ML20212B350
| ML20212B350 | |
| Person / Time | |
|---|---|
| Site: | La Crosse File:Dairyland Power Cooperative icon.png |
| Issue date: | 12/17/1986 |
| From: | Taylor J DAIRYLAND POWER COOPERATIVE |
| To: | Zwolinski J Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20212B357 | List: |
| References | |
| LAC-12018, NUDOCS 8612290226 | |
| Download: ML20212B350 (4) | |
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- P O BOX 817
- 2615 EAST AVE. SO (608) 788-4000 JAMES W. TAYLOR General Manager December 17, 1986 In reply, please refer to LAC-12018 DOCKET No. 50-409 Mr. John A. Zwolinski, Director BWR Project Directorate #1 Division of BWR Licensing U. S. Nuclear Regulatory Commission Washington, DC 20555
SUBJECT:
DAIRYLAND POWER COOPERATIVE LA CROSSE BOILING WATER REACTOR (LACBWR)
PROVISIONAL OPERATING LICENSE NO. DPR-45 APPLICATION FOR AMENDMENT TO LICENSE
Reference:
(1) le CFR 50, Section 50.90 Gentlemen:
In accordance with the provisions of Reference, we are submitting an application to amend Provisional Operating License No. DPR-45 by proposing changes to Technical Specifications for the La Crosse Boiling Water Reactor (LACBWR).
LACBWR purposes to re-arrange the " Partial Scram" trips in the Rod Control and Scram System for the low gas pressure and low oil level in a control rod drive accumulator such that it would require a low oil level in any control rod drive accumulator and a low gas pressure in any control rod drive accumulator to cause a partial scram.
The present system produces a partial scram if a low oil level or a low gas pressure occurs in any of 29 accumulators (a 1 out of 58 logicT A " Partial Scram" in the LACBWR is a rapid full insertion (scram) of 13 control rods of a pre-selected pattern that ensures the reactor will be subcritical in a hot, non-boiling condition at any stage of fuel lifetime. A full scram is a rapid insertion of all 29 control rods into the core.
The purpose of the partial scram is to allow the reactor to attain criticality and return to power more quickly than if all control rods needed to be withdrawn to the operating program.
The selection of the parameters in the original design of the reactor protection scheme was to have all scrams except high neutron flux (during power operation) and neutron flux period (during startups) as partial scrams.
This design was not possible to be licensed, and in the process the concept of the partial scram was relegated to such a low status that only 5 signals; a low gas pressure or low oil volume in an individual control rod drive scram accumulator, loss of power to either 8612290226 861217
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y Mr. John Zwolinski, Director December 17, 1986 BWR Project Directorate #1 LAC-12018 of the 2400 volt electrical buses, closure of the turbine steam stop valve and a manual push button on the control room bench board remain as trip signals.
A reference to the low gas pressure or low oil level partial scram exists on the following non-revised pages of the current Technical Specification, and are enclosed:
17, 2700, 33, 36, 5-10 and 5-14.
The proposed changes in this submittal alter the requirement for a partial scram on a low oil level or a low gas pressure in a Control Rod Drive Mechanism (CRDM) accumulator and institutes a LCO as specification 4.2.7.1 (page 36) which allows operation with a single inoperable accumulator, but requires action if more than one low oil level or low gas pressure develops.
Specifically, specification 2.8.7 (page 17) is deleted. The safety action required on loss of voltage to Reactor Building Motor Control Center lA is specified in Table 1.
The action for low oil level and low gas pressure is also specified in Table 1.
The reference to the partial scram reset or bypassed in specification 2.10.2.3 on page 19 is not changed and all accumulators are still required to be charged prior to obtaining a reactor start permit.
Specification 4.2.4.7 (page 33) is revised to reflect the conditions imposed by an inoperable control rod drive but still require all technical specifications to be met which includes core power distribution limits.
Therefore, there are no consequences of eliminating the restriction that the control rod be either full in or full out for the drive to be disabled.
A separate feature of the rod drive mechanism assures rod insertion into the core even if the accumulator function is lost and the need for a scram occurs.
If the hydraulic motor drives slower than the electric motor during rod insertion, the electric motor exerts torque to drive the control rod completely into the core.
Upon the completion of scramming motion, or completion of shimming motion at any position along its stroke, the control rod is positively prevented from further vertical motion by the action of the mechanical brake which is always engaged.
