NL-14-1416, E. I. Hatch, Unit 2 - Supplemental Information Regarding Proposed Safety Limit Minimum Critical Power Ratio (SLMCPR) License Amendment

E. I. Hatch, Unit 2 - Supplemental Information Regarding Proposed Safety Limit Minimum Critical Power Ratio (SLMCPR) License Amendment

ML14251A579
Person / Time
Site:	Hatch
Issue date:	09/08/2014
From:	Pierce C Southern Co, Southern Nuclear Operating Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NL-14-1416
Download: ML14251A579 (8)

Text

Charles R. Pierce Southern Nuclear Regulatory Affairs Director Operating Company, Inc.

40 Inverness Center Parkway Post Office Box 1295 Birmingham, Alabama 35201 Tel 205.992.7872 Fax 205.992.7601 Fax 205.992.7601 A

SEP 0 8 2014

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SOUTHERN.^

Docket Nos.; 50-366 COMPANY U. S. Nuclear Regulatory Commission NL-14-1416 ATTN: Document Control Desk Washington, D. C. 20555-0001 Edwin I. Hatch Nuclear Plant - Unit 2 Supplemental Information Regarding Proposed Safety Limit Minimum Critical Power Ratio fSLMCPR) License Amendment Ladies and Gentlemen:

By application dated August 8, 2014, Southem Nuclear Operating Company (SNC),

the licensee for Edwin I. Hatch Nuclear Plant (HNP) Unit 2, submitted an amendment that requested changes to Technical Specifications Section 2.1.1.2, "Reactor Core SLs." The amendment proposed revising the cycle-specific safety limit minimum critical power ratio (SLMCPR) for the upcoming Cycle 24. Based upon SNC discussions with the U.S. Nuclear Regulatory Commission (NRC) staff, SNC is providing additional information in the Enclosure for the NRC staff to complete its safety evaluation of the application.

This letter contains no NRC commitments. Ifyou have any questions, please contact Ken McElroy at (205) 992-7369.

Mr. C. R. Pierce states he is Regulatory Affairs Director of Southem Nuclear Operating Company, is authorized to execute this oath on behalf of Southem Nuclear Operating Company and, to the best of his knowledge and belief, the facts set forth in this letter are true.

Respectfully submitted.

CUjLA£i:

C. R. Pierce Regulatory Affairs Director CRP/RMJ/lac T7C^

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Sworn to and subscribed before me this 6

day of

. 2014.

Notary Public My commission expires:

U. S. Nuclear Regulatory Commission NL-14-1416 Page 2

Enclosure:

Supplemental Information Regarding Proposed Safety Limit Minimum Critical Power Ratio (SLMCPR) cc:

Southern Nuclear Operating Company Mr. S. E. Kuczynski, Chairman, President &CEO Mr. D. G. Bost, Executive Vice President & Chief Nuclear Officer Mr. D. R. Vineyard, Vice President - Hatch Mr. B. L. Ivey, Vice President - Regulatory Affairs Mr. D. R. Madison, Vice President - Fleet Operations Mr. B. J. Adams, Vice President - Engineering Mr. G. L. Johnson, Regulatory Affairs Manager - Hatch RType: CHA02.004 U. S. Nuclear Regulatory Commission Mr. V. M. McCree, Regional Administrator Mr. R. E. Martin, NRR Senior Project Manager - Hatch Mr. D. H. Hardage, Senior Resident Inspector - Hatch State of Georaia Mr. J. H. Turner, Environmental Director Protection Division

Edwin I. Hatch Nuclear Plant - Unit 2 Supplemental Information Regarding Proposed Safety Limit Minimum Critical Power Ratio (SLMCPR) License Amendment Enclosure Supplemental Information Regarding Proposed Safety Limit Minimum Critical Power Ratio (SLMCPR)

