05000263/LER-2015-005
| Monticello Nuclear Generating Plant | |
| Event date: | 08-3-2015 |
|---|---|
| Report date: | 10-2-2015 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| LER closed by | |
| IR 05000263/2016004 (13 February 2017) | |
| 2632015005R00 - NRC Website | |
Reported lessons learned are incorporated into the licensing process and fed back to industry.
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EVENT DESCRIPTION
On August 3, 2015, (Mode 1, at 100% power), an extent of condition review for LER 2015-003, "Use of the Reactor Water Cleanup [RWCU] System to Lower Level without Declaring an Operation with a Potential to Drain the Reactor Vessel (OPDRV) with Secondary Containment Inoperable," identified two prior occurrences where this had occurred. On May 26, 2013, during the 2013 Refueling Outage (RFO), the RWCU [CE] System was used to lower reactor cavity level with the Secondary Containment (SCT) [NH] inoperable. On February 4, 2014, during the 2014 recirculation pump seal forced outage, reactor water level was lowered in preparation for startup using the RWCU System while the SCT and the B Standby Gas Treatment (SGT) subsystem [BH] were inoperable. Each occurrence constitutes an operation or condition prohibited by the Technical Specifications (TS), during operations with a potential for draining the reactor vessel (OPDRV), which are reportable in accordance with 10 CFR 50.73(a)(2)(i)(B).
TS Specification 3.6.4.3, "Standby Gas Treatment (SGT) System," and Specification 3.6.4.1, "Secondary Containment," require the SGT System and SCT to be operable during OPDRV. NRC Enforcement Guidance Memorandum (EGM) 11-003, Revision 2, entitled, "Dispositioning Boiling Water Reactor Licensee Noncompliance with Technical Specification Containment Requirements During Operations with a Potential to Drain the Reactor Vessel," indicates that the use of the RWCU System for reactor vessel water level reductions is an OPDRV. The plant procedure, "Operations with Potential to Drain the Reactor," provides guidance on activities related to OPDRVs, including the interim actions specified in EGM 11-003, Revision 2, but incorrectly indicated that use of the RWCU System for reactor vessel level reductions was not an OPDRV.
The specifics of each reportable condition are described below.
2013 Refueling Outage (RFO 26) On May 26, 2013, from 1006 to 1321, in Mode 5 at 0% power, during the final portion of the reactor cavity draindown, the RWCU System was used to lower level from approximately 690 to 650 inches during the 2013 RFO. Contingency actions to establish secondary containment were in place during this draining activity; hence, SCT was inoperable, but available. No other systems, required during OPDRV, were identified as inoperable. Consequently, on May 26, 2013, when the RWCU System was used to lower reactor water level, with the SCT in accordance with Specification 3.6.4.1, inoperable, an operation or condition prohibited by the TS occurred.
2014 Recirculation Pump Seal Outage In late January 2014, the Monticello Nuclear Generating Plant (MNGP) was shut down to repair the 12 Recirculation Pump seal. On February 4, 2014, from 0333 to 1343, in Mode 4 at 0% power, when the RWCU System was used to lower water level in preparation for plant startup, a violation of Specification 3.6.4.1 occurred since the SCT was inoperable. The Primary Containment Exhaust Isolation to Plenum Isolation valve [ISV] was open to support restoring the Drywell Personnel Airlock interlocks. The isolation valve is a single active component with a safety function to close upon SCT isolation. If the isolation valve failed to close, the intake of both SGT subsystem fans [FAN] could be open to the Main Exhaust Plenum Room, which could prevent either SGT subsystem from exhausting sufficient flow to meet the minimum required vacuum (0.25 inches water-gage (wg)) in accordance with Surveillance Requirement (SR) 3.6.4.1.4.
This results in the B SGT subsystem and the SCT being considered inoperable (an NRC commitment).
However, both the SCT and the B SGT subsystem were available at this time as the isolation valve would close on an automatic initiation signal. Consequently, on February 4, 2014, when the RWCU System was used to lower reactor water level, with the B SGT subsystem and the SCT inoperable, in accordance with Specification 3.6.4.1, an operation or condition prohibited by the TS occurred.
EVENT ANALYSIS
These occurrences are being reported in accordance with 10 CFR 50.73(a)(2)(i)(B) as an operation or condition prohibited by the TS.
The plant procedure for controlling OPDRVs did not identify that the use of the RWCU System for performing inventory control activities involving reductions in level was an OPDRV, which resulted in unrecognized entries into OPDRVs. Consequently, this resulted in an operation or condition prohibited by the TS, since the immediate actions of Specification 3.6.4.1, "Secondary Containment," require immediate suspension of an OPDRV with the SCT inoperable.
SAFETY SIGNIFICANCE
The safety significance of these occurrences is minimal. Use of the RWCU System for draining operations is an operational function of the system. The Reactor Vessel Water Level — Low, Low isolation function automatically closes appropriate RWCU System valves to terminate a reactor vessel draindown event above the top of active fuel. Based on the timing in the outage for these events and a review of the narrative logs, it is determined that the primary containment isolation instrumentation was operable for the RWCU System during the period of the OPDRVs.
For the occurrence on May 26, 2013, an Infrequently Performed Test or Evolution briefing was conducted with all participants for the reactor cavity and dryer-separator storage pool draindown evolution, which included requirements for monitoring water levels. The SGT System was operable, and SCT was inoperable, but available, since contingency actions were in place to readily reestablish SCT if required.
During the period on February 4, 2014, when water level was lowered using the RWCU System and the Primary Containment Exhaust Isolation to Plenum Isolation valve was open, while the SCT and the B SGT subsystem are considered inoperable, the isolation valve would have closed, allowing the SGT subsystem fans to exhaust sufficient flow to meet SR 3.6.4.1.4. Therefore, while SCT and the B SGT subsystem were inoperable during this period, they were available.
CAUSE
As identified in LER 2015-003, the plant OPDRV procedure failed to provide adequate guidance to determine an OPDRV activity which resulted in actions taken that were not in accordance with NRC EGM 11-003, Revision 2.
These occurrences were identified as part of the extent of condition review performed for LER 2015-003.
CORRECTIVE ACTION
For systems having a potential to drain the reactor vessel, the OPDRV procedure has been revised to clarify use of RWCU System for steady state water level control and clearly indicate the following are OPDRV activities: use of RWCU for reactor draindown and the use of a system, even with automatic isolation operable, to lower reactor water level.
PREVIOUS SIMILAR EVENTS
A review of MNGP LERs from the last three years was performed. As part of the extent of condition review for LER 2015-003, previous occurrences were identified which are being reported herein. Also, during the 2015 RFO several OPDRV were performed that invoked the guidance of EGM 11-003, Revision 2, which were reported in LER 2015-001, "Operations with a Potential to Drain the Reactor Vessel (OPDRV) Without Secondary Containment Operable.
ADDITIONAL INFORMATION
The Institute of Electrical and Electronics Engineer codes for equipment are denoted by [XX].