ENS 47120
ENS Event | |
|---|---|
18:46 Aug 2, 2011 | |
| Title | Vulnerability from a Potential High Energy Line Break |
| Event Description | The following condition is being reported by Arkansas Nuclear One, Unit 2 (ANO-2) in accordance with 10CFR 50.72(b)(3)(ii)(B), 'Unanalyzed Condition' and in accordance with 10CFR 50.72(b)(3)(v)(D), 'A Condition That Could Have Prevented Fulfillment of a Safety Function.' On 08/02/2011 at 1346 CDT, the ANO Unit 2 Control Room was notified by Engineering that a postulated High Energy Line Break (HELB) could potentially cause both the Red and Green Train Emergency Safeguard Features (ESF) Rooms to exceed their environmentally qualified temperature limits. This postulated condition would be possible due to normally open room purge dampers exposing ESF equipment in these rooms to a common area impacted by HELB conditions. The ESF Rooms contain the Red and Green Trains of High Pressure Safely Injection Pumps, Low Pressure Safety Injection Pumps, Containment Spray Pumps, and Shutdown Cooling Heat Exchangers. Until further Engineering evaluation can be performed to validate this postulated scenario, ANO-2 has closed ESF room purge dampers to provide Red and Green ESF train separation during a potential HELB event.
Refer to [ANO-2] Condition Report CR-ANO-2-2011-02772 for further information. The NRC Resident has been notified.
The purpose of this notification is to retract a previous report made by Arkansas Nuclear One, Unit 2 (ANO-2) on 08/02/2011 at 2127 [EDT] (EN 47120). The initial report documented that a postulated High Energy Line Break (HELB) could potentially cause rooms containing both trains of Emergency Safeguard Features (ESF) equipment to exceed their environmentally qualified temperature limits. The ESF rooms contain the High Pressure Safely Injection Pumps, Low Pressure Safety Injection Pumps, Containment Spray Pumps, and Shutdown Cooling Heat Exchangers. Specifically, normally open ESF room purge dampers exposing both trains of ESF equipment to a common area impacted by postulated HELB conditions were not modeled in the ANO-2 HELB analysis. This condition was reported in accordance with 10CFR 50.72(b)(3)(ii)(B), 'Unanalyzed Condition' and 10CFR 50.72(b)(3)(v)(D), 'A Condition That Could Have Prevented Fulfillment of a Safety Function'. Since the initial report, Engineering has revised the ANO-2 HELB model to include the effects of the open ESF room purge dampers. The resulting analysis shows that a HELB event will not cause the required ESF equipment to exceed analyzed temperature limits with the room purge dampers in the open configuration. Therefore, the condition did not result in 'a condition that could have prevented the fulfillment of a safety function' and did not result in an 'unanalyzed condition that significantly degrades plant safety'. Based on the revised HELB analysis, the previous report (EN#47120) describes a condition that does not meet the reporting requirements of 10CFR 50.72(b)(3)(v)(D) or 10CFR 50.72(b)(3)(ii)(B) and is therefore retracted. The NRC Resident Inspector has been informed of the retraction. Notified R4DO (Hay). |
| Where | |
|---|---|
Arkansas Nuclear  Arkansas (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
| Time - Person (Reporting Time:+2.68 h0.112 days <br />0.016 weeks <br />0.00367 months <br />) | |
| Opened: | Albert Martin 21:27 Aug 2, 2011 |
| NRC Officer: | Vince Klco |
| Last Updated: | Aug 18, 2011 |
| 47120 - NRC Website
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Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |