1.465 2.355 2.911 3.981 5.203 I 1.954 3.048 3.739 5.075 6.603 11 1.411 2.275 2.815 3 .852 5.036 l.854 2.897 3.557 4.828 6.284 12 13 1.366 1.329 2.210 2.155 2.736 2.670 3 .747 3.659 4.900 4.787 I 1.771 1.702 2.773 2.677 3.410 3 .290 I 4 .633 4.472 6.032 5.826 14 1.296 2.108 2.614 3 . 585 4.690 1 1.645 2.592 3.189 1 4.336 5.651 15 1.268 2.068 2 .566 3.520 4.607 I 1.596 2.521 3.102 4.224 5.507 16 1.242 1.220 2.032 2.001 2.523 2.486 3.463 3.415 4.534 I 1.553 4.471 ,, 1.514 2.458 3.028 4.124 5.374 17 2.405 2.962 4.038 5.268 18 19 1.200 1.183 1.974 1.949 2.453 2.423 3 .370 3.331 4.415 4.364 I 1.481 1.450 2.357 2.315 2.906 2.855 3.961 3.893 5.167 5.078 20 1.167 1.926 2.396 3 .295 4.319 1.424 2.275 2.807 3.832 5.003 21 1.152 1.905 2.371 3.262 4 .276 1.397 2.241 2.768 3.776 4.932 22 1.138 1.887 2 .350 3.233 4.238 1.376 2.208 2.729 3.727 4.866 23 l . 126 1.869 2.329 3 .206 4 .204 ! 1.355 2 .179 2.693 3.680 4.806 24 1.114 1.853 2.309 3 . 181 4 .171 1.336 2 .154 2.663 3.638 4.755 25 1 .103 1.838 2 .292 3 .158 4.143 1 1.319 2 .129 2.632 3 .601 4 .706 30 1.059 1. 778 2. 220 3 .064 4 .022 1.249 2.029 2.516 3.446 4.508 35 1.025 1.732 2 .166 2.994 3.934 11 1.195 1 .957 2.431 3.334 4.364 40 0.999 1.697 2.126 2 . 941 3 .866 1.154 1 .902 2.365 3.250 4.255 45 0.978 1.669 2.092 1 2 .897 3.811 .,1 1.122 1.857 2.313 3 .181 4.168 50 0 . 961 1.646 2 .065 1 2 .863 , 3.766 1! 1.096 1.821 2.269* 3 .124 4.096 T- 15 The safety basis for developing the procedure and testing of the Boron-1 O*content for the subject DSCs was based on specifications in Chapter K.9 of CoC 1004, Amendment 9. All the requirements stated in CoC 1004, Amendment 9 were satisfied with no non-conformances_

LG-19-068 Attachment Page 3 of 3 b) identifies the uncertainty in Boron-10 content as measured by wet chemistry and isotopic analysis relative to neutron attenuation measurements. This uncertainty should still provide an adequate safety margin upon considering the reduced design-basis credit of Boron-10 in the criticality analyses.

The information is needed to verify compliance with 10 CFR 72.124(a) and (b).

Response

The design basis credit of Boron-10 content for the Boral plates used in the subject DSCs was based on requirements in the CoC 1004, Amendment 9 for a 61BT DSC. All the specifications and requirements identified in the CoC 1004, Amendment 9 were satisfied for taking 75% credit for the minimum Boron-10 content in the criticality evaluation of these DSCs. There is no requirement in the CoC 1004, Amendment 9 to perform a neutron attenuation measurement or to benchmark the wet chemistry and isotopic analysis. The safety basis for taking 75% credit for the minimum Boron-10 content in the criticality evaluation of the subject DSCs was based on specifications in Chapter K.9 of CoC 1004, Amendment 9. All the requirements stated in CoC 1004, Amendment 9 were satisfied without any exception.

References:

1) AAR Cargo Systems Procedure, BORAL In-Process and Final Inspection, AAR-10012 QAP, Revision 24. This reference was provided as Reference 4 in Enclosure 4 to the Application dated April 8, 2019 (Reference 2).

2) Exelon Generation Company letter to the NRC, ALTERNATIVE REQUEST PERTAINING TO DRY SHIELDED CANISTERS EQUIPPED WITH BORAL NEUTRON ABSORBER PLATES, DATED April 8, 2019.