ML18067A790

Transmits Annual Rept of Changes in ECCS Models,Per 10CFR50.46(a)(3)(ii).Rept Contains Both SBLOCA & Large Break LOCA Evaluation Models

ML18067A790
Person / Time
Site:	Palisades
Issue date:	11/26/1997
From:	Bordine T CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9712010134
Download: ML18067A790 (8)

Text

A CMS Energy Company 111oma* t:. Bordlae Manager Licensing November 26, 1997 U.S. Nuclear Regulatory Commission A TIN: Document Control Desk Washington, DC 20555 DOCKET 50-255 - LICENSE DPR-20 ~ PALISADES PLANT ANNUAL REPORT OF CHANGES IN ECCS MODELS PER 10CFR50.46 Palisades is required to submit an annual report of changes in Emergency Core Cooling System (ECCS) Models in accordance with 10CFR50.46(a)(3)(ii). Attachment 1 of this letter transmits that report and contains both the Small Break Loss of Coolant Accident (SBLOCA) and Large Break Loss of Coolant Accident (LBLOCA) evaluation model information. This report covers the period from May 1996 to May 1997.

Attachment 2 to this letter is a summary of correspondence between Consumers Energy, Siemens Power Corporation (SPC) and the NRC since June 1995 regarding the Palisades LOCA evaluation models. Included in this summary are additional correspondence

• regarding errors and concerns with the SPC LBLOCA methodology which the NRC raised late in 1996. Attachment 2 is provided to serve as a baseline of the Palisades reports made over the previous two years and provide a clear foundation for future reports to NRC.

Attachment 2 is not a required portion of the annual report of changes.

SUMMARY

OF COMMITMENTS This letter contains no new commitments and no revisions to existing commitments.

Thomas C. Berdine f-lcCTD( t/* .

• Manager, licensin*g- - -- - ---- - --- ----- --* -- -- --l----~-

CC Administrator, Region Ill, USNRC Project Manager, NRR, USNRC NRC Resident Inspector - Palisades Attacnments

.-----r-- 97,12010134 971126 f"'*

• I __ __ 11um111111111_11~~Jllll_II"!11111~1 1 PDR ADOCK 05Q0~~.5 .:  :

R _, . -* . -

-Palisades Nuclear Plant

• 27780 Blue Star Memorial Highway

• Cov1Jil, Ml 49043

• Tel: 616 764 2913

• Fax: 616 764 2490

ATTACHMENT 1 CONSUMERS ENERGY COMPANY PALISADES PLANT DOCKET 50-255 ANNUAL REPORT OF CHANGES IN ECCS MODELS PER 10CFRS0.46 2 Pages

ANNUAL REPORT OF CHANGES IN ECCS MODELS PER 10CFR50.46 ABB-CE SBLOCA ECCS EVALUATION

SUMMARY

Asea Brown Boveri-Combustion Engineering (ABB-CE) performed a reanalysis of the Small Break Loss of Coolant Accident (SBLOCA) design basis for Palisades using Palisades plant-specific input data in ABB-GE's NRG-approved 1977 ECCS Evaluation Model. The previous SBLOCA analysis, which was documented in the Palisades FSAR, was an analysis for another plant that had been determined to be applicable to the Palisades design by ABB-CE.

The results of the reanalysis demonstrated conformance to the ECCS performance acceptance criteria of 10CFR50.46(b). A significant change was noted in that the predicted peak clad temperature of 1992°F was 52°F higher than the previous analysis results. This predicted temperature increase was the result of using Palisades plant-specific data and not the result of a change to or an error in the ABB-CE SBLOCA evaluation model, or an error in the application of the model to the Palisades Plant.

Palisades reported this change in the calculated peak fuel cladding temperature in a notification to the NRC dated January 15, 1997.

EXEM PWR LARGE BREAK LOCA MODEL FOR PALISADES The EXEM PWR Large Break Loss of Coolant Accident (LBLOCA) Evaluation Model is used to assess large break loss of coolant accidents in PWRs. The Evaluation Model consists of four primary computer codes: RELAP4 to compute the system and hot channel response; RFPAC to compute the containment pressures, reflood rates, and axial shape factors; TOODEE2 to calculate the hot rod heatup; and RODEX2 to determine the rod conditions at the start of the transient. With the exception of the TOODEE2 code, there were no model or correlation changes made. The changes to the TOODEE2 code are described below.

