United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 94-06: Potential Failure of Long-Term Emergency Nitrogen Supply for the Automatic Depressurization System Valves

                               UNITED STATES
                           WASHINGTON, D.C.  20555

                              January 28, 1994

                                   NITROGEN SUPPLY FOR THE AUTOMATIC
                                   DEPRESSURIZATION SYSTEM VALVES


All holders of operating licenses or construction permits for boiling water


The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees of the potential failure of the long-term nitrogen
supply for the automatic depressurization system valves following a loss-of-
coolant accident (LOCA).  It is expected that recipients will review this
information notice 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

In January 1993, during a review of the components that form the pressure
boundary of the of the safety-related portion of the nitrogen supply system at
the Fitzpatrick Nuclear Power Plant, the licensee found that certain parts of
the drywell cooler air-operated dampers and their associated solenoid valves
were made of Buna-N, an elastomer material that is not suitable for high-
temperature conditions. These air dampers and solenoid valves are supplied by
the same nitrogen header that provides the 100-day nitrogen supply for the
automatic depressurization system (ADS) valves.  Consequently, the failure of
the Buna-N parts as a result of high temperatures that would exist following
a LOCA could lead to depressurization of the nitrogen system and consequent
inability to provide the 100-day supply of nitrogen to the ADS valves.  The
short-term operability of the ADS valves following a LOCA would be maintained
because the ADS valves also are supplied by nitrogen accumulators and supply
lines that are separated from the main nitrogen header by check valves.

The licensee found that there was a sufficient number of components with
Buna-N materials supplied by the nitrogen header, and that their combined
failure at high temperature could lead to a total leakage rate greater than
the available nitrogen header makeup rate.  These components consisted of
12 drywell cooler air-operated damper actuators, the 12 associated actuator


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                                                            January 28, 1994
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pressure regulators, and 5 solenoid valves on separate components.  These
solenoid valves were located on two core spray testable check valves, two
reactor vessel head vent valves, and on the actuator pneumatic control line
for the drywell cooler air actuated dampers.


The problem was caused by the inadequate design of modifications that were
made in 1985 to upgrade the ADS pneumatic supply.  The original nitrogen
supply system at Fitzpatrick was designed to provide the pneumatic supply to
both safety-related and non-safety-related instruments and controls, including
the ADS valves inside the drywell.  The accumulators were included in the
original design to ensure a safety grade pneumatic supply to the safety-
related features.  However, these accumulators only have a capacity sufficient
to open the ADS valves five times at design pressure following a LOCA.   In
1985 the licensee added an NRC-required modification to the nitrogen supply
system, which provides a 100-day post-LOCA pneumatic supply to the ADS valves
(Item II.K.3.28 of NUREG-0737, "Clarification of TMI Action Plan
Requirements").  However, the licensee did not upgrade all of the non-safety-
related components connected to the nitrogen header or provide isolation of
portions of the system that could fail.

Following the discovery of the unsuitable materials, the licensee performed an
evaluation to justify continued plant operation until a planned shutdown on
February 26, 1993.  Since then the licensee has taken the following corrective
actions to limit the potential nitrogen leak rate to an acceptable value:

-    Provided a modification to fix the drywell cooler inlet dampers in the
     open position, isolate the nitrogen supply to these dampers, and replace
     the drywell cooler outlet damper solenoid valves with qualified valves.

-    Isolated the nitrogen supply to the core spray testable check valves.

-    Replaced the solenoid valves on the reactor head vent isolation valves
     with environmentally qualified isolation valves.

-    Modified the annunciator response procedures to require isolation of the
     air-operated damper actuators and the opening of a backup nitrogen header
     supply valve if a low header pressure alarm is received.

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                                                            January 28, 1994
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Evaluations and calculations show that, with the actions taken that are
required by the annunciator procedures cited above, leakage through all 12
air-operated dampers and the solenoid valves on the associated pneumatic
supply lines would be within the nitrogen header makeup capacity.

This information notice requires no specific action or written response.  If
you have any questions about the information in this notice, please contact
the technical contact listed below or the appropriate Office of Nuclear
Reactor Regulation (NRR) project manager.

                                     /s/'d by BKGrimes

                                     Brian K. Grimes, Director
                                     Division of Operating Reactor Support
                                     Office of Nuclear Reactor Regulation

Technical contact:  David H. Shum, NRR
                    (301) 504-2860

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