Bulletin 80-12: Decay Heat Removal System Operability
SSINS No.: 6820
Accession No.:
8005050053
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
May 9, 1980
IE Bulletin No. 80-12
DECAY HEAT REMOVAL SYSTEM OPERABILITY
Introduction:
The intent of this Bulletin is to improve nuclear power plant safety by
reducing the likelihood of losing decay heat removal (DHR) capability in
operating pressurized water reactors (PWRs). PWRs are most susceptible to
losing DHR capability when their steam generators or other diverse means of
removing decay heat are not readily available. Such conditions often occur
when the plants are in a refueling or cold shutdown mode, and during which
time concurrent maintenance activities are being performed.
There is a need to assure that all reasonable means have been taken to
provide redundant or diverse means of DHR during all modes of operation.
(Note: A redundant means could be provided by having DHR Train A AND Train B
operable; a diverse means could be provided by having either DHR Train A OR
Train B operable AND a steam generator available for DHR purposes.) There is
also need to assure that all reasonable means have been taken to preclude
the loss of DHR capability due to common mode failures during all modes of
operation.
Background
On several occasions, operating PWRs have experienced losses of DHR
capability. In each instance, except that of the Davis-Besse Unit 1 incident
of April 19, 1980, DHR capability was restored prior to exceeding the
specified RCS temperature limit for the specific mode of operation.
Nonetheless, the risk and frequency associated with such events dictate that
positive actions be taken to preclude their occurrence or at least
ameliorate their effects.
The most noteworthy example of total loss of DHR capability occurred at
Davis-Besse Unit 1 on April 19, 1980. (See IE Information Notice No. 80-20,
attached hereto as Enclosure 1). Two factors identified as major
contributors to the Davis-Besse event in the Information Notice are: (1)
extensive maintenance activities which led to a loss of redundancy in the
DHR capability, and (2) inadequate procedures and/or administrative controls
which, if corrected, could have precluded the event or at least ameliorated
its effects.
ACTIONS TO BE TAKEN BY LICENSEES OF PWR FACILITIES:
1. Review the circumstances and sequence of events at Davis-Besse as
described in Enclosure 1.
2. Review your facility(ies) for all DHR degradation events experienced,
especially for events similar to the Davis-Besse incident.
.
IE Bulletin No. 80-12 May 9, 1980
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3. Review the hardware capability of your facility(ies) to prevent DHR
loss events, including equipment redundancy, diversity, power source
reliability, instrumentation and control reliability, and overall
reliability during the refueling and cold shutdown modes of operation.
4. Analyze your procedures for adequacy of safeguarding against loss of
redundancy and diversity of DHR capability.
5. Analyze your procedures for adequacy of responding to DHR loss events.
Special emphasis should be placed upon responses when maintenance or
refueling activities degrade the DHR capability.
6. Until further notice or until Technical Specifications are revised to
resolve the issues of this Bulletin, you should:
a. Implement as soon as practicable administrative controls to assure
that redundant or diverse DHR methods are available during all
modes of plant operation. (Note: When in a refueling mode with
water in the refueling cavity and the head removed, an acceptable
means could include one DHR train and a readily accessible source
of borated water to replenish any loss of inventory that might
occur subsequent to the loss of the available DHR train.)
b. Implement administrative controls as soon as practicable, for
those cases where single failures or other actions can result in
only one DHR train being available, requiring an alternate means
of DHR or expediting the restoration of the lost train or method.
7. Report to the NRC within 30 days of the date of this Bulletin the
results of the above reviews and analyses, describing:
a. Changes to procedures (e.g., emergency, operational,
administrative, maintenance, refueling) made or initiated as a
result of your reviews and analyses, including the scheduled or
actual dates of accomplishment; (Note: NRC suggests that you
consider the following: (1) limiting maintenance activities to
assure redundancy or diversity and integrity of DHR capability,
and (2) bypassing or disabling, where applicable, automatic
actuation of ECCS recirculation in addition to disabling High
Pressure Injection and Containment Spray preparatory to the cold
shutdown or refueling mode.)
b. The safeguards at your facility(ies) against DHR degradation,
including your assessment of their adequacy.
The above information is requested pursuant to 10 CFR 50.54(f). Accordingly,
written statements addressing the above items shall be signed under oath or
affirmation and submitted within the time specified above. Reports shall be
submitted
.
IE Bulletin No. 80-12 May 9, 1980
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to the director of the appropriate NRC regional office, and a copy forwarded
to the Director, Division of Reactor Operations Inspection, NRC Office of
Inspection and Enforcement, Washington, D. C. 20555.
Approved by GAO, B180225 (R0072); clearance expires 7-31-80. Approval was
given under a blanket clearance specifically for identified generic
problems.
Enclosure:
IE Information Notice
No.. 80-20
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