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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 53456 | 20 May 2024 20:53:00 | 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded | Pressure Boundary Leakage Identified While Shutdown | On June 12, 2018, at 1500 CDT, a Reactor Coolant System (RCS) Pressure Boundary leak was identified during a Mode 3, hot shutdown walkdown on a High Pressure Injection Line (HPI) to Reactor Coolant Pump (P32C) drain line weld near MU-1066A HPI Line Drain Valve and MU-1066B HPI Line Drain Valve. The 3/4 inch drain line containing drain valves MU-1066A and MU-1066B on the 'C' HPI header (CCA-5 pipe class) has a through-wall defect on the pipe stub or welds between the sockolet and valve MU-1066A. The leak location is in the ASME Class I RCS Pressure Boundary. The hot shutdown walkdown was being performed as part of a planned outage to investigate excessive Reactor Building Sump inleakage. Total unidentified RCS leakage prior to the investigation was determined to be at 0.165 gpm. After the initial investigation of the leakage, the following Tech Specs (TS) were determined be applicable: TS 3.4.5 - RCS Loops Mode 3, TS 3.4.13 - RCS Leakage, TS 3.5.2 - ECCS. Unit 1 is currently in Mode 3 and in progress of an RCS cooldown to comply with Tech Spec requirements. The licensee notified the NRC Resident Inspector. | Reactor Coolant System | |
| ENS 55506 | 4 October 2021 19:33:00 | 10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded | Degraded Condition Discovered on Reactor Vessel Head Penetration | At 1433 CDT, on October 4, 2021, Arkansas Nuclear One, Unit 2 (ANO-2) completed the analysis related to an indication revealed on head penetration 46 during Reactor Vessel Closure Head inspections. It was determined the indication is not acceptable under ASME code requirements. The indication displays characteristics consistent with primary water stress corrosion cracking. No leak path signal was identified during ultrasonic testing. The plant was in cold shutdown at 0 percent power and in Mode 6 for a refueling outage at the time of discovery. Repair actions will be completed prior to plant startup from the outage. This condition has no impact to the health and safety of the public. This report is being made in accordance with 10 CFR 50.72(b)(3)(ii)(A) for degradation of a principal safety barrier. This is the only indication that is currently present, however, if additional indications are found, they will also be repaired prior to the plant startup. The NRC Senior Resident Inspector has been notified. | ||
| ENS 45797 | 27 March 2010 20:31:00 | 10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded | Potentially Degraded Pressurizer Level Tap Identified | Arkansas Nuclear One Unit 1 is currently shut down in Mode 6 for refueling outage 1R22. On March 27, 2010 at 1531 CDT a visual examination of Unit 1 pressurizer level tap 1-RC-1001 A/B indicated evidence of past leakage from the nozzle bore. The leakage is indicated by a small trail of what appears to be dry boron on the lower portion of the nozzle bore accompanied by rust stains on the stainless steel nozzle. The licensee notified the NRC Resident Inspector.
Update per 10CFR50.72(c). During the visual examination of the bore of T1 pressurizer level tap nozzle RC-1001 after the inconel nozzle removal, it is evident that corrosion of the carbon steel base material is present. This nozzle location was identified as leaking during the bare metal visual examination. The licensee notified the NRC Resident Inspector. Notified R4DO (O'Keefe). | ||
| ENS 41473 | 9 March 2005 11:37:00 | 10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded | Pressurizer Heater Sleeve Leakage | The following information was obtained from the licensee via facsimile (licensee text in quotes): ANO (Arkansas Nuclear One) Unit 2 shutdown on 3/9/05 at approximately 0038 (CST) to begin the 2R17 refueling outage. While performing the Mode 3 Hot Shutdown Walk down on ANO Unit 2, evidence of leakage was discovered around three (3) pressurizer heater sleeves. The amount of leakage was minor since no indication of moisture was present and the build up of boric acid was minimal. Investigations are underway as to the repair of the affected nozzles. The licensee notified the NRC Resident Inspector.
The following information was obtained from the licensee via facsimile (licensee text in quotes): ANO Unit 2 shutdown on 3-9-05 at approximately 0038 to begin the 2R17 refueling outage. While performing the Mode 3 Hot Shutdown Walk down on ANO Unit 2, evidence of leakage was discovered around three (3) pressurizer Heater Sleeves. The amount of leakage was minor since no indication of moisture was present and the build up of boric acid was minimal. Investigations are underway as to the repair of the affected nozzles. Update on 3/12/2005 @ 2140: During the followup inspection performed on 3-12-2005, eight pressurizer heater nozzles had evidence of boric acid leakage at the annulus between the nozzle and pressurizer. One plug was also discovered with evidence of boric acid leakage. The nozzle at this location was plugged during the late 1980's. The reactor is presently in cold shutdown. The NRC Resident Inspector was notified.
The following information was obtained from the licensee via facsimile (licensee text in quotes): Following decontamination activities performed on 3-15-2005, 1 (one) additional pressurizer heater nozzle had evidence of leakage at the annulus between the nozzle and pressurizer. The licensee notified the NRC Resident Inspector. Notified R4 DO (T. Farnholtz) | ||
| ENS 40721 | 30 April 2004 19:38:00 | 10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded | "on 4/30/2004, During Refueling Outage 1 R18, Ultrasonic Testing of the Reactor Vessel Head Identified Two Axial Indications on Control Rod Drive Mechanism, Nozzle 61. the Indications Were Located on the Outside Diameter of the Nozzle on the Lower Hillside. One of the Flaws Was at the Toe of the Fillet Weld and Extended Below the Fillet Weld Cap. the Second Flaw Extended the Full Length of the Weld and Just Below the Toe of the Fillet Weld. | There were no indications that either of the flaws was through-wall or through-weld and both were typical of Primary Water Stress Corrosion Cracking. No formal evaluation of these flaws has been completed; however, based on past analysis it is expected that they would not be found acceptable under ASME standards and, therefore, represent degradation of a principal safety barrier reportable under the referenced criterion. This condition was determined to be reportable at 0839 CDT on 5/3/2004. The nozzle will be repaired prior to startup from the current refueling outage. The reactor vessel head inspection was subsequently completed with no additional flaws identified. The licensee notified the NRC Resident Inspector. | Control Rod | |
| ENS 40216 | 2 October 2003 22:15:00 | 10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded | Rcs Boundary Leakage Due to Small Crack on Drain Line Welded Cap | Safety injection tank (SIT) isolation valve (2CV-5043-2) has a drain pipe under the valve body with a welded cap. The welded cap has a small crack with boric acid residue. The welded cap does not have any threads and is considered RCS boundary leakage. There is a check valve between the reactor coolant system (RCS) and the SIT Outlet valve. The crack will be repair welded prior to coming out of the 2R16 outage. The Licensee has notified the NRC Resident Inspector.
This report is being made to retract a notification made at 1715 CDT on 10/02/03 (EN# 40216.) The notification documented the identification of a small amount of boric acid residue on a drain line attached to a Safety Injection Tank isolation valve (2CV-5034-2). The report stated that the indication was within the Reactor Coolant System boundary. However, subsequent review of the condition determined that the indication was not within the Reactor Coolant System boundary since it was isolated from the Reactor Coolant System by an operable check valve. Therefore, the condition did not represent a serious degradation of a principal safety barrier. Note; The drain line is 3/4 inch diameter stainless steel. The licensee notified the NRC Resident Inspector. Notified Claude Johnson - R4DO. | Reactor Coolant System |