05000263/LER-2019-001, RHR Decay Heat Removal Pump Start Permissive Logic Hardening Error
| ML19164A279 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 06/13/2019 |
| From: | Church C Northern States Power Company, Minnesota, Xcel Energy |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-MT-19-032 LER 2019-001-00 | |
| Download: ML19164A279 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2632019001R00 - NRC Website | |
text
fl, Xcel Energy RESP O NS I BL E B V NAT U RE June 13, 2019 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Monticello Nuclear Generating Plant Docket No. 50-263 Renewed Facility Operating License No. DPR-22 2807 West County Road 75 Monticello, MN 55362 L-MT-19-032 10 CFR 50.73 LER 2019-001-00, RHR Decay Heat Removal Pump Start Permissive Logic Hardening Error Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy hereby submits Monticello Nuclear Generating Plant (MNGP) Licensee Event Report (LER) 2019-001-00 "RHR Decay Heat Removal Pump Start Permissive Logic Hardening Error" pursuant to 10 CFR 50.73(a)(2)(i)(B) as an operation or condition which was prohibited by the plant's Technical Specification.
Summary of Commitments This letter es no new commitments and no revisions to existing commitments.
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Christopher R. Church Site Vice President, Monticello Nuclear Generating Plant Northern States Power Company - Minnesota Enclosure cc:
Administrator, Region Ill, USNRC Project Manager, Monticello Nuclear Generating Plant, USNRC Resident Inspector, Monticello Nuclear Generating Plant, USNRC
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 03/31/2020 (02-2018)
, the NRC may not conduct or sponsor, and a nerson is not renuired to resnond to the information collection.
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- 3. Page Monticello Nuclear Generating Plant 05000-263 1 OF4
- 4. Title RHR Decay Heat Removal Pump Start Permissive Logic Hardening Error
- 5. Event Date
- 6. LER Number
- 7. Report Date
- 8. Other Facilities Involved Sequential Rev Facility Name Docket Number Month Day Year Year Month Day Year Number No.
05000 04 13 2019 2019 001 00 06 13 2019 Facility Name Docket Number 05000
- 9. Operating Mode
!Abstract (Limit to 1400 spaces, i.e., approximately 14 single-spaced typewritten lines)
On April 16, 2019 at approximately 0215 with the plant shutdown in Mode 5 with the cavity flooded and fuel pool gates out, 13 Residual Heat Removal (RHR) Pump failed to start from the control room during performance of the RHR System Cold Shutdown Valve Operability Test. Investigation into the failure to start identified that hardening activities on Division 1 of RHR Shutdown Cooling (SOC) conducted on April 13, 2019 resulted in defeating remote start capability of both 11 and 13 RHR pumps. This condition caused the 11 and 13 RHR pumps to be inoperable between April 13 and April 16. With both pumps inoperable, LCOs 3.4.8, 3.9. 7 and 3.9.8 were not met and the Required Action for one or two RHR shutdown cooling subsystems inoperable requiring verification of an alternate method of decay heat removal for each inoperable RHR shutdown cooling system within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and once per 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> thereafter was not performed. This condition was determined to be reportable in accordance with 10 CFR 50. 73(a)(2)(i)(B), "Any operation or condition which was prohibited by the plant's Technical Specifications." There were no actual safety consequences from this condition. The 11 RHR pump was operating in SOC mode for the duration of the condition from when hardening was installed until the hardening error was corrected. At no time during this condition was shutdown cooling lost or not in service controlling reactor water temperature. A low pressure ECCS injection/spray subsystem was operable at all times for the duration of the condition.
NRC FORM 366 (02-2018) (04-2017)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 3/31/2020 LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r30
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. LER NUMBER YEAR Monticello Nuclear Generating Plant 05000-263 2019
EVENT DESCRIPTION
SEQUENTIAL NUMBER 001 REV NO.
