ML20059N206
| ML20059N206 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 09/25/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20059N205 | List: |
| References | |
| NUDOCS 9010100247 | |
| Download: ML20059N206 (6) | |
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' UNITED STATES f'
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NUCLEAR REGULATORY COMMISSION
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-SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 33 TO FACILITY' OPERATING LICENSE N?.'NPF-73 DUQUESNE LIGHT' COMPANY ~
OHIO EDISON COMPANY:
THE-CLEVELAND ELECTRIC ILLUMINATING COMPANY THE TOLEDO EDISON COMPANY BEAVER VALLEY POWER STATION. UNIT NO. 2 DOCKET NO. 50-412
1.0 INTRODUCTION
By letter dated April 16, 1990, Duquesne Light Company proposed a revision to the Beaver Valley Unit.2 Appendix A Technical Specifications-(TSs) Table-2.2-1, 3.2-1, 3.3 and Table 3.3-2.
The proposed revision ~would allow removal of the existing Resistance Temperature Detector (RTD) bypass ' manifold =
system and replacement with thermowell-mounted fast-response RTDs located directly in the reactor coolant system piping. This plant modification.
affects the FSAR response time design basis.for overtemperature/ overpower-Delta T and loss of flow reactor trip functions...The Beaver Valley Unit:2 TSs are also modified to incorporate the revised response times and/or instrument uncertainties into the applicable reactor trip functions.- The reactor.
protection system T average and Delta T-input methodology along with the system inputs of T average and Delta T to the plant-control system are also revised.
Based on a telephone call with the licensee on August 22, 1990, additional changes were made. These changes were administrative in nature (deletions of references to the system to be removed) to achieve consistency-in the TSs.
They do not affect the substance of the amendment, nor do they alter the staff's proposed no significant hazards consideration finding.
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2.0 DISCUSSION 2.1 Existing System Currently, the T-hot and T-cold RTDs used for reactor control and protection are-inserted into reactor coolant bypass loops. Separate bypass loops are-provided for each reactor coolant loop such that individual-loop temperature signals may be developed for use in the reactor control and protection systems. A bypass loop from the hot leg side of each-steam generator to'the-intermediate leg is used for the T hot RTDs. Another bypass loop f rom the cold leg side of the reactor. coolant pump to the-intermediate leg is used for the T cold RTDs. Both T-hot and-T-cold manifolds empty through a' common-header to the intermediate leg between the steam generator'and reactor coolant pump.
The RTDs are located within manifolds and are-inserted directly into the.
reactor coolant bypass flow without thermowells.
The bypass manifoldi system limits high velocity coolant flow to the RTDs and compensates-for the temperature streaming effects present'in the hot leg piping.
For each T-hot bypass loop, flow is provided by three scoop. tubes located at 120 degree
- l intervals around the hot leg. Because of the mixing. effects of the reactor coolant pump only one scoop tube connection is required for bypass flow to the T-cold bypass manifold.
The output from the bypass loop RTDs provides the signals necessary< to calculate the average loop temperature (T average) and the_ loop.differertial temperature (Delta T).
The T average an Delta T signals are then.-input'to the l
reactor protection system and engineered safety features actuation systems.
The input of T average and Delta T signals to the plant control system are der.ived from a separate set of bypass loop RTDs and T average.and Delta T calculations.
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- 2.1 Modified System 1
The modified system hot leg-temperature measurement for eachtloop;will be obtained using three fast-response, narrow-range, single-element RTDs.
These RTDs will be mounted in thermowells within the three existing hot-leg bypass scoop penetrations.
Each bypass scoop-will be modified such'that reactor coolant will flow.in through the extr'ing holes of.the bypass scoop.past the RTD/thermcwell and out through a new nole machined in the' bottom of the bypass scoop. This modified RTD arrangement performs:the sane sampling / temperature _
- i averaging function as the bypass manifold system.
The cold-leg neasurements are obtained by one: fast-response, narrow-range,.
dual-element RTD. located at the discharge'of the reactor' coolant pump.- This-RTD is also mounted in a thermowell within the existing cold leg bypass manifcid penetration.
Because temperature gradients in the' cold. leg are eliminated by.the mixing action of the reactor coolant pumps, only one RID is-necessary for cold-leg temperature measurement.. As in the hot.- leg, the bypass manifold penetration nozzle will be modified to accept'the RTD thermowell.
Additionally, the bypass manifold return line will be capped at the nozzle.on the intermediate leg.
l Neither of these modifications will affect the single existing wide-range RTDs installed in each hot and cold leg of the reactor coolant system.: The RTDs will continue to provide hot and cold leg temperature information for. reactor startup, shutdown or post-accid r" monitoring.
