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UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 April 20, 1989 Information Notice No. 89-41: OPERATOR RESPONSE TO PRESSURIZATION OF LOW-PRESSURE INTERFACING SYSTEMS Addressees: All holders of operating licenses or construction permits for nuclear power reactors. Purpose: This information notice is being provided to alert addressees to potential problems that may arise from the lack of proper procedures to deal with un- expected pressurization of systems designed for low operating pressure such as the residual heat removal (RHR) system. 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 do not constitute NRC requirements; therefore, no specific action or written response is required. Description of Circumstances: On March 9, 1989, when Vogtle Unit 2 was in Mode 3 preparing for initial criticality, the reactor coolant system (RCS) leakage exceeded Technical Specification limits. The leakage was observed during a surveillance test on a cold-leg swing check valve that acts as the inboard pressure isolation boundary between the RCS and the low-pressure RHR system. The RHR system had been taken out of service, but the pressure in it did not reduce to the expected level. To relieve the RHR system pressure, operators opened two normally locked-closed valves that connect the RHR system to the refueling water storage tank (RWST), thereby venting RCS coolant to the tank, and from there, to the atmosphere. The action they took to depressurize the RHR system was inappropriate and taken without the benefit of proper procedures. Subsequent investigations determined that the inboard cold-leg check valve in question had experienced abnormal wear. The operators appear to have considered possible leakage into the RHR system, such as leakage through check valves and through isolation valves from the chemical and volume control system. However, the action taken did not reflect an awareness of the potential seriousness of such leakage. 8904140042 .. IN 89-41 April 20, 1989 Page 2 of 2 Discussion: During this event, public safety was not adversely affected at Vogtle Unit 2 because there was no fission product inventory in the reactor. Also, the potential for damage to the RHR system was minimal because the leakage was well within the relieving capacity of the system. However, leakage of RCS coolant into systems such as the RHR system and responses to such events by operators have been sources of longstanding concern because of the potential for the so-called "Event V" or the "interfacing system loss-of-coolant ac- cident." It is important that licensees have proper procedures that will enable operators to take only appropriate actions to respond to unexpected or unexplained pressurization of systems such as the RHR system. No specific action or written response is required by this information notice. If you have any questions about this matter, please contact the technical contact listed below or the Regional Administrator of the appropriate regional office. Charles E. Rossi, Director Division of Operational Events Assessment Office of Nuclear Reactor Regulation Technical Contact: N. Prasad Kadambi, NRR (301) 492-1153 Attachment: List of Recently Issued NRC Information Notices .. Attachment IN 89-41 April 20, 1989 Page 1 of 1 LIST OF RECENTLY ISSUED NRC INFORMATION NOTICES _____________________________________________________________________________ Information Date of Notice No._____Subject_______________________Issuance_______Issued to________ 88-75, Disabling of Diesel 4/17/89 All holders of OLs Supplement 1 Generator Output Circuit or CPs for nuclear Breakers by Anti-Pump power reactors. Circuitry 89-40 Unsatisfactory Operator Test 4/14/89 All holders of OLs Results and Their Effect on or CPs for nuclear the Requalification Program power reactors. 89-39 List of Parties Excluded 4/5/89 All holders of OLs from Federal Procurement or CPs for nuclear or Non-Procurement Programs power reactors. 89-38 Atmospheric Dump Valve 4/5/89 All holders of OLs Failures at Palo Verde or CPs for nuclear Units 1, 2, and 3 power reactors. 89-37 Proposed Amendments to 4/4/89 All U.S. NRC 40 CFR Part 61, Air licensees. Emission Standards for Radionuclides 89-36 Excessive Temperatures 4/4/89 All holders of OLs in Emergency Core Cooling or CPs for nuclear System Piping Located power reactors. Outside Containment 88-86, Operating with Multiple 3/31/89 All holders of OLs Supp. 1 Grounds in Direct Current or CPs for nuclear Distribution Systems power reactors. 89-35 Loss and Theft of Un- 3/30/89 All U.S. NRC secured Licensed Material byproduct, source and special nuclear material licensees. 89-34 Disposal of Americium 3/30/89 All holders of an Well-Logging Sources NRC specific license authorizing well-logging activities. _____________________________________________________________________________ OL = Operating License CP = Construction Permit ..
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