05000416/LER-2017-009, Regarding Reactor Core Isolation Cooling System Inoperability Due to Lockout Circuit Settings
| ML18085A078 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 03/26/2018 |
| From: | Emily Larson Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| GNR0-2018-00001 LER 2017-009-00 | |
| Download: ML18085A078 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 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) 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(B) |
| 4162017009R00 - NRC Website | |
text
- ~Entergy GNR0~2018-00001 March 26, 201.8
- U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001
- Entergy Operations, Inc.
P. 0. Box756 Port Gibson, MS 39150 Eric A. Larson Site Vice President Grand Gulf Nuclear Station Tel. (601) 437-7500 10CFR50.73
SUBJECT:
Licensee Event Report 2017-009-00., Reactor Core Isolation Cooling System lnoperability Due to Lockout Circuit Settings Grand Gulf Nuclear Station, Unit 1 Docket No. 50-416 License No. NPF-29
Dear Sir or Madam:
Attached is Licensee Event Report 2017-009-00, Reactor Core Isolation Cooling Syster;n lnoperability Due to Lockout Circuit Settings. This report is being submitted in accordance with 1 OCFR50. 73(a)(2)(i)(B) for any event or condition that could have prevented the fulfillment of the safety function.
This letter contains no new commitments. If you have any questions or require additional information, please contact Douglas Neve at 601-437-2103.
- - Sincerely, z:al~
Eric A. Larson Site Vice President Grand Gulf Nuclear Station
- EA Uram
Attachment:
Licensee Event Report 2017-009-00 cc: see next page
GNR0-2018-00001 Page 2 of 2 U.S. Nuclear Regulatory Commission ATIN: Mr. Siva Lingam Mail Stop OWFN 8 81 Rockville, MD 20852-2738 NRC Senior Resident Inspector Grand Gulf Nuclear Station Port Gibson, MS 39150 U. S. Nuclear Regulatory Commission ATIN: Mr. Kriss Kennedy, NRR/DORL (w/2)
Mail Stop OWFN 8 81 Washington, DC 20555-0001
(06-2016) u:s. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
LICENSEE EVENT REPORT (LER)
(See reverse for required number of digits/characters for each block)
- 05000 416 1
- 3. PAGE Grand Gulf NuclearStation, Unit 1 1 OF 3
- 4. TITLE Reactor Core Isolation Cooling System lnoperability Due to Lockout Circuit Settings
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED YEAR I SEQUENTIAL I REV NUMBER NO.
MONTH DAY YEAR 12 12 2017 2017-009-00 MONTH DAY 03 26 YEAR FACILITY NAME NIA FACILITY NAME 2018 NIA DOCKET NUMBER 05000 N/A DOCKET NUMBER 05000 NIA
- 9. OPERA TING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
MODE1 0 20.2201 (b) 0 20.2203(a)(3)(ii) 0 50.73(a)(2)(ii)(B) 0 50.73(a)(2)(ix)(A)
D 20.2201(d)
D 20.2203(a)(4)
D 50.73(a)(2)(iii)
D 50.73(a)(2)(x)
D 20.2203(a)(1)
D 50.36(c)(1)(i)(A)
D 50.73(a)(2)(iv)(A)
D 73.71(a)(4) 11-----------1 D 20.2203(a)(2)(i)
D 50.36(c)(1)(ii)(A)
D 50.73(a)(2)(v)(A)
D 73.71(a)(5)
- 10. POWER LEVEL
.D 2022.0_3(a)(2)(ii)
D.50.3.6(c)(2)
D.5.0..73(a)(2)(v)(B)
.D.7.3.77(a)(1.)
D 20.2203(a)(2)(iii)
D 50.46(a)(3)(ii)
D 50.73(a)(2)(v)(C)
- D 73. 77(a)(2)(i) 16%
D 20.2203(a)(2)(iv)
D 50.73(a)(2)(i)(A)
D 50.73(a)(2)(v)(D)
D 73. 77(a)(2)(ii)
D 20.2203(a)(2)(v)
[gl 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D OTHER D 20.2203(a)(2)(vi)
D 50.73(a)(2)(i)(C)
D 50.73(a)(2)(viii)(A)
Specify in Abstract below 0 20.2203(a)(3)(i)
D 50.73(a)(2)(ii)(A)
D 50.73(a)(2)(viii)(B) or in =
DESCRIPTION
respond to, the information collection..
