ML20002C479
| ML20002C479 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 04/28/1976 |
| From: | Sewell R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8101100355 | |
| Download: ML20002C479 (3) | |
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g DOCKET 50-155, LICENSE DPR G BIG ROCK POINT PLANT Q
The purpose of this letter is to document a minor variation from the fuel description contained in Table 51 of the Big Rock Point Technical Specifi-cations. This minor variation is a result of the continuation of the fuel research and development program that has been conducted during plant opera-tion at the Big Rock Point Plant. This change has been reviewed in accordance with the requirements of 10 CFR 50 59 and it has been concluded that this change does not result in an unreviewed safety question.
It has been further i
concluded that no Technical Specifications change is required.
The change involves replacement of three of the peripheral all urania fuel rods in Assembly G-21 with three solid zirconium rods of the same configuration.
The purpose of removal of these rods is to gain additional information on pellet-clad interaction effects and to compare the performance of three differ-ent cladding types, all zircaloy, but annealed, highly ductile and standard slightly stress relieved. These rods will be destructively examined by Exxon Nuclear.
Table 5 1 states that there are 88 urania rods in a Reload G fuel assembly.
Following the rod swap in G-21 there vill be only 85 urania rods. As stated previously, the three removed all urania rods are being replaced with solid sirconium rods of the same configuration.
The safety evaluation performed pursuant to 10 CFR 50 59 shows that this modification does not result in any additional risk to the health and safety of the public.
The replacement of fuel rods with zircaloy rods has two separate effects on the thermal response of the fuel assembly to a postulated LOCA. First, the passive zircaloy rods act as a thermal radiation hett sink after core un-1 covering, tending to reduce the calculated peak cladding temperature (PCT).
Second, the local power distribution is altered, which could either in-crease or decrease the peak clad temperature. For the G-21 assembly, the
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replacement rods are all on the bundle periphery, which results fn a power shift away from the rod that experiences the highest temperature during a 8101100 3 b wn F
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I LOCA. Thus, the two effects of the replacement rods both tend to decrease the calculated PCT of the G-21 assembly with replaceu.et rods relative to that of i
the unmodified assembly operating at the same average planer linear heat gen-eration rate (APLHGR).
K. for G-21 prior to modification has been compared to the value after modifi-cation. The replacement of the three urania rods with solid zirenley rods results in a slight increase in K. (approximately 0.03% AK/K). This change is insignificant and is consistent with previous modi'ications made to Big Rock Point assemblies.
The replacement of the urania fuel rods with the solid zircaloy rods results in slight changes to the local peaking factors for th-G-21 assembly. The modi-fled assembly local peaking factors represent an. ncrease of 2-3% in the vicinity of the all zirconium rods and a 3% incret.se in the maximam local peaking factor. A decrease in the local peaking factor associated with the fuel assembly interior rods is noted. The resulting maximum local peaking factor is approximately 3% less than the maximum local peaking factor used in core physics calculational codes.
The effect of the modification on mechanical integrity has also been evaluated.
The solid zircaloy rods are essentially equal in length to the deload G-1 fuel rods. At each end they look like G fuel rods with end caps and thus can be satisfactorily accommodated within a fuel bundle cage assembly. Even though a solid rod's weight is different than that of a fuel rod, this is no problem as the spring at the upper end cap will hold the rods in position. Using axial growth rates from solid zircaloy for guide bars at Palisades, it has been determined that axial growth at these solid zircaloy rods should present no problem since there is more than adequate clearance for growth.
Thus, we have concluded that this change does not represent an unreviewed safety question and that the slight variation from the descriptive Table 51 does not require a Technical Specifications change.
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Ralph B. Sewell Nuclear Licensing Administrator CC: JGKeppler, USNRC
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