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'i H.; u;*u Class I August 29,2014 GNF-PLM-001N8437-R0 GNF Response to Requests for Additional Information (RAIs) Regarding the Requested Changes to the Technical Specification SLMCPR HNP Unit 2 Cycle 24 Copyright 2014 Global Nuclear Fuels-Americas, LLC All Rights Reserved HNP Unit 2 Cycle 24 Verified Information

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By application dated August 8, 2014, Southern Nuclear Operating Company (SNC), the licensee for Edwin I. Hatch Nuclear Plant (HNP) Unit 2, submitted an amendment requesting changes to Technical SpecificationsSection 2.1.1.2, "ReactorCore SLs." The amendmentproposed revising the cycle-specificsafety limit minimum critical power ratio (SLMCPR)for the upcoming Cycle

24. Based on discussions between the U.S. Nuclear Regulatory Commission (NRC) staffand SNC, the NRC stafTrequeststhe following additional informationto complete its safety evaluation ofthe application.

SRXB-RAl-1 Figure 5, Enclosure 1 of the license amendment request (LAR) indicates identical behavior relationship between the Minimum Critical Power Ratio (MCPR) Importance Parameter (MIP) and critical power ratio margin for GNF2 fuel and GEM fuel. Explain the differences in the design and geometrical considerations between GNF2 and GE14 and explain the reason for this identical MCPR related behavior.

GNF Response Becausethe SLMCPRcalculation is performed on a core wide basis, the 10x10 (GEM, GNF2) points shown in Figure 5 reflect cores transitioningto GNF2 fuel, so they all have a mix of 10x10 fuel products. Thus, there are no specific GNF2 data points in Figure 5. In general, the MCPR behavior is largelydriven by the fresh fuel. This response is generic since it has no plant or cycle dependency.

SRXB-RAI-2 2-1)

Explain the reload methodology and the loading schemes used for Cycles 23 and 24.

GNF Response RELOAD METHODOLOGY:

The methods used to analyze the core loading pattern are in accordance with the methods and processes defined in GESTAR II.

There is no change in approved core design or SLMCPR methodologies. This Technical Specification (TS) change based on the HNP Unit 2 Cycle 24 design was completed within approved methodologies. SLMCPR is not the primary driver in developingfuel cycle core designs. The energy plan, reactivity and thermal marginsare the primary drivers.

SAFETY LIMIT METHODOLOGY:

HNP Unit2 Cycle 24 Verified Information Page 2 of5

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The SLMCPR methodology uses sets of random perturbations (Monte Carlo) in the calculation process to determine the cycle-specific SLMCPR. For each cycle, cycle-specific SLMCPR calculations are performed for the specific fuel bundle design and core loading used in the cycle reload design. The core radial power distribution must represent a reasonable bound on the number of fuel bundles at or near thermal limits, and the fuel assembly local power distribution must be based on the actual bundle design. The cycle-specific analysis is performed at multiple exposure points throughout the cycle and the most limiting calculated SLMCPR is compared to the TS value. In most cycles, the SLMCPR does not change to the extent that a request for a TS change is necessary. If the calculated cycle specific SLMCPR is bounded by the TS value then no TS change is required. A reduction in the SLMCPR TS could be requested if the calculated value is lower than the existing TS. Although rarely used, there is also an approved provision to use an exposure-dependent SLMCPR. This methodology response applies to all plant-cycles.

LOADING SCHEMES:

The loading pattern is developed by GNF based on Southern Nuclear Operating Company input. Among the inputs are:

Batch size and cycle energy - fuel bundle design (nuclear) and loading patterns are developed together Thermal limit design margins Reactivity margins - Minimum shutdown margin, minimum and maximum hot excess reactivity Discharge exposure limitations and other limits as established by safety analysis Desired control rod patterns - sequences and durations Minimize preconditioning limitations The core designs for Cycles 24 and 23 are similar. Due to differences in the schedules, both cycles were designed to deliver different final energy. Cycle 24 has been specified to operate for 688 Effective Full Power Days (EFPD), while Cycle 23 designed energy was 677 EFPD.

