United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 83-26: Failure of Safety/Relief Valve Discharge Line Vacuum Breakers

                                                           SSINS No.:  6835 
                                                           IN 83-26        

                               UNITED STATES 
                       NUCLEAR REGULATORY COMMISSION 
                    OFFICE OF INSPECTION AND ENFORCEMENT 
                           WASHINGTON, D.C. 20555 
                                     
                                May 3, 1983 

Information Notice No. 83-26:   FAILURE OF SAFETY/RELIEF VALVE DISCHARGE 
                                   LINE VACUUM BREAKERS 

Addressees: 

All nuclear power reactor facilities holding an operating license (OL) or 
construction permit (CP). 

Purpose: 

This information notice is provided as an early notification of a 
potentially significant problem pertaining to recently installed vacuum 
breakers on safety/ relief discharge lines on boiling water reactors. It is 
expected that the recipients will review the information for applicability 
to their facilities. No specific action or response is required at this 
time. 

Description of Circumstances: 

Browns Ferry Unit 1 Event 

Following a reactor scram on February 5, 1983 at Browns Ferry Unit 1, three 
safety relief valves (SRVs), each with a capacity of approximately 865,000 
lb/hr, cycled to control pressure. One SRV stayed partially open, after 
which, unidentified leakage in the drywell increased to greater than 5 gpm. 
The primary system was depressurized at a slow rate and a cold shutdown was 
initiated. During the cooldown the unidentified leak was traced to a vacuum 
breaker (10" GPE check valve) on the discharge line of the leaking SRV. The 
vacuum breaker hinge pin appeared to be damaged, causing the vacuum breaker 
to stick partially open. The licensee replaced the solenoid and pilot 
cartridge on the SRV and replaced the leaking vacuum breaker. The licensee 
then inspected all the SRV vacuum breakers and found that four others were 
damaged and these were also replaced. All three SRVs that actuated following
the scram were scheduled to be cycled during the forthcoming startup at 250 
psig to ensure proper operation. 

On February 8, 1983 with Unit 1 heating up at 178 psig and prior to the 
planned testing of the SRVs, the previously failed SRV again started to leak
(Information Notice No. 83-22). The drywell unidentified leakage again 
increased to greater than 5 gpm. After cooling down it was discovered that 
the SRV discharge line vacuum breaker was again damaged. 

Peach Bottom Unit 2 Event 

During a startup on October 24, 1982 with the reactor pressure at 832 psig, 
relief valve 71J with a capacity of approximately 830,000 lb/hr opened. The 

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resulting vessel level swell tripped the operating reactor feed pump on a 
high level signal and the unit subsequently scrammed on a low level signal 
because the loss of feedwater. The relief valve remained open until the 
reactor pressure dropped to 80 psig. During an inspection of the relief 
valve discharge line piping it was discovered that the vacuum breakers (8" 
Anderson Greenwood check valves) for this valve and a second relief valve 
that was actuated during the transient were damaged. Both vacuum breakers 
showed some binding on the hinge pin such that the normal spring pressure 
was insufficient to close them. The two vacuum breakers were replaced. 

The 10" vacuum breakers on the SRV discharge lines at Browns Ferry Unit 1 
were installed during the previous refueling outage for relief valve 
second-pop transient protection. 

The 8" vacuum breakers on the relief valve discharge lines at Peach Bottom 
Unit 2 were installed in July 1980. These vacuum breakers were also 
installed for relief valve second-pop transient protection. This transient 
in the relief valve discharge line is postulated to result from a failure of 
the previously installed small vacuum breakers to quickly equalize pressure 
in the relief valve discharge lines during the closing and rapid reopening 
(typically at 15 seconds) of the relief valves. Some recently licensed 
plants are using the low-low set point relief function in lieu of vacuum 
breakers for second-pop protection. 

No written response to this information notice is required. If you need 
additional information regarding this matter, please contact the appropriate
NRC Regional Office or this office. 


                              Edward L. Jordan, Director 
                              Division of Emergency Preparedness 
                                and Engineering Response 
                              Office of Inspection and Enforcement 

Contact:  P. R. Farron 
          (301) 492-4766 

Attachment: 
List of Recently Issued Information Notices
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Page Last Reviewed/Updated Tuesday, November 12, 2013