Semantic search
| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 54954 | 19 October 2020 04:13:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Control Room Envelope Inoperable | On October 18, 2020 at 2313 CDT, Arkansas Nuclear One (ANO) discovered that 2VRA-1B (2VSF-9 outside air damper reserve bottle) was below 600 psig. This condition caused the control room envelope to be inoperable in accordance with OP-2104.007 Attachment L. ANO Unit 1 entered TS 3.7.9 Condition B for inoperable control room boundary. ANO Unit 2 entered TS 3.7.6.1 Action D for inoperable control room boundary. A procedurally controlled temporary modification was implemented to install a blank flange on the 2VSF-9 outside air damper. Both Units declared the control room boundary operable at 2358 CDT. The associated control room emergency recirculation fan remains inoperable with the blank flange installed. This is a 7-day shutdown-LCO for both units. The licensee informed the NRC Resident Inspector.
Previously, Entergy notified the NRC that ANO control room envelope was inoperable due to 2VRA-1B (2VSF-9 outside air damper reserve bottle) was below required pressure of 600 psig. After additional engineering evaluation, it was determined the control room boundary remained intact for this condition. As documented in version 2 operability determination for condition report ANO-C-2020-2818, the control room ventilation boundary remained intact for the condition identified and was able to fulfill its function for the required 30-day mission time. In accordance with NUREG-1022, 'Event Report Guidelines 10 CFR 50.72 and 50.73,' a report may be retracted based on a revised operability determination. The CRE remained operable; therefore, this report may be retracted. The NRC Resident Inspector has been informed. Notified R4DO (Pick). | ||
| ENS 54339 | 20 October 2019 15:30:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Control Room Envelope Breach | At 1030 CDT, it was discovered that the loop seal on the condensate drain was empty for VUC-9 Control Room AC Unit. This creates a breach in the Control Room envelope. Unit 2 entered (Technical Specification) T.S. 3.7.6.1 Action D. Unit 1 is in Mode 6; therefore, not in a mode of applicability. Compensatory action were being performed and the licensee was in the process of sealing the loop. The licensee will notify the NRC Resident Inspector.
This report is being retracted. The Control Room Envelope (CRE) provides a safety function which limits radiological dose to occupants to no more than 5 rem for 30 days post-accident. The dose limitation assumes the occupants are stationed within the CRE 24 hours a day for the entire 30-day period. The CRE also functions to protect occupants from potential hazards such as smoke or toxic chemicals. The CRE is declared inoperable when a potential breach is identified, regardless of the ability to seal the breach. With respect to the event of October 20, 2019, the water level in a loop seal could not be maintained at the desired level. Subsequent evaluation determined that sufficient water was maintained in the loop seal to prevent a breach of the CRE. The subject reporting criterion is based on the assumption that safety-related systems, structures, and components (SSCs) may no longer be capable of mitigating the consequences of an accident. In accordance with NUREG 1022, 'Event Report Guidelines 10 CFR 50.72 and 50.73,' a report may be retracted based on a revised operability determination. The CRE remained operable; therefore, this report may be retracted. The licensee notified the NRC Resident Inspector. Notified R4DO (Young). | ||
| ENS 52242 | 15 September 2016 14:08:00 | 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | Potential Unanalyzed Condition Based on Identified Non-Conforming Conditions | During performance of an extent of condition evaluation of protection for Technical Specification (TS) equipment from the damaging effects of tornadoes, Arkansas Nuclear One, Unit 1, identified non-conforming conditions in the plant design such that specific TS equipment on Unit 1 is considered not (to) be adequately protected from tornado missiles. The reportable condition is postulated by tornado missiles entering vital switchgear rooms 99 and 100 and striking vital switchgears in the rooms. A tornado could generate multiple missiles capable of striking the Unit 1 vital switchgear and rendering both safety related AC electrical trains inoperable. This condition is reportable per 10 CFR 50.72(b)(3)(ii)(B) for any event or condition that results in the nuclear power plant being in an unanalyzed condition that significantly degrades plant safety, and per 10 CFR 50.72(b)(3)(v) for any event or condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to (A) safe shutdown capability, (B) residual heat removal capability, or (D) accident mitigation. This condition was identified as part of an on-going extent of condition review of potential tornado missile related site impacts. Licensee Event Report (LER) 50-313/2016-002-00 was recently submitted addressing previously identified tornado missile vulnerabilities at the Unit 1 plant. Enforcement discretion per Enforcement Guidance Memorandum EGM 15-002 has been implemented and required actions taken. Corrective actions will be documented in a follow-on licensee event report. The licensee has notified the NRC Resident Inspector. | Residual Heat Removal | |
