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LER-2014-003, Regarding Operations Prohibited by Technical Specifications Due to Concurrent Inoperability of Reactor Protection System Channels
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i); 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability
	4582014003R01 - NRC Website
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Regarding Operations Prohibited by Technical Specifications Due to Concurrent Inoperability of Reactor Protection System Channels
	ML15300A262
Person / Time
Site:	River Bend
Issue date:	10/13/2015
From:	Brumfield N; Entergy Operations
To:	; Document Control Desk, Office of Nuclear Reactor Regulation
References
	RBF1-15-0166, RBG-47621 LER 14-003-01
	Download: ML15300A262 (5)
	v • d • e

SEntergy Entergy Operations Inc.

River Bend Station 5485 U. S. Highway 61N St. Francisville, LA 70775 Tel 225 381 4157 Fax 225 381 4139 www.entergy.com N. Todd Brumfield Director - Regulatory & Performance Improvement nbrumfi@entergy.com RBG-47621 October 13, 2015 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555

Subject:

Licensee Event Report 50-458 /2014-003-01 River Bend Station - Unit 1 Docket No. 50-458 License No. NPF-47 RBF1 0166

Dear Sir or Madam:

In accordance with 10 CFR 50.73, enclosed is the subject Licensee Event Report.

This is a supplement to the original report dated August 11, 2014. This document contains no commitments. If you have any questions, please contact Mr. Joseph Clark at 225-381-4177.

Sincerely NTB /dhw Enclosure

Licensee Event Report 50-458,/201I4*003-01 i,

RBG-47621

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Operations Prohibited by Technical Specifications Dlue to Concurrent Inoperabthty of Reactor Protection System Channels

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On June 10, 2014, with the plant operating at 100 percent power, technicias performing 8sc*he~dued surveillance test found that one instrument channel in the reactor protection system failed its time response acceptane criterion. This was thp second of two such tests that failed in similar fashion. Since it is conceivable that the seco nd tested eheunnel was out of specifications at the time the first channel was tested, this condition caused indep~endent redundant channels in the same trp system to be inoperable at the samne time. The actions required by the applicable Limiting Condition for Operation were not taken since the operators were not aware of the latent condition at the time of the first surveillance test failure, This condition is reportable in ¢ecordance with IOCFRSO.73(aX)(2Xi)b) as operations prohibited by Technical Specifications, as weli as 10CFR5O.73(a)X2Xvil), a potential eommon-eause inoperability of independent trip channels, Dlu to the design redundancy of the independent channels of the RPS system, this condition would not have prevented the system from performing its safety function. Had an actual fldl MSWV isolation occurred with the channel response times in their as-found condition, the reactor scram signal would have still o~ccure within the specified instrument response time. The investigation of this event determined that the response time test failures were not caused by failed or degraded relays outside of the current design. flue to the design release time of the Agastat relays, th MSIV closure / RPS trip circuits could exceed the TRM acceptance criterion even if all relays in the circuit Operated within design specifications. It was confirmed that this condition affected only the four channels containing Agastat relays. An analysis of the aff'ected scram fimetion determined that a elhange in the acceptance criterion 0.09 seconds to 0.15 seconds is juotified. That change is being implemented in accordance with station procedures, CPOIIMSSO 102.2014)

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REPORTED CONDITION On June 10, 2014, with the plant operating at 100 percent power, technicians performing a scheduled surveillance test found that one instrument channel in the reactor protection system (JC) failed its time response acceptance criterion. This was the second of two such tests that failed in similar fashion. Since it is conceivable that the second tested channel was out of specifications at the time the first channel was tested, this condition caused independent redundant channels in the same trip system to be inoperable at the same time.

The actions required by the applicable Limiting Condition for Operation were not taken since the operators were not aware of the latent condition at the time of the firSt surveillance test failure. This condition is reportable in accordance.with 10CFR50.73(a)(2)(i)(b) as operations prohibited by Technical Specifications,. as well as 10CFR50.73(a)(2)(vii), a potential common-cause inoperability of independent trip channels.

BACKGROUND One of the functions in the reactor protection system is the initiation of a reactor scram in the event of a closure of the main steam isolation valves (MSIVs). Two limit switches on each of the eight MSIV actuators provide input to the individual, redundant RPS trip channels if the valve moves to a nominal 12 percent of stroke length in the "close" direction. The design of the RPS system requires that a channel respond to an input from its MSIV. limit switch and generate a trip signal. The maximum response time specified by the Technical Requirements Manual is 0.09 seconds. The calibration frequency is four years (24 months on a staggered test basis).

The arrangement of the instrumentation includes 16 individua,1 chaannets. Inboard and outboard MSIVs in each of the four main steam lines are instrumented with redundant limit switches monitored by independent trip channels of the RPS system.

IMMEDIATE ACTIONS In the calibrations performed in 2010, a degrading trend in the response times was noted in the four channels containing Agastat relays

(**94**). In the 2010 tests, the response time of each of the~four channels was 89 milliseconds. The as-found response times found in the recent tests ranged. from 0.090 to 0.102 seconds. In each case, the Agastat relay was replaced and the response time was then verified to be within specifications. The response times for the channels with no Agastat relays ranged from 0.041 to 0.051 seconds.

An engineering evaluation of this condition was performed, and the RPS system was declared operable with compensatory measures.

Until this issue is resolved, the frequency of the calibration tests in the channels with Agastat relays has been increased to once per year.

CAUSAL ANALYSIS The investigation of this event determined that the response time test failures were not caused by failed or degraded relays outside of the current design. Due to the design "release time" of the Agastat relays, the MSIV closure!/ RPS trip circuits could exceed the TRM acceptance criterion even if all relays in the circuit operated within design specifications. It was confirmed that this condition affected*

only the four channels containing Agastat relays.

NRC FORM 355A (02-2014)

The nuclear steam supply system vendor performed an analysis supporting a change in the total scram delay time from 0.09 seconds to 0.15 seconds. The analysis concluded that the main steam isolation valve closure event with a scram initiated by the MSIV limit switches remains bounded by other pressurization events described in the Updated Safety Analysis Report. Reactor pressure will remain under the design limit of 1375 psig. Radiation dose is not affected because the conservative assumptions utilized in the analysis documented in the USAR remain unchanged and bounding for the event.

A design change is being implemented to revise the TRIM acceptance criterion from 0.09 to 0.15 seconds. An administrative limit of 0.125 seconds will be enforced by the test procedure.

SAFETY SIGNIFICANCE

Due to the design redundancy of the independent channels of the RIPS system, this condition would not have prevented the system from performing its safety function. Had an actual full MSIV isolation occurred with the channel response times in their as-found condition, the reactor scram signal would have still occurred within the specified instrument response time.

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