United States Nuclear Regulatory Commission - Protecting People and the Environment


ACCESSION #: 9806100377



Consumers Energy



A CMS Energy Company

                    Palisades Nuclear Plant            Tel. 616 764 2276

                    27780 Blue Star Memorial Highway   Fax: 616 764 2490

                    Covert, MI 49043

                                                      Nathan L.  Haskell

                                                      Director, Licensing



June 1, 1998



U.S.  Nuclear Regulatory Commission

ATTN: Document Control Desk

Washington, DC 20555



DOCKET 50-255 - LICENSE DPR-20 - PALISADES PLANT

EVALUATION OF 10 CFR PART 21 REPORT REGARDING IMPACT OF RELAP4

EXCESSIVE VARIABILITY ON PALISADES LARGE BREAK LOCA ECCS RESULTS



In accordance with 10 CFR 50.46(a)(3)(ii), a report is required to be

submitted within 30 days of discovery of a significant change or error in

an Emergency Core Cooling (ECCS) analysis.  The purpose of this letter is

to report a significant change in the calculated peak cladding

temperature (PCT) values as a result of an error in the Palisades large

break loss of coolant accident (LBLOCA) ECCS evaluation model.



On January 15, 1998, per 10 CFR Part 21, the NRC was informed of a

deviation in the Seimans Power Corporation (SPC) EXEM/PWR LBLOCA

evaluation model related to RELAP4 excessive variability.  During a

presentation to the NRC on March 10, 1998, Palisades agreed to report the

results of the evaluation of this deviation based on the corrected model

for both fuel Cycles 13 and 14.  That report is provided in the

attachment.



Based on the currently approved and the corrected LBLOCA evaluation

model, the change in the PCT during Cycle 14 from that during Cycle 13 is

not significant.  However, the evaluation of the corrected model has

shown that a significant (per 10 CFR 50.46) change in the PCT values for

both fuel Cycles 13 and 14 will result from the error correction.





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SUMMARY OF COMMITMENTS



This letter contains no new commitments and no revisions to existing

commitments.





Nathan L.  Haskell

Director, Licensing



CC   Administrator, Region III, USNRC

     Project Manager, NRR, USNRC

     NRC Resident Inspector - Palisades



Attachment





ATTACHMENT



CONSUMERS ENERGY COMPANY

PALISADES PLANT

DOCKET 50-255



EVALUATION OF 10 CFR PART 21 REPORT REGARDING IMPACT OF RELAP4

EXCESSIVE VARIABILITY ON PALISADES LARGE BREAK LOCA ECCS RESULTS



                                 3 Pages





EVALUATION OF 10 CFR PART 21 REPORT REGARDING IMPACT OF RELAP4

EXCESSIVE VARIABILITY ON PALISADES LARGE BREAK LOCA ECCS RESULTS



REFERENCES



1.   Letter, JSHolm (SPC) to Document Control Desk (NRC), "Interim Report

     of Evaluation of a Deviation Pursuant to 10 CFR 21.21 (a)(2)",

     NRC:98:001, January 15, 1998.



2.   Letter, JFMallay (SPC) to Document Control Desk (NRC), "RELAP4

     Excessive Variability", NRC:98:016, March 17, 1998.



3.   Letter, JFMallay (SPC) to Document Control Desk (NRC), "Interim

     Report of Evaluation of a Deviation Pursuant to 10 CFR 21.21

     (a)(2)", NRC:98:020, April 1, 1998.



4.   Letter, JFMallay (SPC) to Document Control Desk (NRC), 10 CFR Part

     21 evaluation and Notification for RELAP4 Excessive Variability",

     NRC:98:026, May 1, 1998.



5.   Letter, TCBordine (Consumers Energy) to Document Control Desk (NRC),

     "Notification Under 10 CFR 50.46 of Change in ECCS Calculation

     Results", dated April 30, 1997.



6.   Letter, TCBordine (Consumers Energy) to Document Control Desk (NRC),

     "Annual Report of Changes in ECCS Models per 10CFR50.46", dated

     November 26, 1997.



BACKGROUND



In a letter dated January 15, 1998, NRC was informed of a deviation in

the SPC EXEM/PWR LBLOCA evaluation model related to RELAP4 excessive

variability (Reference 1).  The nature of the deviation was that small

changes in the input to RELAP4 can result in large changes in the

calculated peak cladding temperature during a LBLOCA.  At that time, SPC

informed Consumers Energy that there was no indication that the RELAP4

excessive variability problem, after correction, would result in a PCT

that would violate 10 CFR 50.46 limits for the Palisades LBLOCA analysis.



