05000289/LER-2012-002
| Three Mile Island, Unit 1 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat |
| 2892012002R01 - NRC Website | |
Event:
A flood protection walkdown (Post Fukushima response required by NRC 50.54(f) letter) in the air intake tunnel (AIT) was required to conduct visual inspection of 43 conduit penetrations. The sealing of all penetrations into the air intake tunnel is required to satisfy a license commitment that the plant can be maintained in a safe shutdown condition during an external flood with river flows up to the Probable Maximum Flood (PMF) (1,625,000 CFS). On 08/02/12, inspection confirmed that an internal seal fitting (Crouse Hinds model EYS) was installed at each penetration and that each conduit penetration through the wall was externally sealed. The inspection team also noted drain holes in the conduit fittings.
Following that inspection, the team discussed a plan to inspect the internal seal. A second inspection was conducted on 08/10/12, and a borescope was inserted into the conduits where possible (i.e., cable configurations with respect to the holes limited the capability to view the internal configuration of all of the conduits). Six conduits were inspected and none contained the internal sealing compound material (Chico A).
Based on the apparent condition (i.e., none of the conduits had the internal seal installed in the EYS fitting), the NRC was notified of the existence of an "Event or Condition that could have prevented fulfillment of a Safety Function" as required by 10 CFR 50.72(b)(3)(v)(B) via Event Notification (EN) 48179 on 08/10/12. A subsequent Licensee Event Report (LER) 2012-002-00 was submitted on 10/09/12 with the planned intent to supplement the LER by 01/15/2013 after an evaluation on the safety significance of the event was completed. Docketed correspondence TMI-13-003 dated 01/15/13 updated the status of the evaluation and provided a revised planned date to supplement LER 2012-002-00 by 02/22/13.
B. CAUSE OF EVENT
When the plant was constructed in the early 1970's the conduit seals were never installed. The conduit seals are internal to the conduit fittings and not visible externally. The cause has been attributed to inadequate configuration management during original construction. The design drawings for the AIT conduit routing (215-162 & 215-163) show the Crouse Hinds EYS fittings, and the EYS fittings are installed. However, the internal sealing compound material, Chico A, was never installed in the EYS fittings.
C. ANALYSIS / SAFETY SIGNIFICANCE
Adequate flood protection was maintained for the emergency power systems, emergency feedwater, river water systems, Reactor Coolant Pump (RCP) seal cooling, and vital instruments. The operations and emergency response staff would have had adequate information concerning plant conditions at all times to maintain core cooling.
The reactor would have been shutdown, and Reactor Coolant System (RCS) temperature and pressure reduced to place the decay heat removal system in service before the deficient flood protection barriers were challenged.
The impact of the leakage from the AIT conduits into the Auxiliary Building was evaluated assuming no mitigating credit was taken by the Emergency Response Organization. A technical evaluation took into account the aggregate impact of identified flood barrier deficiencies. The plant would have been shutdown on Decay Heat Removal (DHR) with the Severe Flood Mitigation System (SFMS) equipment staged and Once Through Steam Generator (OTSG) cooling available as provided in the flood abnormal operating procedure when the inleakage to the Auxiliary Building would have adversely impacted the DHR system. The evaluation concluded the Make-Up (MU) system would have subsequently been adversely impacted as well.
The plant would have been maintained stable on natural circulation using the emergency feedwater system with condensate inventory, then river water supply and a defense in depth supply using the SFMS system from the condenser pit. The RCS inventory would have been maintained. RCP seal cooling would be retained using the Intermediate Closed Cooling Water (ICCW) system. Inventory would be maintained to address nominal operating leakage by using the SFMS system which utilizes the spent fuel pool for its supply. The Core Flood (CF) system additionally would have provided a significant volume as a defense in depth inventory supply to the RCS.
As a result of the missing AIT conduit seals the DHR and MU systems would be lost due to flood water intrusion from the PMF. The emergency feedwater system, emergency diesel generators, reactor river system, SFMS, CF tanks, and RCP seal cooling are maintained. The RCS is maintained on natural circulation core cooling at reduced RCS pressure and temperature with the emergency organization staffed.
D. CORRECTIVE ACTIONS
An industry notification was provided regarding an original construction deficiency where internal conduit seal fittings were installed but the seals were not installed.
The flood protection design was modified for all affected AIT conduits and completed in October 2012.
E. PREVIOUS OCCURENCES
There are no previous occurrences that are applicable for this LER supplement.