ML20210H785
| ML20210H785 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 07/29/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20210H788 | List: |
| References | |
| NUDOCS 9908040099 | |
| Download: ML20210H785 (3) | |
Text
h 4
Calculations were also made for storage rack reactivities of fuel enriched to 4.25 and 4.6 w/o U-235, including the GE-11 (9x9 array) fuel enriched to 4.6 w/o U-235, as a function of the fuel assembly k-infinity (ku) in the standard NMP1 core geometry at 20 *C, defined as an infinite array of fuel assemblies on a 6-inch lattice spacing without any control absorber or voios. The results indicate that a ku of 1.31 for both the 8x8 and 9x9 fuel designs in the standard core geometry results in a rack reactivity less than 0.95, including all appropriate 95/95 uncertainties, for enrichments up to 4.6 w/o U-235. The 4.6 w/o GE-11 fuel was found to be lower in reactivity than the 4.6 w/o 8x8 fuel type.
Based on these results, a BWR fuel assembly appropriate for use in the NMP1 reactor is acceptable for storage in the NMP1 storage racks if it has a peak lattice enrichment of 4.6 w/o U-235 and if its ku in the standard NMP1 core geometry, calculated at the maximum over bumup, is less than or equal to 1.31. These requirements are incorporated into the proposed changes to NMP1 TS 5.5. NMPC has also shown that any fuel with a peak !attice U-235 i
enrichment of 3.1 w/o or less is acceptable regardless of the gadolinium content or the k in the u
standard core geometry.
Most abnormal storage conditions will not result in an increase in the k,, of the racks. However, it is possible to postulate events, such as the accidental insertion of an assembly outside and adjacent to the fuel storage rack or dropping an assembly on top of the rack, which could lead to an increase in reactivity. However, such events were found to have a negligible effect and the resulting reactivity would remain below the 0.95 design basis.
NMP1 TS 5.5 currently states, in part, that " Calculations for k values have been based on on methods approved by the Nuclear Regulatory Commission covering special arrays (10CFR70.55)." The specified reference is inappropriate because 10 CFR 70.55 addresses inspections for special nuclear material, not calculational methods. The existing TS statement does not address a required design feature of the facility, which is the purpose of TS Section 5.0. The statement also does not represent any Commission requirement. Therefore, the NRC staff concludes the existing statement is inappropriate and should be deleted.
The following TS changes to TS 5.5 have been proposed as a result of the requested spent fuel pool reracking. The NRC staff finds these changes acceptable.
(1)
The number of fuei assemblies which can be stored in the spent fuel pool when all the new Boral racks are installed has been increased from 2776 to 4086.
(2)
The spent fuel stored in the Boral racks must have a peak lattice enrichment of 4.6 w/o U-235 or less and the ku in the standard cold core geometry must be less than or equal to 1.31.
(3)-
.The inappropriate statement involving approved calculational methods covering special arrays, including its reference to 10CFR70.55, is deleted.
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Based on the review described above, the NRC staff finds the criticality aspects of the proposed modifications to the NMP1 spent fuel pool storage racks are acceptable and meet the requirements of Appendix A to 10 CFR Part 50, General Design Criterion 62," Prevention of Criticality in Fuel Storage and Handling."
9908040099 990729 PDR ADOCK 05000220 P
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.. 3.2 Soent Fuel Pool Coolina Evaluation The SFP cooling system (SFPCS) at NMP1 is a Seismic Category 1 system consisting of two cooling trains, each primarily equipped with one pump, one filter and one heat exchanger. The SFPCS is designed with both cool;ng trains operable and only one cooling train is required to be operating to maintain the SFP water temperature at or below 140 *F during normal (planned) refueling outages (i.e., during a normal (planned) refueling outage at NMP1, an entire core is offloaded). Heat is removed from the SFPCS heat exchangers by the reactor building closed loop cooling system (RBCLCS). The RBCLCS water temperature is maintained between 40 'F and 95 *F depending upon the water temperature of Lake Ontario (the ultimate heat sink).
