05000458/LER-2015-010, Regarding Potential Loss of Safety Function of High Pressure Core Spray Due to Failure of Main Control Building Ventilation Chiller
| ML16053A098 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 02/08/2016 |
| From: | Olson E Entergy Nuclear Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RBF1-16-0012, RBG-47649 LER 15-010-00 | |
| Download: ML16053A098 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i) 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)(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)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4582015010R00 - NRC Website | |
text
--En tergy Entergy Operations, Inc..
River Bend Station 5485 U. S. H~ighway 61 N St. Francisville, LA 70775 Tel 225 381 4374 Fax 225 381 4872 eolson@entergy.corn Eric W. Olson Site Vice President RBG-47649 February 8, 2016 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555
Subject:
Licensee Event Report 50-458 / 2015-010-00 River Bend Station - Unit 1 Docket No. 50-458 License No. NPF-47 RBFI1-1 6-0012
Dear Sir or Madam:
In accordance with 10 CER 50.73, enclosed is the subject Licensee Event Report.
This document contains no commitments. If you have any questions, please contact Mr. Joseph Clark at 225-381-4177.
Sincerely, EWO /dhw Enclosure cc:
U. S. Nuclear Regulatory Commission Region IV 1600 East Lamar Blvd.
Arlington, TX 76011-4511 NRC Sr. Resident Inspector P. O. Box 1050 St. Francisville, LA 70775
Licensee Event Report 50-458 / 2015-010-00 February 8, 2016 RBG-47649 Page 2 of 2 INPO (via ICES reporting)
Central Records Clerk Public Utility Commission of Texas 1701 N. Congress Ave.
Austin, TX 78711-3326 Department of Environmental Quality Office of Environmental Compliance Radiological Emergency Planning and Response Section Ji Young Wiley P.O. Box 4312 Baton Rouge, LA 70821-4312
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3160-0104 EXPIRES: 01/3112017 (02-2014)
Estimated burden per response to comply with this mandatory collection request: 80 houm.
o?*
=Reported lessons learned are incorporated into the licensing process and fed back to industry.
- Send comments regarding burden estimate to the FO1A, Privacy and Information Collections LC N E EV N REO T(
R)
Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by IEN E EETREO T LR internet e-mail to Infocotlects.Resource~nrc.gov, and to the Desk Officer, Office of Information and (See Page 2 for required number of Regulatory Atfairs, 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 0MB digits/characters for each block) control number, the NRC may not condsct or sponsor, and a person is not required to respond to, the information collection.
'1. FACILITY NAME 2
OKTNME
.PG River Bend Station - Unit 1 000481O
- 4. TITLE Potential Loss of Safety Function of High Pressure Core Spray Due to Failure of Main Control Building Ventilation Chiller
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MOT A
ER YAR SQETA E
FAcILITY NAME oOCKET NUMBER MOTUDMYER YER E
R N."
MONTH 1DAY YEAR 050 FACIITY NAME EDOCKTNNMBER 12 11 2015 2015 010 00 0
08 2016000
- 9. OPERATING MODE
'11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
El 20.2201 (b)
[] 20.2203(a)(3)(i)
El 50.73(a)(2)(i)(C)
[] 50,73(a)(2)(vii) 1 E 20.2201(d)
El 20.2203(a)(3)(ii)
[] 50.73(a)(2)(ii)(A)
[] 50.73(a)(2)(viii)(A)
El 20.2203(a)(1)
[] 20.2203(a)(4)
[]
50.73(a)(2)(ii)(B)
[]
50.73(a)(2)(viii)(B)
E 20.2203(a)(2)(i)
El 50.36(c)(1)(i)(A)
[]
50,73(a)(2)(iii)
[] 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL El 20.2203(a)(2)(ii)
[] 50.36(c)(1)(ii)(A)
[]
50.73(a)(2)(iv)(A)
[]
50.73(a)(2)(x)
[] 20.2203(a)(2)(iii)
[]
50.36(c)(2)
[]
50.73(a)(2)(v)(A)
[] 73.71 (a)(4) 83 El 20.2203(a)(2)(iv)
[]
50.46(a)(3)(ii)
[] 50.73(a)(2)(v)(B)
[]
73.71 (a)(5)
El 20.2203(a)(2)(v)
[] 50.73(a)(2)(i)(A)
[]
50.73(a)(2)(v)(C)
[]
OTHER E
20.2203(a)(2)(vi)
El 50.73(a)(2)(i)(B)
[]
50.73(a)(2)(v)(g)
Specify fn Abstract below or in
- 12. LICENSEE CONTACT FOR THIS LER LICENSEE CONTACT TLPOENME(IcueAaCde Joseph A. Cla~rk, Manager - Regulatory Assurance J
(2)3147IAS SYTE IOPNN MANU-REPORTABLE CASISSTM COPNET MANU-REPORTABLE CAS YTM CMOET FACTURER TO EPIX
CAUSE
SYSTECCOMPNENTTO EPIX
- 14. SUPPLEMENTAL REPORT EXETD15.
