Information Notice No. 91-82: Problems with Diaphragms in Safety-Related Tanks
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
All holders of operating licenses or construction permits for nuclear power
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
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.
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.
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
Frank Jape, RII
Attachment: List of Recently Issued NRC Information Notices
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