ML20247B675

Part 21 Rept Re Evaluation & Notification for RELAP4 Excessive Variability at Millstone Unit 2.Caused by Small Changes in Input to RELAP4 That Can Result in Large Changes in Calculated Peak Cladding Temp.Informed NRC of Deviation

ML20247B675
Person / Time
Site:	Millstone
Issue date:	05/01/1998
From:	Mallay J SIEMENS POWER CORP. (FORMERLY SIEMENS NUCLEAR POWER
To:	NRC (Affiliation Not Assigned), NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
REF-PT21-98 NRC:98:026, NRC:98:26, NUDOCS 9805080178
Download: ML20247B675 (3)

Text

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SIEMENS l

' May 1,'1998 NRC:98:026 Document Control Desk ATTN: Chief, Planning, Program and Management Support Branch U. S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 10 CFR Part 21 Evaluation and Notification for RELAP4 Excessive Variability This letter provides notification of a reportable defect per 10 CFR Part 21 reported to the NRC Operations Center by facsimile at 08:15 PDT on May 1,1998. Report No. 34162 was assigned to the notification by the Duty Officer.

The affected PWR utilities have been informed, and the actions taken and to be taken to address the issue are provided in the Attachment to this letter.

Very truly yours, James F. Mallay, Director Regulatory Affairs

/arn Attachment cc: Mr. E. W. Merschoff (USNRC)

Mr. E. Y. Wang (USNRC)

R. L. Feuerbacher (SPC)

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9805000178 980501 PDR ADOCK 05000336 ri S PDR

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NRC:98:026 Attachment Page 1 I

REPORTABLE DEFECT (i.) Name and address of the individualinforming the Commission James F. Mallay, Director, Regulatory Affairs, Siemens Power Corporation - Nuclear Division,2101 Horn Rapids Rd., Richland, WA 99352.

(ii.) Identification of the facility, the activity, or the basic component supplied for such facility or such activity within the United States which fails to comply or contains a defect.

l The Siemens Power Corporation (SPC) EXEM/PWR LBLOCA evaluation model.

(iii.) Identification of the firm constructing the facility or supplying the basic component which fails to comply or contains a defect.

Siemens Power Corporation - Nuclear Division, Richland, WA.

(iv.) Nature of the defect or failure to comply and the safety hazard which is created or could be created by such a defect or failure to comply.

Small changes in the input to RELAP4 (part of the EXEMIPWR LBLOCA evaluation model) can result in large changes in the calculated peak cladding temperature during a LBLOCA.

l These results are considered excessive given the size of the input changes. The application of a corrected model may result in the analysis exceeding the 10 CFR 50.46 acceptance criteria on peak cladding temperature.

(v.) The date on which the information of such defect or failure to comply was obtained.

Condition Report 6169 Rev.1 uted December 2,1997 identified a possible deviation.

(vi.) In the case of a basic component which fails to comply, the number and the location of all such components in use at, supplied for, or being supplied for one or more facilities or activities subject to the regulations in this part.

The LBLOCA analyses for Millstone Unit 2.

(vii.) The corrective action which has been, is being, or willbe taken; the name of the individual or organization responsible for the action; and the length of time that has been l

or willbe taken to complete the action.

The NRC was informed of a deviation in the SPC EXEM/PWR LBLOCA evaluation model related to RELAP4 excessive variability in Reference 1. A presentation to the NRC on the status of the evaluation was made in a meeting on March 10,1998. A letter

documenting the future actions proposed by SPC in that meeting was provided in

! Reference 2 in response to a request from Ralph Caruso of the NRC. A modification to the schedule established in Reference 1 for the evaluation of this deviation was provided to the NRC in Reference 3.

t The current model is the currently approved EXEMIPWR model modified by the interim FCTF correlation which has previously been discussed with the NRC staff. The following corrections have been made, on a preliminary basis, to the current SPC EXEMIPWR LBLOCA evaluation model to reduce the RELAP4 excessive variability.

i. NRC:98:026 Attachment Page 2 l

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• Revised numerical solution scheme.

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• Revised definition of volume average flow.

• Combined system and hot channel blowdown calculations.

e increased nodalization and elimination of enthalpy transport model.

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• Improved consistency between RODEX2 and RELAP4 fuel rod models.

The plants for which SPC provides LBLOCA analyses have all been evaluated with the corrected model. The results for four of these plants indicate that the results from the current model, with the deviation, are conservative (i.e., result in higher peak cladding temperatures) relative to the results from the corrected model. The peak cladding temperatures are lower using the corrected model for these four plants by about 30 to 130 degrees F.

The results for a fifth plant, Millstone Unit 2, increase by more than 50 degrees F and exceed the 2200 degrecs F criteria in 10 CFR 50.46. The Millstone Unit 2 plant is i currently shutdown. A revised LBLOCA analysis will be provided by SPC to Northeast Utilities to support the restart of Millstone Unit 2 to operation.

l List of

References:

1. Letter, J. S. Holm (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, James F. Mallay (SPC) to Document Control Desk (NRC), "RELAP4 Excessive Variability," NRC:98:016, March 17,1998.

3. Letter, James F. Mallay (SPC) to Document Control Desk (NRC), " Interim Report of i Evaluation of a Deviation Pursuant to 10 CFR 21.21(a)(2)," NRC:98:020, April 1, l- 1998.-

' (viii.) Any advice related to the defect or failure to comply about the facility, activity, or basic component that has been, is being, or willbe given to purchasers or licensees.

Estimates of the impact of the deviation upon the LBLOCA analyses will be provided to each SPC customer.

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