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Information Notice No. 91-52: Supplement 1: Nonconservative Errors in Overtemperature Delta-Temperature (OTdT) Setpoint caused by Improper Gain Settings
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 July 16, 1992 NRC INFORMATION NOTICE 91-52, SUPPLEMENT 1: NONCONSERVATIVE ERRORS IN OVERTEMPERATURE DELTA-TEMPERATURE (OTdT) SETPOINT CAUSED BY IMPROPER GAIN SETTINGS Addressees All holders of operating licenses or construction permits for Westinghouse (W)-designed nuclear power reactors. Purpose The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to supplement information provided in the original information notice regarding errors in OTdT settings and to alert addressees to new information on this problem. 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 The Commonwealth Edison Company and the Duke Power Company recently notified the NRC of a problem with the saturation of the OTdT reactor trip function of the Westinghouse Type 7300 Plant Protection System (PPS) at the Byron, Braidwood, McGuire and Catawba nuclear power plants. The problem was that the OTdT reactor trip setpoint was not being automatically reduced to the extent required in response to a rising Tavg. The NRC alerted the industry to the problem in Information Notice (IN) 91-52, dated August 29, 1991. In response to IN 91-52, the Westinghouse Nuclear and Advanced Technology Division (WNATD) prepared Westinghouse Technical Bulletin NSD-TB-91-08-RO, which was issued by the Westinghouse Nuclear Services Division on December 13, 1991. This bulletin (Attachment 1): (1) addressed the effect of the rate of increase of Tavg in transient situations, (2) revealed that Westinghouse Type 7100 and Foxboro analog PPS equipment can also be affected, and (3) provided a recommended scaling method to ensure that the OTdT setpoint reaches its minimum design value before the Tavg channel becomes saturated under "worst case" transient conditions. WNATD developed a generic safety analysis, ET-NSA-TA-II-91-436, "Overtem- perature Delta-T Rescaling-Transient Analysis," dated November 20, 1991. 9207100239. IN 91-52, Supplement 1 July 16, 1992 Page 2 of 2 In this analysis WNATD concluded that even though the DNB ratio dropped below the design value of 1.3, it could not go beyond 1.0. However, the WNATD generic safety analysis may not envelope the worst case conditions at all affected plants. This information notice requires no specific action or written response. If you have any questions about the information in this notice, please contact the technical contact 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 contact: S. D. Alexander, NRR (301) 504-2995 Attachments: 1. WNSD Technical Bulletin NSD-TB-91-08-RO 2. List of Recently Issued NRC Information Notices .
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