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UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 November 1, 1991 NRC INFORMATION NOTICE 91-69: ERRORS IN MAIN STEAM LINE BREAK ANALYSES FOR DETERMINING CONTAINMENT PARAMETERS Addressees All holders of operating licenses or construction permits for pressurized water reactors (PWRs). Purpose The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alert addressees to a safety problem that may result from not considering the possibility that feedwater could continue to flow following a main steam line break (MSLB) inside the containment. This problem is applicable to plants equipped with feedwater isolation susceptible to single failure. It is expected that recipients will review the information for applicability to their facilities and consider actions, as appropriate, to avoid similar problems. However, suggestions contained in this information notice are not NRC requirements; therefore, no specific action or written response is required. Description of Circumstances On October 18, 1991, the Northeast Nuclear Energy Company notified the NRC of a problem at the Millstone Nuclear Power Station, Unit 2, that could cause the facility to exceed containment design limits. The licensee found this concern during MSLB analyses for the forthcoming replacement of the steam generators. In performing the analyses, the licensee identified that during full power operation, with a break on a main steam line, and with offsite power available, a single failure of a feedwater control valve to close could result in higher peak containment temperature and pressure than the design limits. The containment design limits for temperature and pressure were 289�F and 54 psig; the new analysis shows preliminary values of 420�F and 68 psig, respectively. Previously, the licensee's worst case analysis assumed loss of offsite power with a MSLB. Discussion NRC Bulletin No. 80-04, "Analysis of a PWR Main Steam Line Break with Continued Feedwater Addition" and Standard Review Plan (NUREG 800) Section 220.127.116.11 provide guidance for assuming a single failure of any active component, with and without offsite power available, and discuss the effect of such a failure on the ability to ensure containment integrity following a MSLB. The Bulletin also addresses the possibility of the reactor returning to power. Offsite power remaining available could be more limiting for containment parameters. 9110290103 . IN 91-69 November 1, 1991 Page 2 of 2 This information notice requires no specific action or written response. If you have any questions about the information in this notice, please contact one of the technical contacts listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager. Charles E. Rossi, Director Division of Operational Events Assessment Office of Nuclear Reactor Regulation Technical contacts: Thomas Koshy, NRR (301) 492-1176 William LeFave, NRR (301) 492-2385 Attachment: List of Recently Issued NRC Information Notices .
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