Information Notice No. 87-38: Inadequate or Inadvertent Blocking of Valve Movement
SSINS No.: 6835 IN 87-38 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 August 17, 1987 Information Notice No. 87-38: INADEQUATE OR INADVERTENT BLOCKING OF VALVE MOVEMENT Addressees: All nuclear power reactor facilities holding an operating license or a con- struction permit. Purpose: This notice is provided to alert recipients to a potentially significant safety problem pertaining to inadequate or inadvertent blocking of valves. It is expected that recipients will review the information for applicability to their facilities and consider actions, if appropriate, to preclude a similar problem occurring at their facilities. However, suggestions contained in this notice do not constitute NRC requirements; therefore, no specific action or written response is required. Background: The NRC Office for Analysis and Evaluation of Operational Data (AEOD) issued Engineering Evaluation Report AEOD/E706, "Inadequate Mechanical Blocking of Valves," on March 31, 1987. This report, initiated by an event at a foreign reactor, describes a number of events caused by inadequate or inadvertent mechanical blocking of valve movement. Electrically disabling or locking the valve handwheel with a lock or chain was not included in the study. In addition to the event at the foreign reactor, there were nine events at licensed U.S. power reactor facilities. Two of these events are discussed below. Description of Circumstances: On December 21, 1985, an emergency core cooling system pump room at the Edwin I. Hatch Nuclear Plant, Unit 1, was flooded to a level of 14 feet when a maintenance isolation valve opened. At the time of the event, the plant was in a refueling mode with a residual heat removal (RHR) loop suction valve disassembled for repairs. The maintenance isolation valve, which was located between the RHR loop suction valve and the torus, was shut, and its control switch was "red tagged" (an administrative control that prohibits switch operation) in the control room. The maintenance isolation valve is an air- operated butterfly valve that opens on loss of power to its solenoid valve. 8708110476 . IN 87-38 August 17, 1987 Page 2 of 3 Power to the solenoid valve was lost when the station conducted a planned loss-of-offsite-power test that also interrupted use of the plant's communi- cations systems. Before control room personnel could be notified of the flooding, the water level in the pump room had stopped rising because the level had equalized with the torus water level. On June 16, 1982, during a quarterly valve functional operational test at Oconee Unit 2, an air-operated valve in the emergency feedwater system would not fully open from the control panel. The valve was declared inoperable, thereby making one of the emergency feedwater flowpaths to the two steam generators inoperable. The emergency feedwater valve would not cycle to the open position because its handwheel was engaged in the manual operation position. The reason why the handwheel was in the wrong position could not be determined. The valve's handwheel was disengaged from the manual operation position to allow automatic movement of the valve, and the valve was tested satisfactorily. To prevent recurrence of this event, the handwheels for the valves in both loops of the emergency feedwater system at each of the three units were locked in the disengaged position. Discussion: The AEOD report notes that the actual effects of the 10 events ranged from a reduction in redundant protection without any actual consequences to signifi- cant damage to safety-related equipment. Specifically, it reports that the potential exists for (1) a reactor transient; (2) an unisolable steam and water release; (3) a harsh environment with steam and flooding damage to major safety-related equipment, components, and other control systems; and (4) personnel injury. The AEOD report concludes that the root cause of the inappropriate mechanical blocking of valves was almost evenly divided between personnel error involving both acts of omission and commission and inadequate procedures. In conclusion, the AEOD report suggests that licensees (1) verify the adequacy of the temporary procedures regarding modifications to piping systems so that there is adequate assurance that a single isolation valve will remain in the safe position when needed (2) identify potential causes of unintended valve actuation (e.g., temporary loss of power, surveillance tests) that could occur during maintenance, which would result in an unblocked valve cycling to an unsafe position, especially when this would result in an "open" system (3) ensure that procedures for restoring blocked valves to service are clear and provide for adequate verification. . IN 87-38 August 17, 1987 Page 3 of 3 No specific action or written response is required by this information notice. If you have any questions about this matter, please contact the Regional Administrator of the appropriate regional office or this office. Charles E. Rossi, Director Division of Operational Events Assessment Office of Nuclear Reactor Regulation Technical Contacts: Theodore C. Cintula, AEOD (301) 492-4434 Richard J. Kiessel, NRR (301) 492-9605 Attachment: List of Recently Issued NRC Information Notices
Page Last Reviewed/Updated Tuesday, March 09, 2021
Page Last Reviewed/Updated Tuesday, March 09, 2021