05000499/LER-2018-001, Condition Prohibited by Technical Specifications That Could Have Prevented the Fulfillment of a Safety Function Due to Two Inoperable Extended Range Monitors
| ML18144B014 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 05/24/2018 |
| From: | Connolly J South Texas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NOC-AE-18003577 LER 2018-001-00 | |
| Download: ML18144B014 (9) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 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)(iv)(A), System Actuation 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)(B), Loss of Safety Function - Remove Residual Heat 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) |
| 4992018001R00 - NRC Website | |
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May 24, 2018 NOC-AE-18003577 10 CFR 50.73 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555-0001 South Texas Project Unit2 Docket No. STN 50-499 Licensee Event Report 2018-001-00 Unit 2 Condition Prohibited by Technical Specifications That Could Have Prevented the Fulfillment of a Safety Function Due to Two Inoperable Extended Range Monitors Pursuant to reporting requirements 10 CFR 50. 73(a)(2)(i)(B) and 10 CFR 50. 73(a)(2)(v)(A) and (D},
STP Nuclear Operating Company hereby submits the attached South Texas Project Unit 2 Licensee Event Report 2018-001-00 for a condition prohibited by the plant Technical Specifications that could have prevented the fulfilment of a safety function.
Additional evaluation is ongoing to confirm whether this event resulted in a condition that could have prevented the fulfilment of a safety function. A supplement to this Licensee Event Report will
- be submitted once this evaluation is complete.
The event did not have an adverse effect on the health and safety of the public.
There are no commitments in this submittal.
If there are any questions, please contact Mr. Drew Richards at 361-972-7666 or me at 361-972-7344.
amr/JC James Connolly Site Vice President Attachment: Unit 2 LER 2018-001-00, Unit 2 Condition Prohibited by Technical Specifications That Could Have Prevented the Fulfillment of a Safety Function Due to Two Inoperable Extended Range Monitors STl34673696
cc:
(paper copy)
Regional Administrator, Region IV U.S. Nuclear Regulatory Commission 1600 East Lamar Boulevard Arlington, TX 76011-4511 Lisa M. Regner Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint North (09E01) 11555 Rockville Pike Rockville, MD 20852 NRC Resident Inspector U.S. Nuclear Regulatory Commission P. 0. Box 289, Mail Code: MN116 Wadsworth, TX 77 483 NOC-AE-18003577 Page 2 of2
Attachment Unit 2 LER 2018-001-00 NOC-AE-18003577 Attachment Unit 2 Condition Prohibited by Technical Specifications That Could Have Prevented the Fulfillment of a Safety Function Due to Two Inoperable Extended Range Monitors
NRCFORM366 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 oerson is not reauired to resoond to the information collection.
- 13. Page South Texas Unit 2 05000499 1 OF6
- 4. Title Condition Prohibited by Technical Specifications That Could Have Prevented the Fulfillment of a Safety Function Due to Two Inoperable Extended Range Monitors
- 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 N/A Number No.
05000 03 25 2018 2018 001 00 05 24 2018 Facility Name Docket Number N/A 05000
- 9. Operating Mode
- 11. This Report is Submitted Pursuant to the Requirements of 10 CFR §: (Check all that apply) 3 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)
D 20.2203(a)(1)
D 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) 0 50.73(a)(2)(iv)(A)
D 50.73(a)(2)(x)
- 10. Power Level D 20.2203(a)(2)(ii)
D 50.36(c)(1)(ii)(A) 181 50.73(a)(2)(v)(A)
D 73.71 (a)(4)
D 20.2203(a)(2)(iii)
D 50.36(c)(2)
D 50.73(a)(2)(v)(B)
D 73.71 (a)(5) 000 D 20.2203(a)(2)(iv)
D 50.46(a)(3)(ii)
D 50.73(a)(2)(v)(C)
D 73.77(a)(1)
D 20.2203(a)(2)(v)
D 50.73(a)(2)(i)(A) 181 50.73(a)(2)(v)(D)
D 73.77(a)(2)(ii)
D 20.2203(a)(2)(vi) 181 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 73.77(a)(2)(iii) 0 50.73(a)(2)(i)(C)
D Other (Specify in Abstract below or in summary of the event NOTE: all times are Central Standard Time
- YEAR 2018
- 3. LERNUMBER SEQUENTIAL NUMBER
- - 001 March 25, 2018 00:50 South Texas Unit 2 performed a fast reactor shutdown per procedure by opening the reactor trip breakers with the reactor at approximately 7.5% rated thermal power. The Unit entered Mode 3.
