ML20128F244

Requests Exemption from Specified Sections of 10CFR50.72 & 50.73 Re LERs of Spurious Reactor Protection Sys Actuations. Actuations Caused by Neutron Instrumentation Electrical Noise & Not Safety Concern

ML20128F244
Person / Time
Site:	Big Rock Point File:Consumers Energy icon.png
Issue date:	07/02/1985
From:	Vandewalle D CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	Office of Nuclear Reactor Regulation
References
TAC-56946, TAC-56947, NUDOCS 8507080181
Download: ML20128F244 (5)

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Direaor of Nsulear Lkensing l

General offmes: 1945 West Parnali Raad, Jackson. MI 49201 .(517) 788 1636 July 2, 1985 Director.

Nuclear Reactor Regulation US Nuclear Regulatory Commission Washington, DC 20555 DOCKET 50-155 - LICENSE DPR BIG ROCK FOINT PLANT -

REPORTING REQUIREMENT EXEMPTION REQUEST - SPURIOUS REACTOR PROTECTION SYSTEM ACTUAT10NS Exemptions to NRC requirer.es.ts are allowable under 10CFR50.12(a) for any requirement and under I WFR50.73(f) for written reporting requirements. As descr$ bed herein, Consumers Power Company requests exemption from the specified sections of 10CFR50.72 and 10CFR50.73.

Since the adoption of reporting requirements in 10 CFR 50.72 and 73, Big Rock Point has experienced 18 reportable events. Of these, eight have been due to inadvertent Reactor Protection System (RPS) actuations while the plant was shutdown or at low power levels during plant shutdown. Due to its sensitivity, our neutron instrumentation is susceptible to spurious trips due to electrical noise at low power levels. The following list outlines these occurrences LER 84-04 (05/30/84) - Spurious electrical noise caused upscale /downscale trip, plant in process of shutdown (Power Level 4 x 10 -5%) . A few control rods were still partially withdrawn and did successfully insert.

LER 84-06 (06/01/84) - Spurious electrical noise caused liigh neutron flux trip, plant shutdown, no control rod movement.

LER 84-07 (06/11/84) - Spurious electrical noise caused liigh neutron flux trip, plant shutdown, no control rod movement.

I.ER 84-08 (06/27/84) - Spurious electrient noise caused upscale /downscale trip, plant shutdown, no control rod movement.

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Director, Nuclear Reactor Regulation 2

- Big Rock Point Plant Exemption Request July 2, 1985 LER ,84-10 (07/27/84) - Spurious electricil noise caused a short period trip, plant at 220 psig, no control rod movement.

LER 85-01 (01/05/85) - Spurious electrical noise caused an upscale /downscale trip, plant shutdown, one control rod withdrawn which successfully inserted.

LER 85-03 (04/14/85) - Spurious electrical noise caused upscale /downscale trip, plant shutdown, no control rod movement.

LER 85-04 (05/25/85) - Spuriots electrical noise caused upscale /downscale trip, plant shutdown, ro control rod movement.

In all cases, there have been no adverse safety consequences associated with these events since the challenges to the RPS occurred with plant shutdown or at very low power levels. Historically, spurious RPS actuations have existed at I;ig Rock Point because ~

of neutron instrumentation sensitivity at low neutron flux levels (<10 %). Investigations of the spurious actuations have concluded that corrective ac'. ion is neither necessary, useful or cost beneficial. Prior to implementation of the revised 10CFR50.72 and 50.73, such events did not require notification to the NRC.

The reactor is monitored by seven channels of neutron instrumentation in three ranges. These are the start-up range, intermediate range and the power range.

Start-up Channels Channels 6 and 7 provide logarithmic neutron flux level and

~9 ree level to five decades above source level period (approximately information 10 from sog% of rated power). A short period (<20 seconds) on to 10

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either channel is annunciated in the contrci room. Indication of core power level is also provided to the operators in the control room. These channels are not connected to the Reactor Protection System (PPS), since their useful range is far below the power level where the effects of a neutron excursion are minimal.

Log-N Channels Channels 4 and 5 g ovide logarithmic neutron flux and period information from approximately 10 to 100% of rated power. These channels are interfaced with the RPS and provide a short period alarm (<15 seconds) and scram (<10 seconds). The scram is bypassed when the range switches are at or above the 4% scale. This feature was included to eliminate the possibility of a spurious trip signal caused by the appearance of voids (due to boiling) in the core. Power Icvel changes above this point are in a sense self-controlled by void action, and flux level protection by the power range instrumentation is adequate.

