ML20010J246
| ML20010J246 | |
| Person / Time | |
|---|---|
| Site: | FitzPatrick  |
| Issue date: | 08/26/1981 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20010J243 | List: |
| References | |
| NUDOCS 8109300021 | |
| Download: ML20010J246 (5) | |
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_ SAFETY FVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMEND 1ENT NO.59 TO FACILITY OPERATING LICENSE NO. OPR - 59 POWER AUTHORITY OF THE STATE OF NEW YORK
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DOCKET NO. 50-333 1.
Introduction By letter dated December 6,1979(l) the Power Authority of the State of New York (PASNY) requested an amendment to the Technical Specifications for the James A.
FitzPatrick Nuclear Power Plant (JAF). The proposed Technical Specification changes provide for spiral unloading / reloading of the core, permits spiral reloading without th~e requirement that all control rod blades be fully inserted, and redefines Source Range Monitor (SRM) operability during the spiral unloadir.g/ reloading operations.
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2.
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.
Unicading 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-fflied cavities surrounded on all sides by fuel).
It is not necessary to accomplish a full core offload or onload in order to utilize the spiral movement procedure as long as the partial unloaoing/ reloading plan ccmplies with the description given above.
BWR Technical Specifications normally require that all but one control blade be inserted into the core during core alterations. This is no problem during nomal refueling and control blade drive maintenance since only one core cell (defined as a control blade olus the four adjacent fuel assemblies) is worked on at any given time. However, a removal of the entire core would require all the fuel to be removed before any control blade was removed. This is not possible unless the plant has a full complement of control blade guides. These guides are needed to provide lateral support to control blades in defueled cells.
The JAF facility does not have this many guides.
During the spiral unloading procedure described above the cells are removed sequentially in a spiral sequence with the cells closest to i
the center of the core removed last. During unloading of a fuel cell the control rod is removed or withdrawn. For the reasons justified here-in it is not necessary to replace or insert the control rod for the given fuel assembly prior to removing the next fuel cell in the spiral sequence. Therefore, during the spiral unloading sequence more than one control rod may be absent at any point in time since control rods are I
not required in defueled cells. The, loading sequence is the reverse of the unloading sequence with fuel loaded and control rods inserted in the center of the core first, and core perimeter cells loaded and control rods inserted last.
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. The effect of the amendment would also all sw the count rate ir. the Source Range Monitor (SRM) channels to drop bel : 3 counts per second (cps) when the entire reactor core is being removed or replaced.
During any core alteration, and especially during core loading, it islnecessary 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 c61ticality would be detected in time to halt operat-lons.
Thus the minimum count. rate requirement (3 cps) in the present Technical Specifications' accomelishes three safety functions:
(1) it assures the presence of some neutrons in the core (2) it provides assurance that the analog portion of the SRM channels is operable, and (3) it provides
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assurance that the SRM detectors are close enough to the array of fuel assemblies to monitor core flux levels.
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 Ski 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 nea'r the fuel.
Besides being operationally inconvenient, dunking chambers suffer from signal variations due to movement. More-over, the use of dunking chambers increases the risk of loose objects,
being dropped into the vessel.
Our evaluation of the proposed change in the Technical Specifications approving count rates below 3 cps during the spiral unloading / reloading' procedures is provided in Section 3.2.
3.0 Evaluation 3.1 Subcriticality in Spiral Unloading / Reloading The spiral unloading / reloading procedure described in Section 2 allows only cells on the edge of the fuel array to be unloaded or reloaded.
Thus the intermediate fuel arrays resulting from such a program will pr eclude the formation of flux traps.
In such a case, the neutron multiplication factor of the intermediate fuel arrays must be less than or equal to that of a fully loaded core.
It is also noted that any control cell which contains 4 fuel bundles and a fully inserted control blade is more reactive than the same control cell after the fuel bundles l
and control blade have been withdrawn. Thus, during spiral loading or "
unloading, the shutdown margin of the partially loaded core can not possibly be less than the shutdown margin of the complete core which is assured by other Specification's.
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-3 3.2 Neutron Flux Monitoring 3.2.1 Flux Attenuation The four SRM detectors are located, one per quadrant, roughly half a core radi e G om the center. Although these are incore detectors and thus very sensitive when the reactor is fully loaded, they lose some of their effectiveness when the reactor is partially defueled and the detictors l
are located some distance from the array of remaining fuel. '
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GE's spent fuel pool studies have shown(2) that 16 or more fuel assem-l blies (i.e., four or more control cells) must be loaded together before criticality is possible.
In spiral loading sequences in the JAF core, an array containing four or more control cells will be at most two control cells (i.e., about two feet) away fmm an SRM dete)ctor.
We have previously examined the sensitivity loss in such a case (3 and found it to be at most one decade of sensitivity (i.e., about one fifth of the SRM's logarithmic scale). As in Reference 3, we find this to be accept-a bl e.
3.2.2 Minimum Flux in tha Core
. We find the proposed amendment to be acceptable from the point of view of minimum flux provwed the spiral reload includes fuel which has previously accumulated exposure in the reactor. We do not find the amendment to be applicable to the loading of a new core centaining only fresh fuel. Such a loading cust use lumped neutron sources and dunking chambers to neet the normal 3 cps minimum count rate.
3.2.3 SRM Operability Specification 4.10.B requires a functional check of the SRM channels, including a check of neutron response, prior to making any alteration to' the core and daily thereafter. This would be sufficient for core unloading and reloading, except that the more extensive fuel handling operations involved imply a greater possibility of SRM failure.
During spiral unloading and reloading Proposed Specification 3.10.B.4 would increase this frequency to every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> or, as an alternative, allow some exposed fuel to be loaded adjacent to the SRM detectors to provide a minimum 3 cps count rate continuously. We agree that this increased l
testing is sufficient.
4.0 Summa ry We have examined the proposed amendment and found it acceptable pro-vided it is understood that spiral reload will include a significant quantity of exposed fuel.
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5.0 E'avironmental Considerations We have determined that the' amendment does 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 amsadment involves an action which 1,s insignificant from the standpoint of environmental impact, and pursuanc to 10 CFR Section 51.5(d)(4) that an environmental impact statement, or negative declaration and environmental impact appraisal need not be prepared in connection with the issuance of the amendment.
6.0 Concl usion 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 proposed 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 de'ense and security or to the health and safety of the public.
Date: August 26, 1981 S
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References 1.
Letter, P. J. Early (PASNY) to T. A. Ippolito (NRC), dated December 6,1979.
2.
General Electric Standard Safety Analysis Report, 251-GESSAR,.
Section 4.3.2.7, pg. 4.3-27.
3.
" 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 (NRC) to D. P. Dise (Niagara Mohawk Power Corporation), dated March 2,1979.
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