05000254/LER-2018-005, Loss of Safety Bus and Automatic Actuation of a Safety System During Undervoltage Relay Surveillance
| ML18355A350 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 12/21/2018 |
| From: | Ohr K Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| SVP-18-090 LER 2018-005-00 | |
| Download: ML18355A350 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(iv)(B), System Actuation 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) |
| 2542018005R00 - NRC Website | |
text
~ Exelon Generation SVP-18-090 December 21, 2018 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Quad Cities Nuclear Power Station, Unit 1 Renewed Facility Operating License No. DPR-29 NRC Docket No. 50-254 10 CFR 50.73
Subject:
Licensee Event Report 254/2018-005-00 "Loss of Safety Bus and Automatic Actuation of a Safety System During Undervoltage Relay Surveillance" Enclosed is Licensee Event Report (LER) 254/2018-005-00, "Loss of Safety Bus and Automatic Actuation of a Safety System During Undervoltage Relay Surveillance", for Quad Cities Nuclear Power Station, Unit 1.
This report is submitted in accordance with 1 O CFR 50.73(a)(2)(iv)(A) for an event or condition that results in manual or automatic actuation of any of the systems listed in paragraph 1 O CFR 50.73(a)(2)(iv)(B). This report is submitted also in accordance with 1 O CFR 50.73(a)(2)(v)(B) for an event or condition that could have prevented fulfillment of the safety function of structures or systems that are needed to remove residual heat.
There are no regulatory commitments contained in this letter.
Should you have any questions concerning this report, please contact Mark Humphrey at (309) 227-2800.
Res/¥ Kenneth S. Ohr Site Vice President Quad Cities Nuclear Power Station cc:
Regional Administrator - NRC Region Ill NRC Senior Resident Inspector-Quad Cities Nuclear Power Station
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150*0104 EXPIRES: 03/31/2020 (04-2018)
, the NRG may not conduct or sponsor, and a Q,.***""'
person is not required to respond to, the infonnation collection.
3.Page Quad Cities Nuclear Power Station Unit 1 05000254 1
OF 5
- 4. Title Loss of Safety Bus and Automatic Actuation of a Safety System During Undervoltage Relay Surveillance
- 5. Event Date
- 6. LER Number
- 7. Report Date
- 8. Other Facilities Involved I
Sequential I Rev Facility Name Docket Number Month Day Year Year Number No.
Month Day Year n/a 05000 Facility Name Docket Number 10 24 2018 2018 - 005 00 12 21 2018 n/a 05000
- 9. Operating Mode
- 11. This Report is Submitted Pursuant to the Requirements of 10 CFR §: (Check all that apply)
D 20.2201(b)
D 20.2203(a)(3)(i)
D 50. 73(a)(2)(ii)(A)
D 50.73(a)(2)(viii)(A)
D 20.2201(d)
D 20.2203(a)(3)(ii)
D 50.73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B) 1 D
D 20.2203(a)(1) 20.2203(a)(4)
D 50.73(a)(2)(iii)
D 50.73(a)(2)(ix)(A)
D 20.2203(a)(2)(i)
D 50.36(c)(1)(i)(A)
~ 50.73(a)(2)(iv)(A)
D 50.73(a)(2)(x) 1 O. Power Level D 20.2203(a)(2)(ii)
D 50.36( c)( 1 )(ii)(A)
D 50.73(a)(2)(v)(A)
D 73.71(a)(4)
D 20.2203(a)(2)(iii)
D 50.36(c)(2)
~ 50.73(a)(2)(v)(B)
D 73.71(a)(5)
D 20.2203(a)(2)(iv)
D 50.46(a)(3)(ii)
D 50.73(a)(2)(v)(C)
D 73.77(a)(1) 100 D 20.2203(a)(2)(v)
D 50.73(a)(2)(i)(A)
D 50.73(a)(2)(v)(D)
D 73.77(a)(2)(i)
D 20.2203(a)(2)(vi)
D 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 73.77(a)(2)(ii)
D 50.73(a)(2)(i)(C)
D Other (Specify in Abstract below or in
- 3. LER NUMBER SEQUENTIAL NUMBER 005 REV NO.
00 3.5.1 Condition B for the A and B Low Pressure Coolant Injection (LPCI) sub-systems and the A Core Spray sub-system.
3.5.1 Condition E for two LPCI sub-systems 3.5.1 Condition K for A and B LPCI sub-systems and CS sub-system 3.0.3 as directed by 3.5.1 Condition K 3.5.3 Condition A for Reactor Core Isolation Cooling (RCIC) System due to Room Cooler 3.8.1 Condition A for off-site line unavailable to Bus 13-1 3.8.1 Condition D for off-site line and the 1 /2 EDG unavailable 3.8. 7 Condition A for Bus 13-1 and Bus 18 Unit 1 also remained in TS LCO 3.8.1 (b) until the 1/2 EDG was restored.
