Information Notice No. 81-15: Degradation of Automatic ECCS Actuation Capability by Isolation of Instrument Lines

                                                            SSINS No.: 6835 
                                                            Accession No.: 
                                                            IN 81-15       

                                UNITED STATES
                           WASHINGTON, D.C, 20555
                               April 22, 1981

                                   CAPABILITY BY ISOLATION OF INSTRUMENT 

Description of Circumstances: 

On March 23, 1981 at Georgia Power Company's Hatch Unit 2, an instrument 
technician, while investigating a drywell low-pressure alarm, found that 
seven of eight isolation valves were closed. The eighth valve was found 
slightly open and was considered as being functionally closed. These 
safety-related valves (also identified as panel or root valves) isolated 
twelve instruments that automatically actuate emergency core cooling systems
(ECCS), reactor protection system, and containment isolation systems on high
drywell pressure. The capability for manual actuation of the affected 
systems was continuously available from the control room. However, had a 
loss-of-coolant accident occurred, all systems would have been actuated by a 
redundant signal of low reactor water level, except for the automatic 
depressurization system. Those valves discovered to be closed were opened, 
valve alignment checks were performed, and no other discrepancies were 
found. These isolation valves were incorrectly identified as instrument 
drain valves and were closed on March 9, 1981 during completion of a valve 
lineup procedure. The drain valves that were being closed were on other 
safety-related lines that were of the same size and appearance as the high 
drywell pressure instrument lines that were isolated. 

Another event involving closure of some similar isolation valves was 
recently reported by the Peach Bottom Unit 2 licensee on April 1, 1981. The 
closed valves were found by a licensee employee who was troubleshooting an 
intermittent drywell pressure switch trouble alarm. Only one isolation valve
was found fully closed, whereas two other valves were found one-eighth turn 
open (but considered closed for review of protective system responses). 
Redundant channels were verified to be operable; thus, no automatic 
protective or emergency cooling system actuation would have been lost from 
the high drywell pressure signal. 

This information is provided as an early notification of a possibly 
significant matter that is still under review by the NRC staff. In case the 
continuing NRC review finds that specific licensee actions would be 
appropriate, an IE bulletin or circular may be issued. In the interim, we 
expect that licensees will review this information for applicability to 
their operating procedures, paying particular attention to valve alignment 
checklists and requirements for independent verification of valve alignments
including instrument valves. 

                                                             IN 81-15      
                                                             April 22, 1981 
                                                             Page 2 of 2   

No written response to this information notice is required. If you need 
additional information with regard to this matter, contact the Director of 
the appropriate NRC Regional Office. 

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