TOODEE2 The FCTF reflood correlation was modified such that a linear interpolation of reflood heat transfer coefficients is used between effective reflood rates of 1.0 to 1. 77 in/sec. This is an interim model update approved by the NRC for use until SPC receives approval for updates to the TOODEE2 code submitted to the NRC in December 1996.

1

Peak Cladding Temperature Impact Due to Changes The Palisades Cycle 13 LBLOCA analysis of record utilized the TOODEE2 interim model -----=:__

update. The Peak Cladding Temperature (PCT) predicted for Cycle 13 with the interim FCTF model was 1892°F. The PCT predicted (not submitted to NRC; used only to assess PCT change) for Cycle 13 with the 1991 FCTF model (model the NRC determined to be unacceptable) was 1862°F. Thus, an increase of 30°F is associated with the TOODEE2 model change.

The Palisades Cycle 13 LBLOCA analysis was affected by the TOODEE2 interim model update, even though the PCT of 1862°F predicted without the interim model update occurred at a time when the effective reflood rate was greater than 1.77 in/sec. Use of the interim 'FCTF model results in lower heat transfer coefficients than the 1991 FCTF model when the effective reflood rate becomes less than 1. 77 in/sec. The effect is that elevations high in the core experience higher cladding temperatures with the interim model as the reflood rate reduces below 1. 77 in/sec. Depending on plant specific operating conditions and the particular axial shape being analyzed (particularly top skewed shapes), the PCT may occur on a node farther downstream from the peak powered node and at a later time in the transient than with the previous 1991 FCTF model. With the previous 1991 model, the PCT typically occurred on the peak powered node, which was also the ruptured node.

With the interim model, and for top skewed axial shapes, the PCT occurs downstream of the peak powered node and at a time after the effective reflood rate has gone below 1. 77 .

in/sec.

Use of Dougall-Rohsenow Correlation The PCT temperature predicted during this reporting period was calculated using an interim update to the TOODEE2 code and, consequently, was not referenced back to the originally-approved 1986 EM model. Future use of the Dougall-Rohsenow correlation is

• addressed in the topical report (EXEM/PWR Large Break LOCA ECCS Model Updates, XN-NF-82-20(P), Revision 1, Supplement 6) submitted to the NRC by the following quoted statement from page 1-2 of the topical report:

"In the event that the 1996 reflood model combined with other changes could significantly reduce the peak cladding temperature (PCT) compared with the 1986 model, the conservatism of the Dougall-Rohsenow correlation must be addressed.

To do this, SPC will limit the reduction of conservatism by applying a conservative multiplier to the 1996 FCTF reflood heat transfer coefficient for that reactor. The multiplier will be determined and reported on a plant-specific basis until a revision to the Dougall-Rohsenow correlation in the SPC model is approved."

2

ATTACHMENT 2 CONSUMERS ENERGY COMPANY PALISADES PLANT DOCKET 50-255

SUMMARY

OF CORRESPONDENCE WITH NRC REGARDING PALISADES LOCA ECCS EVALUATION MODELS June 1995 to September 1997 3 Pages

~ummary of Correspondence with NRC Regarding Palisades LOCA ECCS Evaluation Models June 16, 1995 - CPCo Letter to NRC, "Notification of Significant Change to ECC Calculation".

Due to new fuel enrichment of reload batch 'P', a reanalysis of the Palisades LBLOCA was performed for cycle 12 and a change of >50°F in PCT was calculated. The calculated peak clad temperature (PCT) changed from 2192°F to 2095°F.

May 29, 1996 - SPC letter to NRC, "Annual Reporting of Changes and Errors in ECCS Evaluation Models".

Summary of minor changes and errors in SPC LOCA evaluation models for the period of March 1995 to May 1996.

October 11, 1996 - NRC letter to CPCo, "1 OCFR50.46 LBLOCA Evaluation Model For -

Palisades Plant (TAC No M96355)."

