Information Notice 2005-11, Internal Flooding/Spray-Down of Safety-Related Equipment Due to Unsealed Equipment Hatch Floor Plugs And/Or Blocked Floor Drains
| ML050870351 | |
| Person / Time | |
|---|---|
| Issue date: | 05/06/2005 |
| Revision: | 0 |
| From: | Hiland P L NRC/NRR/DIPM |
| To: | |
| Telson, R - NRR/DIPM/IROB - 415-2256 | |
| References | |
| IN-05-011 | |
| Download: ML050870351 (5) | |
May 6, 2005
NRC INFORMATION NOTICE 2005-11:INTERNAL FLOODING/SPRAY-DOWN OFSAFETY-RELATED EQUIPMENT DUE TO UNSEALED EQUIPMENT HATCH FLOOR PLUGS AND/OR BLOCKED FLOOR DRAINS
ADDRESSEES
All holders of operating licenses for nuclear power reactors, except those who havepermanently ceased operations and have certified that fuel has been permanently removed from the reactor vessel.
PURPOSE
The U.S. Nuclear Regulatory commission (NRC) is issuing this information notice (IN) to informaddressees of the possibility of flooding safety-related equipment as a result of (1) equipment hatch floor plugs that are not water tight and (2) blockage of the equipment floor drain systems that are credited to mitigate the effects of flooding in the final safety analysis report (FSAR) and plant design basis calculation It is expected that recipients will review the information for applicability to their facilities andconsider actions, as appropriate, to avoid similar problem However, suggestions in this IN arenot NRC requirements; therefore, no specific action or written response is required.
DESCRIPTION OF CIRCUMSTANCES
On August 18, 2004, during an extended backwash evolution on the reactor water cleanupdemineralizer at Susquehanna Unit 1, approximately 1,500 gallons of contaminated water from the backwash-receiving tank overflowed into the reactor building equipment floor drain system. The drain header became blocked by the resin from the receiving tank and rust displaced from inside the drain pipe The water flowed up and out of the blocked drains on a lower elevation, across the floor, and down into the Division II core spray and the high-pressure coolant injection system compartment The water entered these compartments by flowing though unsealedspaces between the equipment hatch floor plugs and the floo The equipment floor drains in the emergency core cooling system (ECCS) compartments were isolated, as per design, andthe water accumulated on the floo Approximately 2 inches of water accumulated on the floor of the Division II core spray and high-pressure injection system compartments. The licensee disabled the automatic start feature of the Division II core spray pumps anddeclared the pumps inoperable but functional for approximately 2hours until an assessment was completed to verify operabilit The licensee's immediate actions were to perform system walkdowns and determine the effect of the flooding on the Division II core spray and high- pressure coolant injection system The walkdowns determined that the water leakage into the room did not significantly impact the systems and that the systems remained operabl Thewalkdowns also confirmed that the other ECCS compartments were not affected.
DISCUSSION
The licensee's FSAR flooding analysis stated that the ECCS compartments were water tight. However, the equipment hatch floor plugs were not sealed and therefore did not constitute a water-tight barrie The plant-specific design calculations did not address leakage around these plug Water leaked through the ceiling into the Division II core spray and high-pressure coolant injection compartments through gaps between the equipment hatch floor plug and the floo The licensee did not scope the equipment floor drain system function (mitigating internal flooding) into the Maintenance Rul The FSAR and flooding design calculations credited the equipment floor drain system to assist in removal of water from internally flooded area Part ofthe licensee's corrective actions were to place the floor and equipment drain functions within the scope of the Maintenance Rule and to revise the plant calculations to reconcile the plant design analysis and the FSA The licensee has also developed and installed a modification to seal the equipment hatch floor plugs above the ECCS compartments.CONCLUSIONThe event described above illustrates the potential for degradation of multiple trains of ECCS asa consequence of potential flooding of safety-related equipment outside containmen All holders of reactor operating licenses should be aware of the effect of unsealed equipment hatch floor plugs and malfunctioning drains on their plant-specific FSARs and plant design analyses for floodin Unsealed reactor building equipment hatch floor plugs and less than optimal maintenance monitoring of the equipment floor drain systems can result in additional internal flooding vulnerabilitie Licensees should consider several actions to mitigate these vulnerabilities:(1) Verify that the actual plant configuration and design of the equipment hatch floor plugsmeet the FSAR description and design basis calculations for water-tight compartment Consider appropriate actions to achieve floor plug water tightness, such as the use of gaskets and sealer Additionally, if the analysis allows for leakage through the equipment hatch floor plugs, the qualification of equipment below these plugs should consider water spray as well as submergence.(2) In addition, if the drain system is required for water removal, periodically verify that thefloor drain system performs as intended and perform maintenance to assure that the system can perform the water removal function assumed in the FSAR and design calculation GENERIC IMPLICATIONSFlooding due to internal causes has been shown to be a significant contributor to risk at somefacilitie Flooding also has the potential to make multiple trains of equipment and support equipment inoperable, significantly increasing plant ris Flooding also has the significant consequence of preventing or limiting operator mitigation and recovery action As a result, semiannually, NRC inspectors select one or two plant areas and inspect internal flood protection features for risk-significant structures, systems, and components in accordance with Inspection Procedure Attachment 71111.06 "Flood Protection Measures."Multiple previous NRC generic communications have addressed flood protection issues:
1.Circular POTENTIAL COMMON MODE FLOODING OF ECCS EQUIPMENT ROOMSCR 78-06AT BWR FACILITIES 2.IN 83-44POTENTIAL DAMAGE TO REDUNDANT SAFETY EQUIPMENT AS ARESULT OF BACKFLOW THROUGH THE EQUIPMENT AND FLOOR DRAIN SYSTEM3.IN 83-44 S1POTENTIAL DAMAGE TO REDUNDANT SAFETY EQUIPMENT AS ARESULT OF BACKFLOW THROUGH THE EQUIPMENT AND FLOOR DRAIN SYSTEM4.IN 87-49DEFICIENCIES IN OUTSIDE CONTAINMENT FLOODING PROTECTION5.IN 92-69WATER LEAKAGE FROM YARD AREA THROUGH CONDUITS INTOBUILDINGS6.IN 94-27FACILITY OPERATING CONCERNS RESULTING FROM LOCAL AREAFLOODING7.IN 98-31FIRE PROTECTION SYSTEM DESIGN DEFICIENCIES AND COMMON-MODE FLOODING OF EMERGENCY CORE COOLING SYSTEM ROOMS AT WASHINGTON NUCLEAR PROJECT UNIT 2 IN 2005-11