EXPECTED MONTH DAY YEAR El YES (If yes, complete 15. EXPECTED SUBMISSION DATE)
[]
NO SUBMISSION ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)
On December 11, 2015, at 4:16 a.m. CST, with the plant operating at 83 percent power, the high pressure core spray system (HPCS) was declared inoperable following the failure of the operating chiller in the Division 2 control building ventilation system (HVK).
Chiller "D" was in service when it tripped automatically due to a high bearing temperature signal. The "C" chiller in the Division 1 subsystem automatically started as designed, and was confirned to be operating correctly within approximately 5 minutes. The Technical Specifications for the Division 3 DC distribution system requires that the HPCS system be immediately declared inoperable.
This condition potentially causes the I-PCS system to be incapable of performing its safety function. The investigation determined that, during a recent corrective maintenance activity, too much oil was added to the chiller prior to its return to service. A subsequent load increase on the chiller caused excess oil to migrate into the compressor sump, where it contributed to the high bearing temperature condition. The HVK system continued to support the safety function of Division 3 electrical equipment after chiller trip, since the time required to restore an operable chiller is significantly less than the time limit for restoration of equipment room cooling. This event had no actual adverse effect on the ability of the Division 3 HPCS electrical system to perform its design safety function since there was more than sufficient time to align the other chiller in the same division to provide control building switchgear room cooling. This event, thus, did not Constitute an actual loss of the ability of the HPCS system to perform its design safety function.
NRC FORM 366 (02-2014)
REPORTED CONDITION On December 11, 2015, at 4:16 a.m. CST, with the plant operating at 83 percent power, the high pressure core spray system (HPCS)
(BG) was declared inoperable following the failure of the operating chiller (**CHUJ**) in the Division 2 control building ventilation (HVK) system. HVK chiller "D" was in service when it automatically tripped due to a high bearing temperature signal.' The "C" chiller in the Division 1 HVK subsystem automatically started as designed, and was confirmed to be operating normally within approximately 5 minutes. The "B" chiller was aligned to the standby configuration approximately 23 minutes after the "D" chiller tripped. The HPCS system was again declared operable at 4:39 a.m.
The HVK system provides cooling to the equipment rooms housing the battery chargers and inverters for the safety-related onsite electrical distribution systems. The loss of cooling to the various equipment rooms in the control building requires that the supported equipment in those areas be declared inoperable. The Technical Specifications for the Division 3 DC distribution system requires that the HPCS system be immediately declared inoperable. This condition potentially causes the HIPCS system to be incapable of performing its safety function, and is, thus, reportable in accordance with 10 CFR 50.73(a)(2)(v)(D).
CAUSAL ANALYSIS HVK chiller "D" had recently undergone corrective maintenance to replace an oil seal on the compressor drive shaft. When the unit was being prepared for return to service, oil was added to raise the level to the band required by the operator's logs. The chiller was started on December 8, and operated until the automatic trip on the December 11. During this period, a change in the prevailing weather conditions caused the load on the compressor to increase significantly. When the load increases on this type of chiller, the oil inventory tends to migrate from the evaporator to the compressor sump, raising the oil level as monitored in the compressor sight glasses. This rise in level was sufficient to cause the compressor drive gears to entrain oil, increasing the load on the driveshaft bearings. The bearing temperature increased to the point where it caused an automatic trip of the compressor.
CORRECTIVE ACTIONS to PREVENT RECURRENCE The following actions are being planned to address the causes of this event:
- The acceptance criterion for compressor oil level on the operators' logs will be revised to lower the upper end of the range.
- Maintenance instructions will be revised to provide for optimization of oil inventory prior to return to service.
These actions are being tracked in the site corrective action program.
PRIOR OCCURRENCE EVALUATION No previous similar events have been reported at River Bend Station in the last three years.
SAFETY SIGNIFICANCE
Within the bounds of the site accident analysis, there is a plausible (albeit, highly unlikely) scenario in which a complete loss of offsite power occurs following an unrelated failure of the operating H1KV chiller, concurrent with the assumed failure of the emergency diesel generator in the division opposite that of the failed chiller.
Each of the two divisions of the HVK system has two 100 percent capacity chillers. The chilled water and service water subloops are configured such that manual operator action is required to shift service between the two chillers within a division. In the normal alignment, one chiller is carrying the building heat loads, and one chiller in the opposite division is in standby, capable of automatically starting in the event that the running chiller fails.
