ML19207C410

Request for Tech Specs Change Incorporation Procedure for Reactor Startup in Event Neutron Source Strength Is Below Level Necessary to Provide Min Count Rate on out-of- Core Nuclear Instrumentation

ML19207C410
Person / Time
Site:	Big Rock Point File:Consumers Energy icon.png
Issue date:	09/11/1979
From:	CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:
Shared Package
ML19207C405	List: ML19207C404 ML19207C410
References
NUDOCS 7909110593
Download: ML19207C410 (4)

Text

,

e CCNSUMERS POWER COMPANY Docket 50-155 Request for Change to the Technical Specifications License DPR-6 r

For the reasons hereinafter set forth, it is requested that the Technical Specifications contained in Facility Operating License DPR-6, Docket 50-155, issued to Consumers Power Company on May 1, 196h for the Big Rock Point Plant be changed as described in Section I below:

I.

Ch ance Add a new paragraph to Section T.3.2.(d) reading:

"In the event that neutron source strength is insufficient to produce the required count rate, an approach to criticality for reactor start-up shall be allowed provided that the following conditions are met.

This procedure shall also be used for any subsequent start-ups as may be nec-essary until sufficient pcVer operation has been accumulated to irradiate the antimony-berylium sources sufficiently to produce the required count rate.

(i) Prior to the first start-up after development of the lov source strength condition, a critical approach (es) with the reactor vessel head off shall be performed to evaluate the out-of-vessel low-level detector response and the control rod withdrawal sequence.

Two additional low-level detectors shall be temporarily inserted in the vessel to monitor this head-off critical approach (es). These addi-tional detectors shall indicate a minimum of 3 counts p ar second with a signal-to-noise ratio of 3 to 1.

(ii) Evaluation of instrument responses during the head-off critical approach (es) shall demonstrate that, by the time the estimated kerr of the core reaches 0.995, each low-level out-of-core start-up detector is reading at least 3 cps with a 3 to 1 signal-to-noise ratio.

(iii) Critical approaches with the head on and without the temporary in-vessel low-level detectors in service shall be permitted provided that the instrument response requirements of (ii) above have been demonstrated and provided that these same requirements are also met during each critical approach with the head on.

Normal start-up may continue any time start-up count rate is at least 3 counts per second with a minimum signal-to-noise ratio of 3 to 1.

(iv) The procedure of (i) and (ii) above shall be repeated by conducting additional head-off critical approach (es) in the event of either a core configuration change or a significant change in that part of the control rod withdrawal sequence for which the minimum count rate and signal to noise ratio specified above are not attainable.

7909110 I3353 940 2"6

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2 (v) The site reactor engineer or his alternate vill be on site during all head-off critical approaches and instrument response evaluations and during the initial head-on start-up following head-off evalua-tions.

II.

Discussion The Big Rock Point Plant was shut down in early February 1979 for mainte-nance and refueling. The shutdown was extended to repair a control rod drive penetration leak and to replace recirculation inlet diffusers.

(REF LER 79-18 and 79-20). Start-up from this shutdown is estimated for early tober 1979 Start-up count rates obtained during initial critical approaches in April 1979 vere 13 counts per second with a h to 1 signal-to-noise ratio.

The control rod drive penetration leak and inlet diffuser problems were identi-fled within the first several hours of reacter operation, thus the antimony-berylium start-up sources were not subjected to significant irradiation during April 1979 critical operations.

Based upon this experience and the Q day half life of the anticony-berylium sources, Consumers Power Company estimates that start-up count rates may be as lov as 2 counts per second during the scheduled October 1979 start-up.

This low count rate may also make the required 3 to 1 signal-to-noise ratio unattainable.

Several criticals are proposed for the start-up planned for a:tober.

The' first vill be a head-off critical and vill begin with reactor conditions as follows:

(a) 8h fuel assemblies in the core loaded in a configuration nearly identi-cal to the initial Cycle 16 core loaded in April.

(b) Pritary neutron sources located in Positions 0252 and 0959, auxiliary neutron sources in core locations defined by Technical Specifications Section 5.1.6.

(c) Additional fission chambers temporarily inserted in the vessel located near the core reading 3 cps minimum with a signal-to-noise ratio greater than or equal to 3 to 1.

(d) All seven cut of core instruments (two start-up range, two intermediate range, and three power range monitors) in service.

(e) Reactor water temperature at achient.

(f) All rods fully inserted and core initial kef; near.93 This critical approach vill be performed using a control rod withdrawal sequence developed to stay within Technical Specifications control rod and notch vorth limits. The temporary in-core fission chambers vill be used to conitor flux increase during the start-up and the seven out-of-core instru-ments vill be in service to provide their normal safety functions.

Based on count rates encountered during the initial critical in April, it is 9zioL'o7/

t 3

expected that the count rate on the out-of-core start-up monitors will meet both the 3 cps and the 3 to 1 signal-to-noise ratio before reaching a core k pt of.995 Records of count rate vs control rod ccnfiguration e

and k rr will be taintained throughout this critical approach.

By the e

time the estimated.995 k ff configuration is attained, the out-of-core 9

start-up range monitors vill be tested to assure required counts and signal-to-noise ratio will be available during subsequent start-ups.

The first head-on critical during the coming start-up will be at the same conditions described for the head-off critical except that the vessel head vill be in place and the temporary fission chambers will no longer be in the vessel.

Reactor water temperature vill be greater than or equal to 190 F as required by Technical Specification h.1 and 10CFR50 App G.

Signal-to-noise ratio and gross count rate with all rods inserted are ex-pected to be near but possibly less than the specified minimum values.

If start-up range monitor count rate and signal-to-noise ratio do not meet the requirements of Technical Specifications Section 7.3.2.(d), the con-trol rods will be withdrawn in a pattern identical to that for the head-off critical and start-up range monitor 1/m plots as a function of keff vill be ccmpared to those generated for the head-off critical.

If, prior to or at the time of the estimated.995 keff centrol rod configuration established during the head-off critical app:cach is attained, a minimum signal-to-noise ratio of 3 to 1 and a gross count rate of greater than or equal to 3 cps are displayed by the start-up range monitors, normal start-up will continue.

All rods will be returned to their fully inserted positions should these in-strumentation requirements not be met by the time the head-off.995 keff control rod configuration is attained.

The head-off.995 keff control rod configuration has been chosen a?s the point at which start-up can continue for the following reasons:

1.

Start-up count rate is expected to be acceptable at this configuration.

2.

5% A K margin is available prior to going critical. This is more than twice the taximun predicted notch vorths to be enecuntered during this part of the withdrawal sequence and.2% greater than the Technical Specification limit for notch vorth. Additional margin vill exist at 190 F due to the negative effect of the water tempera-ture on reactivity.

Subsequent start-ups with targinal start-up count rates may be necessary due to shutdowns which may be encountered during the early part of the cycle.

Until such time as the strength of the neutron sources has been reestablished, similar start-up procedures will be followed.

That is, control rods may be pulled as far as the.995 keff c ntrol rod config-uration established for the head-off critical apprcach observing qOO

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