05000370/LER-2015-001
| Mcguire Nuclear Station, Unit 2 | |
| Event date: | 10-07-2015 |
|---|---|
| Report date: | 12-07-2015 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| LER closed by | |
| IR 05000369/2015004 (21 January 2016) | |
| 3702015001R00 - NRC Website | |
BACKGROUND:
This event is being reported under the following criterion:
10 CFR 50.73(a)(2)(iv)(A), for any event or condition that resulted in automatic actuation of the PWR auxiliary feedwater system.
The Auxiliary Feedwater (CA) System [EIIS: BA] automatically supplies feedwater to the SGs to remove decay heat from the Reactor Coolant (NC) System [EIIS: AB] upon the loss of Main Feedwater (CF) System supply [EIIS:SJ]. The CA pumps [EIIS: P] take suction from the CA System Storage Tank (CAST) [EIIS: KA] and pump to the Steam Generator (SG) secondary side.
The CA System consists of two motor driven CA pumps (MDCAP)s and one steam turbine driven pump (TDCAP), configured into three trains. Each of the MDCAPs supplies 100% of the flow requirements to two of the four SGs, and each MDCAP has the capability to be realigned to feed the other SGs. The TDCAP provides 200% of the flow requirements and supplies water to all four SGs. Each MDCAP is powered from an independent Class 1 E power supply. The TDCAP receives steam from two Main Steam (SM) System [EIIS: SB] lines upstream of the Main Steam isolation valves [EIIS:SA]. Each of the steam feed lines will supply 100% of the requirements of the TDCAP. The SGs function as a heat sink for core decay heat, and the CA System is designed to supply sufficient water to the SGs to remove decay heat. The CA System is capable of supplying feedwater to the SGs during normal unit startup, shutdown, and hot standby conditions. The MDCAPs actuate automatically on SG water level Lo-Lo in one out of four SGs by the Engineered Safety Features Actuation System (ESFAS) [EIIS:JE]. The MDCAPs also actuate on loss of offsite power, safety injection, ATWS (Anticipated Transients Without Scram) Mitigation System Actuation Circuitry (AMSAC) and trip of all CF pumps. The TDCAP actuates automatically on SG water level Lo-Lo in two out of four SGs and on loss of offsite power.
Technical Specification 3.7.5 governs the CA System. Limiting Condition of Operation 3.7.5 requires three CA trains to be operable in Modes 1, 2, and 3. In Mode 4 when the SGs are relied upon for heat removal, one motor driven CA train is required to be operable.
NRC FORM 3. 66A U.S. NUCLEAR REGULATORY COMMISSION .- No" ",0,413.
- ,r. ( i LICENSEE EVENT REPORT (LER)
- CONTINUATION SHEET APPROVED BY OMB: NO. 3150:0104 EXPIRES: 01/31/2017 Reported lessons learned are incorporated into the licensing process and fed back to industry.
Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by Internet e-mail to infocollects Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- McGuire Nuclear Station, Unit 2 05000370 _ - : 2015 _ 01 _ 00
EVENT DESCRIPTION:
On October 7, 2015, an actuation of the CA system occurred while Unit 2 was in Mode 4 and operators were restoring from testing the 2A Train Solid State Protection System (SSPS) Safety Injection (SI) trip functions for the Main Turbine and the CF pump turbines. The testing was performed under the guidance of procedure PT/2/N4200/026A, "Turbine and Main Feedwater Pump Turbine (MFWPT) Trips from SSPS".
The CA actuation caused the 2A CA train flow control valves to fully open. The signal also caused the associated SG sampling and blowdown valves to close. The actuation occurred as designed and there was no adverse impact to plant operation.
The operating crew responded to the 2A CA Auto Start signal and managed SG levels by taking manual control of the 2A CA flow control valves. Affected components were aligned for the plant conditions using normal operating procedures. Nuclear Safety was not impacted by this event.
During and after SSPS testing, the CF pumps were shut down and SG levels were being maintained by the 2A and 2B MDCAPs. During restoration-from SSPS testing, a conditional step in the procedure did not clearly require the reset of at least one CF pump. Leaving both CF pumps in the tripped state provided the logic for the CA actuation signal (trip of all CF pumps). However, the actuation signal was blocked until the 2A CA auto start defeat switch was placed in "reset" during restoration by the test procedure. The test procedure should have ensured that at least one CF pump was reset frOm the tripped state before the 2A CA Train auto start defeat switch was placed in "reset".
