Information Notice No. 83-44, Supplement 1: Potential Damage to Redundant Safety Equipment as a Result of Backflow Through the Equipment and Floor Drain System
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 August 30, 1990 Information Notice No. 83-44, SUPPLEMENT 1: POTENTIAL DAMAGE TO REDUNDANT SAFETY EQUIPMENT AS A RESULT OF BACKFLOW THROUGH THE EQUIPMENT AND FLOOR DRAIN SYSTEM Addressees: All holders of operating licenses or construction permits for nuclear power reactors. Purpose: This notice supplements information contained in NRC Information Notice 83-44 concerning potential damage to redundant safety equipment as a result of backflow through the equipment and floor drain system and addresses the effect of internal flooding of nuclear power plants on safety-related equipment. 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 regulatory requirements; therefore, no specific action or written response is required. Background: The NRC issued Information Notice No. 83-44 to amplify the information provided in IE Circular 78-06, "Potential Common Mode Flooding of ECCS Equipment Rooms of BWR Facilities," in response to an event at a PWR facility. IE Circular 78-06 applied specifically to Emergency Core Cooling System (ECCS) equipment rooms and flooding of areas at lower elevations. Information Notice No. 83-44 expanded this concern to other safety-related compartments and to damage as a result of backflow through equipment and floor drainage systems. Since the issuance of Information Notice No. 83-44, the NRC has received an unexpectedly high number of reports from the nuclear industry pertaining to actual and possible occurrences of internal flooding. Description of Circumstances: On July 7, 1990, the Quad Cities licensee, Commonwealth Edison, was investigating a backed-up sump pump in the basement of the Unit 2 reactor building. While attempting to clear the lines, the licensee discovered that the check valves were inoperable in the floor drain lines from the ECCS equipment rooms. Each drain line has both a flap-type and a ball-type check valve in series between the ECCS equipment room and its respective sump. Upon inspection, the licensee found that the flap-type check valves were stuck open as a result 9008240057 . IN 83-44, Supplement 1 August 30, 1990 Page 2 of 3 of debris and corrosion buildup and that three of the four balls in the ball-type check valves had corroded and eroded away completely. In addition, these eight check valves had been omitted from the licensee's maintenance programs. These inoperable check valves could have enabled flood water from the following sources to render ECCS equipment inoperable: service water piping, ECCS suction piping, the reactor building drain tank, and possibly the fuel pool and suppression pool. As a corrective action, the licensee has replaced and tested all the check valves in the ECCS room floor drains and has included these valves in its maintenance programs. It should be noted that this situation is not adequately covered in the Quad Cities Final Safety Analysis Report (FSAR) or properly addressed in available probabilistic risk assessment (PRA) analyses for similar plants. Recently, the Office for Analysis and Evaluation of Operational Data (AEOD) completed an Engineering Evaluation Report, AEOD/E90-07, "Effect of Internal Flooding of Nuclear Power Plants on Safety-Related Equipment." This report documents a review of operational events from 1980 to 1989 that resulted in internal flooding in the secondary containment, auxiliary building, and turbine building of nuclear power plants. The study also presents reported conditions since 1984 that could have led to the flooding of safety-related equipment compartments. Some of these events caused a loss of a significant amount of safety-related equipment needed for decay heat removal, plant shutdown, and plant cooldown, and have resulted in precursors that could have resulted in severe core damage accidents. One plant probabilistic risk assessment has identified internal flooding to be a significant contributor to the risk of core damage. Discussion: Evaluation of the operational events identified errors by maintenance personnel, procedural deficiencies, and inadequate design as the key elements leading to internal flooding. Based upon the findings, the following were identified as potentially generic inadequacies: o Existing Flood Protection The areas of particular concern include the adequacy of flood barriers to prevent unisolable flooding and common-mode flooding, adequacy of the floor drain system to prevent flooding of one area of the plant from propagating to other areas, and adequacy of flood warning instrumentation to provide the operators with an early signal of flooding in the plant. o Maintenance Procedures and Personnel Training Some licensees have not always conducted adequate reviews of maintenance procedures and personnel training to minimize the risk of unanalyzed internal flooding events caused by single component failures or personnel errors. In addition, the AEOD report indicated that several significant flooding events occurred during cold shutdown or refueling outages. This indicates weaknesses in maintenance planning and administrative controls intended to minimize the risk of flooding during such outages. . IN 83-44, Supplement 1 August 30, 1990 Page 3 of 3 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 NRR project manager. Charles E. Rossi, Director Division of Operational Events Assessment Office of Nuclear Reactor Regulation Technical Contacts: N. Su, AEOD (301) 492-4434 J. Raleigh, NRR (301) 492-1172 Attachment: List of Recently Issued NRC Information Notices
Page Last Reviewed/Updated Tuesday, March 09, 2021
Page Last Reviewed/Updated Tuesday, March 09, 2021