00 On April 16, 2019 at 0215 with the plant shutdown in Mode 5 with the cavity flooded and fuel pool gates out, 13 (P-202C) Residual Heat Removal (RHR) Pump [P] failed to start from the control room during performance of the RHR System Cold Shutdown Valve Operability Test. Investigation into the failure to start identified that hardening activities on Division 1 of RHR Shutdown Cooling (SOC) conducted on April 13, 2019 to prevent inadvertent trips of SOC resulted in defeating remote start capability of both 11 (P-202A) and 13 (P-202C)
RHR pumps. The hardening was installed on April 13, 2019 at 1418 with the plant shutdown in Mode 4 and was corrected on April 16, 2019 at 0431 restoring the ability to start the 11 and 13 RHR pumps from the control room. Subsequently, the 11 and 13 SOC subsystems [BO] were determined to be inoperable during this time frame. However, 11 RHR pump was in service in SOC mode from April 13, 2019 at 1150 with the plant in Mode 3 prior to the installation of hardening and remained continuously in service in SOC mode throughout the condition providing the required decay heat removal.
In 2018, changes to the SOC hardening procedure were initiated to create a stand-alone procedure and to incorporate changes resulting from implementation of Technical Specification Task Force (TSTF)-542, REACTOR PRESSURE VESSEL WATER INVENTORY CONTROL, License Amendment 198. This License Amendment added LCO 3.3.5.3, Reactor Pressure Vessel (RPV) Water Inventory Control Instrumentation, identifying what instrumentation must be maintained in Modes 4 and 5 for water inventory control. Per this LCO, isolation of the Shutdown Cooling System on low water level is no longer required in Modes 4 and 5 provided isolation of the associated penetration flow path is not credited in calculating DRAIN TIME.
Consequently, changes to the hardening procedure were made to open both SOC suction valves MO-2029 [ISV] and MO-2030 [ISV] and open their associated breakers, 83333 (MO-2029, RHR S/D COOLING ISOL INBD 480) [52], and D313-07 (MO-2030, SHUTDOWN CLG OUTBD ISOL (250vdc)) [72] respectively, to prevent automatic isolation on reactor vessel low water level. However, during development of the stand-alone hardening procedure a step to install a jumper to bypass an open contact in the 11 and 13 RHR pumps remote start logic with MO-2029 breaker open did not migrate from the original procedure to the new document. The cause of this condition was inadequate rigor applied to the development and review of a new hardening procedure stemming from a narrow focus on preventing inadvertent trips of the SOC function.
EVENT ANALYSIS
The condition causing the 11 and 13 RHR pumps to be inoperable existed between April 13 and April 16 prior to identification. With both pumps inoperable, LCOs 3.4.8, 3.9.7 and 3.9.8 were not met and the Required Action for one or two RHR shutdown cooling subsystems inoperable requiring verification of an alternate method of decay heat removal for each inoperable RHR shutdown cooling system within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and once per 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> thereafter was not performed. This condition was determined to be reportable in accordance with 10 Page 2 of 4 (04-2017)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 3/31/2020 LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form http://www. n re. gov/reading-rm/doc-collections/nu regs/staff/sr1 022/r3D
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. LER NUMBER YEAR Monticello Nuclear Generating Plant 05000-263 2019 SEQUENTIAL NUMBER 001 REV NO.
00 CFR 50.73(a)(2)(i)(B), "Any operation or condition which was prohibited by the plant's Technical Specifications."
This condition is not classified as a safety system functional failure as the shutdown cooling mode of RHR is not intended to mitigate the consequences of an accident as discussed in section 6.2.3.1.2 of the USAR.
SAFETY SIGNIFICANCE
There were no actual safety consequences from this condition. The 11 RHR pump was operating in SOC mode for the duration of the condition from April 13, 2019 at 1418 when hardening was installed until April 16, 2019 at 0431 when the hardening error was corrected. At no time during this condition was shutdown cooling lost or not in service controlling reactor water temperature. A low pressure ECCS injection/spray subsystem was operable at all times for the duration of the condition.
