Information Notice No. 92-28: Inadequate Fire Suppression System Testing
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
April 8, 1992
NRC INFORMATION NOTICE 92-28: INADEQUATE FIRE SUPPRESSION SYSTEM TESTING
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 potential inadequate performance of carbon
dioxide (CO2) and Halon fire suppression systems caused by excessive leakage
from the protected enclosure or by deficient operation of the system's
components. Limited acceptance testing may not be adequate to identify
these problems. 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.
Background
In Section 50.48 of Title 10 of the Code of Federal Regulations, the NRC
established fire protection requirements for operating nuclear power plants.
This rule requires automatic and manual fire suppression systems to function
so that the capability to safely shut down the plant is ensured. Many
licensees use total flooding CO2 and Halon fire suppression systems to
protect systems necessary for safe shutdown. In Branch Technical Position
APCSB 9.5-1, "Guidelines for Fire Protection for Nuclear Power Plants," the
staff referenced National Fire Protection Association (NFPA) standards, NFPA
12-1973, "Carbon Dioxide Extinguishing Systems," and NFPA 12A-1973, "Halon
1301 Fire Extinguishing Systems." These standards emphasized the need to
minimize leakage from the enclosure in order to retain the fire suppressing
agent for the required soak time and the importance of thoroughly inspecting
the fire suppression system to ensure that it will operate properly.
Licensees frequently use full discharge tests to demonstrate that fire
suppression systems perform properly and that leakage from protected
enclosures is acceptable.
Description of Circumstances
On February 23, 1988, the Connecticut Yankee Atomic Power Company, the
licensee for the Haddam Neck Power Plant, performed a full discharge test of
the CO2 fire suppression system for the containment cable vault. The test
results indicated that the CO2 concentration within the cable vault failed
to meet NFPA 12 requirements. Consequently, on February 27, the licensee
declared the
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fire suppression system for the cable vault inoperable. The licensee deter-
mined that the root cause of the failure was excessive leakage of CO2 from
the enclosure area through numerous unsealed electrical conduits in the
lower level of the cable vault. These conduits were in the original plant
design, but were not considered in the design of the CO2 system.
While performing an inspection the week of April 3, 1989, at the Susquehanna
Steam Electric Station (Susquehanna), the NRC found a concern regarding the
adequacy of initial testing of the plant's CO2 fire suppression systems. In
1982, the Pennsylvania Power and Light Company (PP&L), the licensee for
Susquehanna, had performed a full discharge test for one of seven areas pro-
tected by automatic CO2 fire suppression systems. The test found that the
required concentration of CO2 was not maintained in the enclosure for the
required soak time. The test results may have been caused solely by the
failure of a temporary seal around an access door. However, the licensee
did not perform additional testing to confirm the cause of the test failure.
The licensee then performed limited acceptance tests of the CO2 fire
suppression systems.
To address the NRC's concern, PP&L performed testing in the first quarter of
1990 using room pressurization to measure enclosure leakage and to determine
a projected agent retention time. The licensee based the testing on the
enclosure integrity procedure in Appendix B to NFPA 12A-1989. The test
results indicated that three of the seven areas included enclosures with
leakage greater than that which would ensure retention of the required CO2
concentration for the required soak time. The failure of these enclosures
was attributed to their small enclosed volume and the corresponding small
allowable leakage area. In general, a smaller allowable leakage area should
be expected for small enclosures because of the higher ratio of boundary
area to enclosed volume.
On April 21, 1990, at the Catawba Nuclear Station (Catawba), an inadvertent
steam release actuated a CO2 fire suppression system. Although the fire
suppression system is designed to discharge to only one area at a time, the
three selector pilot valves installed in the system directed the CO2
discharge to all three areas protected by the system. Duke Power Company,
the licensee for Catawba, investigated the incident and discovered that the
solenoids operating the three selector pilot valves were installed
backwards. The licensee determined that the required CO2 concentration
could not be obtained within the protected areas when the system discharged
into more than one area at a time. Therefore, the licensee declared the
system inoperable. The licensee attributed the improper solenoid
installation, in part, to a preoperational test procedure which did not
adequately test the system for the incorrectly installed components.
Discussion
Retaining an adequate concentration of fire suppressing agent for the
required soak time is important for enclosures containing equipment that
could develop "deep seated" fires. In a study of deep seated cable fires,
Sandia National Laboratory determined that, for certain configurations of
cables qualified to Standard 383 of the Institute of Electrical and
Electronic Engineers (IEEE), it
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was necessary to retain a 50% concentration of CO2 for a minimum soak time
of 15 minutes to extinguish fully developed fires. Sandia National
Laboratory documented the results of the study in NUREG/CR-3656, "Evaluation
of Suppression Methods for Electrical Cable Fires," dated October 1986.
Full discharge testing of CO2 fire suppression systems may present certain
hazards at operating nuclear power plants. These hazards include thermal
shock to safety-related components, uncontrolled electrostatic discharge,
and hazards to personnel from high concentrations of CO2. Some licensees
have used alternative testing methods which avoid these hazards. For
example, the licensee for the Vermont Yankee Atomic Power Station responded
to the NRC's concern regarding the adequacy of initial tests of the plant's
fire suppression systems by performing an alternative test that incorporated
methodology from the enclosure integrity procedure in Appendix B to NFPA
12A-1989. That methodology is conservative because the effects of the
thermal expansion of the mixture of CO2 and air are not included and a
"worst case" distribution of measured leakage area is assumed. The licensee
also performed a rigorous engineering evaluation of the installed CO2 system
to verify that the system would operate as designed to deliver a sufficient
amount of CO2.
The testing described in Section 1-7.4 of NFPA 12A-1989 was developed to
alleviate concerns for both the cost and the environmental damage associated
with repeatedly performing full discharge tests of Halon fire suppression
systems. The testing described in NFPA 12A provides an alternative method
to full discharge testing of Halon systems to demonstrate that the fire
suppression system and the enclosure function as designed.
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.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical contact: S. R. Jones, NRR
(301) 504-2833
Attachment: List of Recently Issued NRC Information Notices
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