ML19345E404
| ML19345E404 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 02/11/1965 |
| From: | Boyd R US ATOMIC ENERGY COMMISSION (AEC) |
| To: | |
| Shared Package | |
| ML19345E403 | List: |
| References | |
| NUDOCS 8101160310 | |
| Download: ML19345E404 (3) | |
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V HAZARDS ANALYSIS BY THE RESEARCH AND POWER PIACTOR SAFETY BRANCH DIVISION OF REACTOR LICENSING IN THE MATTER OF CONSUMERS POWER COMPANY BIG ROCK POINT NUCLEAR PLANT DOCKET NO. 50-155 PROPOSED CHANGE NO. 4 - CONTROL ROD BLADE DESIGN CHANGES Introduction Consumers Power Company, by letter dated December 2,1964, has requested changes to the Technical Specifications to Operating License DPR-6.
The changes, involving the control rod blade rollers, number and location if ooison tubes in the blades, and substitution of stainless steel tubes for L C tubes, are hereafter described as Proposed Change No. 4 4
Back ground Thirteen of the 32 present control rod blades have either lost lower stellite rollers or have defective rollers resulting from excessive wear. Accordingly, Consumers has requested authority to replace all control rods in the Big Rock plant. The manufacture of new control rods would permit optimization of the design for the 16 inner control rods which had been previously modified in the field to reduce their worth. The design of the 16 peripheral control rods would not be changed except for the substitution of smaller diameter rollers.
All 32 new control rods would not be available for the Big Roc < reactor startup in 1965. Those that are available would be installed. All ccatrol rod blades with missing rollers or indication of severe roller pin wear would be replaced.
It has been observed that all of the rollers which broke off from the blades were from the lower region of the blades while upper blade rollers remained intact.
Evaluation Consumers also proposes to substitute stainless tubes for the stainless steel rods which are used as blade fillers in the present control rods and to relo-cate the poison tubes (B C) to optimize their effectiveness. The B C tubes 4
g in the new control rods will be placed at the outside of the blade. Since there is no need for any poison effect frcm the new stainless steel tubes we believe that they may be used instead of stainless steel rods as fillers.
In addition, Consumers has stated that the control worth of the Big Rock Point control rods. is more a function of the placement of the B C rather than the q
amount of B C.
Placing the BqC filled tubes towards the outer edge of the q
control blades permits the number of B C filled tubes to be reduced for the q
same worth control rod. The reduced number of B C filled tubes is expected to q
increase control rod lifetime by 10-20% because (1) the maximum neutron capture 7/OH6o 3/O
] rate in the peak B C tubes will be lowered, and (2) the average capture rate g
per B C tube will be increased. The design specifies 17 B C filled tubes and g
g 12 empty stainless steel tubes (open on each end) in each blade of the control rod..
The worth of the new Type 2 control rods, according to Consumers, will be approximately 5% higher than the present control rods, but will not present any significant difference in maximum control rod worth or maximum notch worths. Based on these considerations, we believe the new control rods are -
of an acceptable design from a reactivity control standpoint.
It has been reported that the excessive wear experienced on the blade rollers, especially the lower blade rollers, was the result of substituting roller pins tapered at both ends, because of procurement problems during original fabrication.
The new control rod rollers will utilize pins of the same material and diameter as used originally, but the pins will be longer, not tapered, and fixed in the pinholes by a weld over the end of the hole. The possibility that the roller pin wear experienced in Big Rock operation to date could have been due to bow on adjacent support-tube-and-channel-assemblies, causing the roller to move the support-tube-and-channel-assemblies apart slightly as the control rod scrammed,
_also prompted a slight reduction in the diameter for the new control rod blade rolle rs.
The purpose of the rollers is to reduce metal-to-metal contact between control rod sheath and the support-tube-and-channel-assemblies in order to minimize lifetime wear. Since the rollers are installed only to reduce long term wear and do not affect the scram characteristics or normal operating characteristics of the control rods, we do not believe that reactor safety will be affected by the change in roller design.
Technical Specifications To provide authorization of Proposed Change No. 4, the Technical Specifications of License No. DPR-6 should be changed as follows:
1.
Section 4.1.1(g) Control Rod Guidance Change the second sentence to read:
"Each control rod shall contain 8 rollers of either a nominal 0.485 inch diameter or each control rod shall contain 8 rollers of a nominal 567 inch diameter; the bottom four of which shall move in a minimum intersupport tube space of 0.658 inches and the top four of which shall move in a minimum interfuel channel space of.628 inches."
2.
Section 5.1.1 Principal Core Materials.
Change the Control Rods description to:
"B C filled 304-SS tubes and solid 304-SS rods or B C filled 304-SS g
q tubes with 304-SS tubes in cruciform shaped 304-SS sheaths."
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3-
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i 3.
Section 5.1.2 Control Rods.
change the Poison Material description to read:
"3 C powder in 304-SS cubes and solid 304-SS rods or BqC powder g
in 304-SS tubes and 304-SS tubes."
4 Section 5.1.2 Change the number of Type 2 B C filled 304-SS tubes from "88" to g
"68 or 88"; Change " number of solid 304-SS rods per control rod" to " number of solid-SS rods per Control Rod or Number of 304-SS tubes per Control Rod"; and also after " Type 2" change "28" to
" 2 8 or 4 8".
5.
Section 5.1.2 At the end of Section 5.1.2 add the following new item:
"304-SS Tube, Outer Diameter Inches:
0.175".
Conclusions ion the basis of the foregoing considerations, we have concluded that Proposed Change No. 4 does not present significant hazards considerations not described or implicit in the hazards summary report and there is reasonable assurance that the health and safety of the public will not be endangered. The re fore,
we believe the Technical Specifications of License No. DPR-6 may be revised as indicated above to permit reorientation of B C poison within the control q
blades and reduction of the control blade roller diameter.
Orfdtral signed by-Roger S. Boyd Roger S. Boyd, Chief Research 6 Power Reactor Safety Branch Division of Reactor Licensing Date:
FEB 11 D66 I
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