ML20008E435
| ML20008E435 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 02/25/1971 |
| From: | James Shea US ATOMIC ENERGY COMMISSION (AEC) |
| To: | US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20002E033 | List: |
| References | |
| NUDOCS 8101260160 | |
| Download: ML20008E435 (3) | |
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D. L. Zibnana, Chief, ORE #2, DRL EVALUATION OF " TYPE 2A" CONTROL RODS FOR THE BIG ROCK POINT REACTOR (CONSUMERS POWER COMPAM)
Consumers Pcwcr Company, by Proposed Change No. 26 (redesignated Pro-posed Change No. 25) dated January 28, 1971, requested approval to use
" Type 2A" control rods in the Big Rock Point reactor in place of existing control rods whenever it is necessary to replace any of the existing control rods.
" Type 2" control rods were installed in the sixteen interior positions in 1965 (ref. Technical Specifications Change No. 4 dated February 11, 1965) when wear on lover rollers of the original control rods (" Type 1") became excessive.
Smaller rollers were used to eliminate the wear on the sixteen peripheral ~)ntrol rods, which are either fully inserted durias reactor shutdown ar fully uithdrawn during reactor operation, and it was not necessary to replace the out-side control rods with the " Type 2" control rods.
After about six years of reactor operation, during which the interior control rods were used for reactor control purposes and were partially inserted into the core during reactor operation, it has beco=c necessary, as anticipated, to replace the sixteen (Type 2) interior control rods due to boron deple*. ion at the tips.
Consumers has proposed that " Type 2A" control rods be used to replace the sixteeu depleted control rods.
The " Type 2A" control rods diff er from the " Type 2" control rods in the followir.g respects:
1.
The 304 SS tubes in each wing of the cruciform-shaped control rod blade are nonswaged in contrast to the " Type 2" tubes which were swaged down to 0.175 inch 0 D f rom 0.188 inch OD, 2.
The " Type 2A" control rod tubes arc 0.188 inch OD compared with 0.175 inch for " Type 2" and the tube walls are 25%
- thicker, 3,.
The " Type 2A" centrol rod tubes are slightly dimpled on either side of the ball spacers that are c= ployed to com-partmentize the boron carbide and minicize the possible effects of densification or settling of the B C powder compared with 4
" Type 2" where the ball positions were fixed by the swaging operation, D
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A 4.
The sheath thickness of the " Type 2A" control rod blades is 0.006 inch less than the 0.062 inch thickness of the " Type 2" sheathing, and 5.
The number of empty tubes in each wing is 10 compared with 12 in the " Type 2" control rods and the number of poison tubes is 16 compared with 17.
The change oliminates the large amount of cold working during the st. aging
. operation te the advantage of the f abricator (Cencral Electric Company).
The same nonsuaged design has been adopted by GE for the new product-line control rods.
We concur that the 25% increase in tube wall thickness is sufficient to maintain wall strength because the yield strength is not reduced a corresponding cmount by o=ission of cold working, but note that the increase in diameter does not completely explain the reduction in the number of tubes per blade.
Consumers rechecked the fabrication drawings and by telecon on 2/19/71 reported that the metal stack at the center of the blade had been increased from 0.571 inch to 0.758 inch. This increase accounts for one less tube in each wing and the increased
" Type 2A" tube diameter, we agree, then accounts for the remaining reduction of two tubes per wing.
The proposed change reduces the B C content by about 2% and increases 4
the surface by about 1%.
The neutron absorbing characteristics of these changes are opposite and small; therefore, we have concluded that the nuclear characteristics are not changed significantly in relation to normal reactor operation or accident considerations.
The 10% reduction in the thickness of the sheath provided to maintain the tubes in the cruciform configuration and preserve alignment will result in less resistance to distortion stresses; however, in the absence of such symptoms in " Type 2" control rods and considering the 30% increase in center metal resulting in less longitudinal flexibility (increased axial stiffness), we have concluded that the thinner sheathing for the-control rod tubes necessitated by the increased diameter of the tubes is acceptable.
In addition to the applicant's state =ent that his Quality Assurance Program meets the criteria of 10 CFR 50, Appendix B, a measure of the effectiveness of his program was demonstrated by the fact that these design changes were initially detected by Consumers Power Company during routine radiographing examination of the control rods after receipt from GE before the changes were identified by GE.
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File FEB 2 51971 A
On the basis of the above, we.have concluded that the mechanical and
'I nualcar dif ferences between " Type 2" control rods, which have been
.used successfully for control of the Big Rock Point reactor for the past six years, and the " Type 2A" control rods to be substituted are minor and reactor operation with the " Type 2A" control rods installed in the Big Re h Point reactor will not increase the probability of an accident, impair the effectiveness of the installed engineered safety features, or change the consequences of the design basis acciden,t.
The proposc-d change does not present significant hazards considerations not descriined or implicit in the Safety Analysis Report and there is reason-able assurance that operation of the Big Rock Point reactor in the manner proposed will not endanger the health and safety of the public.
Therefore, the Technical Specifications should be revised as proposed.
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James J.'Shea Operating Reactors Branch #2 ss -Division of Reactor Licensing cc:
D. J. Skovholt, DRL R..H. Vollmer, DRL D. L. Zicmann, DRL J. J. Shea, DRL
- k. M. Diggs, DRL
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Centermelt bundle power, page 17.
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Consumers Power Company -- Answers to DRL questions - dated August 15, 1967, a.
Table 1, MCl!FRs, page 10.
6.
Special Report - February 1971
" Failure Analysis and Performance Eval-uation of Intermediate Performance Centermelt Fuel after 10,000 mwd /T Exposure":
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Page 4, no hydriding of the cladding at the inside surfaces, s,
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