05000423/LER-2020-005, Loss of Safety Function - Secondary Containment
| ML20324A632 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 11/19/2020 |
| From: | Daugherty J Dominion Energy Nuclear Connecticut |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 20-356 LER 2020-005-00 | |
| Download: ML20324A632 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 4232020005R00 - NRC Website | |
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Dominion Energy Nuclear Connecticut, Inc.
Millstone Power Station 314 Rope Ferry Road, Waterford, CT 06385 Dominion Energy.com U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.
MILLSTONE POWER STATION UNIT 3 LICENSEE EVENT REPORT 2020-005-00 LOSS OF SAFETY FUNCTION-SECONDARY CONTAINMENT i; Dominion p
Energy Serial No.: 20-356 MPS Lie/LO RO Docket No.: 50-423 License No.: NPF-49 NOV 1 9 2020
- This letter forwards-Licensee Event Report (LER) 2020-005-00, documenting an event that occurred at Millstone Power Station Unit 3, on October 1, 2020. This LER is being submitted pursuant to the requirements of 10 CFR 50.73(a)(2)(v)(C) and 10 CFR 50.73(a)(2)(v)(D) reporting a condition or event that could have prevented the fulfillment of the safety function for systems or structures that are needed to control the release of radioactive material, and to mitigate the consequences of an accident.
Should you have any questions, please contact Mr. Jeffry A. Langan at (860) 444-5544.
Sincerely, Johiaugherty
- Site Vice President - Millstone Enclosure: LER 423/2020-005-00
. Commitments made in this letter: None
cc:
U.S. Nuclear Regulatory Commission Region I 2100 Renaissance Blvd.
Suite 100 King of Prussia, PA 19406-2713 R.V. Guzman NRC Senior Project Manager Millstone Units 2 and 3 U.S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 08 C-2 Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station Serial No.20-356 Docket No. 50-423 Licensee Event Report 2020-005-00 Page 2 of 2
ATTACHMENT Serial No.20-356 Docket No. 50-423 Licensee Event Report 2020-005-00 LICENSEE EVENT REPORT 2020-005-00 LOSS OF SAFETY FUNCTION-SECONDARY CONTAINMENT MILLSTONE POWER STATION UNIT 3 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.
Abstract
On October 2, 2020, at 9:45, with Millstone Power Station Unit 3 (MPS3) in Mode 4, at approximately 230 degrees Fahrenheit, a security door in the Secondary Containment was identified as blocked open rendering Secondary Containment inoperable.
Investigation determined that the door had been blocked open on October 1, 2020, at 18:42. The door was closed by Operations on October 2, 2020, at 9:55. An 8-hour report was made to the NRG pursuant to the requirements of 10 CFR 50.72(b)(3)(v)(C) and 10 CFR 50.72(b)(3)(v)(D) reporting the event as condition that could have prevented the fulfillment of the safety function of structures or systems needed to control the release of a radioactive material, and mitigate the consequences of an accident.
The cause was identified to be a weakness in the process of notifying the Control Room prior to blocking open a door as it is not fully bounded by procedures and lacks clear ownership. Operations closed the door, which restored the Secondary Containment to operable status. There were no safety consequences to the public or the environment related to this event.
This event is being reported as a 60-day LER in accordance with the requirements of 10 CFR 50. 73(a)(2)(v)(C) and 10 CFR 50.73(a)(2)(v)(D) reporting an event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of a radioactive material and mitigate the consequences of an accident.
1. EVENT DESCRIPTION
On October 2, 2020, at 9:45, with Millstone Power Station Unit 3 (MPS3) in Mode 4, at approximately 230 degrees Fahrenheit, a security door in the Secondary Containment was identified as blocked open. The blocked open door rendered Secondary Containment inoperable. As part of COVID19 preventative measures, all Radiological Controlled Area (RCA) entry traffic during the Fall 2020 refueling outage was to be redirected to Door 311 (A-24-9), located on the North wall area of the MPS3 Auxiliary Building [NF]. On October 1, 2020, plant staff completed the preparation stage of setting up the new RCA entrance through the Auxiliary Building [NF]. At 18:42, with Millstone Power Station Unit 3 (MPS3) in Mode 1, 28 percent reactor power, door 311 was blocked open without notifying the Control Room. Door 311 is part of the Secondary Containment boundary which is required to be operable in Mode 1-4. The blocked open door was closed on October 2, 2020 at 09:55, which resulted in the Secondary Containment being inoperable for approximately 15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br /> without the Control Room being logged into the Technical Specification Action Statement. All security and radiation protection controls were in place during this event. An 8-hour report was made to the NRC pursuant to the requirements of 10 CFR 50.72(b)(3)(v)(C) and 10 CFR 50.72(b)(3)(v)(D) reporting the event or condition that could have prevented the fulfillment of the safety function for structures or systems that are needed to control the release of a radioactive material, and mitigate the consequences of an accident.
