ML20237G854
| ML20237G854 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 08/26/1987 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20237G852 | List: |
| References | |
| NUDOCS 8709020436 | |
| Download: ML20237G854 (3) | |
Text
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- Ecuqk UNITED STATES
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p, NUCLEAR REGULATORY COMMISSION g
.j WASHINGTON, D. C. 20555
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 50 TO FACILITY OPERATING LICENSE NO. DPR-22 NORTHERN STATES POWER COMPANY MONTICELLO NUCLEAR GENERATING PLANT DOCKET NO. 50-263
1.0 INTRODUCTION
t By application dated February 18, 1987 and additional information submitted on June 18, 1987, Northern States Power Company (the licensee) requested an amendment to the Technical Specification for Facility Operating License No. DPR-22 for the Monticello Nuclear Generating Plant.
The amendment would clarify the Technical Specification operability requirements for Intermediate Range Monitor (IRM) and Average Power Range Monitor (APRM) scram instrumentation.
This change will provide relief to the licensee from the Technical Specification requirement of placing the plant in a
" half scram" condition while performing required APRM channel testing and mairstenance activities.
t 2.0 DISCUSSIONS The Monticello Technical Specification Table 3.1.1, Reactor Protection System (scram) Instrument Requirements, item 3, requires that the IRM i
channels be capable of performing a scram function while the reactor is in the RUN mode.
Note c indicates that this scram function is permissible to be bypassed when the associated APRM is operable and indicating at least 3/125 full scale.
The proposed change will delete this requirement and I
the note c.
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Table 3.1.1 item 4.e requires that at Neutron flux APRM Downscale condition i
l trips the reactor while the reactor plant is in the RUN mode.
The proposed j
l change will delete this requirement.
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The licensee stated that two problems exist with the Technical Specifica-tions in Table 3.1.1.
The first problem involves the requirement for an APRM downscale scram.
The second problem involves the bypassing of the APRM channels.
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- t By examining the circuitry of IRM/APRM scram circuits (Fig.1 in February 18, 1987 sbmittal), the APRM downscale scram function is bypassed by the IRM circuit even when the reactor mode switch is in the RUN position.
The wording of the current Technical Specification implies that an APRM downscale should cause a half scram.
The APRM Downscale Scram function exists in severs 1 early BWR plants including Monticello, but this function was deleted in the later BWR plants and the requirement removed from the standard BWR Technical Specification (NUREG-0123, Revision 3).
The licensee has stated that the only function performed by the APRM Downscale Scram is during the plant startup or shutdown.
This scram function will provide protection against operator error if the reactor mode switch was improperly switched.
During a normal plant startup, the mode switch is placed in RUN position when the power is above 5%.
If an operator were to prematurely place the mode switch in the RUN position, the APRM will be Downscale and the IRM Scram function will not be bypassed (the IRM Scram circuit will be bypassed when the mode switch is in RUN position and the APRM's are not downscale).
If this should happen, all safety concerns are addressed without reliance on the APRM downscale scram function.
The Control Rod Drop Accident is prevented by the APRM scram at the 120% thermal power setpoint, and the Rod Withdrawal Error is prevented by the APRM Downscale Rod Block system.
Prematurely placing the mode switch in the RUN mode is also protected by the main steam isolation valve (MSIV) closure scram function (due to low steamline pressure when the reactor mode switch is placed in RUN).
Another example of operator error can occur during power descent if the operator delays changing the reactor mode switch from the RUN mode to the STARTUP mode, thus bypassing the IRM's for a longer period of time and to a lower l
power level.
The consequences of this error are no different than those described above for power ascension.
The Control Rod Drop Accident and the Rod Withdrawal Error are protected by the APRM scram and the Rod Block system.
The IRM and the APRM Scram circuits are associated.
When an APRM is bypassed the associated IRM is also bypassed.
There are eight IRM channels while only six APRM channels.
Each Reactor Trip System (half scram logic) requires a minimum of three IRM channels and two APRM channels operational to satisfy j
the Technical Specification requirements.
The APRM Channel No. 3 and No. 4 4
g each have two IRM's associated with them.
During a channel test or maintenance I
of APRM Channels, bypassing APRM Channel No. 3 will also bypass IRM Channels No. 13 and No, 14.
Bypassing APRM Channel No. 4 will bypass IRM channels No. 15 and No. 18.
The minimum number of operable IRM channels cannot be
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met whenever APRM Channel No. 3 or No. 4 is bypassed.
Therefore, the I
plant has to be in a " half scram" condition while performing an APRM channel
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testing and maintenance.
The proposed change will eliminate this requirement during testing and maintenance of the APRM channels as discussed above.
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. 3. 0 EVALUATION The staff has reviewed the schematic diagram of the IRM/APRM scram circuitry and the justification for removal of APRM Downscale Trip.
The Technical Specification changes do not involve any modification of the reactor protection system wiring or circuitry.
The proposed chang'es y
clarify the intent of the original specification by clearly defining the scram functions needed to be operable in each mode of operation.
The-licensee is taking credit on the APRM scram and the APRM downscale trip in tha. Control Rod Block actuation circuitry.
Since both the APRM scram and the Control Rod Block actuation circuitries are required by the plant Technical Specifications for operability and surveillance testing, there is reasonable assurance that those circuitries will perform their protec-tive functions when needed.
Furthermore, the plant procedures instruct the operator to place the reactor mode switch in "RUN" position when the APRM's indicate above 5% power with all the downscale control l
board lights of.'.
The APRM downscale scram setpoint is 3/125 full scale.
The power level for switching the mode switch is above the APRM downscale scram setpoint.
The staff has verified that the standard BWR Technical Specification and all later plants do not require the APRM Downscale Scram nor the IRM Scram when the reactor is in RUN mode.
Based on its review, the staff finds that the proposed changes are acceptable.
4.0 ENVIRONMENTAL CONSIDERATION
l This amendment involves a change to a requirement with respect to the installation or use of a facility' component located within the restricted area as defined in 10 CFR Part 20. The staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite and that there is no significant increase in individual or cumulative occupational radiation exposure.
The Commission has previously j
issued a propo. sed finding that this amendment involves no significant hazards consideration and there has been no public comment on t,uch finding.
Accordingly, this amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b) no environmental imoact statement or environmental assessment need be prepared in connection with the issuance of this amendmant.
5.0 CONCLUSION
The staff has concluded, based on the considerations discussed above, l
that: (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner; and (2) such activities will be conducted in compliance with the Commission's regulations and the issuance of this amendment will not be inimical to the common defense and security or to the health and safety i
of the public.
Principal Contributor:
H. Li Dated: August 26, 1987 l
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