REV NO.
- - 00 March 25, 2018 01 :55 Extended range monitor Nl-0045 was declared inoperable due to failure to meet required channel check criteria. Nl-0045 was reading 10 counts per second (cps), the lowest reading on the scale, and Nl-0046 was reading 90,000 cps; the maximum allowed deviation with the highest reading monitor reading over 1,000 cps is by a factor of ten. The applicable Technical Specification Action statements were entered for one extended range monitor being inoperable in Mode 3:
Technical Specification 3.3.1 (Reactor Trip System Instrumentation), Action Sa [Applicable in Modes 3, 4, 5]
Technical Specification 3.3.3.5 (Remote Shutdown System) [Applicable in Modes 1, 2, 3]
Technical Specification 3.3.3.6 (Accident Monitoring Instrumentation), Action 42 [Applicable in Modes 1, 2, 3]
Extended range monitor Nl-0046 was later determined to be the inoperable extended range monitor. Although declared inoperable at this time, Nl-0045 was later determined to have been Operable prior to being removed from service for corrective maintenance.
March 25, 2018 09:16 Extended range monitor calibration procedure commenced for Nl-0045. Performance of this calibration resulted in extended range monitor Nl-0045 being removed from service and becoming inoperable.
Extended range monitor Nl-0046 was later determined to be inoperable (see above), so at this time both extended range monitors Nl-0045 and Nl-0046 were inoperable. The Technical Specification 3.3.1, Action Sb, requirements for two inoperable extended range monitors were not met for this condition. The Technical Specification 3.3.3.5 and 3.3.3.6 Action requirements for both extended range monitors being inoperable were met; these specifications have a 30-day and 7-day, respectively, shutdown action statement.
March 25, 2018 10:07 South Texas Unit 2 entered Mode 4. Technical Specifications 3.3.3.5 and 3.3.3.6 are no longer applicable.
March 25, 201812:34 Extended range monitor Nl-0045 calibration procedure completed satisfactorily; Nl-0045 remains inoperable pending completion of work package review.
March 25, 2018 13:30 South Texas Unit 2 entered Mode 5.
March 25, 2018 15:27 Extended range monitor Nl-0045 declared Operable following review of calibration work package and channel check. Although extended range monitor Nl-0046 was later determined to be inoperable, sufficient time had elapsed such that it was tracking with Nl-0045 and the channel check criteria was met.
March 25, 2018 15:44 Extended range monitor 1\\11-0046 was declared inoperable due to exhibiting sluggish response during and following plant shutdown. It was determined that Nl-0046, and not Nl-0045, was inoperable at 01 :55 following failure to meet required channel check criteria.
March 25, 2018 20:33 Extended range monitor calibration procedure commenced for Nl-0046.
March 28, 2018 20:12 South Texas Unit 2 entered Mode 6; extended range monitors no longer required to be Operable per Technical Specifications.
summary of the event ( continued)
April 7, 2018 01 :25 Extended range monitor Nl-0046 calibration procedure completed satisfactorily; Nl-0046 remains inoperable pending completion of work package review.
April 16, 2018 02:51 South Texas Unit 2 entered Mode 5 (exited Mode 6 planned refueling outage). Technical Specification 3.3.1 Action requirements were met.
April 23, 2018 03:04 Extended range monitor Nl-0046 declared Operable following review of calibration work package and channel check.
F.
Method of discovery
This event was discovered after Engineering review of the event determined that extended range monitor Nl-0046 was the faulty instrument.
II. Component failures
A. Failure mode, mechanism, and effects of failed component Extended range monitor Nl-0045 became inoperable when removed from service to perform corrective maintenance (i.e., testing and repair). It was later determined that extended range monitor Nl-0045 was Operable prior to being removed from service for testing.
The most likely cause for the sluggish response of extended range monitor Nl-0046 was the development of moisture within the cabling inside the Reactor Containment Building (RCB) between the detector and the RCB inboard penetration due to a leak in its environmental enclosure.
The extended range monitors are used in Modes 3, 4, and 5 to alert the Control Room that a potential unmonitored return to criticality due to an inadvertent Reactor Coolant System dilution event was occurring. The effect of both extended range monitors being inoperable is the loss of this function.
B. Cause of component failure
There was no failure of extended range monitor Nl-0045; it became inoperable when removed from service to perform corrective maintenance.
