United States Nuclear Regulatory Commission - Protecting People and the Environment

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
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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.


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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


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