05000317/LER-2018-001, For Calvert Cliffs Nuclear Power Plant, Units No. 1 and 2, Both Unit 2 Emergency Diesel Generators Inoperable Due to Depressurization in Common Air Start Headers
| ML18345A048 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 12/07/2018 |
| From: | Tierney T Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 2018-001-00 | |
| Download: ML18345A048 (7) | |
| 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) |
| 3172018001R00 - NRC Website | |
text
Exelon Generation December 07, 2018 U.S. Nuclear Regulatory Commission ATIN: Document Control Desk Washington, DC 20555 Calvert Cliffs Nuclear Power Plant, Units No. 1 and 2 Todd A. Tierney Plant Manager Calvert Cliffs Nuclear Power Plant 1650 Calvert Cliffs Parkway Lusby, MD 20657 410 495 5205 Office 484-459-0142 Mobile www.exeloncorp.com todd.tierney@exeloncorp.com 10 CFR 50.73 Renewed Facility Operating License Nos. DPR-53 and DPR-69 NRC Docket Nos. 50-317 and 50-318
Subject:
Licensee Event Report 2018-001, Revision 00 Both Unit 2 Emergency Diesel Generators Inoperable Due to Depressurization in Common Air Start Headers The attached report is being sent to you as required by 1 O CFR 50. 73.
There are no regulatory commitments contained in this correspondence.
Should you have questions regarding this report, please contact Mr. Larry D. Smith at (410) 495-5219.
Respectfully,
~. a.~A /JljAA/
Todd A. Tierney
~ -.........., --(/
Plant Manager TAT/KLG/lmd
Attachment:
As stated cc:
NRC Project Manager, Calvert Cliffs NRC Regional Administrator, Region I NRC Resident Inspector, Calvert Cliffs D. A. Tancabel, DNR
Document Control Desk December 07, 2018 Page2 bee:
J. B. Fewell, GDC D. P. Ferraro, AGC J. Barstow D. T. Gudger R. Villar M. D. Flaherty T. A. Tierney H. A. Daman J. S. Gaines R. C. Jones L. D. Smith J. L. Jackson File# 02.09 EDMS 318/2018-001-00
NRC FORM366 (04-2018)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 03/31/2020 LICENSEE EVENT REPORT (LER)
(See Page 2 for required number of digits/characters for each block)
(See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/n uregs/staff/sr1 022/r3D Esti'nated, the NRG may not conductor sponsor, and a person is not required to respond to, the information coUection.
- 1. Facility Name Calvert Cliffs Nuclear Power Plant, Unit 2
- 4. Title
- 2. Docket Number 05000318 3.Page 1
OF 5 Both Unit 2 Emergency Diesel Generators Inoperable Due to Depressurization in Common Air Start Headers
- 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 Calvert Cliffs Nuclear Power Plant, Unit 1 05000317 Facility Name Docket Number 2018 -
001 0
12 07 2018 05000 10 11 2018
- 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)(3J(il D 50.73(a)(2)(ii)(A)
D 50.73(a)(2)(viii)(A) 1 D 20.2201(d)
D 20.2203(a)(3)(ii) rgi 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)
D 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)(Ai D 50.73(a)(2)(v)(A)
D 73.71 (a)(4)
D 20.2203(a)(2)(iii)
D so.36(c)(2J D 50.73(a)(2)(v)(B)
D 73.71(aHsi D 20.2203(a)(2)(iv)
D so.46(a)(3)(iiJ D 50.73(a)(2)(v)(C)
D 73.77(a)(1J 100 D 20.2203(a)(2)(v)
D 50.73(a)(2)(i)(A) rgi 50.73(a)(2)(v)(D)
D 73.77(a)(2)(iJ D 20.2203(a)(2)(vi)
D 50.73(a)(2)(i)(B) rgi 50.73(a)(2)(vii)
D 73.77(a)(2J(iiJ
.,.,.. ~:(*
,..:.* ;::z D 50.73(a)(2)(i)(C)
D Other (Specify in Abstract below or in circuitry. The air start CVs remain open until EOG reaches an operating speed of 250 rpm when the associated relays actuate to deenergize the air start SVs thus closing the air start CVs.
During this post maintenance start, the control relays actuated on the EOG start signal thus energizing the air start SVs that opened EOG 18 air start CVs, starting EOG 18. Before EOG 18 reached 250 rpm, one of the newly installed diodes shorted which caused two control circuitry fuses [FU] to fail, thereby removing power to actuate the relays when EOG 18 reached 250 rpm.
As a result, no shut signal was sent to the EOG 18 air.start SVs and the EOG 1 B*air start CVs remained open. Because of the original design vulnerability of the common air start headers inter-connecting all the FM EDGs, air start pressure to the Unit 2 EDGs decreased to a point where there was insufficient air pressure to start EDGs 2A and 28 should a start demand on these diesels occur. This condition existed for 30 minutes. Having both Unit 2 EDGs incapable of being started meant Unit 2 was in a condition that would have prevented fulfillment of a safety function and thus an 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> Emergency Notification System (ENS) report was made to the NRG at 0358 on Oct 12, 2018 pursuant to 10 CFR 50.72(b)(3)(v)(D) and pursuant to 1 O CFR 50.72 (b)(3)((ii)(B) for being in an Unanalyzed Condition.