This event was reported under 10 CFR 50.72(b)(3)(iv), 'Event or Condition that results in valid actuation of any of the systems listed in paragraph (b)(3)(iv)(B),' because the 1/2 EDG auto started due to the loss of power condition, and 1 O CFR 50.72(b)(3)(v)(B), 'Event or Condition that Could Have Prevented Fulfillment of a Safety Function,' because both loops of LPCI were inoperable for a short time period.
C. CAUSE OF EVENT
The most probable cause of the event was a testing-induced ground on a surveillance related terminal in conjunction with a DC system ground that actuated two auxiliary relays associated with the undervoltage monitoring function.
A short duration (approximately 1.5 seconds) U1 125 VDC Ground alarm on the positive battery rail was received roughly 23 seconds prior to the loss of Bus 13-1. The magnitude of the ground decreased below the alarm threshold, but did not fully dissipate for an hour after the alarm.
The undervoltage surveillance already in progress had installed a jumper into a banana jack at a terminal point designated YG8, but the other end of the jumper had not yet been installed into a banana jack. A review of the sequence of events recorder indicates that only two of four parallel relays picked up momentarily, likely caused by the positive rail DC ground condition, and the YG8 jumper causing a momentary short to ground on the negative side of these relay coils. Relay 1 X3 pick up caused a Low Voltage alarm and initiated the trip of the feed breaker to Bus 13-1. Relay 1X4 pick up caused a start signal to the 1/2 EDG. The two parallel relays, 1X1 and 1X2, did not appear to pick up based on the lack of equipment status changes related to these two relays.
Troubleshooting following the event did not reveal any human performance issues nor any equipment issues. A subsequent re-performance of the test did not result in any unexpected equipment issues.
Additional inspections and troubleshooting of normally energized equipment will take place during the next refuel outage. A supplemental report will be submitted based on those results.
D. SAFETY ANALYSIS
System Design
Bus 13-1 is the Division I 4KV AC supply to the Division 1 Emergency Core Cooling System (ECCS) loads on Unit 1. It can be fed by an EDG if the normal feed from the Reserve Auxiliary Transformer is lost. Bus 18 is a YEAR 2018 -
- 3. LEA NUMBER SEQUENTIAL NUMBER 005 480 V essential services (ESS) bus. Undervoltage protection is provided to protect equipment from sustained degraded voltage, and for the ECCS related busses, to start the applicable EDG.
Safety Impact No Division II ECCS equipment was impacted by this event.
REV NO.
00 Bus 13-1 was unavailable for approximately 10 minutes. No significant plant transients took place during this time period.
The trip of Bus 13-1 took place during surveillance testing on the undervoltage trip circuit. The subsequent surveillance test was completed satisfactorily with additional circuits isolated to preclude inadvertent tripping of Bus 13-1. No further testing will be performed on this protective relaying circuit until the next refuel outage.
The 1/2 EDG started, but did not load to the bus as a result of intentional test configurations. Following the surveillance, logic was returned to a normal configuration, and post maintenance testing was satisfactorily performed on the 1/2 EDG.
DC system grounds are routinely monitored per station procedures.
Based on this, no significant safety impact exists.
Risk Insights A plant Probabilistic Risk Assessment (PRA) review was performed to evaluate Bus 13-1 and Bus 18 being de-energized, and also evaluated the 1/2 EDG cooling water pump failure to start despite the EDG starting.
While risk-significant functions were impacted, the condition lasted only a few minutes. A model reflecting plant conditions resulted in Core Damage Frequency and Large Early Release Frequency both well below the 1 E-07 threshold for significance.
This is a Maintenance Rule Functional Failure.
In conclusion, the overall safety significance and impact on risk of this event were minimal.
E. CORRECTIVE ACTIONS
Immediate:
- 1.
Bus 13-1, Bus 18, and other equipment was recovered.
- 2.
The surveillance was re-performed with satisfactory results utilizing temporary revised procedural guidance to block trip signals to the bus by opening knife switches.
Follow-up:
- 1.
Perform troubleshooting and verifications of Bus 13-1 Cubicle 2 during the next refuel outage.
- 2.
Implement permanent procedure revisions to open knife switches prior to relay testing to preclude the bus trip.
F.
PREVIOUS OCCURRENCES
The station events database and LERs were reviewed for similar events at Quad Cities Nuclear Power Station in the last 1 O vears. One LER, 265/2011-001-00, described a loss of the Unit 2 ESS Bus due to inadvertent contact with the bus feed breaker local trip pushbutton by a station employee during unrelated work in the areas. While both events resulted in the loss of an important bus, there is no apparent connection or unresolved vulnerabilities identified between the two events.
G. COMPONENT FAILURE DATA
No equipment failure has been identified. Information below is for the relays that were inadvertently actuated.
Equipment: HFA Multicontact Auxiliary Relay Component Manufacturer: General Electric Component Model Number: HFA Component Part Number: 12HFA151A2F This event has been reported to ICES.
00 Page _5_ of _5_