Power Range Channels Channels i g 2 and 3 provide linear neutron flux information from approxiately 10 to 125% of rated power. Besides providing power level indication, these channels are interfaced with the RPS and initiate a reactor scram when 2 out of 3 channels detect a power level greater than 96% of full acale. An " upscale /downscale" reactor scram is also utilized OC0685-0218-NLO4

Director, Nuclear Reactor Regulation 3 Big Rock Point Plant Exemption Request July 2, 1985 to provide protection against instrument failure. With one channel greater than 96% and one less than 5% this feature is actuated. To eliminate the majority of spurious scram signals on the sensitive ranges.Sthis feature is bypassed when all 3 range switches are at or below 40 x 10- range. This feature was added after initial start-up to avoid spurious actuations.

-4 Below, a power level of approximately 10 %, the Log-N's and power range channels are susceptible to electrical noise causing spurious trips and

" nuisance" alarms. This causes the chort period trips from channels 4 or 5 and Hi flux or upscale /downscale trips from channels 1, 2 and 3. These spurious actuations occur during the process of a shutdown or start-up (rod motion), while the plant is shutdown (no rod motion), or during control rod drive testing or refueling activities (rod motion). Although the upscale /

downscaletripwouldnormallybebypassedattheselowpowerlevejs, plant ~

operators "up-range" the power range selector switches (>40 x 10 range) to avoid the " nuisance" alarms which occur at these low power levels. This action sets up the logic for the upscale /downscale trips which have occurred and have been reported since January 1, 1984.

Experience has shown that above approximately 10 % power the potential for electrical noise related spurious trips is significantly reduced and is the basis for this exemption request. At this power level or above, sufficient current flow is present in the neutron instrumentation channels to minimize the short spikes caused by electrical noise.

The plant is currently investigating the possibility of replacing the neutron instrumentation cht.nnels due to the unavailability of spare parts. This may eliminate the noise problem, but this change out would not occur for a few operating cycles.

Based on the above, the following exemptions are requested:

I. Requirement 10 CFR 50.72 (b)(2)(ii) "Any event or condition that results in manual or automatic actuation of any Engineered Safety Feature (ESF), including the Reactor Protection System (RPS). . ."

Requested Exemption Under 10CFR50.12(a)

Reactor Protection System (RPS) spurious actuations caused by internal l or external electrical noise in neutron instrumentation with reactor

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l power less than 10 % need not be reported to the NRC in accordance with 10CFR$0. 72(b) (2) (11) .

Dineussion It is our understanding that the purpose of the 10 CFR 50.72 verbal reporting requirements is to notify the NRC Operations Center as soon as possible to impicment the following:

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e Director, Nuclear Reactor Regulation 4 Big Rock Point Plant Exemption Request July 2, 1985

1. To provide immediate safety consequence assessment of the event, and provide mitigation support if needed.

2. To assess applicability to other nuclear units and determine whether prompt notification is warranted.

Since the events described above have no adverse safety consequences nor specific applicability to other nuclear units, reportability provides no apparent useful purpose.

II. Requirement 10 CFR 50.73 (a)(2)(iv) "Any event or condition that resulted in manual or automatic actuation of any Engineered Safety Feature (ESF),

including the Reactor Protection System (RPS). . ."

Requested Exemption Under 10CFR50.73(f)

Reactor Protection System (RPS) spurious actuations caused by internal or external electrical noise in neutron instrumentation with reactor power less than 10~4% need not be reported to the NRC in accordance with 10CFR50. 73 (a) (2) (iv) .

Discussion It is our understanding that the purpose of the 10 CFR 50.73 written reporting (LER's) is to provide the NRC a detailed description of events and safety consequences to enstre that appropriate corrective actions have taken place. Additionally, review of these events can be performed to assess applicability to other nuclear units. Since these events have no adverse safety consequences, appropriate corrective actions, or applicability to other nuclear units, reportability provides no apparent useful purpose.

Although these events would no longer be reported under 10 CFR 50.72 (b)(2)(ii) or 10 CFR 50.73 (a)(2)(iv), we would continue to review the events in detail to ensure that all systems function satisfactorily. Should deficiencies in system performance be discovered, reportability under 10 CFR 50.72 (b)(2)(iii) and 10 CFR 73 (a)(2)(v) would be pe rfo rmed .

The Big Rock Point Plant Review Committee has reviewed and determined that spurious RPS actuations caused by neutron instrumentation electrient noise are not a safety concern.

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Director, Nuclear Reactor Regulation 5 Big Rock Point Plant Exemption Request July 2, 1985 A check in the amount of $150.00 (application fee) is enclosed in accordance with 10CFR170.12(c) .

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David J [ deWa11e Director, Nuclear Licensing CC. Administrator, Region III, USNRC j NRC Resident Inspector - Big Rock Point I

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