ML20247Q580
| ML20247Q580 | |
| Person / Time | |
|---|---|
| Site: | Fermi  |
| Issue date: | 09/19/1989 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20247Q561 | List: |
| References | |
| NUDOCS 8909290029 | |
| Download: ML20247Q580 (4) | |
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UNITED STATES
$ r. 3 g NUCLEAR REGULATORY COMMISSION
$ %7 j W ASmNGTON, D. C. 20555
( M. i SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 36 TO FACILITY OPERATING LICENSE NO. NPF-43 DETROIT EDISON COMPANY WOLVERINE POWER SUPPLY COOPERATIVE, INCORPORATED FERMI-2 DOCKET NO. 50-341
1.0 INTRODUCTION
By letter dated April 3,1989, the Detroit Edison Company (Deco or the licensee) requested amendment to the Technical Specifications (TS) appended to Facility Operating License No. NPF-43 for Fermi-2. The proposed amendment woulo revise the TS by changing the current requirement of TS 3.9.2 relating to the Source Range Monitors (SRM) to permit complete core off-loading during the first refueling outage. The proposed amendment also increases the minimum signal-to-noise ratio required for a reduced SRM minimum count rate requirement and eliminates a related TS provision which is no longer needed.
The associated Bases are also revised.
2.0 EVALUATION Detroit Edison has scheduled the first refueling outage for Fermi-2 to begin during September 1989. During the outage, complete core off-loading is planned in order to more efficiently complete and accommodate refueling outage work. The removal of the assemblies adjacent to the Source Range Monitors (SRMs), which are the last fuel assemblies to be removed, would cause the loss of SRM detector count rate. This is contrary to the requirements of Specification 3/4.9.2, Surveillance Requirement 4.9.2.c, which requires a minimum SRM detector count rate be maintained at all times during CORE ALTERATIONS. The proposed amendment requests a revision to the requirement for a minimum SRM count rate so that when 16 or fewer fuel assenblies, each of which are installed in 1 of the 4 positions directly adjacent to 1 of the 4 permanently installed SRM nuclear detectors fuel assemblies (4 fuel assemblies surrounding each SRM detector), are in the core the minimum SRM count rate requirement does not apply. The proposed change is necessary to allow complete core off-loading.
Part of the proposed changes are directed at the Limiting Conditions for Operation for core monitoring during core alterations, and addresses Source Range Monitoring (SRM) operability, via count rate, and fuel assembly loading limits.
It specifically involves Specification 3/4.9.2 and the related Bases.
During reload operations the Technical Specifications require minimum count rate levels to be met by the SRM. During reload operations in a BWR in which the entire core is to be unloaded, especially if sources are not present, 8909290029 890W 2 PDR ADOCK 05000341 P
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, r there:may be times, when there are few fuel assemblies in the core, when this minimum cannot be met with the usual SRM. The current Technical Specification requirements are based upon the use of "Special Movable Detectors" connected
'to the " normal SRM circuits." Experience at other BWR stations indicates that these "Special Movable Detectors," i.e., " Fuel Loading Chambers"'(FLCs) do not function as originally anticipated. Experience has shown that the FLCs produce signal variations because of the lack of fixed core geometry during refueling operations'and tend to saturate because of gamma flux.. Further,
'because the FLCs are attached in a: temporary manner to facilitate ease of relocation, their use increases' the risk-of dropping them into the vessel.
The FLCs have been-found to be unreliable, and increase the probability of having a' loose object fall-in the reactor.
The proposed amendment would allow the licensee to go below the required SRM count l rate when there are not more than four fuel assemblies in each core
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quadrant, loaded around each of the four SRM positions for either loading or Junloading operations. For example, for a reload in which all fuei assemblies
,and normal sources-have.been removed from the core, they first load up to four
'(as necessary) irradiated assemblies next to each of the four SRM locations, without,necessarily meeting the required count rate until this loading is finished. The loading would then continue and would have to meet the usual counting rate requirement. General Electric has calculated that the con-figuration of (any GE) four assemblies (2x2 array) at the maximum reactivity
' condition'(as a function of burnup), without control rods inserted and
_. separated from other assemblies by a distance of two fuel cells, would have a k
of less than 0.95. Thus, the above configuration is well below a sub-cbicallevel.