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To accomplish the hot-leg temperature averaging function previously done by-u 3
the bypass manifold system, the modified hot-leg' RTD temperature signals are
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electronically averaged in the reactor protection system..This averaged T-hot signal will thm be used with the T-cold signal to calculate reactor coolant l
l loop Delta T and T average values utilized in the reactor protection and-control systems.
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j i i The present bypiss system uses separate ' dedicated RTDs for the control-and protection systems.
However, the modified system thermowell-mounted RTDs are used for both protection and control.
This Class 1E and Non Class 1E interface will require the use of isolation _ devices' for the control system T average and Delta T signals derived from the reactor protection system.
Additionally, the T. average and Delta T signals used in the control gra m l
logic are input into a median signal selector (MSS) in lieu of the high.
q auctioneered T average or Delta T signal used by the'present plant control i
sys tem.
The MSS selects the signal' that is between the highest and lowest values of the three T average and Delta T' loop inputs.
By selecting the median value the MSS provides the plant control system with a valid T average and Delta T value. The MSS will also preserve the functional independence between corirol and protection systems that now share comon -sensors within RPS.
To ensure proper operation of the median signal selector the existing manual switches that allow for defeating a T average or Delta T signal from a single loop will be eliminated. Also, the conversion to thermowell-mounted RTDs will result in the elimination of the control grade RTDs.and their associated control board indicators.
The protection system channels will now provide inputs to the control system.thr'ough isolators and the MSS. ' Existing control board alarms, indicators and T average and Delta-T deviation alarms will provide the means to identify some RTD failures.
A failure of a~ hot' leg RTD can be handled by having plant personnel disconnect the'affected channel and rescaling the electronics to average.the remaining two hot leg inputs. A bias value is then added.to the T-hot average signal to compensate for the failed RTD and maintain a'value comparable'with the previous three RTD average, This bias value is developed per procedure /TS requirements using data recorded at 100% power and during normal protection system surveillances.
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.. 2.3 Evaluation l
' Based on our~ review the modified RTD system is not functionally different from the unmodified system except for the use cf three RTDs instead.of one.
The reactor-L protection or engineered safety features actuation systems will operate as before. The FSAR as do umented in section-7 for Beaver Valley Unit 2 remains valid. The additional electronics for averaging the three T-hot RTD signals are to be qualified to the same level.as the existing 7300 electronics.
The 1 solation devices are also standard 7300 series equipment and were previously reviewed under WCAP 8892A. The RTD qualification will satisfy the requirement of 10 CFR 50.49. Based on the above,.the staff finds the proposed plant modification to replace the RTD bypass manifold system with thermowell mounted, p
fast response RTDs located directly in the reactor coolant system piping. to be acceptable.
To support'the modifications required to eliminate the RTD bypass manifold.
system, _ changes to the Beaver Valley Unit 2 Technical Specifications.were proposed. These TS revisions are a result of the difference in the uncertainties between the thermowell mounted RTDs and.the bypass. manifold system.
Revised values for allowable values of 2, S-and,TA for 0vertemperature Delta T, Overpower Delta-T and Loss.of. Flow were calculated using essentially the same setpoint methodology as _previously approved by the
-3 staff.
Evaluations performed by the licensee determined that' the revised values.of allowable values, 2 and S remain valid for the proposed: bypass system elimination.
The remaining TS changes revise Table 3.2-1 (DNB parameters) and _ reactor coolant T~ average from 580.2 to 580.3-' degrees to reflect revised RCS temperature uncertainties. The staff finds'the proposed
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changes to be acceptable based on our review of the licensee submittal and the Beaver Valley Unit 2 TS.
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3.0 ENVIRONMENTAL CONSIDERATION
i This amendment changes'a requirement with respect to the-installation or use of' a facilu; wpnent located within the restricted area as defined in.10.-
CFR Part 20. We have 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.
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increase in individual or cumulative ~ occupational radiation exposure.
The s.taff has previouslycissued a proposed finding-that'this amendment involves no I
significant hazards consiaeration and there has been no public connent on suc.h j
finding. Accordingly, the amendment meets the eligibility criteria for
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categoricalexclusionsetforthin10CFR51.22(c)(9).
Purs9 ant to 10 CFR l
51.22(b) no environmental impact' statement or environmental assessment need be i
prepared in connection with the issuance of the amendment.
4.0 CONCLUSION
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We have' concluded, based on the considerations-discussed above, that: (1)-
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h there is reasonable assurance that the health and safety of the public I
l will not be endangered by operation'in the proposed manner,'and (2) such' activities will be conducted in compliance with-the Connission's regulations, and-(3) th'e issuance of the amendment will not be inimical to the common j
defense and security or to the health and safety of the public.
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j Dated: September 25, 1990 l
P icipal Contributor:
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Clifford K. Doutt 4
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