05000289/FIN-2008009-02
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Finding | |
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| Title | Potential CO2 Migration Outside the Relay Room fire Area |
| Description | The team performed document reviews and plant walkdowns to verify that redundant trains of systems required for hot shutdown are not subject to damage from fire suppression activities or from the rupture of inadvertent operation of fire suppression systems. Specifically, the team verified that: • A fire in one of the selected fire areas would not directly, through production of smoke, heat or hot gases, cause activation of suppression systems that could potentially damage all redundant safe shutdown trains. • A fire in one of the selected fire areas (or the inadvertent actuation or rupture of a fire suppression system) would not directly cause damage to all redundant trains (e.g. sprinkler caused flooding of other than the locally affected train). • Adequate drainage is provided in areas protected by water suppression systems. b. Findings The team identified a potential concern regarding operation of the carbon dioxide (CO2) extinguishing system for the relay room. Specifically, the potential may exist for CO2 to migrate outside the relay room and affect the ability of operators to perform alternative shutdown activities. Likewise, with CO2 migration potential outside the relay room, the potential existed for less than adequate CO2 concentration in the relay room for fire suppression. This issue will remain unresolved pending further NRC review of AmerGens analysis of the issue. The team reviewed the design and testing of the CO2 system for the relay room. The original CO2 discharge test in 1976 had some complications which required followup evaluations, further testing, and design change modifications. After the team reviewed the subsequent testing and design change documentation, the team had two remaining concerns: potential migration of CO2 into rooms outside the relay room and the concentration of CO2 in the relay room. The original test report identified significant CO2 migration. CO2 levels were found as high as 6% in lower elevations of the adjacent fuel handling building patio area. The CO2 migration was addressed by several corrective actions including greater sealing of the room by installing tighter penetration seals and maintaining the doors closed instead of automatic door closing mechanisms. Because the room would then be sealed tighter, pressure relief dampers were added to prevent over pressurization of the relay room. The team also made the following observations: • The gaps under the two doors from the relay room to the 1D 4160VAC switchgear room and the ESAS room were approximately one inch high. This represented a potential CO2 migration path to areas required for alternative shutdown operations. • The relay room ventilation ducts were automatically isolated upon a CO2 discharge with two series dampers on both the exhaust plenum and the supply plenum. On the exhaust plenum, one isolation damper (fire damper) was between the relay room and the relief dampers and the other isolation damper (ventilation damper) was downstream of the relief dampers. The relief dampers appeared to be set at a very low differential pressure (0.007 psid), and would relieve pressure into the Engineered Safeguards and Actuation System (ESAS) room, a room that required entry for alternative shutdown. This represented a potential CO2 migration path if the fire damper did not seal tightly, and this also represented a potential for over pressurization of the relay room if the fire damper did seal tightly. • The ESAS room contained the remote shutdown A transfer panel, which was required for the alternative shutdown lineup in the event of a control room evacuation. There were also remote shutdown transfer switches in the IE 4160VAC switchgear room, which were only accessible by transiting through the ESAS room. Therefore, if CO2 was present in the ESAS room, it may impact alternative shutdown actions. • There was a louvered control rod drive mechanism power supply bus duct between the relay room and the fuel handling building patio area. This represented an additional potential CO2 migration path. The team questioned AmerGen about the potential for CO2 to migrate from the relay room to areas required for alternative shutdown and about the potential for CO2 over pressurization in the relay room. AmerGen was unable to locate design documentation for the modifications to the relay room after the initial testing. AmerGen entered this issue in their corrective action program (AR 815641815641, isolated the CO2 system, placed a continuous fire watch in the relay room, and began a formal calculation to determine the pressure buildup in the relay room and the CO2 migration, if any. The team concluded that the identified issue concerning the migration and concentration of CO2 for the relay room CO2 system is an unresolved item pending further NRC review AmerGens evaluation. URI 05000289/2008009-02, Potential CO2 Migration Outside the Relay Room Fire Are |
| Site: | Three Mile Island  |
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| Report | IR 05000289/2008009 Section 1R05 |
| Date counted | Sep 30, 2008 (2008Q3) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.05 |
| Inspectors (proximate) | J Lilliendahl M Patel D Orr J Rogged Spindlerr Bellamy H Gray E Burket D Everhart J Lilliendahl P Kaufman R Nimitz J Brand D Kern |
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Finding - Three Mile Island - IR 05000289/2008009 | |||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Three Mile Island) @ 2008Q3
Self-Identified List (Three Mile Island)
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