ML20082Q015
| ML20082Q015 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 11/28/1983 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20082Q010 | List: |
| References | |
| NUDOCS 8312090280 | |
| Download: ML20082Q015 (3) | |
Text
o UNITED STATES
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NUCLEAR REGULATORY COMMISSION-E WASHIN2 TON, D. C. 20555
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, SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO.18 TO FACILITY OPERATING LICENSE NO. DPR-22 NORTHERN STATES POWER COMPANY
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. MONTICELLO NUCLEAR GENERATING PLANT
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DOCKET NO 50-263 1.0 Introduction By letter d ted September 24, 1982, Northern States Power Company (the licensee) proposed changes to the Technical Specifications (TS) of Facility Operating License No. DPR-22 for the Monticello Nuclea'r Generating Plant.
The revisions to the Technical Specifications concern the' temperature switches in the main steamline tunnel. The current Technical Specifications specify a trip setpoint of 2000F, with an allowable deviation of 20F. The proposed' changes would authorize an increase of the allowable deviation to 10 F.
Other changes requested in the September 24, 1982 submittal are still under staff review and will be addressed by separate Safety Evaluation and license amendment.
2.0 Background and Discussion The main steamline tunnel provides a passage for the main steamlines bet-ween the reactor and the main turbine. When a steamline break inside the tunnel is detected, the main steamlines will automatically isolate.
For small breaks, those on the order of five to ten gallons per minute (gpm),
the temperature' switches inside the tunnel provide the primary means of detection.
For large breaks, the temperature switches backup.the high steam f, low instrumentation.
As part of the September 24r 1982 application, the licensee attached a report which was prepared by its consultant, EDS Nuclear, Inc.
This evaluation includes a safety analysis supporting a temperature limit of
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2120F for the main steamline tunnel.
That is, a five to ten gpm break in a main steamline will raise the tunnel temperature to 2120F., The establishment of the trip setpoint is based upon this value and instru-mentation considerations.
The establishment of the allowable deviation is based upon the drift of the setpoint.
8312090280 831128
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PDR ADOCK 05000263 P
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'3.0 Evaluation
. High Temperature Switches in the Main Steamline Tunnel,- Allowable Deviation The staff. reviewed the licensee's application and associated report which was prepared by EDS~ Nuclear Inc.
In a January 5,1983 letter to the licensee, the staff requested additional information.
In a February 7, 1983 letter, the licensee addressed the staff's concerns and provided data on the drift of the switch setpoint.
Safety Analysis Limit of-2120F EDS Nuc$ ears Inc. performed an evaluation.for the iicensee, to determine the temperature rise in the main steam line tunnel area.
EDS Nuclear considered a break size on the order of five to ten gpm in either the main steamline or the three inch main steam' drain.line. Their results indicate that a break of this size is sufficient to increase the main 0
steamline tunnel ' temperature to at least 212 F.
The present trip setting for the temperature switches located in the main steamline tunnel is specified by Technical Specifications, at 2000F with an allowable deviation of 20F. The current trip setting of the temperature switches is not being changed, but the allowable deviation is being increased. With the 0
new temperature switch deviation.of 10 F, the new maximum allowable trip setting will be 2100F, which is less than the calculated safety limit of 212 F.
Therefore, we conclude that because sufficieht m'rgin exists between the a
trip setpoint (2000F) and the safety limit (2120F), the proposed increase in the allowable deviation is acceptable.
Allowable Deviation of the Trip Setp6 int In the February 7,1983 response to the NRC, the licensee provided data on the drift of'the switch setpoints.
The. drift data shows a Gaussian 0
distribution with a standard deviation of 3.8 F from the setpoint (2000F).
The probability of a temperature switch drifting beyond 2100F (setpoi'nt 0
of 2009F plus the proposed allowable deviation of 10 F) is very low.
Therefore, reasonable assurance exists that an allowable deviation of 100F is adequate.
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The total allowance in the protection channel, i.e., the margin of 120F between the safety analysis limit and the trip setpoint, needs to equal at least the combined channel uncertainties and errors.
By increasing the allowable deviation, or uncertainty due to drift from 20 to 100F, the adequacy of the total allowance, and thus the trip setpoint, was determined.
Previously only 2 F of the 120F total allowance 0
was allocated to drift. The requested amendment will change that to 10 F, leaving the difference to account for all other uncertainties.
One acceptable method 6f combining channel uncertainties is to combine
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them into indep'endent groups and then take the square root of the sum of the squares of each group. Using this method, the allowance for the other independent uncertainties comes to 6.630F. This value provide's adequate margin for. all the other channel uncertainties.
As such, there is sufficient margin in the present value of the setpoint.
Evaluation Summary The proposed changes that would increase the main steamline tunnel temper-ature switches allowable deviation from 20F to 100F for the Monticello Huclear Gent: rating Plant are found to be acceptable.
Furthermore, the trip setpoint remains adequate in the context of a larger allowed drift...
Therefore, we find acceptable the revision to TS -Table 3.2.7 that inc.reases,
the allowable deviation, from 20 to 10 F that is associated with the trip 0
setpoint of the temperature switches in the main"steamline tunnel.
4.0 Environmental Considerations We have determined that the amendment does' not authorize a change in effluent types or total amounts nor an. increase in power levei and will not result in any significant environmental impact. Having made this determination, we have further concluded that the amehdment involves an action which is insigni-I ficant from the standpoint cf environmental impact, and pursuant to 10 CFR Section 51.5(d)(4) that an environmental impact statement, or negative declaration l
and environmental impact appraisal need not be prepared in connection.with the I
issuance of the amendment.
5.0 Conclusions We have concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and safety of the public will l
not be endangered by operation in the proposed-manner, and (2) such act-ivities will be conducted in compliance with the Comission's regulations and the issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public.
Date: November 28, 1983 Principal Contributor:
M. Wigdor G. Thomas
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