United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 91-82: Problems with Diaphragms in Safety-Related Tanks

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF NUCLEAR REACTOR REGULATION
                           WASHINGTON, D.C.  20555

                              December 18, 1991


NRC INFORMATION NOTICE 91-82:  PROBLEMS WITH DIAPHRAGMS IN SAFETY-RELATED 
                               TANKS


Addressees

All holders of operating licenses or construction permits for nuclear power 
reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information 
notice to alert addressees of problems that could occur with diaphragms 
installed in safety-related tanks.  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 are not NRC requirements; therefore, no 
specific action or written response is required.

Description of Circumstances

On June 14, 1991, while performing a quarterly inspection of the diaphragm 
in the condensate storage tank at the V. C. Summer Nuclear Station, the 
licensee found a tear in the diaphragm, across the diameter of the tank, 
which had caused a large section of the diaphragm to sink to the bottom of 
the tank.  The diaphragm is attached to the perimeter of the tank and 
normally floats on top of the water to provide a barrier to oxygen.  The 
Summer staff decided to remove the diaphragm to prevent it from clogging the 
emergency feedwater suction line.  However, strips of material and small 
debris were stripped from the diaphragm as it was pulled through the manway 
at the top of the tank.  This debris settled to the bottom of the tank where 
it presented a clogging hazard to the emergency feedwater flow control 
valves.  This condition required the Summer staff to conduct a long and 
difficult cleaning process.  The only other readily available supply of 
emergency feedwater, which is required for any shutdown, was untreated 
service water. 

The Summer plant has several safety-related tanks with diaphragms.  These 
tanks include the condensate storage tank, the boric acid tanks, and the 
reactor makeup water storage tank.  The licensee for the Summer plant had 
previously had problems involving the diaphragms in each of these tanks.

     In 1987, the licensee found 14 holes in the condensate storage tank 
     diaphragm that had the recent failure.  These were attributed to damage 
     caused during the original installation.  The licensee had patched 
     these holes using a diaphragm repair kit.

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                                                       December 18, 1991
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     In August of 1988, the licensee detected abnormal amounts of magnesium 
     and sulphates in the "B" boric acid tank.  The licensee investigated 
     these chemistry problems and found that the binder material in the 
     diaphragm was failing and allowing small particles to come off of the 
     diaphragm and become suspended in the tank fluid.

     In October of 1988, the "A" boric acid tank pump lost suction when the 
     diaphragm ruptured and settled to the bottom of the tank, partially 
     covering the pump suction line opening to the tank.  
     
     In December 1988, during an inspection to identify the cause of 
     increased oxygen in the reactor makeup water storage tank, the licensee 
     found a large tear in the diaphragm in this tank.

Discussion

The Summer staff attributed the 1988 problems to the diaphragms having 
exceeded their service lifetimes.  These diaphragms had all exceeded their 
estimated 10-year service lifetimes by about 3 years.  A design engineering 
report, written before the recent condensate storage tank diaphragm failure, 
recommended that this diaphragm be replaced every 9 years, or more 
frequently if inspections so indicated.  

The diaphragm fitted tanks were supplied by the Pittsburgh Des Moines 
Corporation.  This supplier originally purchased the diaphragms from the 
Goodyear Company but now obtains them from the Lorel Corporation.  A 
Pittsburgh Des Moines Corporation representative said that his company and 
its competitors supplied many tanks with diaphragms to nuclear power plants 
around 1979 and 1980.  These diaphragms, if not already replaced, may now be 
reaching or exceeding their expected reliable service lifetimes.

Diaphragms in safety-related tanks have a finite service life and can cause 
various safety hazards if they fail.  Consequently, the regular inspection 
and replacement of these diaphragms can be an important part of the plant's 
preventive maintenance program.

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 Office of 
Nuclear Reactor Regulation (NRR) project manager.


                                   Charles E. Rossi, Director
                                   Division of Operational Events Assessment
                                   Office of Nuclear Reactor Regulation

Technical contacts:  L. A. Keller, Resident Inspector, V. C. Summer
                     (803) 345-5683

                     Frank Jape, RII
                     (404) 331-4182

Attachment:  List of Recently Issued NRC Information Notices
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