The refueling system interlocks continue to be required during all CORE i
ALTERATIONS, including those involving the 16 fuel assemblies directly adjacent to the permanently installed SRM nuclear detectors, which are proposed to be allowed with the SRM count rate below minimum. These interlocks, along with the associated refueling procedures, provide additional assurance that inadvertent criticality does not occur during proposed operations with SRM count rate below minimum. These interlocks and procedures ensure the control rods are and remain inserted during such operations. The refueling interlocks are not affected by the loss of SRM channels due to loss of minimum count rate.
l-The reactor period circuit provides indication and alarm functions for the rate of change of reactor power as measured by the SRM. These functions are designed to provide operational information during reactor startup.
L Therefore, the impact on the reactor period functions of the SRM system from allowing SRM count rate to fall below the minimum requirement during certain CORE ALTERATIONS is not of concern.
The SRM rod block functions are provided to ensure that when necessary SRM indication exists prior to rod withdrawal. These rod block functions tre required to be OPERABLE per Specification 3.3.6 in OPERATIONAL CONDITION 5.
Although this proposal exempts the SRM channels from minimum count rate requirements during certain CORE ALTERATIONS, the rod block functions are still required. The SRM downscale rod block will actuate and provide additional assurance that rod motion does not occur without SRM monitoring i
capability. Therefore, the impact of the change on the SRM rod block functions is not of concern.
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In summary, the proposed changes which allow core off-loading and reloading without the use of FLCs will result in improved safety based on the following:
o The SRMs are more reliable than FLCs o
The risk of dropping loose objects into the reactor is reduced by eliminating the use of FLCs o
The elimination of the SRM count rate requirement when there are 16 or fewer fuel assemblies, each of which are installed in 1 of the 4 adjacent to 1 of the 4 permanently installed SRM positions directly(4 fuel assemblies surrounding each SRM detector),
nuclear detectors installed in the core does not, as discussed above, result in degradation of any feature necessary for safety.
The Technical Specification requirements for minimum count rate specify that a count rate of at least 3 counts per second (cps) be present unless a signal-to-noise (S/N) ratio of greater than 2 exists, in which case 0.7 cps is the specified minimum count rate. Recent studies by General Electric have indicated that an S/N ratio of at least 20 is required to reduce the minimum count rate to 0.7 cps. The increased S/N ratio is necessary to maintain the original level of source range monitoring uncertainty assumed by a 3 cps minimum count rate. Based upon the above, Detroit Edison is proposing to increase the S/N ratio necessary for a minimum SRM count rate requirement of 0.7 cps to 20. This change will return the plant to the original design bases and UFSAR requirements.
Further, the change provides a more conservative S/N ratio requirement in that, as proposed, a much greater S/N ratio will be required than is presently.
Amendment 1 to the TS provided special provisions to reduce the minimum count rate requirements to facilitate replacement of the start-up neutron sources.
These requirements were effective only prior to achieving a burnup of 2000 MWD /T on the first core. Since the effective period for these provisions has expired, the proposed amendment will eliminate the expired Amendment No. 1 provisions. This change is strictly administrative in nature and therefore the staff finds it acceptable.
Finally, the proposed amendment will reword the TS Sections 4.3.7.6.C and 4.9.2.C with the 3 cps requirements specified in the surveillance requirements of the specification and the 0.7 cps provision being included in a footnote.
This change provides clarification and is strictly an administrative change to the TS.
Based on the above evaluation, the staff finds that the proposed changes to the TS are acceptable.
3.0 ENVIRONMENTAL CONSIDERATION
Pursuant to 10 CFR 51.21, 51.32 and 51.35, an environmental assessment and finding of no significant impact have been prepared and published in the Federal Register on August 29, 1989 (54 FR 35735). Accordingly, based upon the environmental assessment, we have determined that the issuance of this amendment will not have a significant effect on the quality of the human l
environment.
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,4 if 2 4.0 ". CONCLUSION '
- We.have concluded, based on the considerations discussed above, that-(1)~there "is1 reasonable assurance that the health and safety of the public will' not be
- endangered bycoperation in'the proposed manner, and (2) sur.h' activities will be' conducted in compliance with the Commission's regulations, and the issuance-i of this amendment will-.not be inimical to the conunon defense and security or to the. health and safety of the public.
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Prinsipal Contributor: : John Stang Date:.. August 30,19d9 1
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