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Information Notice No. 89-77, Supplement 1: Debris in Containment Emergency Sumps and Incorrect Screen
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 December 3, 1993 NRC INFORMATION NOTICE 89-77, SUPPLEMENT 1: DEBRIS IN CONTAINMENT EMERGENCY SUMPS AND INCORRECT SCREEN CONFIGURATIONS Addressees All holders of operating licenses or construction permits for nuclear power reactors. Purpose On November 21, 1989, the U.S. Nuclear Regulatory Commission (NRC) issued Information Notice (IN) 89-77 to alert addressees to problems that could occur with post-accident debris blocking emergency core cooling systems. The IN was based, in part, on an event that occurred at the Trojan Nuclear Plant where debris were found in the containment sump and portions of the sump screen were found to be missing. The NRC is issuing this supplement to IN 89-77 to alert addressees to additional potential problems that may not have been previously considered. 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 do not constitute NRC requirements; therefore, no specific action or written response is required. Description of Circumstances On October 1, 1993, personnel at Arkansas Nuclear One (ANO), found several breaches in the integrity of the Unit 1 reactor building sump. These breaches consisted of (1) 22 semicircular holes (scuppers) at the base of the sump curb, each approximately 15.2 cm [6 in.] in diameter; (2) 4 conduit penetrations in the sump screen, totaling approximately 930 cm2 [1 ft2]; (3) a small conduit penetration in the sump curb, approximately 2.5 cm [1 in.] in diameter; (4) two defects in the screen mesh covering the sump, one L-shaped cut approximately 30.5 cm by 35.6 cm [12 in. by 14 in.], one straight cut approximately 30.5 cm [12 in.] long; and (5) reactor building drain headers, ranging in size from approximately 5.1 cm to 25.4 cm [2 in. to 10 in.] that lacked protective screen material. On October 22, 1993, seven 7.3 cm [3 in.] long by 2.5 cm [1 in.] high holes were identified in the grout at the base of the Unit 2 containment sump curb. Although these two containment sumps had been inspected for debris on several occasions, the breaches in the integrity of the sump screens and the lack of 9311190457. IN 89-77, Supplement 1 December 3, 1993 Page 2 of 3 reactor building drain header screens had gone unnoticed. The licensee had focused its inspections on debris and did not question the existence of penetrations through the screen and curb. In Unit 1, the scuppers were part of the original design and while shown on plant drawings, the drawings were unclear with respect to screen installation; whereas, the holes in the grout at the base of the Unit 2 containment sump curb were not identified in the design nor on drawings. These holes in Unit 2 were only visible after close examination because of the construction of the sump curb. The penetrations and cuts in the screen were not recognized as a problem until an electrician questioned the existence of the penetrations while working in the Unit 1 containment. Discussion The ability of the pressurized-water reactor containment emergency recirculation sump or the boiling-water reactor (BWR) suppression pool to provide an adequately filtered source of water for the ECCS is essential during the long-term cooling phase of a loss-of-coolant accident (LOCA). Failure to adequately filter the ECCS water source could result in degradation and eventual loss of ECCS function as a result of damaged pumps or clogged flow paths. This latest event and other events discussed in earlier related generic communications listed below have demonstrated various problems in ensuring an adequate source of recirculating water. In particular, the consideration of flow paths that bypass the sump screens (such as the reactor building drain headers in the ANO case) is a potential concern which has not been previously noted. Failure to ensure that the physical condition and as- built configuration of the screening material, and the screening of other penetrations that communicate with the sump, preclude bypass of the filtering function could lead to loss of the ECCS function. Related Generic Communications * Generic Letter 85-22: "Potential for Loss of Post LOCA Recirculation Capability Due to Insulation Debris Blockage." * NRC Information Notice 88-28: "Potential for Loss of Post LOCA Recirculation Capability Due to Insulation Debris Blockage." * NRC Information Notice 89-77: "Debris in Containment Emergency Sumps and Incorrect Screen Configurations." * NRC Information Notice 92-71: "Partial Plugging of Suppression Pool Strainers at a Foreign BWR." * NRC Information Notice 93-34: "Potential for Loss of Emergency Cooling Function Due to a Combination of Operational and Post-LOCA Debris in Containment." . IN 89-77, Supplement 1 December 3, 1993 Page 3 of 3 * NRC Information Notice 93-34, Supplement 1: "Potential for Loss of Emergency Cooling Function Due to a Combination of Operational and Post-LOCA Debris in Containment." * NRC Bulletin 93-02: "Debris Plugging of Emergency Core Cooling Suction Strainers." 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. /s/'d by BKGrimes Brian K. Grimes, Director Division of Operating Reactor Support Office of Nuclear Reactor Regulation Technical contacts: Chuck Paulk, RIV (817) 860-8236 Ramon Azua, RIV (402) 426-9611 Linda Smith, RIV (501) 968-3290 John Hickman, NRR (301) 504-3017 Attachment: List of Recently Issued NRC Information Notices .
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