Per Technical Specification, Secondary Containment OPERABILITY must be maintained to ensure proper operation of the Supplemental Leak Collection and Release System (SLCRS) and auxiliary building filter system and to limit radioactive leakage from containments to those paths and leakage rates assumed in the accident analyses. Additionally, Technical Specification 3.6.6.2 states that with Secondary Containment inoperable, restore Secondary Containment to OPERABLE status within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />. The Secondary Containment was inoperable for less than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. Therefore, this event or condition is not a reportable as condition prohibited by Technical Specification.
This event is being reported as a 60-day LER pursuant to the requirements of 10 CFR 50.73(a)(2)(v)(C) and 10 CFR 50.73(a)(2)(v)(D) as a condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material, and to mitigate the consequences of an accident.
2. CAUSE
The cause was identified to be a weakness in the process of notifying the Control Room prior to blocking open a door as it is not fully bounded by procedures and lacks clear ownership.
3. ASSESSMENT OF SAFETY CONSEQUENCES
There were no safety consequences to the public or the environment related to this event.
Secondary Containment ensures that the release of radioactive materials from the primary containment atmosphere will be restricted to those leakage paths and associated leak rates assumed in the safety analyses. This restriction, in conjunction with operation of the Supplementary Leak Collection and Release System (SLCRS), and Auxiliary Building Filter System will limit the SITE BOUNDARY radiation doses to within the dose guideline values of 10 CFR 50.67 during accident conditions.
SLCRS is designed to mitigate the radiological consequences of postulated accidents by filtering the exhaust air from the Secondary Containment. SLCRS is comprised of two redundant trains of exhaust fans and filter units. The safety function of SLCRS is to maintain a negative pressure in the Secondary Containment to ensure there is no unfiltered leakage to the outside environment from these areas in the event of a Loss of Coolant Accident (LOCA), other than those releases from SLCRS bypass and damper leakage accounted for in the dose analysis.
SLCRS is not normally in operation but is required to be OPERABLE in Modes 1-4. The SLCRS system starts on receipt of a Safety Injection Signal (SIS). SLCRS is required to draw down the Secondary Containment to a negative pressure within 120 seconds after the accident. The negative pressure provided by SLCRS ensures the containment releases occur through the release pathways modeled in the design basis dose analysis. The ability of SLCRS to achieve negative pressure was challenged by the door being blocked open. The door remained open for approximately 15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br />. However, the control room Operators had not logged Secondary Containment as inoperable and had not entered the appropriate Technical Specification Action Statement. The door was fully capable of being immediately closed throughout the evolution. Security was posted at the door [DR] to control access and could have closed the door [DR], if required.
The consequence of this condition with respect to the station dose analysis is established on the basis that Operations can complete the actions contained within plant Emergency Operating Procedures (EOPs) to verify that the SLCRS doors (DR) are closed, or to close the SLCRS doors within 58 minutes of a LOCA, which begins SLCRS filtration within 60
.minutes. 100 percent SLCRS bypass [i.e., no filtration and ground level release] is assumed before 60 minutes. The calculated potential dose rates to the public and control room operators from a postulated LOCA event under these conditions remains below the 10 CFR 50.67 limits. In addition, the troubleshooting performed after the event with the Secondary Containment door A-24-9 open showed slight negative pressure in the Secondary Containment with one train of SLCRS running. Therefore, this event is determined to be of low safety significance.
4. CORRECTIVE ACTION
Operations closed the door upon discovering the door blocked open and the system was restored to operable status on October 2, 2020 at 09:55. Additional corrective actions are being taken in accordance with the Corrective Action Program.
5. PREVIOUS OCCURRENCES
There was a similar occurrence at MPS3 in 2017 (LER 2017-001-00) that was due to the failure of a SLCRS door latch mechanism which prevented a door from fully closing, rendering Secondary Containment inoperable. Though similar in impact, the cause of the October 1, 2020 event is different from that of the 2017 event.
- 6. Energy Industry Identification System (EIIS) codes
- SLCRS -VF, VG, VH
- Door-DR
- Auxiliary Building - NF
- Secondary Containment - NH Page 3
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