In the event of a trip of the operating 11 RHR pump, restart of 11 RHR pump or start of 13 RHR pump from the control room would not have been possible. Operators would have responded to a loss of Division 1 SOC by attempting to establish Division 2 RHR in SOC mode via the operations manual procedure which directs the operators to remove the hardening from Division 1, place Division 2 RHR in SOC and then install the hardening on Division 2. This method would allow a Division 2 RHR pump to be started and the pump would remain operating following installation of hardening. In all cases, the ability to start an RHR pump locally at the breaker using the pushbutton for mechanical closure of the breaker was always available and unaffected by the hardening error.
In the unlikely case that no RHR pump was able to be started in shutdown cooling mode, a preliminary engineering analysis was performed for the limiting time to boil for the period between April 13, 2019 at 1418 until the plant was in Mode 5 and flooded up on April 15, 2019 at 1838. The analysis shows that the limiting time to boil was approximately 40 minutes. Additionally, the analysis shows that if boiling had occurred prior to head removal, reactor pressure would have remained below the RHR pump shutoff head for six hours, providing time for operator action to address the condition.
CAUSE
During RHR hardening activities, jumpers to provide RHR pump start permissive were not installed. Causal evaluation determined that an Operations mindset of preventing trips of Decay Heat Removal led to inadequate rigor applied to the new hardening procedure. TSTF-542 implementation supported an expanded hardening strategy including preventing trips of the SOC suction valves on low level by opening the breakers to prevent valve closure.
Reviewers of the new hardening procedure were focused on logic changes to prevent events that would result in a loss of flow (i.e., removing trips) and overlooked logic changes Page 3 of 4 (04-2017)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 3/31/2020 LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nureqs/staff/sr10221r3D
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. LER NUMBER YEAR Monticello Nuclear Generating Plant 05000-263 2019 SEQUENTIAL NUMBER 001 REV NO.
00 necessary to ensure pump permissive signals remained. Because of the "trip prevention" mindset, two individuals reviewed the changes but neither identified the omission of the needed jumper in the start logic.
A contributing cause to the procedure error was an inappropriate safety classification of the new procedure that led to inadequate procedure processing. Appropriately classifying the document would have driven additional reviews.
CORRECTIVE ACTIONS
Upon discovery of the inability to remotely start 13 RHR pump, Operations installed a jumper in the start circuitry that allowed the pump to be started from the control room. A temporary procedure change to the hardening procedure was created to add jumpers for all four RHR pumps to ensure the pump start permissives are maintained while the system is hardened.
Additional corrective actions to be implemented:
Provide Operations case study on the requisite mindset for technical rigor Perform Bypass review of the new hardening procedure in accordance with fleet procedure process Change fleet procedure process to clarify definition of Important to Safety/Augmented Quality to allow proper classification of refueling outage Controlled Documents Correct the safety classification of the hardening procedure to Augmented Quality Change fleet 50.59 procedure to clarify that application of Notes does not supersede Regulatory Review for changes to SSCs important to safety
PREVIOUS SIMILAR EVENTS
LER 2017-006-00, Loss of Reactor Protection System Scram Function During Main Steam Isolation Valve and Turbine Stop Valve Channel Functional Tests Due to Use of a Test Fixture, reported a condition where revision of procedures to use the Reactor Protection System (RPS) test fixture resulted in the loss of two RPS reactor scram functions. The cause of this error was attributed to procedures that were inappropriately revised due to an inaccurate mental model that the use of the test fixture could be used to bypass any function within a trip logic to prevent a half scram. This was considered a legacy issue that occurred circa 2009 and the individuals involved in the issue were no longer in the organization. Therefore, additional corrective actions beyond correcting the procedure error were not performed.
ADDITIONAL INFORMATION
The Institute of Electrical and Electronics Engineer codes for equipment are denoted by (XX]. Page 4 of 4