On March 10, 1998, SPC made a presentation to the NRC regarding the

status of the RELAP4 excessive variability evaluation.  In response to a

request by NRC, SPC provided a summary of the meeting presentation and

documented the future actions proposed (Reference 2).  It was agreed that

SPC would continue to use the currently approved EXEM/PWR LBLOCA model,

modified by the interim fuel cooling testing facility (FCTF) correlation,

to perform plant analyses in the near term.  In the longer term, SPC

would correct the current model for excessive variability and submit a

topical



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EVALUATION OF 10 CFR PART 21 REPORT REGARDING IMPACT OF RELAP4

EXCESSIVE VARIABILITY ON PALISADES LARGE BREAK LOCA ECCS RESULTS



report to NRC for review.  Additionally, in an effort to ensure that

Palisades LBLOCA calculations based on the current RELAP4 model continue

to be conservative with respect to the excessive variability, SPC agreed

to perform confirmatory calculations with a corrected model for

comparison purposes.  Palisades agreed to report the results of the 10

CFR Part 21 evaluation based on the corrected model for both fuel Cycles

13 and 14.



A modification to the original (Reference 1) 10 CFR Part 21 evaluation

schedule was transmitted to NRC by SPC on April 1, 1998, (Reference 3),

indicating that the evaluation would be completed on May 1, 1998, rather

than April 3, 1998.  In a letter dated May 1, 1998, (Reference 4), SPC

transmitted the results of their 10 CFR Part 21 evaluation.  A summary of

the evaluation results, with respect to the Palisades LBLOCA analyses

follows.



IMPACT OF RELAP4 EXCESSIVE VARIABILITY ON PALISADES CYCLE 13 LBLOCA

ANALYSIS



In letters dated April 30, 1997, and November 26, 1997, (References 5 &

6), Consumers Energy reported that the PCT predicted by the LBLOCA

analysis for fuel Cycle 13 was 1892 Degrees F.  The Cycle 13 analysis and

resultant PCT were based on the currently approved SPC RELAP4 LBLOCA

model.  The results of confirmatory calculations indicate that when the

RELAP4 model is corrected for excessive variability, the predicted PCT

will be lower by about 113 Degrees F.  Therefore, the deviation

identified in Reference 1 and further identified as a reportable error in

Reference 4 is significant per 10 CFR 50.46.  This deviation is

considered conservative for the Palisades Cycle 13 LBLOCA analysis.



IMPACT OF RELAP4 EXCESSIVE VARIABILITY ON PALISADES CYCLE 14 LBLOCA

ANALYSIS



Re-analysis of the LBLOCA event based on the current RELAP4 model has

recently been completed by SPC for Palisades fuel Cycle 14, resulting in

a PCT of 1869 Degrees F.  This result constitutes a 23 Degrees F drop in

calculated PCT from fuel cycle 13 to fuel cycle 14.  The change in PCT

between Cycle 13 and Cycle 14 was due primarily to revised core fuel

design (pellet diameter and clad thickness) and neutronics values (radial

peaking factors) which were used to reflect the Cycle 14 core design and

reload "R" fuel.  The change in PCT between Cycle 13 and Cycle 14 does

not constitute a significant change per 10 CFR 50.46.



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EVALUATION OF 10 CFR PART 21 REPORT REGARDING IMPACT OF RELAP4

EXCESSIVE VARIABILITY ON PALISADES LARGE BREAK LOCA ECCS RESULTS



The results of confirmatory calculations for Cycle 14 indicate that when

the RELAP4 model is corrected for excessive variability, the predicted

PCT will be lower by about 70 Degrees F.  Therefore, the deviation

identified in Reference 1 and further identified as a reportable error in

Reference 4 is significant per 10 CFR 50.46.  This deviation is

considered conservative for the Palisades Cycle 14 LBLOCA analysis.



CONCLUSION



The Palisades Cycle 13 and 14 LBLOCA analyses demonstrate that the

acceptance criteria of 10 CFR 50.46 continue to be satisfied based on

calculations performed with both the currently approved EXEM/PWR LBLOCA

model, modified by the interim FCTF correlation, and the EXEM/PWR LBLOCA

model corrected for excessive variability.  Confirmatory calculations

performed indicate that PCT will drop by greater than 50 Degrees F when

the current model is corrected for excessive variability, which

constitutes a significant change per 10 CFR 50.46.  However, the

resulting changes in the PCT for fuel Cycles 13 and 14 will be in the

conservative direction.



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