Part 21 Report - 1998-410

ACCESSION #: 9805190348 SIEMENS May 11, 1998 NRC:98:030 Document Control Desk ATTN: Chief, Planning, Program and Management Support Branch U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Interim Report of Evaluation of a Deviation Pursuant to 10 CFR 21.21(a)(2) The following information is provided pursuant to the requirements of 10 CFR 21 to submit an interim report on issues that will not be completed within 60 days of discovery. An interim report for an issue under evaluation by Siemens Power Corporation is enclosed: Interim Report No. 98-003 "Steam Line Break" Those SPC customers potentially impacted by this issue will be provided a copy of this interim report. If you have any questions or if I can be of further assistance, please call me at (509)375-8757. Very truly yours, James F. Mallay, Director Regulatory Affairs /arn Enclosure cc: Mr. E. Y. Wang (USNRC) Project No. 702 Siemens Power Corporation Nuclear Division 2101 Horn Rapids Road Tel: (509) 375 8100 Engineering & P.O. Box 130 Fax: (509) 375 8402 Manufacturing Richland, WA 99352-0130 Interim Report (98-003) Subject: Interim report of evaluation of a deviation. pursuant to 10 CFR 21.21(a)(2) Title: Steam Line Break Identification of Basic Activity: PWR Steam Line Break Analysis Basic Activity Supplied by: Siemens Power Corporation - Nuclear Division Nature of Deviation: Three deviations have been identified that are applicable to either the SPC Steam Line Break methodology or its application to individual plants. The first deviation is that power distributions which may not bound potential plant conditions during a Steam Line Break event have been identified in the Steam Line Break analyses for some plants. The inadequate determination of power distributions results from the following: 1. variations in cycle to cycle radial peaking factors due to loading pattern changes which were not accounted for in the Steam Line Break analysis, and 2. the iteration technique between the XCOBRA-IIIC thermal hydraulic code and the XTGPWR neutronics code may not ensure that a conservative power distribution is calculated for cases where the pumps are turned off. A second deviation is that the iteration between XCOBRA-IIIC and XTGPWR may result in non-conservative reactivity calculations with XTGPWR. This is a deviation in the SPC Steam Line Break methodology. A third deviation is that the reactivity control system input for the ANF-RELAP HFP analyses were constructed for some plants such that a step change occurs in the Doppler reactivity when switching between two reactivity models. This deviation results in an under prediction of the positive reactivity insertion due to the cool down of the fuel during the Steam Line Break event. An evaluation of whether these deviations represent reportable defects under 10 CFR 21 has been initiated. A schedule for completing the evaluation is provided below. Discovery Date: March 13, 1998 Corrective Actions to Date: Condition Report (CR) 6571 was initiated on March 13, 1998 and CR 6599 on March 21, 1998. A self-assessment is being performed to assess the deviations identified in the condition reports and any other issues which may be identified by a review of the Steam Line Break methodology. A set of recommendations from the self-assessment team will be issued during May. It is apparent from the initial self-assessment team findings that a change in the approved Steam Line Break methodology will be necessary to correct the identified deviation with respect to the iteration between XCOBRA-IIIC and XTGPWR. An evaluation of the impact of the combined effects has been made for two representative plants. The evaluations indicate that no significant increase in fuel rod failures is expected from the correction of the identified deviations. The criteria for the Steam Line Break event is the radiological criteria in 10 CFR 100. Evaluation Completion Schedule Date: December 1, 1998 *** END OF DOCUMENT ***

Page Last Reviewed/Updated Friday, January 31, 2020