This letter requests assessment of the impact of SPC LBLOCA evaluation model errors and changes ensuring compliance with 10CFR50.46. Also requests CPCo to attend a public meeting at NRC headquarters on 10/16/96.

October 24, 1996 - CPCo Letter to NRC, "1 OCFR50.46 LBLOCA Evaluation Model for Palisades Plant".

Summary of initial conclusions and justification that current LBLOCA analyses are conservative with respect to the SPC LBLOCA model errors and LBLOCA analyses for Palisades plant. Presents a summary of conference calls and meetings held between SPC, CPCo and NRC in October of 1996. This letter was requested by NRC at a meeting in Washington on 10/16/96.

November 5, 1996 - NRC letter to CPCo (et al), "Meeting on the 10CFR50.46 LBLOCA Evaluation Model Error and Changes (TAC No M96355)."

This--letter summarizes the referenced _meeting held at the request of NRC staff in Washington on 10/16/96.

November 22, 1996 - CPCo Letter to NRC, "Clarification of October 24, 1996 Response to NRC Request for Assessment".

1

Q

~ummary of Correspondence with NRC Regarding Palisades LOCA ECCS Evaluation Models This letter clarifies a statement made during the October 16, 1996 presentation at NRG and subsequently submitted in the October 24, 1996 letter.

December 13, 1996 - NRG letter to CPCo, "Palisades Plant - 10CFR50.46 LBLOCA Evaluation Model (TAC M96355)".

In this letter, NRG requests additional information regarding Palisades LBLOCA methodology and current analysis which will permit the staff to determine if the application of the corrected 1991 model for Palisades is consistent with the database on which the SPC reflood heat transfer coefficient correlation is based.

January 15, 1997 - CPCo Letter to NRG, "Notification Under 10CFR50.46 of Change in ECCS Calculation Results".

Report of recently performed Palisades plant specific SBLOCA model. This was the first Palisades plant specific SBLOCA ECCS evaluation. PCT of 1992°F was calculated which was 52°F higher than the previous analysis (which had been performed for another plant but deemed applicable to Palisades).

January 20, 1997 - CPCo Letter to NRG, "Notification Under 10CFR50.46-of Change in ECCS Calculation Results".

This reported an error in the Palisades LBLOCA model discovered by SPC in May of 1995 which was not reported by SPC to Palisades until December 1996. The error resulted in an over prediction in PCT of 104°F. With the errors corrected, the PCT of cycle 12 was 1991°F versus 2095°F previously reported on June 16, 1995.

April 9, 1997 - Consumers Letter to NRG, "Response to NRG Request for Additional Information Regarding 10CFR50.46 LBLOCA Evaluation Model" Consumers Energy responses to eight additional questions regarding our Cycle 13 LBLOCA evaluation model which were raised by NRG (NRC letter dated December 13, 1996) while reviewing SPC LBLOCA methodology.

April 30, 1997 - Consumers-Letter to NRG, "Notification Under 10CFR50.46 of Change in ECCS Calculation Results".

• This reported a reduction in analyzed PCT of greater than 50°F for the fuel cycle 13 Palisades LBLOCA analysis. The LBLOCA analysis for fuel cycle 13 predicted a PCT of 1892°F which constituted a 99°F reduction from the cycle 12 predicted PCT of 1991°F. This reduction was not due to errors in analysis models but rather to 2

$ummary of Correspondence with NRC Regarding Palisades LOCA ECCS Evaluation Models changes in SPC LBLOCA methodology and input assumptions specific to Palisades cycle 13 operation.

June 19, 1997 - NRG letter to Consumers, "Information Regarding Open Technical Issues Related to SPC's 10CFR50.46 LBLOCA Evaluation Model."

This letter is a NRG summary of open technical issues associated with recent audit of SPC and regulatory requirements pertaining to the computer codes used to perform LOCA analyses.

September 2, 1997 - SPC Letter to NRG, "96/97 Annual Reporting of Changes and Errors in ECCS Evaluation Models".

A description of the minor changes and errors in the SPC LOCA evaluation models for the period May 1996 to May 1997.

3