An unanticipated trip of an operating chiller automatically initiates the start sequence of the standby chiller. If the start of that standby chiller is closely followed by the loss of offsite power, the assumed subsequent failure of the diesel generator then leaves the HVK system with no chillers aligned for service. These circumstances result in the failure of the cooling function of the HYK system until the operators take the manual actions. The maximum time needed to perform the realignment has been conservatively estimated to be 76 minutes. Calculations have determined temperatures in the Division 3 equipment rooms will remain below the 122 F limit of the equipment for at least 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
In the event on December 11, the "C" chiller automatically started as designed, and it was confirmed to be operating correctly within approximately 5 minutes. The HVK system continued to support the safety function of Division 3 electrical equipment after chiller trip, since the time required to restore an operable chiller is significantly less than the time limit for restoration of equipment room cooling. This event had no adverse effect on the ability of the Division 3 H-]PCS electrical system to perform its design safety function following the trip of a HVK chiller since there is more than sufficient time to align the other chiller in the same division to provide control building switchgear room.
(NOTE: Energy Industry Component Identification codes are annotated as (**XX**))
REPORTED CONDITION On December 11, 2015, at 4:16 a.m. CST, with the plant operating at 83 percent power, the high pressure core spray system (HPCS)
(BG) was declared inoperable following the failure of the operating chiller (**CHUJ**) in the Division 2 control building ventilation (HVK) system. HVK chiller "D" was in service when it automatically tripped due to a high bearing temperature signal.' The "C" chiller in the Division 1 HVK subsystem automatically started as designed, and was confirmed to be operating normally within approximately 5 minutes. The "B" chiller was aligned to the standby configuration approximately 23 minutes after the "D" chiller tripped. The HPCS system was again declared operable at 4:39 a.m.
The HVK system provides cooling to the equipment rooms housing the battery chargers and inverters for the safety-related onsite electrical distribution systems. The loss of cooling to the various equipment rooms in the control building requires that the supported equipment in those areas be declared inoperable. The Technical Specifications for the Division 3 DC distribution system requires that the HPCS system be immediately declared inoperable. This condition potentially causes the HIPCS system to be incapable of performing its safety function, and is, thus, reportable in accordance with 10 CFR 50.73(a)(2)(v)(D).
CAUSAL ANALYSIS HVK chiller "D" had recently undergone corrective maintenance to replace an oil seal on the compressor drive shaft. When the unit was being prepared for return to service, oil was added to raise the level to the band required by the operator's logs. The chiller was started on December 8, and operated until the automatic trip on the December 11. During this period, a change in the prevailing weather conditions caused the load on the compressor to increase significantly. When the load increases on this type of chiller, the oil inventory tends to migrate from the evaporator to the compressor sump, raising the oil level as monitored in the compressor sight glasses. This rise in level was sufficient to cause the compressor drive gears to entrain oil, increasing the load on the driveshaft bearings. The bearing temperature increased to the point where it caused an automatic trip of the compressor.
CORRECTIVE ACTIONS to PREVENT RECURRENCE The following actions are being planned to address the causes of this event:
- The acceptance criterion for compressor oil level on the operators' logs will be revised to lower the upper end of the range.
- Maintenance instructions will be revised to provide for optimization of oil inventory prior to return to service.
These actions are being tracked in the site corrective action program.
PRIOR OCCURRENCE EVALUATION No previous similar events have been reported at River Bend Station in the last three years.
SAFETY SIGNIFICANCE
Within the bounds of the site accident analysis, there is a plausible (albeit, highly unlikely) scenario in which a complete loss of offsite power occurs following an unrelated failure of the operating H1KV chiller, concurrent with the assumed failure of the emergency diesel generator in the division opposite that of the failed chiller.
Each of the two divisions of the HVK system has two 100 percent capacity chillers. The chilled water and service water subloops are configured such that manual operator action is required to shift service between the two chillers within a division. In the normal alignment, one chiller is carrying the building heat loads, and one chiller in the opposite division is in standby, capable of automatically starting in the event that the running chiller fails.
An unanticipated trip of an operating chiller automatically initiates the start sequence of the standby chiller. If the start of that standby chiller is closely followed by the loss of offsite power, the assumed subsequent failure of the diesel generator then leaves the HVK system with no chillers aligned for service. These circumstances result in the failure of the cooling function of the HYK system until the operators take the manual actions. The maximum time needed to perform the realignment has been conservatively estimated to be 76 minutes. Calculations have determined temperatures in the Division 3 equipment rooms will remain below the 122 F limit of the equipment for at least 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
In the event on December 11, the "C" chiller automatically started as designed, and it was confirmed to be operating correctly within approximately 5 minutes. The HVK system continued to support the safety function of Division 3 electrical equipment after chiller trip, since the time required to restore an operable chiller is significantly less than the time limit for restoration of equipment room cooling. This event had no adverse effect on the ability of the Division 3 H-]PCS electrical system to perform its design safety function following the trip of a HVK chiller since there is more than sufficient time to align the other chiller in the same division to provide control building switchgear room.
(NOTE: Energy Industry Component Identification codes are annotated as (**XX**))