ML19259B050
| ML19259B050 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 12/28/1978 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19259B049 | List: |
| References | |
| NUDOCS 7901160022 | |
| Download: ML19259B050 (4) | |
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- e, UNITED STATES a '.
NUCLEAR REGULATORY CCMMisslON WASHINGTON D.C.20555 s, m SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMEN 0 MENT NO. 46 TO FACILITY OPERATING LICENSE NO. OPR-65 NORTHEAST NUCLEAR ENERGY COMPANY, ET AL MILLSTONE NUCLEAR POWER STATION, UNIT NO. 2 DOCKET NO. 50-336 1.0 Introduction By application dated October 24, 1977, as supplemented by letter dated March 21, 1978, Northeast Nuclear Energy Company (NNECO or the licensee) requested an amendment to Technical Specifications (TS) appended to Facility Operatin License No. CPR-65 for Millstone Nuclear Power Station, Unit No. 2 MNPS-2).
The proposed change to the TS for MNPS-2 consists of increasing the allowed Resistance Temperature Detector (RTD) response time used in the Reactor Protection System (RPS) channels from less than or equal to five seconds to a variable value up to a maximum of ten seconds, i
2.0 Backcround i
The MNPS-2 RPS has three trip functions which require an input of the reactor coolant temperature as determined by one or more RTD's. These RTD's, located in instrument wells in the primary coolant system, provide inputs to the " Local Power Density-High," "Themal Margin / Low Pressure" and " Power Level-High" trip functions of the RPS.
TS 3.3.1.1 requires all RPS trip functions to undergo periodic tests to confim that their response times are within specified limits. A footnote to Table 3.3-2 defines RTD response time as the time interval required for the RTD's output to achieve 63.2". of its total change when subject to a step change in RTD tamperatt..
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. TS Table 3.3-2 contains the limits for the RPS respcnse times. The instrumentation channel response time has been listed separate from tht RTD response time since the issuance of Amendnent No. 32 on October 27, 1977. The existing TS requires an RTD response time of equal to or less than 5.0 seconds.
The RTD's initially installed in the RPS were qualified by the manu-facturer (Rosemount Engineering CompW) to have a response time of less than 5 seconds. The T5 response time surveillt. ace requirement states:
"The REACTOR TRIP SYSTEM RESPONSE TIME of each reat* r trip function shall be demonstrated to be within its lid. at least once per 18 months. Each test shall include at least one channel per function such that all channels are tested at least once every N times 18 months where N is the total number
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of redundant channels in a specific reactor trip fsnction as shown in the " Total No. of Channels" column of Table 3.3.1."
By letter dated June 15, 1977, NNECO informed us that while performing the first surveillance testing, Rosemount found one of the four RTD's had significant degradation in the response time. As a result, all RTD's were tested and 16 acceptable ones reinstalled in the RPS. This significant degradation in the RTD response time of some of the RTD's prompted NNECO to reanalyze the various limiting safety system settings (LSSS) dependent on instrumentation response times for RTD.
Response times in the range of five to fifteen secones maximum were reanalyzed in the October 24, 1977 request for a TS chance.
In their March 21. 1978 letter, NNECO modified the request to limit the response time to less than or, equal to ten seconds.
In discussions with the licensee, we have indicated that little is to be c?.inaf by having a variable RTD response time limit. We suggesta ' that tha revised TS specify a maximum RTD response time of 10 seconds. NNECO has agreed to this modification of their request. A similar request has been evaluated and approved for St. Lucie Unit No.1 in our May 26, 1978 issuance of license Amendment No. 27.
3.0 Discussion and Evaluation The proposed change in the RTD response time TS requires a reanalysis of the Power Level-High, the Local Power Density-High and the Thermal fiargin/ Low Pressure (TM/LP) trip setpoints.
3-3.1 Power Level-Hich and Local Power Density-Hich Trio Setooint Reanalysis NNECO has reanalyzed the trip setpoints for the Power Level-High and the Local Power Density-High reactor trips with an RTD response time of 10 seconds. This reanalysis shows that the existing setpoints are conservative for these trip functions. Based on our review of the reanalysis, we find that it was properly perfomed and that it properly accounts for the increase in RTD response time.
We find that the reanalysis demonstrates that it is acceptable to increase the RTD response time to less than or equal to ten seconds for these two functions without changing the trip setpoint.
Since these two setpoints still meet the criterion opon which the present setpoint analysis was based, we find the continued use of these setpoints acceptable with no reduction in the margin of safety.
3.2 Theral Marcin/ Low Pressure Trio Setooint The Tit /LP trip setpoint provides Departure frem Ecleate Boiling (DNS) protection Tor the core using as inputs the reactor power level, inlet temperature, pressure anti axial shase index. Details of the TM/LP circuitry and trip setpoint computation are presented in CENPD-199-CE Setpoint Methodology, April 1976.
lncreasing the RTD response time from less than or equal to five seconds to less than or equal to ten seconds has two effects on the TM/LP trip setpoint. First, the shape of the TS Figure 2.2-4 would be modified for low power level operation.
(The OR-1 function of Figure 2.2-4 is a function of the TM/LP trip setpoint to account for increased radial peaking due to rod insertion assuming the rods are inserted anywhere up to the power dependent insertion limit.)
However, since NNECO proposed Figure 2.2-4 based on a ten second RTD response time for the Cycle 2 reload, and we issued the proposed figure in Amendment No. 38 dated Wil 19, 1978, no change is required in regard to the shape of this LSSS figure.
The second effect of increasing the RTD response time is to change the value of the end term of the TM/LP equations. At the present time.
6240 psi is subtracted from the computed variable value for the low pressure trip setpoint. Changing the response time from less
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than or equal to five seconds to less than or equal to ten seconds decreases the tem to 6230 psi according to curves supplied by NNECO in their application.
Based on our review of their analysis methods for deriving these curves, the methods are acceptable and demonstrate that the changed curves adequately account for new RTD response tire with no change in margin to trio. This change has the effect of raisinn the low pressure trio setpoint by 10 psi for all reactor conditions. This change in trip setting compensates for the five second increase in RTD response time thus there is no change in the safety limit trargin of protection.
We find this reanalysis acceptable and ha eby change the TM/LP equations on TS pages 24 and 2-9 by replacing the value of 6240 psi with 6230 psi.
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4.0 Environmental Consideration We have determined that the amendment does not authorize a change in effluent types or total amounts noe an increase in power level and will not result in any significant environmental impact. Having made this determination, we have further concluded that the amendment involves an action which is insignificant from the standpoint of environmental impact and, pursuant to 10 CFR 551.5(d)(4), that an environmental impact statement, or negative declaration and environ-mental impact appraisal need not be prepared in connection with the issuance of this amendment.
5.0 conclusion We have concluded, based on the considerations discussed above, that:
(1) because the amendment does not involve a significant increase in the probability or consequences of accidents previously considered and does not involve a significant decrease in a safety margin, the amendment does not involve a significant hazards consideration (2) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the prooosed manner, and (3) 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 of the public.
Dated: December 28, 1978