05000410/LER-2017-002

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LER-2017-002, Secondary Containment Inoperable Due to Wind Conditions
Nine Mile Point Unit 2
Event date: 09-30-2017
Report date: 11-29-2017
Reporting criterion: 10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material
4102017002R00 - NRC Website
LER 17-002-00 for Nine Mile Point Nuclear Station, Unit 2 Regarding Secondary Containment Inoperable Due to Wind Conditions
ML17346A745
Person / Time
Site: Nine Mile Point Exelon icon.png
Issue date: 11/28/2017
From: Kreider R E
Exelon Generation Co
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
NMP2L2659
Download: ML17346A745 (6)


comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. LER NUMBER

2017 002 - 00

I. DESCRIPTION OF EVENT

A. PRE-EVENT PLANT CONDITIONS:

Prior to the event, Nine Mile Point Unit 2 (NMP2) was operating at 100 percent power.

B. EVENT:

On September 30th, 2017 at approximately 0130 the Unit 2 Main Control Room was notified by the building rounds operator of Reactor Building differential pressure (D/P) fluctuations observed at the local ventilation control panel. All Reactor Building fans and dampers were found in a normal configuration. Reactor building D/P readings in the control room were noted as less than .25 inches vacuum water gauge (WG) and remaining negative as compared to atmospheric pressure. Secondary Containment was declared inoperable due to exceeding the Technical Specification (TS) allowed value of .25 inches vacuum WG and TS Limiting Condition for Operation (LCO) 3.6.4.1 Condition A was entered.

One minute later Operations started Standby Gas Treatment (GTS) Train "B" per procedure.

Secondary Containment vacuum was restored to greater than 0.25 inches of vacuum WG, TS LCO 3.6.4.1 Condition A was exited and Secondary Containment was declared Operable.

Nine Mile Point Unit 1 (NMP1) was unaffected by the inoperability of Secondary Containment at NMP2.

The event has been entered into the plant's corrective action program as IR# 04057558

C. INOPERABLE STRUCTURES, COMPONENTS, OR SYSTEMS THAT CONTRIBUTED TO

THE EVENT:

There were no inoperable systems, structures, or components that contributed to this event.

D. DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES AND OPERATOR

ACTIONS:

The dates, times, and major occurrences and operator actions for this event are as follows. All times are 09/30/2017.

0130 Reactor Building Operator reports the Reactor Building D/P fluctuating at the local control panel.

0134 Control Room Operator observes control room indicators for Reactor Building pressure reading above -0.25 inches water gauge, Secondary Containment was declared inoperable and Technical Specification 3.6.4.1 was entered.

comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission. Washington, DC 20555-0001, or by e-mail to 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 OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. LER NUMBER

2017 002 - 00 0135 Control Room Operator starts Standby Gas Treatment Fan per procedure, Reactor Building D/P improves to -0.45 inches water gauge.

0135 Secondary Containment was declared operable and Technical Specification 3.6.4.1 was exited

E. METHOD OF DISCOVERY:

The condition was recognized by Operations as they monitored Secondary Containment vacuum during the period of changing wind conditions.

F. SAFETY SYSTEM RESPONSES:

This event was caused by changing wind conditions. The GTS equipment performed as expected.

II. CAUSE OF EVENT:

Secondary Containment was declared inoperable because of changing wind conditions.

Though the effect of high winds on normal Reactor Building ventilation was recognized in 2015, attempts to mitigate building D/P changes due to high winds did not prevent the wind conditions during this event (East to Northeast) from affecting Reactor Building D/P enough to enter Technical Specifications.

III. ANALYSIS OF THE EVENT:

The event described in this LER is reportable under 10 CFR 50.72 (b)(3)(v)(C) and 10 CFR 50.73(a)(2)(v)(C) as any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material.

Analysis concluded that Secondary Containment was declared inoperable because of changing wind conditions. The effect of high wind on Reactor Building ventilation was recognized in 2015 and actions were taken attempting to mitigate building D/P changes during sustained high wind conditions. However, these actions did not prevent the wind conditions during this event from affecting Reactor Building D/P enough to enter Technical Specification required action.

TS 3.6.4.1 Condition A was entered and subsequently exited once Secondary Containment vacuum was restored to above the required TS value (required action) within the associated completion time. The Secondary Containment structural integrity, the ability to automatically isolate the non-safety related Reactor Building Ventilation System, and GTS comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to Infccollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. LER NUMBER

2017 002 - 00 availability were not impacted. Secondary Containment would have continued to perform its intended safety function throughout the duration of the event.

Based on the above discussion, it is concluded that the safety significance of this event is low and the event did not pose a threat to the health and safety of the public or plant personnel.

This event does not affect the NRC Regulatory Oversight Process Indicators.

IV. CORRECTIVE ACTIONS:

A. ACTION TAKEN TO RETURN AFFECTED SYSTEMS TO PRE-EVENT NORMAL

STATUS:

Operators declared Secondary Containment inoperable and entered TS LCO 3.6.4.1 Condition A with a required action to restore Secondary Containment to operable within

4 hours
4.62963e-5 days
0.00111 hours
6.613757e-6 weeks
1.522e-6 months

. Operators placed GTS in operation and returned the Secondary Containment to pre-event status (operable).

B. ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE:

One action has been completed to aid in preventing recurrence; this action changes "Building Rounds" Attachment 1 to align Reactor Building D/P bands with Reactor Building Ventilation procedure. This revision changed the range for Reactor Building D/P from -0.25 to -0.80 inches WG to -0.47 to -0.90 inches WG, providing more margin to inoperability.

Additionally, the site has submitted a license amendment request to allow for containment vacuum to be momentarily less than the required vacuum due to changes in wind conditions in accordance with TSTF-551, Revision 3 "Revise Secondary Containment Surveillance Requirements".

V. ADDITIONAL INFORMATION:

A. FAILED COMPONENTS:

There were no failed components that contributed to this event.

comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to 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 OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. LER NUMBER

2017 002 - 00

B. PREVIOUS LERs ON SIMILAR EVENTS:

NMP2 LER-2014-005, dated 05/09/2014, was submitted for Secondary Containment Inoperable due to Sustained high winds. The corrective actions following this event included revising a plant procedure to provide direction to initiate the Standby Gas Treatment System and isolate the Reactor Building during sustained high wind conditions prior to exceeding the Technical Specification (TS) D/P limit for Secondary Containment. These actions do not mitigate the change in wind conditions associated with this LER (2017-002) NMP2 LER-2015-001, dated 03/12/2015, was submitted for Secondary Containment Inoperable due to Sustained high winds. The wind conditions of the event described within this LER differ from those captured in LER-2015-001. Actions resulting from the 2015 event have successfully mitigated the challenge posed from sustained high winds from West to East but did not prevent D/P challenges presented from the wind conditions during the event described in this LER (2017-002) C. THE ENERGY INDUSTRY IDENTIFICATION SYSTEM (HIS) COMPONENT FUNCTION

IDENTIFIER AND SYSTEM NAME OF EACH COMPONENT OR SYSTEM REFERRED TO

IN THIS LER:

COMPONENT

IEEE 803 FUNCTION IEEE 805 SYSTEM

IDENTIFIER IDENTIFICATION

Reactor Building (BWR) Standby Gas Treatment System N/A NG N/A BH

D. SPECIAL COMMENTS:

None