2-2)

For the initial core loadings of Cycles 23 and 24, specify the fuel type, number of fresh, once burned, twice and thrice burned fuel.

GNF Response HNP Unit 2 Cycle 23 consisted of 224 fresh GE14, 216 once-burnt GE14, 4 once-burnt GNF2, 116 twice-burnt GE14.

HNPUnit 2 Cycle24 VerifiedInformation Page3 of5

Global Nuclear Fuel HNP Unit 2 Cycle 24 consisted of 224 fresh GNF2, 224 once-bumt GE14, 104 twice-burnt GE14, 4 twice-burnt GNF2, 4 thrice-burnt GE14.

2-3)

For Cycles 23 and 24, provide calculated beginning of cycle (BOC) core excess hot reactivity and the core average burnup at end of cycle (EOC).

GNF Response Cycle 23 core excess hot reactivity at BOC is 1.92%dk. Core average burnup at end-of-cycle is 31,478 MWD/ST.

Cycle 24 core excess hot reactivity at BOC is 1.73%dk. Core average burnup at end-of-cycle is 32,108 MWD/ST.

SRXB-RAI-3 For Cycles 23 and 24, provide the expected maximum cell-averaged bow, the methodology used and the analysis that determined its value.

GNF Response The core-average cell-averaged bow used for both Cycles 23 and 24 is -55 mils.

The amount of bow is characterized as a function ofbatch average discharge exposure and fresh batch fraction. The bow is determined by a technical design procedure table lookup based on the given discharge exposure, batch fraction, lattice type (C/S or D) and loading pattern style (either

'conventional', or 'control cell core'*). The channel bow that isused inthe calculations throughout the cycle is conservatively based upon end ofcycle exposures. This methodology response applies to all plant-cycles.

' HNP Unit 2 isa 'D' lattice plant. Cycles 23 and 24were both loaded using a 'conventional' pattern.

HNP Unit 2 Cycle 24 Verified Information Page 4 of5

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-.t C,L T-r! -t..i SRXB-RAl-4 Table 3 of Enclosure 1 of the LAR indicates that HNP Unit 2 is affected by the off-rated flow condition as explained in the GNF SLMCPR Part 21 report dated August 24, 2004 (MFN 04-081).

Explain the reason for the change in the "estimated SLMCPR value" for Cycle 24 compared to the previous cycle where the MIPRIP correlation (combines the MIP and R-Factor Importance Parameter (RIP) values) and the Monte Carlo were used for the analysis (see Table 3 of Enclosure I.)

GNF Response MFN 04-081 concerned the discovery that the SLMCPR for some plants was more limiting when calculated at the condition of minimum licensed flow for rated power than at the rated flow /

rated power condition. Following that discovery in 2004 it has been standard procedure for GNF to calculate the SLMCPR at the minimum flow / rated power condition in addition to the rated power / rated flow condition. Previously, SLMCPR was calculated only at the rated power /

flow condition.This response paragraph is generic since it has no plant or cycle dependency.

For HNP Unit 2 Cycle 24 the flow for the limiting SLMCPR is rated flow. Thus, the limiting SLMCPR is not affected by the off-rated flow SLMCPR.

The reason for the change in the "estimated SLMCPR value" for Cycle 24 compared to the previous cycle is directly related to the different values of MIP and RIP for the two cycles. For example, for the rated flow case, the Cycle 24 MIPRIP is greater than that ofCycle 23. This is consistent with the higher Cycle 24 estimated SLMCPRcomparedto that of Cycle 23. For the minimum core flow cases, the Cycle 24 MIPRIP is greater than that ofCycle 23. This is consistent with the greater Cycle 24 estimated SLMCPR compared to that ofCycle 23. Please note that the use of the MIPRIP empirical correlation is only a reasonableness check of the approved licensing basis Monte Carlo analysis.The calculated SLMCPR is always based on the approved licensing basis Monte Carlo analysis.

HNP Unit2 Cycle 24 Verified Information Page 5 of 5