ML20031C208
| ML20031C208 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 04/24/1969 |
| From: | Skovholt D US ATOMIC ENERGY COMMISSION (AEC) |
| To: | |
| Shared Package | |
| ML20031C204 | List: |
| References | |
| NUDOCS 8110060635 | |
| Download: ML20031C208 (3) | |
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UCENSE AUTHORJTY FEE (XE3 DOIi0t M M.
l Consumers Paaer Company Docket No.~ 50-155 Propos d Change No. 18 s
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S.~ ATOMIC ENERGY COMMISSION SAFETY _ EVALUATION BY THE DIVISION OF REACTOR LICENSING BIG ROCK POINT ~ NUCLEAR PLANT.
" MODIFIED E-G" BUNDLE ZIRCALOY CLAD VARIATIONS By letter dated February 12, 1969, Consumers Power Company proposed Change No. 18 to the Technical 1Specificaticas of License No. ' DPR-6 for the Big Rock Point Nuclear Plant. The change would permit operation with four fuel bundles, designated " Modified E-G" fuel bundles, in the Big Rock Point reactor following the next refueling ' outage scheduled for April 1969.
The proposed " Modified E-G" fuel bundles will have (a) five different rod enrichments with nine of the lowest enrichment rods in the center of the bundle and (b) 24 removable fuel rod posi-tions with four of the corner positions occupied by non-fueled flux suppressor rods and the remaining 20 positions occupied by high enrich-ment fuel rods with various mechanical properties.
Previously approved Reload "E-G" fuel bundles contain (a) three rod enrichments with the highest enrichment in the 25 center rods and (b) six removable fuel rods with cobalt targets normally occupying the four corner positions and low enrichment rods in the two remaining removable rod positions.
The purpose of placing the 96 special removable fuel and poison rods in the core is to evaluate the irradiation-induced mechanical property changes in-zirconium-base alloy cladding as a function of niloy-compc-sition and fabrication method. Four types of zirconium alloys (three of basic Zr-2 with variations in thermomechanical processing and one of Zr-3Eb-lSn alloy) would be incorporated into these fuel bundles along with the normal Zr-2 fuel rod cladding.
The enrichment distribution and resultant local peaking factors will enable as many of the 20 test fuel rods in each " Modified E-G" fuel assembly as possible to operate up to,but not in excess of,the steady state Reload "E" and "E-G" fuel rod limit of 17.7 kw/ft or 410,000 2
Btu /hr-ft surface heat flux.
The capability to selectively position fuel and poison rods within the fuel bundle so that these limits are not exceeded during operation is dependent upon calculational methods which have been used for previous core loadings. We have previously evaluated and accepted these calculational methods and are satisfied 8110060635 690424 PDR ADOCK 05000155 P
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' 1 in this application that there continues to be sufficient nargin during normal reactor operation between the peak calculated fuel temperature and the celting temperature.
The thermal performance limit, minimum critical heat flux ratio of 1.5 at 1227. of rated power, remains unchanged.
Although we note in the licensee's proposal that the increased fuel red power peaking (as high as 1.41) places additional restrictions on the core radial positions which can be occupied by the 'tbdified E-G" fuel bundles, we have concluded that the heat transfer limits can be met by placing t'ae bundles in core positions of lower than average power density.
The principc1 nuclear characteristics of the 'Hodified E-G" bundles, as presented by the applicant, are not changed significantly, therefore, the magnitude of power excursiona associated with accidental reactivity insertions is not changed significantly.
If a control rod with a reactivity worth of 0.021 delta k/k is dropped, the amount of fuel which reaches enthalpies greater than 265 cals/gm is the same for the Reload "E" core with or without the four 'Tbdified E-G" fuel bundles.
As shown in Consumers Proposed Change No. 14 requasting approval for Reload "E" fuel, essentially all of the prompt energy released into the coolant moderator originates in the hottest rods of the six center-melt fuel bundles.
Since the centermelt fuel rods are controlling, our previous conclusion (Safety Evaluation of Proposed Change No. 14, July 2, 1968) that the primary system integrity will not be impaired as a result of a rapid power excursion is still valid.
The temperature rise in the " Modified E-G" fuel following a lost.-of-coolant accident has been shown by calculations to be less than in the Reload "E" fuel bundles.
This is the result of locating the highly peaked fuel. rods on the periphery of the " Modified E-G" fuel bundles where the rods are more effectively cooled by the channel walls which are wetted and cooled by the emergency spray water.
The fuel cladding strength of eight of the special removable rods in each bundle is reported to be less than normal, therefore it is conceivable that the cladding of these rods could perforate at lower temperatures than the value of 1500 F normally assumed for zircaloy.
At higher temperatures, there is a paucity of zircaloy strength data.
However, the available data indicates that differences in strength evident at room temperature are gradu.ily eliminated as the temperature is increased. At temperatures above 1100 F, differences in strength properties are essentially non-existent.
Since the temperature rise
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of the " Modified E-G" fuel bundles'following loss of coolant is-calcu-laced to be less than.for the Reload "E" fuel bundle, fit is concluded that. fewer rods ine the '4 odified E-G"_ bundles would perforate.
If, contrary to' expectations, the eight fuel rods with_ reduced room temper-ature tensile strength do fail, the release of. fission products to the containment environment will be well below levels which we htve previ-ously determined to be acceptable for the Big Rock Point reactor facility.
Zr-3Nb-lSn alloy is reported to exhibit the best= combination'of corro-ston; resistance and high temperature strength of the proposed zirconium base cladding alloys'and it has been tested as fuel cladding ~in a boiling water reactor environment.. On the basis of this information, the integrity;of Zr-3Nb-lSn clad is expected to be a further improvement of the Zr-2 alloys.-
There are no new design' features associated with the " Modified E-G" bundles as tha. mechanical features of the removable fuel rods are the same as they were in the previously approved Reload "E" bundle.
Like the Reload "E-G" bundles, the " Modified E-G" bundles will be designed-to operate for three cycles and achieve an average burn-up of 20,000 Msd/T. Withdrawal and inspection of the removable fuel rods in the
" Modified E-G" bundles during core refueling outages will permit periodic
. determination of their condition.
on:che oasis of these considerations, we have concluded that Proposed 1
Change No. 18 does not present significant hazards considerations not t
' described or implicit in the safety analysis report and there is rea-sonable assurance that the: health and safety of the public will not be l
endangered by operation of the Big Rock Point reactor with the " Modified E-G" fuel bundles.
Therefore, the Technical Specifications of License No. DPR-6 may be revised as indicated fu Attachment A.
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Donald J. Skovholt Assistant Director for Reactor Operations Division of Reactor Licensing Date: April 24, 1969 l'
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