| ENS 52234 | 11 September 2016 19:51:00 | 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | Inadequate Design Protection of Safety-Related Equipment Identified During Tornado Missile Impact Evaluation | During performance of an extent of condition evaluation of protection for Technical Specification (TS) equipment from the damaging effects of tornados, Arkansas Nuclear One, Unit 1, identified non-conforming conditions in the plant design such that specific TS equipment on Unit 1 is considered not be adequately protected from tornado missiles. The reportable condition is postulated by tornado missiles entering the Unit 1 Controlled Access area, elevation 386', Upper North Electrical Penetration Room (UNEPR) through penetrating a hollow metal door and then striking safety related cables. A tornado could generate multiple missiles capable of striking the Unit 1 UNEPR and rendering both safety related emergency feedwater trains inoperable. This condition is reportable per 10 CFR 50.72(b)(3)(ii)(B) for any event or condition that results in the nuclear power plant being in an unanalyzed condition that significantly degrades plant safety, and per 10 CFR 50.72(b)(3)(v)(B) and (D) for any event or condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to (B) Remove residual heat, or (D) Mitigate the consequences of an accident. This condition was identified as part of an on-going extent of condition review of potential tornado missile related site impacts. Licensee Event Report (LER) 50-313/2016-002-00 was recently submitted addressing previously identified tornado missile vulnerabilities at the Unit 1 plant. Enforcement discretion per Enforcement Guidance Memorandum EGM 15-002 has been implemented and required actions taken. Corrective actions will be documented in a follow-on licensee event report. The licensee has notified the NRC Resident Inspector. A similar evaluation is on going for Unit 2. | Feedwater | |
| ENS 52195 | 24 August 2016 13:41:00 | 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | Unanalyzed Condition Associated with Damaging Effects of Tornados | During performance of an extent of condition evaluation of protection for Technical Specification (TS) equipment from the damaging effects of tornados, Arkansas Nuclear One, Unit 1, identified non-conforming conditions in the plant design such that specific TS equipment on Unit 1 is considered to not be adequately protected from tornado missiles. The reportable condition is postulated by tornado missiles entering the Unit 1 Cable Spreading Room through penetrating the hollow metal door or potentially from spalling of the block wall separating Room 96 and 97. A tornado could generate multiple missiles capable of striking the Unit 1 Cable Spreading Room and rendering both safety related electrical trains inoperable. This condition is reportable per 10 CFR 50.72(b)(3)(ii)(B) for any event or condition that results in the nuclear power plant being in an unanalyzed condition that significantly degrades plant safety, and per 10 CFR 50.72(b)(3)(v) for any event or condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to (A) Shut down the reactor and maintain it in a safe shutdown condition, (B) Remove residual heat, or (D) Mitigate the consequences of an accident. This condition was identified as part of an on-going extent of condition review of potential tornado missile related site impacts. Licensee Event Report (LER) 50-313/2016-002-00 was recently submitted addressing previously identified tornado missile vulnerabilities at the Unit 1 plant. Enforcement discretion per Enforcement Guidance Memorandum EGM 15-002 has been implemented and required actions taken. Corrective actions will be documented in a follow-on licensee event report. The licensee has notified the NRC Resident Inspector. | ||
| ENS 48644 | 2 January 2013 19:08:00 | 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | Inadvertent Actuation of Safety Injection, Containment Cooling and Containment Isolation Signals | At 1308 hours (CST) on January 2, 2013, Arkansas Nuclear One Unit 2 (ANO-2) experienced an inadvertent safety injection actuation signal (SIAS), containment cooling actuation signal (CCAS) and containment isolation actuation signal (CIAS) during matrix testing on 'C' channel plant protective system (PPS). All components actuated as designed for the stated actuation signals. After verification that the actuation signal was not valid the high pressure safety injection (HPSI) pumps and low pressure safety injection (LPSI) pumps were secured and their hand switches placed in pull-to-lock as directed by the abnormal operating procedure for inadvertent SIAS at 1312 hours. The HPSI and LPSI pumps were the restored to normal standby condition and available for automatic operation at 1352 hours. The unit did down power to approximately 87% power when all three coolant charging pumps ran with suction aligned to the boric acid makeup tanks. The unit currently remains in mode 1. SIAS, CCAS, and CIAS have been reset. The cause of the inadvertent actuation signals is under investigation. The NRC Resident Inspector has been informed. Unit 2 entered Technical Specification 3.0.3 for approximately 40 minutes while the LPSI and HPSI pumps were in pull-to-lock. | 05000368/LER-2013-001 | |
| ENS 47120 | 2 August 2011 18:46:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | Vulnerability from a Potential High Energy Line Break | 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). | Shutdown Cooling Containment Spray |