ML20053B069
| ML20053B069 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 05/07/1982 |
| From: | Van Vliet J Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20053B068 | List: |
| References | |
| NUDOCS 8205270726 | |
| Download: ML20053B069 (4) | |
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 47 TO FACILITY LICENSE NO. DPR-71 AND AMENDMENT NO. 70 TO FACILITY LICENSE N0. DPR-62 CAROLINA POWER & LIGHT COMPANY BRUNSWICK STEAM ELECTRIC PLANT, UNITS 1 ' AND 2 DOCKET N05. 50-325 AND 50-324 I.
Introduction By letter dated April 30, 1982, the Carolina Power & Light Company (the licensee) submitted proposed changes to the Technical Specifications appended to Facility Operating License Nos. DPR-71 and DPR-62 for the Brunswick Steam Electric Plant (BSEP), Units 1 and 2 The proposed changes redefine source range monitor (SRM) operability during spiral unloading and spiral reloading operations.
II. Discussion A spiral unloading pattern is one in which the fuel in the outer-most cells (four fuel bundles surrounding a control blade) is removed first. Unloading continues by removing the remaining outermost fuel by cell so that the center cell will be removed last. Spiral loading is the reverse of unloading.
Spiral loading and unloading preclude the formation of flux traps (moderator-filled cavities surrounded on all sides by fuel).
The changes proposed by the licensee would allow the count rate of the SRM channels to drop below three counts per second (cps) when the entire reactor core is being removed or replaced in a spiral pattern. During any core alteration, and especially during core loading, it is necessary to monitor flux levels.
In this manner, even in the highly unlikely event of multiple operator errors, there is reasonable assurance that any approach to criti-cality would be detected in time to halt operations.
Thus the minimum count rate requirement (three cps) in the present Technical Specifications accomplishes three safety functions:
(1) it provides assurance that the SRM detectors are close enough to the array of fuel assemblies to monitor core flux levels, (2) it assures the presence of some neutrons in the core, and (3) it provides assurance that the analog portion of the SRM channels is operable.
Unloading and reloading of the entire core leads to some difficulty with this minimum count rate requirement. When only a small number of assemblies are present within the core, the SRM count rate will drop below the minimum due to the small number of neutrons being produced.
Likewise, with the decreasing geometry of the fuel array and the fixed position of the SRM detectors, the neutron attenuation by the increased distance and moderation will also affect the measurable count rate.
Past practice has been to connect temporary " dunking" chambers to the SRM channels in place of the normal detectors, and to locate these detectors 82052707260
BSEP :
near the fuel, Besides being operationally inconvenient, dunking chambers suffer from signal variations due to movement. Moreover, the use of dunking chambers increases the risk of loose objects being dropped into the vessel.
III.
Evaluation A.
Flux Attenuation The four SRM detectors are located, one per quadrant, roughly half a core radius from the center. Although these are incore detectors and thus very sensitive when the reactor is fully loaded, they lose some of their effective-ness when the reactor is partially defueled and the detectors are located some distance from the array of remaining fuel.
Spent fuel pool studies conducted by General Electric have shown 1/ that sixteen or more fuel assemblies (i.e., four or more control cells) must be loaded together before criticality is possible.
In spiral loading sequences in the BSEP core,-an array containing four or more control cells will be at most two control cells (.i.e., about two feet) away from an SRM detector.
I We have previously examined the sensitivity loss in such a case
- and found it to be acceptable.
Therefore, we similarly find the sensitivity loss at BSEP to be acceptable.
B.
Minimum Flux in the Core Assuring the presence of neutrons in the core eliminates the possibility of positive reactivity additions remaining undetected by the nuclear instrumenta-tion because of the lack of an initial neutron to start the neutron multipli-cation process.
In this case, the proposed Technical Specifications will permit the loading of fuel to proceed only to the point where eight fuel assemblies are in place before 'the three cps minimum count rate must be achieved; thus indicating the presence of neutrons in the core. As stated above, sixteen fuel assemblies must be loaded together before criticality is possible.
Therefore, the presence of neutrons in the core will be assured well before criticality is even remotely achievable. We find this acceptable.
C.
SRM Operability As in the preceding discussion, the proposed Technical Specifications will permit the spiral reload to proceed only to the point where eight fuel assemblies are loaded into the core before the three cps minimum count rate must be achieved.
Thus, SRM operability will be demonstrated well before criticality is achievable.
We find this acceptable.
D.
Sunmary We have examined the proposed amendment as described above and find it to be acceptable.
BSEP lV. Environmental Considerations We have determined that the amendments do not authorize a change in effluent types or total amounts nor an increase in power level and will not result in any significant environmental impact.
Having made this determination, we have further concluded that the amendments involve an action which is insignificant from the standpoint of environmental impact and,, pursuant to 10 CFR 551.5(d)(4),
that an environmental impact statenent, or negative declaration and environ-mental impact appraisal need not be prepared in connection with the' issuance of these amendments.
V.
Concl usion We have concluded, based on the considerations discussed above,-that:
(1) because the amendments do not involve a significant increase in the probability or consequences of accidents previously considered and do not involve a signi-ficant decrease in a safety margin, the amendments do 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 proposed manner, and (3) such activities will be conducted in compliance with the Commission's regulations and the issuance of these anendments will not be inimical to the common defense and security or to the health and safety of the public.
Dated: May 7, 1982 Author:
J, A. Van Vliet l
l
t BSEP '
4 References l.
General Electric Standard Safety Analysis Report, 251-GESSAR, Section 4.3.2.7, pg. 4.3-27.
2
" Safety Evaluation by the Office of Nuclear Reactor Regulation Supporting Amendment No. 27 to Facility Operating License No.
DPR-63", Docket No. 50-220, enclosed with letter, T, A. Ippolito 3
(fiRC) to D. P. Dise (Niagara Mohawk Power Corporation), dated March 2, 1979.
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