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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 9204020186 . IN 92-28 April 8, 1992 Page 2 of 3 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 . IN 92-28 April 8, 1992 Page 3 of 3 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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