05000440/LER-2017-004

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LER-2017-004, Loss of Safety Function for High Pressure Core Spray Suppression Pool Level Instrumentation
Perry Nuclear Power Plant
Event date: 08-08-2017
Report date: 10-4-2017
Reporting criterion: 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
Initial Reporting
ENS 52891 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
4402017004R00 - NRC Website
LER 17-004-00 for Perry re Loss of Safety Function for High Pressure Core Spray Suppression Pool Level Instrumentation
ML17278A069
Person / Time
Site: Perry FirstEnergy icon.png
Issue date: 10/04/2017
From: Hamilton D B
FirstEnergy Nuclear Operating Co
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
L-17-304
Download: ML17278A069 (5)


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 - 004 - 00 Perry Nuclear Power Plant Unit 1 05000-440 YEAR 2017 Energy Industry Identification System (EIIS) codes are identified in the text as [XX].

INTRODUCTION

On August 8, 2017, at

1554 hours
0.018 days
0.432 hours
0.00257 weeks
5.91297e-4 months

, while the plant was at 100 percent rated thermal power, during restoration from testing of the High Pressure Core Spray (HPCS) [BG] Suppression Pool (SP) [BT] Level High Instrumentation, [LIT] unexpected as-left indications were found that impacted both of the required channels of instrumentation. With both SP level instruments inoperable, a loss of safety function existed.

EVENT DESCRIPTION

On August 8, 2017, at

1321 hours
0.0153 days
0.367 hours
0.00218 weeks
5.026405e-4 months

. surveillance testing commenced on the HPCS SP level high instrumentation and one channel was declared inoperable. On August 8, 2017, at

1554 hours
0.018 days
0.432 hours
0.00257 weeks
5.91297e-4 months

, during restoration from surveillance testing of the HPCS SP level high instrumentation, unexpected as-left indications were found that impacted both of the required channels of instrumentation. Technical Specification (TS) 3.3.5.1 "Emergency Core Cooling System (ECCS) Instrumentation" condition D was entered. Condition D requires HPCS to be aligned to the SP; however, HPCS was already aligned to the SP since earlier in the day in anticipation of the testing. On August 8, 2017, at

1635 hours
0.0189 days
0.454 hours
0.0027 weeks
6.221175e-4 months

, venting was performed on the level instrumentation sensing line and the erroneous reading was corrected. The restoration from the venting was completed and the level instrumentation was declared operable on August 8, 2017, at

1747 hours
0.0202 days
0.485 hours
0.00289 weeks
6.647335e-4 months

. On August 8, 2017, at

2022 hours
0.0234 days
0.562 hours
0.00334 weeks
7.69371e-4 months

, event notification EN# 52891 was made to the NRC Operations Center to report a loss of safety function.

Suppression Pool Water Level High — TS 3.3.5.1 SP Water Level-High signals are initiated from two level transmitters. The logic is arranged such that either transmitter and associated trip unit can cause the suppression pool suction valve to open and the Condensate Storage Tank (CST) [KA] suction valve to close. This function is implicitly assumed in the accident and transient analyses, which take credit for HPCS, since the analyses assume that the HPCS suction source is the suppression pool.

CAUSE

The cause for the unexpected as-left indications that impacted both of the required channels of instrumentation is related to air entrained in the sensing line caused by air being introduced from air accumulation in the suppression pool over time which moved to a vertical section of the sensing line during venting.

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 Infocollects.Resource@nrc.gov. and to the Desk Officer, Office of Information and 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 currently valid OMB control number. the NRC may not conduct or sponsor, arid a person is not required to respond to. the information collection.

EVENT ANALYSIS

While venting the instrumentation, the HPCS system was aligned to the suppression pool water source. This source of water is HPCS's safety-related source of water. The automatic suction swap on high suppression pool level is implicitly assumed in the accident and transient analysis since it assumes that the HPCS suction source is the suppression pool. Since the HPCS system was aligned to the suppression pool when the failure occurred, the assumptions of the accident analysis are met, and no safety system functional failure occurred.

Probabilistic Risk Assessment review concludes that the associated event, from a qualitative analysis, is of low risk (small safety) significance. The condition was introduced during the surveillance activity, was identified in a timely manner, and was immediately corrected. Additionally, HPCS was aligned to the inventory source that would have been the inventory source that would have been transferred to given the subject instrumentation functioned appropriately. The function/availability of HPCS was never affected. On this basis, there would be no corresponding change (delta) in core damage frequency (CDF). and no corresponding change (delta) in the large early release frequency (LERF). The delta CDF and delta LERF values would therefore be well below the acceptable thresholds of 1.0E-06/yr and 1.0E-07/yr, respectively, as discussed in Regulatory Guide 1.174. Therefore, the risk of this event is considered small in accordance with the regulatory guidance.

CORRECTIVE ACTIONS

Corrective actions include revising local leak rate testing instruction of the sensing line penetration to perform a fill and vent of the sensing line during every performance to reduce the buildup of entrained air.

PREVIOUS SIMILAR EVENTS

A review of LERs and the corrective action database for the past three years identified no similar events.

COMMITMENTS

There are no regulatory commitments contained in this report. Actions described in this document represent intended or planned actions, are described for the NRC's information, and are not regulatory commitments.