C.
DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES
October 11, 2018 2255 - Commenced a slow speed start of EOG 18.
2303 ~ Declared EOG 2A and 28 inoperable following receipt of Low Starting Air Pressure alarm for both Unit 2 EOGs.
j I
2306 - Operations shut manual valves (1 DSA 114 and 1 OSA 117), to isolate air to HOG 18 air start CVs (1 C_V4834 and 1 CV48~. 5). Air pressure in FM common air start headers begah to increase.
2310 - EOG 18 was manually stopped locally by Operations.
I 2333 - Unit 2 EOGs Low Starting Air Pressure alarm cleared. Emergency Diesel Generators 2A and 28 were declared operable.
October 12, 2018 0358 - The eight-hour ENS report (ENS#53663) was made to the Nuclear Regulatory Commission (NRC).
D.
CAUSE OF EVENT
The method of discovery for this event was self-revealing and is documented in the site's Corrective Action Program under IR 4182707. Field troubleshooting isolated the cause of failure to a newly installed diode which shorted, causing a current surge which blew two control power fuses thus interrupting power to the relays and preventing the air start SVs from receiving a signal to shut the air start CVs. The failed diode was sent to an offsite lab for analysis. Based on the lab's analysis, the most probable cause of the diode's failure was an undetected manufacturing defect.
While the introduction of the diode into EOG 18 air start control circuitry caused a new equipment failure it did not cause a new failure mode. The fuses could have blown due to any other component failure in the circuitry which would have caused the same result. However, during the si_te's analysis of this event it was discovered that an original design vulnerability has existed since 00 SEQUENTIAL NUMBER 001 REV NO.
00 initial operation (IR 4183896). The vulnerability is that a single fuse failure, at just the right time in the FM EOG start sequence, would cause a similar result where the respective FM EOG air start CVs would not receive a shut signal, thus resulting in depressurizing the FM common air start headers. This vulnerability only exists in the very short time frame (less than five seconds) between the time a FM EOG is started and before the FM EOG reaches the engine speed (250 rpm) where the relays are energized to shut the air start CVs. Should the fuse fail at any other time this resultant unanalyzed condition would not occur.
E.
SAFETY ANALYSIS
The actual consequence resulting from this identified event was causing both Unit 2 EDGs to be inoperable for 30 minutes. With both Unit 2 ~DGs inoperable, Unit 2 was in an unanalyzed condition where the EDGs would have beeri unable to mitigate the consequences of either loss of coolant accident or loss of offsite power event. The event is reportable pursuant to the following:
1 O CFR 50.73(a)(2)(v)(D) - Event or Condition that Could Have Prevented Fulfillment of a Safety Function 10 CFR 50.73 (a)(2)(ii)(B) - Degraded or Unanalyzed Condition*
10 CFR 50.73(a}(2)(vii)(D) - Common Cause lnoperability of Independent Trains or Channels Due to short period of time that both Unit 2 EDGs were inoperable, the probabilistic risk assessment analy~is d~termin~d that th_e estimated increase in core dam1ge frequency was less than 1 E-07 and the estimated increase m large early release frequency was less than 1 E-08 per year for the subjec~. condition. This issue would be "GREEN" using the N~C's Significance Determination Process.
I This event marks the third occurrence of the NRC Safety System Functional Failure Performance Indicator for Unit 2 in the last 12 months. Therefore, the performance indicator remains within the
'GREEN' band for this performance indicator.,
F.
CORRECTIVE ACTIONS
Immediate corrective actions were to replace the failed fuses, remove the newly installed electronic relays and diodes, and reinstall the original Agastat relays. Following completion of this action, EOG 1 B was successfully tested and subsequently returned to operating status. To prevent any future failure in the air start circuitry of one FM EOG from impacting the other FM EDGs, a modification was performed to install manual isolation valves within the common air start headers so that each FM EOG air start header would be isolated from the other two FM EDGs.
G.
PREVIOUS OCCURRENCES
The modification to replace existing Agastat relays within the FM DG air start control circuit with new electronic relays was first done on EOG 2A. No issues with the installation of the new electronic relays have occurred on EOG 2A. The same modification was then installed on EOG 28.
Issues were encountered on starting EOG 28 resulting from inductive voltage spikes that caused these new relays to inadvertently actuate. The new electronic relays were removed and the Agastat relays were reinstalled on EOG 28.
The issues on EOG 28 did not result in any impact to the other FM EDGs. To address this issue that was observed on EOG 28, it was determined to add the installation of diodes to dampen the inductive voltage spikes when the modification on EOG 1 8 was done.
H.
COMPONENT FAILURE DATA
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