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
                            WASHINGTON, D.C.  20555

                                 July 16, 1992

                                             OVERTEMPERATURE DELTA-TEMPERATURE
                                             (OTdT) SETPOINT CAUSED BY
                                             IMPROPER GAIN SETTINGS


All holders of operating licenses or construction permits for Westinghouse
(W)-designed nuclear power reactors.


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

1.   WNSD Technical Bulletin NSD-TB-91-08-RO
2.   List of Recently Issued NRC Information Notices

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