05000321/LER-2021-002, Low Pressure Coolant Injection Inoperable Longer than the Allowed Technical Specification Completion Time
| ML21274A738 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 10/01/2021 |
| From: | Dean S Southern Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NL-21-0850 LER 2021-002-00 | |
| Download: ML21274A738 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3212021002R00 - NRC Website | |
text
~ Southern Nuclear October 1, 2021 ATTN: Docum~nt Control Deik U.S. NueJegJr Regul~tory Comml$slon Washington, DC 20555---0001 Sonny Do n Vice Pro ident - Plant Hatch Edwin L H~teh Nuele~r Pl~nt e Unit 1 Licensee ~vent Report 2021°002°00 Low Pressure Coolant lnjeetkm Inoperable Hatch Nuclear Plant 11028 Hatch Park,tJy North Bal<ley, OA 31513 912 537 5859 lei 912 388 2017 fl)l(
Longer th~ril the Allowed Teetmieal Speelficatiolil Compl~tion Time In ~ecordg1nce with th requiremenui of 10 CrR S0.73(i)(2)(i)(B), Southern Nuele~r Operg1tlng Company hereby $Ybmits the ene!o£ed Lleen$ Ev~f'lt R~port.
This letter eemtihli no NRC eommitmenui. If you h~ve imy qu~stlon~. ple~se eontillet the Plant H~tch Licensing Manillg~r, Jimmy Collins, it 912.453.2342.
SD/CJC ee:
NRC Region~! Administrg;]tor ~ Region ll NRR Project Mg1n~ger = Pl'1!11t Hatch NRC Senior Re$idtmt Inspector~ Pl~nt H~tch RTYPE: CHA02.004
Edwin I. Hatch Nuclear Plant - Unit 1 Licensee Event Report 2021-002-00 Low Pressure Coolant Injection Inoperable Longer than the Allowed Technical Specification Completion Time Enclosure LER 2021-002-00
Abstract
On 08/03/2021 at 11 :50 EDT, while Unit 1 was at 0% power and in MODE 3 following an unplanned reactor SCRAM, the 'B' reactor recirculation discharge isolation valve failed to initially close when required to do so during the restart of the 'A' reactor recirculation pump. The safety function of the reactor recirculation discharge isolation valve is to ensure that Low Pressure Coolant Injection (LPCI) flow does not bypass the core when it injects into the recirculation lines as described in Technical Specification (TS) Bases 3.3.5.1.
Further investigation revealed that a loose fuse connection caused intermittent contact within the control power circuitry, resulting in the valve being unable to reliably function. Because the same intermittent position indication of the 'B' reactor recirculation discharge isolation valve was identified on 07/05/2021, it is likely that the reactor recirculation discharge isolation valve and subsequently the 'B' LPCI loop was inoperable for longer than allowed by TS 3.5.1. The corrective action to replace the loose bayonet connectors for the fuse holders has been completed.
This condition is reportable per 10 CFR 50.73(a)(2)(i)(B).
EVENT DESCRIPTION
At approximately 11 :50 EDT on 08/03/2021, while Unit 1 was at 0% power and in MODE 3 following an unplanned SCRAM, the 'B' reactor recirculation pump discharge valve (1B31-F031B) [EIIS Code: AD, ISV] was taken to the closed position per procedure during the restart of the 'A' reactor recirculation pump. Light indication immediately extinguished as soon as the 1 B31-F031 B switch was taken to the closed position. Maintenance was dispatched and reported that neither the breaker or overloads were tripped. A few seconds later the light indication came on and the 1 B31-F031 B valve was successfully closed.
EVENT CAUSE ANALYSIS
The site's investigation into the brief loss of control power indication revealed that the continuity issues were the result of a loose bayonet connector in the fuse holder for fuse 1 B31-F239. The loose bayonet connector was most likely caused by the maintenance troubleshooting activities performed on 07/05/2021 for a failed MOV motor. The prior troubleshooting activities included the removal and re-installation of both control fuses for the 1B31-F031B valve, which likely loosened the bayonet connectors.
A loose bayonet connector would have caused the power supply to the control circuit of the 1 B31-F031 B valve to become intermittent, and would have ultimately prevented stroking the 1B31-F031B valve when the switch was placed in the closed position.
REPORTABILITY AND SAFETY ASSESSMENT
The normal position for the 1B31-F031 B valve is open with an active safety function to close. This safety function ensures that Low Pressure Coolant Injection (LPCI) [EIIS Code: BO] flow does not bypass the core when it injects into the recirculation lines as described in Technical Specification (TS) Bases 3.3.5.1, and provides for core cooling and reactor coolant pressure boundary integrity. With unreliable control circuitry continuity, the closure of valve 1B31-F031B could not be guaranteed during a Loss of Coolant Accident (LOCA). and thus provided reasonable assurance that operability could not be maintained.
Because the operation of valve 1B31-F031B was unreliable from at least 07/05/2021 through 08/05/2021, the 'B' LPCI loop would have been inoperable for a period of time longer than allowed by Condition B of TS Limiting Condition of Operation (LCO) 3.5.1.
The were no safety consequences as a result of this event. The other low pressure Emergency Core Cooling Systems, the 'A' loop of LPCI and both Core Spray pumps [EIIS Code: BM], remained operable through the event.
CORRECTIVE ACTIONS
The 'B' LPCI loop was declared inoperable, and the loose bayonet connectors for the fuse holders were replaced (control fuses 1B31-F239 and 1B31-F240) on 08/05/2021.
PREVIOUS SIMILAR EVENTS
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