05000458/LER-2015-007, Unit 1 Regarding Potential Loss of Safety Function of High Pressure Core Spray Due to Failure of Main Control Building Ventilation Chiller

Unit 1 Regarding Potential Loss of Safety Function of High Pressure Core Spray Due to Failure of Main Control Building Ventilation Chiller

ML16050A389
Person / Time
Site:	River Bend
Issue date:	01/18/2016
From:	Olson E Entergy Operations
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RBF1-16-0001, RBG-47640 LER 15-007-00
Download: ML16050A389 (5)

LER-2015-007, Unit 1 Regarding Potential Loss of Safety Function of High Pressure Core Spray Due to Failure of Main Control Building Ventilation Chiller

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 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) 10 CFR 50.73(a)(2)(viii) 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)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function
LER closed by
IR 05000458/2017001 (1 May 2017)
4582015007R00 - NRC Website

text

SEntergy Entergy Operations, Inc.

River Bend Station 5485 U. S. Highway 61N St. Francisville, LA 70775 Tel 225 381 4374 Fax 225 381 4872 eolson@entergy~GGm Eric W. Olson Site Vice President RBG-47640 January 18, 2016 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555

Subject:

Licensee Event Report 50-458 / 2015-007-00 River Bend Station - Unit1I Docket No. 50-458 License No. NPF-47 RBFI 0001

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.Boxl1050 St. Francisville, LA 70775 J1JgQ%~

Licensee Event Report 50-458 / 2015-007-00 January 18, 2016 RBG-47640 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. 3150-0104 EXPIRES: 0113112017 (02-2014)

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 />.

2.

Reported lessons learned are incorporated into the licensing process and fed back to industry.

, ).,*,

Send comments regarding burden astimate to the FOIA, Privacy and Information Collections

% *,*.#Branch (T-5 F:53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by

°... LICENS EE E TR P T(L

)

SEE VENTREP RT (ER) internet e-mail to Infocollects.Resource@nrc, gov, and to the Desk Officer, Office of Information and (See Page 2 for required number of 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 currentfy valid OMB digits/characters for each block) control numberthe NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. PAGE River Bend Station - Unit 1 05000 458 1 OF 3

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 MONTH DAY YEAR YEAR ISEQUENTIALuME REV~o MONTH IDAY YEAR FCLT AE000OKTNME FACILITY NAME DOCKET NUMBER 11 1 05 21 0

o 01 1

20605000

9. OPERATING MODE

11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)

Li 20.2201(b)

[]

20.2203(a)(3)(i)

[]

50.73(a)(2)(i)(CJ)

[] 50.73(a)(2)(vii) 1 L 20.2201(d)

[]

20.2203(a)(3)(ii)

Li 50.73(a)(2)(ii)(A)

Li 50.73(a)(2)(viii)(A)

[] 20.2203(a)(1)

Lii 20.2203(a)(4)

Li 50.73(a)(2)(ii)(g)

Li 50.73(a)(2)(viii)(g)

Li 20.2203(a)(2)(i)

Li 50.36(c)(1)(i)(A)

[]

50.73(a)(2)(iii)

[]

50.73(a)(2)(ix)(A)

10. POWER LEVEL Li 20.2203(a)(2)(ii)

[]

50.36(c)(1)(ii)(A)

[]

50.73(a)(2)(iv)(A)

[]

50.73(a)(2)(x)

Li 20.2203(a)(2)(iii)

[]

50.36(c)(2)

[j] 50.73(a)(2)(v)(A)

[]

73.71 (a)(4) 71 Li 20.2203(a)(2)(iv)

[]

50.46(a)(3)(ii)

[] 50.73(a)(2)(v)(B)

Li 73.71 (a)(5)

Li 20.2203(a)(2)(v)

[]

50.73(a)(2)(i)(A)

[]

50.73(a)(2)(v)(C)

[]

OTHER

[] 0.203()(2(vi

[]

50.3(a(2)i)()

[

5073()(2(v)g)Specify in Abstract below orin Li20.203a)()(v)

Li50.3(a(2)i)()

[] 5.73a)()(v(D)

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 would result in the failure of the cooling function of the HVK 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 122F 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 November 17, approximately 46 minutes elapsed from the declaration of inoperability of the "C" chiller until the "D" chiller was placed into service. The HYK 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 HPCS 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 cooling. This event, thus, did not constitute an actual loss of the ability of the HIPCS system to perform its design safety function.

(NOTE: Energy Industry Component Identification codes are annotated as (**XX**).)

REPORTED CONDITION On November 17, 2015, at 11:55 p.m. CST, with the plant operating at 71 percent power, the high pressure core spray system (HPCS)

(BG) was declared inoperable following the failure of the operating chiller in the Division 1 control building ventilation (HVK)( VI) system. HVK chiller "C" was in service when the building operator found a freon leak in the system. The leakage was determined to be of such magnitude as to cause the chiller to be inoperable, and the operators took action to shift the building cooling loads to the standby Division 2 chiller.

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 redundant 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 HIPCS 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 The HYK chillers reject building heat loads to the safety-related loop of the plant service water system. Each chiller (**CHU**) is equipped with a service water flow control valve (**FCV**) that regulates flow to maintain a relatively constant freon pressure. The flow control valve is automatically positioned by a mechanical actuator that uses freon pressure as its motive force. Maintenance technicians disassembled the valve, and found that the cause of the freon leak was failed rubber diaphragm. System engineers were unable to positively identify the failure mode of the diaphragm, so it was shipped to the valve vendor for further analysis.

CORRECTIVE ACTIONS to PREVENT RECURRENCE Long-term corrective actions to prevent recurrence will be implemented as needed following receipt of the vendor's failure analysis.

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 would result in the failure of the cooling function of the HVK 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 122F 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 November 17, approximately 46 minutes elapsed from the declaration of inoperability of the "C" chiller until the "D" chiller was placed into service. The HYK 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 HPCS 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 cooling. This event, thus, did not constitute an actual loss of the ability of the HIPCS system to perform its design safety function.

(NOTE: Energy Industry Component Identification codes are annotated as (**XX**).)