As a result of the increase in SFAs to be stored in the SFP, the dacay heat generated in the SFP will increase. To maintain the SFP water at or belovv the temperature limit of 140 *F, SFAs must be held in the reactor for a minimum period of time after shutdown before being transfened to the SFP. In any event, based upon adiological exposure requirements, SFAs may not be off-loaded from the reactor prior to a minimum shaidown time of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. Since the heat removal capability of the SFPCS lo a function of RBCLCS water temperature, NMPC performed analyses to determine the reactor si,ufdown time taqi/ red before discharging SFAs from the reactor in order to maintain the SFP water temperature at or below 140 *F with RBCLCS water temperatures at 40 *F,60 *F. 80 "F, and 95 *F. In the analyses, one SFPCS train is assumed to be operatin0, with both SFPCS trains operable. The following summarizes the results of these analyses:
i f
RSCLCS Reactor Coincident Time' Coincident Time-to-Max. Boil-Water Shutdown After Reactor Net Heat Boil off Rate Temp.
Time.
Shutdown (hours)
Load (hours)
(gpm)
(*F)
Required (Mbtu/hr)
(hours) j
~40 72 177 20.72 P 97 43.72 2
i 60 141 250 18.39 8.87 39.05 80 458 Sy 13.80 11.79 29.41 i
95 1008 1129 10 35 15.70 22.09 As indicated in the above table, maintaining the SFP temperature limit of 140 "F is based on two primary parameters. The first is the RBCLCS water temperature which, in tum, is a function of the, water temperature of Lake Ontario; The second is the SFAs in reactor decay time following reactor shutdown. Therefore, NMPC established the following constraints which are applicable to ali full-core discharge operations:
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The time after reactor shutdown at which the SFP water reaches its temperature limit of 140 *F.
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The calculated peak SFP temperature for this case is 130.1 "F.
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. The results of the analysis of the deep drop scenario show that the load transmined to the liner through the rack structure is properly distributed through the bearing pads located near the fuel handling area. Therefore, the liner would not be ruptured by the impact as a result of the fuel assembly drop through the rack structure. The results of the analysis of the shallow drop scenario show that damage would be restricted to a depth of 7.3 inches below the top of the rack, which is above the active fuel region. The NRC staff reviewed NMPC's analysis results in NMPC's letter dated May 15,1998. The NRC staff finds that NMPC's structural!a:agrity conclusions are appropriately supported by the parametric studies, and the NRC staff, therefore, concurs with NMPC's findings.
3.4.4 Conc!usion Based on its review and evaluation of NMPC's submittal dated May 15,1998, rcid additional infctmation regarding structural evaluations provided by NMPC in letters dated December 9, 1998, and April 22,1999, the NRC staff concludes that NMPC'a structural ana!ysis and design of the spent fuel rack modules and the SFP structures are adequate to withstand the effects of s
the applicable loads, includng that of the SSE. The analysis and design are in compitnce with i
the r,urrent licensing basis set forth in the FSAR and app'icable provisions of the SRP, and are, tnerefore, acceptable.
3.5 Qqquoational Radiation Exposure f
The NRC staff has reviewed NMPCb plan for the modification of the NMP1 SFP storage racks wAh respect to occupational radiation exposure. As previously noted, for this modification NMPC plans to ultimately instrdi a totcl of 16 new fuel rack modules in tt.e SFP. A number of l
nuclear power facilities have performed similar operations iri the past. With the benefit of the kcsons loamed from these previcus operations, NMPC estimates that the proposed fuel rack insta!!ation can be impleuented while maintaireirig occupational radiation exposure between 6 and 13 person-rem.
All of the operations involved in the fuel rack installation will utilize detailed procedures prenared with full c.)nsideration of as-low ac-is-reasenobly-achiovable (ALARA) principles. NMPC's Radiation Protection department will prepare Radiation Work Permits for the various jobs essociated with the raracking operation. Each member of the project team will receive radiation protection training on the reracking operation. Personnel will wear protective clothing and will i
be required ;o wear personnel monitoring equWnent consis'ing, at a minimum, of thermoluminescent dosimeters (TLCs) and self-reading dosimeters.
NMPC may also use divers for the removal of the existing SFP rack modules and installaticn of the replacement high-density racxs. These divers may also be needed to remove certain uncerwater appurtenances in the SFP. Each diver will 4 equipped with whole body and extremity dosimetry with remote, above surface, readouts that will be continuously monitored by NMPC's Radiation Protection personnel. Divers will also be equipped with underwater survey instrumentation with rernote readout capabilitiee. NMPC will utilize underwater cameras to permit remote monitoring of the diver's locatLn at all times. Divers will a!so be in continuous cornmunication with the Radiation Protection personnel. NMPC will conduct radiation survays of the diving area before each diving operation and following the movement of any irradiated hardware in the SFP. NMPC will use either visual or physical barriers to ensure that divers J