Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555-0001
March 28, 1997
NRC INFORMATION NOTICE 97-14: ASSESSMENT OF SPENT FUEL POOL COOLING
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 to results of an assessment performed by the Office
for Analysis and Evaluation of Operational Data (AEOD) on operating experience
involving spent fuel pool (SFP) cooling and inventory control. The AEOD
assessment is detailed in NUREG-1275, Volume 12, "Assessment of Spent Fuel
Cooling," February 1997. 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
NRC's Executive Director for Operations directed AEOD to independently assess
the likelihood and consequences of an extended loss of SFP cooling or
inventory. The assessment focused on the collection and analysis of operating
experience involving SFP cooling and inventory control and comprised of six
major tasks:
(1) Develop generic configurations delineating SFP cooling and inventory
control equipment for a boiling-water reactor (BWR) and a pressurized-
water reactor (PWR).
(2) Review and assess more than 12 years of operating experience for
domestic and foreign reactors.
(3) Visit six sites to gain an understanding of the physical configurations,
practices, and operating procedures for the licensees' SFPs.
(4) Review applicable SFP regulations and the NRC Standard Review Plan
(NUREG-0800) for the acceptance criteria and the applicable regulatory
guides.
(5) Perform independent assessments of electrical systems, instrumentation,
heat loads, and radiation levels associated with the SFP.
(6) Estimate near-boiling frequencies utilizing probabilistic techniques.
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March 28, 1997
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The findings and conclusions of the AEOD assessment are summarized below.
. The loss of SFP coolant inventory in excess of 1 foot has occurred 10
times over the last 12 years at a rate of about once every 100 reactor-
years. Loss of SFP cooling with a temperature increase in excess of 11
�C [20 �F] has occurred 4 times in the last 12 years at a rate of
approximately 3 times every 1000 reactor-years. The consequences of
these actual events have not been severe; however, some events resulted
in loss of several feet of SFP coolant level and have continued for more
than 24 hours. The primary cause of these events has been human error,
most preva- lently, valve mispositionings. These errors are discussed
in greater detail in NUREG-1275, Volume 12.
. The relative risk due to loss of spent fuel pool cooling is low in
comparison with the risk of events not involving SFPs. The review
determined that the likelihood and consequences of SFP loss-of-cooling
events are highly dependent on human performance (e.g., valve
manipulations, crane manipulations, spent fuel handling equipment
manipulations) and individual plant design features.
. The efforts by utilities to reduce outage durations have resulted in
full core off-loads early in outages. This increased fuel pool heat
load reduces the time available to recover from a loss-of-SFP-cooling
should such an event occur early in the outage.
On a plant specific basis the following observations are provided:
. Failures of reactor cavity seals or gate seals or ineffective antisiphon
devices could potentially cause loss of SFP coolant inventory, which
could potentially result in uncovering the fuel or endangering makeup
capability.
. Ineffective configuration control was the most frequent cause of SFP
loss-of-inventory events and loss-of-cooling events.
. At multi-unit sites with common pools, there is the potential for SFP
boiling conditions to affect safe-shutdown equipment for the operating
unit, particularly during full core off-loads.
. Improved procedures and training which recognize the time frames over
which SFP events can proceed, the heat load and possibility of loss of
inventory, could enhance control room operator response to loss-of-
inventory and loss-of-cooling SFP events.
. Insufficient control room instrumentation and non-safety-related power
supplies to SFP instrumentation may hinder operator response to SFP
events.
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March 28, 1997
Page 3 of 3
Discussion
The AEOD assessment found large variations in the designs and capabilities of
SFPs and related systems at individual nuclear plants. The AEOD assessment
identified that the frequency of loss-of-inventory events was relatively high
compared to loss-of-cooling events, and prompt off-loads will lead to reduced
time to boil if cooling is lost. A loss of SFP inventory in combination with
higher heat loads reduces the time to respond to SFP events. Thus, the
emphasis of the findings were on instrumentation to quickly alert the
operators and effective procedures and training to facilitate prompt operator
response. The operating experience review determined that loss-of-SFP-cooling
events are infrequent and the consequences of actual events have been small.
The risk assessment indicates that the SFP events are not a dominant
contributor to overall plant risk. However, human error initiators and
operator actions required to mitigate an error are subject to large
uncertainties, and there are large variations in design vulnerabilities among
plants. In summary the following areas need emphasis:
(1) Procedures and training to detect and respond to SFP loss-of-inventory
and loss-of-cooling events, including those caused by loss of offsite
power are needed and should address configuration controls that can
prevent and/or mitigate such events. They should be consistent with the
time frames over which SFP events can proceed at the specific plant,
recognizing the plant-specific heat load and the possibility of loss of
inventory because of cavity seal or gate failures.
(2) Reliable instrumentation is necessary to monitor SFP temperature and
level and SFP area radiation, including periods following a loss of
offsite power, in order to detect SFP loss-of-inventory events and loss-
of-cooling events in a timely manner.
(3) Testing, maintenance, and configuration control of plant features such
as reactor cavity seals, gate seals, or antisiphon devices need to be
examined for those plants where failures could potentially cause loss of
SFP coolant inventory sufficient to endanger makeup capability or result
in fuel uncovery.
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.
signed by
Thomas T. Martin, Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contacts: Jose G. Ibarra, AEOD Stephen Koenick, NRR
(301) 415-6345 (301) 415-2841
E-mail: [email protected] E-mail: [email protected]