The requirement of specification 4.2.4.7 to electrically disconnect the clutch and drive member is deleted because it would have prevented the electric motor from driving the control rod in as a back-up to the scram signal.
Items 21 and 22 of the Table on Minimum Frequencies for Testing, Calibrating, and/or Checking of Instrumentation have been revised to show that the trips from CRDM accumulator low gas pressure or low oil level are tested at a minimum frequency. The trip setpoints will be the same as the previous setpoints for a partial scram (page 5-10).
Items 12 and 13 of Table 1-Operating Limits are revised to show instrument setpoints and action ( page 5-14).
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Mr. John A. Zwolinski, Director December 17, 1986 BWR Project Directorate #1 LAC-12018 The bases for Control Rod Drive Accumulators (specification 4.0.2.2 on page 27oo) has been deleted from this page, revised and becomes the bases for specification 4/5.2.7 (pages 36 and 36a).
All revisions are incorporated on enclosed replacement pages.
The proposed amendment would allow the low gas pressure and low hydraulic oil level trips to be combined in the Partial Scram circuit to be combined in an "and" configuration instead of "or".
There are 29 switches capable of initiating a low gas pressure partial scram, and 29 more switches used to initiate a low oil level partial scram. One partial scram from low oil level or low gas pressure occurred in 1968; one in 1971; one in 1975; from 1979 thru 1984 there was a total of six, but in 1985 to the pressent there have been four.
In none of these, except the first one (in 1968), was the plant able to utilize the feature of being able to restore the plant to power from the partial scram condition.
It is incumbent on the LACBWR staff to reduce the number of scrams of the plant, as they may initiate undesirable challenges to the plant safety systems.
The change from a 1 in 58 logic for a partial scram to a logic that allows continued plant operation with one low gas pressure trip or one low hydraulic oil level (but not both) is in line with the single failure analysis of the control rod drive mechanism.
That analysis showed that even if a single rod failed to scram, the reactor would still be shut down. The LCO action statement allowing troubleshooting for more than one low gas pressure trip or low oil level trip is deemed reasonable.
Each accumulator has a low oil level alarm and a low gas pressure alarm prior to the trip setpoints.
We have reviewed the hazards considerations referenced in 10 CFR 50.92 and have determined that no significant hazards result from this proposed amendment because it does not:
(1) Involve a significant increase in the probability or consequences of an accident previously evaluated because the low oil level or low gas pressure partial scram was not utilized as the shutdown mechanism in any accident analysis.
(2) Create the possibility of a new or differnt kind of accidem from any accident previously analyzed, however, different operation of th control rod drives may occur.
If an accumulator develops a low gas condition, or the accumulator loses hydraulic fluid, the control rod may not fully insert hydraulically upon a scram signal, but a separate feature of the rod drive mechanism assures rod insertion even if the accumulator function is lost and the need for a scram occurs.
The electric shim motor is also energized upon a scram signal, and if the hydraulic (scram) motor drives slower than the electric motor, then the electric motor drives the control rod completely into the core.
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Mr. John A. Zwolinski, Director December 17, 1986 BWR Project Directorate #1 LAC-12018
-(3) Involve a significant reduction in the margin of safety because there would be no serious consequences if a failure of a control rod drive mechat. ism prevented a withdrawn rod from entering the core under scram conditions. The core would be subcritical by at least 0.5 percent delta k/k, even if the failed rod was of maximum worth and it did not enter the core.
If more than one of the same type of accumulator trip occurs, the proposed LCO requires action to be taken within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> and if ineffective in restoring the system to operability - then hot shutdown is achieved in the next 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.
History of the LACBWR rod control system has demonstrated that the probabil.ity of having more than one control. rod drive inoperable is negligible.
An application fee of $150 will be forthcoming for this license amendment request.
If there are any questions, please contact us.
Sincerely, JWT: HAT:sks Enclosure cc:
Mr. James C. Keppler, Region III NRC Resident Inspector Mr. John Stang, LACBWR Project Manager Mr. L. L. Smith, Director of Electric and Water Bureau Wisconsin Public Service Commission P. O. Box 7854 Madison, Wisconsin 53707 STATE OF WISCONSIN )
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l COUNTY OF LA CROSSE )
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Personally came before me this
/f
_ day of
, 1986, the above named James W. Taylor, to me known to be the person who executed the foregoing instrument and acknowledged the same.
b}tH LJ J
Notary Public, /La Crosse County Wisconsin My commission expires February 21, 1988.
WPl.3.6