ML16007A034

Request for Additional Information Related to Benchmarks for Quantifying Fuel Reactivity Depletion Uncertainty and Utilization of the EPRI Depletion Benchmarks for Burnup Credit Validation.

ML16007A034
Person / Time
Site:	Nuclear Energy Institute
Issue date:	02/04/2016
From:	Joseph Holonich Licensing Processes Branch (DPR)
To:	Mccullum R Nuclear Energy Institute
Holonich J
References
Download: ML16007A034 (3)

Text

February 4, 2016 Rod McCullum, Director Used Fuel Programs Nuclear Energy Institute 1201 F Street, NW, Suite 1100 Washington, DC 20004

SUBJECT:

REQUEST FOR ADDITIONAL INFORMATION RELATED TO "BENCHMARKS FOR QUANTIFYING FUEL REACTIVITY DEPLETION UNCERTAINTY" AND "UTILIZATION OF THE EPRI DEPLETION BENCHMARKS FOR BURNUP CREDIT VALIDATION"

Dear Mr. McCullum:

By letter dated June 6, 2012 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML12165A455), the Electric Power Research Institute (EPRI) submitted two reports, "Benchmarks for Quantifying Fuel Reactivity Depletion Uncertainty" and "Utilization of the EPRI Depletion Benchmarks for Burnup Credit Validation" to the U.S. Nuclear Regulatory Commission (NRC). Both of these reports support the ongoing revision of NEI 1216, "Guidance for Performing Criticality Analyses of Fuel Storage at LightWater Reactor Power Plants." Upon review of the information provided, the NRC staff has determined that additional information is needed to complete the review.

In an email dated January 6, 2016, Mr. Kristopher Cummings, representing the Nuclear Energy Institute, and I agreed that the NRC staff will receive your response to the enclosed request for additional information (RAI) questions by March 31, 2016.

If you have any questions regarding the enclosed RAI questions, please contact me at (301) 415-7297.

Sincerely, /RA/

Joseph J. Holonich, Sr. Project Manager Licensing Processes Branch Division of Policy and Rulemaking Office of Nuclear Reactor Regulation Project No. 689

Enclosure:

RAI questions

ML16007A034; *concurred via e-mail NRR-106 OFFICE DPR/PLPB DPR/PLPB* DSS/SRXB DPR/PLPB DPR/PLPB NAME WMacFee DHarrison EOesterleKHsuehJHolonich DATE 01/07/2016 01/22/2016 02/02/2016 02/02/2016 02/04/2016 REQUEST FOR ADDITIONAL INFORMATION (RAI) QUESTIONS REGARDING EPRI REPORT 1025203, "UTILIZATION OF THE EPRI DEPLETION BENCHAMRKS FOR BURNUP CREDIT VALIDATION," AND EPRI REPORT 1022909, "BENCHMARKS FOR QUANTIFYING FUEL REACTIVITY DEPLETION UNCERTAINY"

1) For the resulting benchmark model to be applicable, the uncertainty of the benchmark must be established such that a 95/95 confidence assessment can be established on the subsequent criticality calculations. As such the uncertainty in the reactivity of a specific assembly at a specific burnup needs to be determined. The variance of the average of multiple assemblies will be smaller than the variance of a single assembly.

The statistics in the proposed approach appears to only derive the uncertainty of the CASMO/SIMULATE code that is applicable to the reactor core average decrement.

Clarify how the variance in the reactivity decrement for a specific assembly and burnup can be established to support subsequent criticality benchmark analyses.

2) Benchmarks have historically been "measurements" with some minor calculation adjustments for clarity or simplification. The approach, as presented in the reviewed documents and revised statistical approach, presents a case to assess the uncertainty of the code methodology based indirectly on core measurements with adjustments to minimize the code difference (error). The "benchmark" is then manufactured from the code using the code's relative uncertainty. Thus, the benchmark is based on the code, not on the measurement. To be based on the measurement, only those measurements (i.e., directly from flux map data) applicable to a benchmark case would be used with the establishment of case-specific absolute variances or errors. Explain why EPRI's reactivity decrement error deduction approach is appropriate given that the benchmark is based on the code rather than direct measurement.

3) Discuss how extrapolation of the EPRI work will be extrapolated to other fuel designs given that the benchmarks contain a limited subset of fuel designs.

4) Discuss the range of method applicability with respect to the use of different depletion codes and clarify the general validation procedure outlined in EPRI report 1025203.

Specifically, the procedure described in EPRI report 1025203 describes how depletion code validation is to be performed, but does not discuss any of the procedure limitations. For example, the implications of excessive depletion code bias is not addressed. Additionally, how are the 11 calculational benchmarks robust to consideration of different fuel designs that have different physical characteristics? That is, why isn't it necessary to define application-specific calculational benchmarks? The EPRI report 1025203 procedure is also vague with respect to expectations regarding incorporation of biases and uncertainties from EPRI report 1022909 into a user's depletion code validation analysis as part of an overall criticality safety analysis.

Enclosure