The CA actuation occurred during the performance of PT/2/A/4200/026A, "Turbine and MFWPT Trips from SSPS", system restoration section. When the CA Auto Start Defeat switch was placed in "reset", with both CF Pumps in the tripped condition, the trip of all CF pumps signal was enabled. The trip of all CF pumps provides protection for a loss of main feedwater. SG levels were being maintained by the MDCAPs, and therefore, plant conditions did not require the CA actuation.
Use of PT/2/A/4200/026A and the testing that resulted in the CA actuation have been successfully performed in the past; however, performance of the test usually occurs before completion of .
OP/2/A/6250/002, "Auxiliary Feedwater System"- enclosure 4.1, "Alignment for Standby Readiness" with in operation. The re-sequencing of these activities exposed the deficiency in PT/2/A/4200/026A, which resulted in the CA actuation.
Sequence of Events
CF
Date/Time Activity 10/6/15 / 1350 Unit 2 entered Mode 4 10/7/15 / 0027 CA Aligned for Standby Readiness (OP/2/N6250/002) 10/7/15 / 0600 Turbine and MFWPT Trips from SSPS started (PT/2/A/4200/026A) 10/7/15 / 0630 Turnover occurred to Dayshift (realignment from test not complete) 10/7/15 / 0655 Unblocked 2A CA Auto Start Defeat per PT/2/A/4200/026 A (2A CA Actuation) APPROVED BY OMB: NO. 3150-0104 EXPIRES: 01/31/2017 Reported lessons learned are incorporated into the licensing process and fed back to industry.
Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to infocollects Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
CAUSAL FACTORS:
The cause of this event was a procedure weakness that did not clearly define the CF pump restoration conditions after testing was complete.
PT/2/A14200/026A has been performed successfully in the past. In this instance, the CA system was aligned for Standby Readiness before the PT was performed. This set up conditions that had not been present during previous performances of the PT, which led to the CA actuation. As a result of the SSPS test, both CF pumps were still tripped. The test procedure did not realign at least one CF pump to the as-found ("reset") condition during restoration after testing was complete. In this event, because the CA system was aligned for Standby Readiness when the test was performed, the test procedure should have ensured the as-found condition was "reset" on at least one of the CF pumps. The procedure did not account for the CA system to be aligned for Standby Readiness even though the procedure tripped the CF pumps in a previous step. Without placing at least one CF pump in "reset" before resetting the CA auto start defeat switch to "reset" allowed the CA actuation to occur. Adequate guidance was missing for proper performance of step 12.4.20 in the test procedure.
CORRECTIVE ACTIONS:
Immediate:
1. Operators took manual control of CA control valves and restored plant conditions.
2. The affected test procedures were placed on Administrative Hold to prevent use until revised.
Planned:
1. PT/1/A/4200/026A and PT/2/A/4200/026A, "Turbine and MFWPT Trips from SSPS" will be revised to ensure this event does not reoccur.
APPROVED BY OMB: NO. 3150-0104 EXPIRES: 01/31/2017 . - Reported lessons learned are incorporated into the licensing process and fed back to industry.
Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by Internet e-mail to infocollects Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
SAFETY ANALYSIS:
At the time of the CA system actuation, the CF system was shut down and the CA system was supplying feedwater to the SGs. No actual loss of feedwater occurred. The plant was returning from a refueling outage with low decay heat level due to the extended shutdown and new fuel in the reactor. Decay heat removal using the SGs was not challenged. The signal (trip of all CF pumps) that caused the CA actuation was not required to be operable in Mode 4. The signal is required by TS 3.3.2 to be operable in Modes 1-3 only.
In conclusion, this event is considered to be of low safety significance. The CA system responded as designed. This event was of no significance to the health and safety of the public.
ADDITIONAL INFORMATION:
A three year search of the McGuire corrective action database revealed no other CA actuation events resulting from a latent procedural deficiency. Therefore, this event is not recurring.
This event is not considered to constitute a Safety System Functional Failure. This event only involved the actuation of the CA System. It was determined through the extent of condition review that the condition described in this LER affects both CA Trains on both units. The planned action will address the extent of condition. There was no release of radioactive material, radiation overexposure, or personnel injury associated with the event described in this LER.