ML20236D941
| ML20236D941 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 03/14/1989 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20236D939 | List: |
| References | |
| NUDOCS 8903230370 | |
| Download: ML20236D941 (3) | |
Text
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+f UNITED STATES
- 8
'o NUCLEAR REGULATORY COMMISSION g
<~j WASHINGTON, D. C. 20555 k...../
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION
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RELATED TO AMENDMENT NO. 31 TO FACILITY OPERATING LICENSE NO. NPF-49 NOPTHEAST NUCLEAR ENE*tGY COMPANY, ET AL.
I MILLSTONE NUCLEAR POWER STATION, UNIT NO. 3 DOCKET NO. 50-423 INTRODUCTION
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By letter dated June 15, 1988, NortheastNuclearEnergyCompany(thelicensee) proposed changes to the Millstone 3 Technical Specification Tables 2.2-1, "Peactor Trip System Instrumentation Trip Setpoints" and Table 3.3-4, j
" Engineered Safety Features Actuation System Instrumentation Trips Setpoints."
l These proposed changes would decrease the reactor trip and auxiliary'feedwater initiation setpoints for " Steam Generator Water Level Low-low" from 23.5% to
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18.10% of the narrow range instrument span. The proposed changes reflect the results of a revised calculation of the error associated with this instruments-1 tion. The corresponding total allowance (TA), allowable value, and "Z" and "S" l
values in the aforementioned tables would also be revised accordingly. This proposed change would increase the margin between the " Steam Generator Water Level Low-Low" trip and the nomal operating band.
DISCUSSION i
The existing and revised steam generator water level low-low trip setpoints are calculated by the methodology described in WCAP-10991 " Westinghouse Setpoint Methodology for Protection System, tiillstone Unit No. 3," which is the same method used in calculating other setpoints in Tables 2.2-1 and 3.3-4 of the Technical Specifications. This methodology was approved by the NRC staff.
The licensee has evaluated four components associated with the " Steam Generator Low-Low" trip setpoint as follows:
- 1) the reference leg temperature 2) i environmental allowance for the transmitters, 3) safety analysis limit error, i
and 4) cabling insulation resistance error. The results of this evaluation are
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summarized as follows:
j 1)
The maximum post-accident reference leg water temperature was assumed to i
be equel to the maximum calculated containment temperature in the original j
analysis. The revised analysis considers the effect of the reference leg thertral insulation on the post-accident heatup rate and evaluates the.
reference leg water temperature 5 minutes into the accident scenario.
This is conservative because the FSAR accident analysis expects the steam i
generator water level low-low reactor trip to occur within 20 seconds following the accident scenario.
(The limiting accident is the feedwater 8903230370 890314 "x
PDR ADOCK 05000423 P
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l system pipe break described in FSAR Chapter 15, Table 15.2-1). The licensee has also collected plant data that indicates a nominal reference leg temperature of 125 F, rather than the 100'F assumed in the original calculation.
Because the span between the initial temperature and the accident conditions temperature is smaller, the heatup error is smaller.
e The original calculated error associated with reference leg heatup was 5.75%. Based on the new analysis the reference leg heatup error is 0.85%.
2)
The steam generator water level is monitored by Rosemount and Veritrak transmitters. Westinghouse reported an additional 1.68% environmental allowance error (from 10% to 11.68%) associated with the Veritrak level transmitters. The new setpoint calculation accounts for the updated environmental allowance. The previous calculation did not account for the new environmental allowance error.
l 3)
The safety analysis limit used in the design basis accident analysis was 0%. The FSAR erroneously reported a 3% margin to the safety analysis l
limit for the steam generator level low-low reactor trip. The effect of l
this error was an extra 3% margin in the steam generator level low-low reactor trip setpoint. This extra 3% is not included in the new setpoint a nalysis.
4)
The new setpoint calculation accounts for an additional cabling insulation resistance error,1.93% for Veritrak transmitters and 2.09% for Rosemount transmitters.
As the Veritrak transmitters exhibit the larger channel statistical allowance (CSA) than Rosemount transmitters, they are the limiting case and were used to l
determine the setpoint. Based upon the above, the licensee proposed that the new reactor trip setpoint and ESFAS instrumentation trip setpoint (auxiliary l
feedwater initiation) for the steam generator water level low-low trip setpoint will be 18.10% of narrow range instrument span.
The staff had previously approved the methodology for calculating the reactor trip and Engineered Safety Features Actuation System (ESFAS) setpoints. Therefore the methodology is acceptable. The setpoint is determined by adding an allowance for instrument error (18.10%) to the value of the parameter used in the FSAR analysis (0.0%). Therefore we find the proposed setpoint and the associated changes to the TS Tables 2.2-1 and 3.3-4, to be acceptable.
ENVIRONMENTAL CONSIDERATION l
This amendment changes a requirement with respect tn 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 signific6nt increase in individual or cumulative occupational radiation
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exposure. The Commission has previously published a proposed finding that the amendment involves no significant hazards consideration and there has been no l
public comment on such finding. Accordingly, the amendment meets the eligibility criteriaforcategoricalexclusionsetforthin10CFR51.22(c)(9). Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
CONCLUSION We have concluded, based on the considerations discussed above, 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 the amendment will not be inimical to the common defense and security or to the health and safety of the public.
l Dated:
March 14, 1989 d
Principal Contributor:
D.H. Jaffe I
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