ENS 41618
ENS Event | |
|---|---|
20:10 Apr 20, 2005 | |
| Title | Both Penetration Room Ventilation System Trains Temporarily Inoperable |
| Event Description | At 16:10 on 4-20-05, Oconee Unit 3 entered Technical Specification 3.0.3 due to [valve] 3PR-20 being failed closed for testing on the Penetration Room Ventilation System. 3PR-20 is the suction cross connect valve for the two trains of the Penetration Room Ventilation System. Technical Specification Surveillance requirement 3.7.10.5 requires that 3PR-20 be verified capable of being opened every 18 months. This surveillance cannot be met if 3PR-20 is failed closed. Therefore, both Penetration Room Ventilation System trains had to be declared inoperable since the LCO was declared not met. Entry into Technical Specification 3.0.3 conservatively indicates that a loss of safety function could have occurred. Therefore, this condition warrants reporting via an eight-hour non-emergency report as a condition which could result in a loss of safety function. The Technical Specification 3.0.3 entry condition was recognized 'after the fact' by the Shift Technical Advisor. Following recognition of this condition, operating air was restored to 3PR-20 and it was returned to operable at 18:24 on 4-20-05.
The Penetration Room Ventilation System functions to channel Reactor Building penetration leakage to a high-efficiency carbon/HEPA filtration system prior to release via a ventilation stack. The Penetration Room Ventilation System consists of two trains. Each Penetration Room Ventilation System train has a fan, ducting, suction and discharge valves, and in-line carbon and HEPA filters. The Penetration Room Ventilation System discharges to a larger high-efficiency carbon/HEPA filtration system before being released via a ventilation stack. 3PR-20 is the suction cross connect valve for the two trains of the Penetration Room Ventilation System. 3PR-20 was originally installed to provide cooling of an idle filter train if one trains of the Penetration Room Ventilation System failed. However, subsequent analyses have concluded that 3PR-20 is no longer required to provide this cooling since natural circulation around the idle train filter assembly is adequate to remove decay heat to prevent carbon bed ignition. Appropriate changes to the Technical Specification for this issue have not yet been completed. Therefore, the safety significance of this condition is LOW. Corrective Action(s): 1) 3PR 20 was returned to operable. 2) A Technical Specification change will be developed to address the discrepancies between design basis and Technical Specifications requirements (licensing basis). The licensee has notified the NRC Resident Inspector.
Withdrawal of Event Number 41618 On 04/20/2005 at 22:40 [ET] Oconee reported Unit 3 entry into Technical Specification (TS) 3.0.3 due to valve 3PR-20 being failed closed. 3PR-20 is the suction cross connect valve for the two trains of the Penetration Room Ventilation System. TS Surveillance Requirement 3.7.10.5 can not be met if 3PR-20 is failed closed. Further review concluded that it was inappropriate to enter TS 3.0.3. The appropriate TS condition was TS 3.7.10 Conditon A for one train inoperable. Therefore this event does not meet reportability requirements and is hereby retracted. Initial Safety Significance: UFSAR sections 6.5.1.3 and 9.4.7.2 clarify that 3PR-20 was originally installed to open in the event of failure of one fan to allow air flow to be maintained through that fan's filters by connecting to the other train which is assumed to be operating. This would prevent carbon bed ignition by removing decay heat of radioactive materials trapped on the filters. Analysis performed in 1990 concluded that natural circulation around the idle train filter assembly provides adequate heat transfer. Therefore there is no physical or analytical need for 3PR-20 to perform its TS function. A TS amendment was approved 6-1-2004 which will delete TS 3.7.10, and the requirement for 3PR-20, but the implementation of that TS change is awaiting completion of certain modifications. However, since the existing TS credits 3PR-20 with mitigating a single failure, the result of the inoperability of 3PR-20 is that it cannot mitigate that single failure. It is noted that Oconee Unit 3 is currently in TS 3.7.10 Condition A due to indicated low flow in the 3A PRVS train. While in that TS condition, it is not required to assume a single failure which would make the remaining train inoperable. Therefore 3PR-20 is not required while in Condition A. NRC R2DO (C. Julian) notified. The NRC Resident Inspector was notified of this retraction by the licensee. |
| Where | |
|---|---|
Oconee  South Carolina (NRC Region 2) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material | |
| Time - Person (Reporting Time:+2.5 h0.104 days <br />0.0149 weeks <br />0.00342 months <br />) | |
| Opened: | David Nix 22:40 Apr 20, 2005 |
| NRC Officer: | Bill Huffman |
| Last Updated: | Apr 21, 2005 |
| 41618 - NRC Website
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Unit 3 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |