05000483/LER-2022-002, Containment Spray and Cooling Systems, and a Condition Which Could Have Prevented Fulfillment of the Safety Function of the Containment Spray System
| ML22230C934 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 08/18/2022 |
| From: | Ameren Missouri, Union Electric Co |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML22230C932 | List: |
| References | |
| ULNRC-06759 LER 2022-002-00 | |
| Download: ML22230C934 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| 4832022002R00 - NRC Website | |
text
Abstract
On June 21, 2022 during performance of the B Train Containment Spray (CS) Pump lnservice Test quarterly surveillance, the discharge pressure of the 8 CS Pump failed to meet its Technical Specification (TS) minimum allowable value. A valve lineup for the 8 CS train identified that the CS Pump 8 Recirculation Throttle Valve, ENV0127, was locked open instead of its correct position, locked closed. Subsequently, ENV0127 was placed in the correct locked-closed position, and the 8 Train CS Pump lnservice Test quarterly surveillance was re-performed with results meeting the acceptance criteria.
Investigation determined that ENV0127 was last positioned on May 11, 2022 during a fill-and-vent operation of the 8 CS rain when the plant was shutdown, after which ENV0127 was not properly restored to a locked-closed position. A review
!Of past operation determined that the condition resulted in the failure to meet TS Limiting Condition of Operation 3.6.6 from May 23, 2022, when the plant entered the mode of applicability at 0601, until ENV0127 was restored on June 21, 2022 at 1000.
rThe cause of this error was determined to be a failure of Operations Technicians to appropriately utilize human performance event prevention tools prior to operating ENV0127 during the fill-and-vent restoration activity and ensure ENV0127 was returned to the appropriate configuration. As a corrective action, the Operations staff will receive training on the requirements, expectations, and tools to ensure plant equipment is positioned correctly.
- 1.
DESCRIPTION OF STRUCTURE(S), SYSTEM(S), AND COMPONENT(S)
YEAR 2022 SEQUENTIAL NUMBER
- - 002 The systems and components affected by this event include the 8 Train of the Containment Spray (CS) System [EIIS:BE].
REV NO.
- - 00 The CS System at Callaway Plant is responsible for providing containment atmosphere cooling to limit post-accident containment pressure and temperature to less than the design values. Additionally, reduction of containment pressure and the iodine removal and retention capability of the spray reduces the release of fission product radioactivity from containment to the environment, in the event of a Design Basis Accident, to within limits. The CS System consists of two separate trains of equal capacity, each capable of meeting the design bases.
- 2.
INITIAL PLANT CONDITIONS
Callaway Plant was in MODE 1 at approximately 100% rated thermal power at the time of discovery of this event. No major safety related systems were out of service at the time of discovery of the event, with the exception of the 8 Train CS System, which was inoperable for the surveillance testing leading to discovery of the event. The condition which led to this event occurred when the plant was in MODE 6, Cold Shutdown.
- 3.
EVENT DESCRIPTION
On June 21, 2022 Operations performed OSP-EN-P001 B, Train 8 Containment Spray Pump lnservice Test," to run the B Containment Spray Pump for a quarterly surveillance. During the test the discharge pressure of the 8 CS Pump was identified as 225 psig, which is lower than the Technical Specification (TS) minimum discharge pressure of 250 psig. Operations staff walked down the valve lineup for the 8 CS train and identified that ENV0127, Containment Spray Pump 8 Recirculation Throttle Valve, was not in the correct position. The normal TS-required position of ENV0127 is locked closed, but ENV0127 was found locked open.
Operations repositioned ENV0127 to its correct position and reperformed OSP-EN-P0018, resulting in meeting the acceptance criteria with a discharge pressure of 255 psig.
After investigation, it was determined that ENV0127 was last positioned during Refueling Outage 25, during a fill-and-vent operation for the 8 CS train on May 11, 2022. During this operation, restoration steps directed that ENV0127 be locked-closed; however, the valve was mistakenly left in a locked-open position.
On May 23, 2022 at 0601, the plant entered MODE 4, which is one of the the Modes of applicability for TS Limiting Condition of Operation (LCO) 3.6.6, "Containment Spray and Cooling Systems" (Modes 1, 2, 3, 4). Callaway Plant remained in a Mode of applicability for TS LCO 3.6.6 from that time on, including when the condition was discovered on June 21, 2022.
With respect to opposite Train A of the CS System, the period of operation from May 23 through June 21, 2022 was reviewed for concurrent inoperability of both trains. Train 'A' of the CS System was inoperable for planned surveillance activities on June 1, 2022, from 0346 until 0601 that day.
An extent-of-condition review was performed per the Callaway Plant Corrective Action Program under Condition Report (CR) 202204246 as part of the causal investigation for this event to ensure other similar valves were not subject to similar positioning errors. Of the five similar-style valves, i.e., those with 90-degree operators oriented in a similar manner that could lend themselves to possible mispositioning and which are installed in safety related systems, none were identified with a similar mispositioning issue.
- 4.
ASSESSMENT OF SAFETY CONSEQUENCES
There were no actual nuclear, radiological, or personnel safety impacts associated with this event. The potential impact was on radiological safety with respect to ensurinq that the function of the CS system was met, if a transient had occurred that required the Page i of~ (08-2020)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 08/31/2023 LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET
- 3. LER NUMBER YEAR Callaway Plant Unit 1 05000-483 2022 SEQUENTIAL NUMBER
- - 002 REV NO.
- - 00 system's function during the period when TS LCO 3.6.6 was not met. A review of plant parameters and system capability performed by Callaway Engineering determined that even though the 8 CS train was degraded during the period ENV0127 was locked-open, adequate flow would still have been delivered had the system been called upon to respond to an actual event, i.e, the safety functions of the system remained met. Additionally, with the exception of the time period on June 1 from 0346 to 0601, Train 'A' of the CS System remained operable throughout the affected period.
- 5.
REPORTING REQUIREMENTS
This LER is submitted pursuant to 10 CFR 50. 73{a}(2){i)(B) to report a condition prohibited by TS LCO 3.6.6, "Containment Spray and Cooling Systems," which was not met from May 23, 2022 when the plant entered the Mode of Applicability (Modes 1, 2, 3, 4),
until the time when ENV0127 was restored to its correct configuration of locked closed at 1000 on June 21, 2022.
This LER is also submitted pursuant to 10 CFR 50. 73(a}{2)(v)(C) and (0) as an event which could have prevented fulfillment of a safety function of a system that is needed to control the release of radioactive material and mitigate the consequences of an accident, since both 'A' and 8 Trains of CS were concurrently inoperable from June 1, 2022 at 0346 until 0601 the same day, when the 'A' Train was removed from service for planned surveillance testing.
Based on the satisfactory results of the flow analysis performed for this event, this event does not represent a safety system functional failure per the reporting guidelines of NEI 99-02, Revision 7, "Regulatory Assessment Performance Indicator Guideline,"
for the purpose of the NRC Reactor Oversight Process Performance Indicator Program.
- 6.
CAUSE OF THE EVENT
The cause of the event was the failure of Operations Technicians to appropriately use human performance event prevention tools prior to operating equipment. Specifically, in restoring the 8 CS Train from the fill-and-vent operation on May, 11, 2022, ENV0127 was left in a locked-open position instead of the appropriate locked-closed position.
- 7.
CORRECTIVE ACTIONS
Corrective Actions taken in response to this event include repositioning ENV0127 to the appropriate locked-closed configuration, which was completed on June 21, 2022 at 1000.
Corrective Actions planned in response to this event include providing training to Operations to reinforce requirements, expectations, and tools to ensure SSCs are positioned correctly. This corrective action is currently planned for completion by September 30, 2022.
- 8.
PREVIOUS SIMILAR EVENTS
A review of internal operating experience was performed as part of the cause evaluation process and identified the following similar events:
CR 199900079 identified a broken locking device for a similar component (valve) in a different system, EGV0004, Component Cooling Water Pump A Discharge Isolation. This event was reviewed and determined to have dissimilar causal factors when compared to the subject event of this LER.
LER 2018-001-00 reported an event involving mispositioning of manual containment isolation valve KA V0118, Service Air Containment Supply Outer Isolation Valve, due to inadequate procedural control to ensure the valve was in the correct position prior to plant startup from Refueling Outage 22. Page~ of~ (08-2020)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 08/31/2023
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rr_j LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET
- 3. LERNUMBER YEAR Callaway Plant Unit 1 05000-483 2022 SEQUENTIAL NUMBER
- - 002 REV NO.
- - 00 CR 201802129 documents a valve misposition for KA V0600, Instrument Air Branch Isolation to Auxiliary Boiler Fuel Module. This valve is of a different design than ENV0127, but the valve similarly does not have position indication and is also in an unusual orientation to operate. This event is similar in that multiple operators performed an incorrect postion verification of the valve, ultimately resulting in the valve being left in a closed position instead of the required open position. Page~ of~