As discussed above, the most likely cause for the sluggish response of extended range monitor Nl-0046 was the development of moisture within the cabling inside the Reactor Containment Building (RCB) between the detector and the RCB inboard penetration due to a leak in its environmental enclosure. Page 4 of 6 (04-2017)
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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. LERNUMBER YEAR South Texas Unit 2 05000499 2018 C. Systems of secondary functions that were affected by failure of components with multiple functions The extended range monitors have several functions:
SEQUENTIAL NUMBER
- - 001 REV NO.
- - 00
- 1.
In Modes 3, 4, and 5, the extended range monitors provide input to a flux multiplication alarm. The flux multiplication alarm is used to detect a potential unmonitored return to criticality due to an inadvertent Reactor Coolant System dilution event. This function was affected by this event.
- 2.
In Modes 1, 2, and 3, the extended range monitors provide remote shutdown monitoring capability at the auxiliary shutdown panel in the event that the Control Room becomes unavailable. Although, this function was affected by this event, the Technical Specification Action statement was met with both extended range monitors inoperable.
- 3.
In Modes 1, 2, and 3, the extended range monitors provide accident monitoring capability following an accident. Although, this function was affected by this event, the Technical Specification Action statement was met with both extended range monitors inoperable.
- 4.
In Mode 6, one extended range monitor may be substituted for one inoperable source range neutron flux monitor. This function was not affected by this event.
D. Failed component information (Energy Industry Identification System (EIIS) designators provided in {brackets})
System: Nuclear Instrumentation System (lncore/Excore Monitoring System) {IG}
Component Type: Control, Indicating, Power {JIC}
Component Manufacturer: Thermo Fisher Scientific Inc.
Ill. Analysis of the event A. Safety system responses that occurred No safety systems were required to respond as a result of this event.
8. Duration of safety system inoperability
Extended range monitor Nl-0045 was inoperable from 3/25/2018 09: 16 until 3/25/2018 15:27 ( six hours and eleven minutes)
Extended range monitor Nl-0046 was inoperable from 3/25/2018 01 :55 until 4/23/2018 03:04 (twenty-nine days, one hour, and nine minutes). Page 5 of 6 Page 6 of 6 (04-2017)
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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/r3/)
- 3. LER NUMBER South Texas Unit 2 05000499 YEAR SEQUENTIAL NUMBER REV NO.
2018
- - 001
- - 00
C. Safety consequences and implications
For six hours and eleven minutes, while in Modes 3, 4, and 5, both extended range monitors were inoperable. The STP UFSAR Chapter 15 accident analysis for Chemical and Volume Control System Malfunction That Results in a Decrease in Boron Concentration in the Reactor Coolant states that with both extended range monitors inoperable, the potential exist for an unmonitored return to criticality in Modes 3, 4, and 5. The analysis assumes that the Operators secure flow paths from the Reactor Makeup Water System within 15 minutes. Operators are also required to restore at least one extended range monitor to Operable status within one hour, or to secure other dilution flow paths within two hours after initiation of the event. The implications of this event are that the Control Room Operators would not have been able to use the extended range monitors to detect a potential unmonitored return to criticality due to an inadvertent Reactor Coolant System dilution event. Note that the Operators would most likely detect a rise in counts with the source range monitors with the associated audible count rate well before the extended range monitors would provide indication of an approach to criticality.
IV. Cause of the event
The cause of this event is that the operating crew did not have adequate technical knowledge of extended range monitor response following a fast reactor shutdown. A contributing cause is that when faced with the situation with extended range monitor NI-0045 reading 10 cps and extended range monitor NI-0046 reading 90,000 cps, the Control Room did not initially seek input from Engineering regarding proper monitor response. Instead, the decision was made to declare NI-0045 inoperable based on the belief that 10 cps was an abnormal reading when compared to the source range monitor counts.
The most likely cause for the sluggish response of extended range monitor NI-0046 was the development of moisture within the cabling inside the Reactor Containment Building (RCB) between the detector and the RCB inboard penetration due to a leak in its environmental enclosure.
V. Corrective actions
- 1. Develop and implement training for Licensed Reactor Operators on extended range monitor response and behavior following a fast reactor shutdown.
- 2. Enforce management expectation that Operations seek assistance from Engineering and other groups to understand and resolve issues.
- 3. Extended range monitor NI-0046 was corrected and returned to service on April 23, 2018 at 03:04. The leak in the in-containment cable environmental enclosure was corrected on April 22, 2018.
VI. Previous similar events
An operating experience review over the past five years was conducted for similar events regarding extended range, source range, and intermediate range responses. No similar events were found at South Texas Unit 1 or Unit 2.