YEAR I
- 3. LER NUMBER SEQUENTIAL NUMBER 2017-009-00 I On December 12, 2017, at approximately 0918 hours0.0106 days <br />0.255 hours <br />0.00152 weeks <br />3.49299e-4 months <br />, Grand Gulf Nuclear Station (GGNS) experienced an essential transformer (ESF-11) lockout. Concurrent with the ESF-11 transformer lockout, the Reactor Core Isolation Cooling (RCIC) [BN] system received a Division I isolation signal. Leak detection NUS [NUS] temperature switches (NUS switches) for the main steam line tunnel installed in 2007 were discovered to actuate and de-actuate instantaneously upon both loss of power and upon restoration of power. The initialization sequence which occurs upon restoration of power resulted in a RCIC isolation signal. Because the condition persisted for a period of time greater than the existing logic time delay, RCIC isolation occurred.
The RCIC isolation circuits have a one second time delay to prevent spurious isolation of RCIC.
Because the sequence duration of 1.58 seconds exceeded the existing logic time delay of one second, RCIC isolation occurred. RCIC was placed back in standby at 1440 hours0.0167 days <br />0.4 hours <br />0.00238 weeks <br />5.4792e-4 months <br /> on December 12, 2017.
Analysis of the RCIC isolation initiation circuits has determined that RCIC received the isolation signal only upon restoration of power. The direct cause of RCIC isolation was the response of temperature switches to power restoration. The response, which testing has confirmed, is that the NUS temperature switches remain in the tripped state for a brief period of time when their power is restored. Because of this response the leak detection circuit begins a one second time delay to prevent spurious isolation of RCIC. Because the described condition persists for approximately 1.58 seconds, the existing one second time delay setpoint is exceeded, thereby permitting RCIC isolation.
Although the event occurred in December 2017, the final reportability was not determined until February 20, 2018, due to the time required to analyze the condition.
REPORTABILITY STATEMENT This event is reportable as a licensee event report in accordance with 1 OCFR50.73(a)(2)(i)(B) as an operation or condition which was prohibited by the plant Technical Specifications. The plant configuration that could have prevented the RCIC system from being available under all expected plant conditions existed for a time longer than allowed by Technical Specification Completion Time for the system. This event was included in ENS notification 53115.
CAUSE
In 2007 the subject RCIC temperature switches were changed from a Riley brand to a NUS brand. Discussion with the vendor determined that the observed response to loss and restoration of power to NUS switches is a design feature.
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NRC FORM (6-2016) 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />.
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 bye-mail to lnfocollects.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 OMS control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection..
- 1. FACILITY NAME
- 2. DOCKET YEAR Grand Gulf Nuclear Station, Unit 1 05000 416 NARRATIVE I
- 3. LER NUMB.ER SEQUENTIAL NUMBER 2017-009-00 I Testing confirmed that the NUS switches remain in the tripped state for approximately 1.58 seconds after their power is restored. The power bus monitor time delay relay de-energizes while the NUS switch is tripped resulting in the completion of the leak detection circuits. The
- completion of the leak detection circuit begins a 1-second time delay to prevent spurious isolation of RCIC. Because the tripped condition persists for approximately 1.58 seconds and exceeds the existing 1-second time delay setpoint of power bus monitor time delay relay, a RCIC isolation signal is generated.
- Discussion with the vendor has determined that the NUS switches cannot be modified in such a way that would prevent the observed response to loss and restoration of power from occurring In order to resolve this condition, power bus monitor time delay relays were adjusted from a 1-second delay to a 10-second delay. The relays are capable of a time delay range of 0.55 to 15 seconds, and the total time delay for the main steam tunnel RCIC isolation circuits remains below the analytical value of 30 minutes. A time delay of greater than approximately 1.58 seconds is required to prevent a RCIC isolation signal on loss and restoration of power. The increased time delay was selected to provide sufficient margin.
The cause of this event as determined to be a lack of a rigorous post modification testing plan that included all possible scenarios with the RCIC isolation initiation circuits.
CORRECTIVE ACTIONS
The power bus monitor time delay relays were adjusted from a 1-second delay to a 1 a-second delay. (Completed)
Perform a review of engineering change testing involving NUS switch installations to verify the post modification testing requirements of the Entergy testing philosophies are met. (Scheduled Completion March 2018)
SAFETY SIGNIFICANCE
While the latent design condition could have prevented the RCIC system from responding as designed, Grand Gulf analyses do not credit RCIC for mitigation of any transient or accident. In addition, using off normal procedures the operators were able to identify the cause of the isolation and restore RCIC functionality within two and a half hours. Therefore, there was no potential increase to any accident consequences, and no impact on plant safety or the safety of the public.
PREVIOUS SIMILAR EVENTS
Entergy conducted a three-year review of the relevant licensee event reports and determined that there were no similar known events.
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