ML20037B160
| ML20037B160 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 05/10/1968 |
| From: | Skovholt D US ATOMIC ENERGY COMMISSION (AEC) |
| To: | |
| Shared Package | |
| ML20037B158 | List: |
| References | |
| NUDOCS 8009050627 | |
| Download: ML20037B160 (6) | |
Text
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(('* 4 UN'TED STATES FN t
ATOMIC ENERGY COMMISSION Ui' )
- WASHINGTON. D.C.
20545.
's, d' f
V si,in e May 10, 1968 In Reply Refer To:
Docket.No. 50-10
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Commonwealth Edison Company 72 West Adams Street Chicago, Illinois 60690 Attention:
Mr. R. E. Reder, Nuclear Change No. 15 Licensing Administrator License No. DPR-2 Gentlemen:
In accordance with the provisions of Section 50.59 of 10 CFR Part 50, we have reviewed your Proposed Change No. 15, dated January 17, 1968, to the Technical Specifications of Facility Operating License No.
DPR-2, as amended.
The proposed change would authorize elimination of the present requirement for a coc,ked control rod during fuel
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assembly additions, and impose a, condition requiring withdrawal and reinsertion of a control rod in the vicinity of the. core posi-tion being refueled before and after each fuel assembly is inserted into the core.
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We have concluded that the proposed change, with minor modification of the wording for clarification, designated as Change No. 15, does not present significant hazards consideraticns not described or implicit in the Hazards Summary Report (hereaf ter called the Safety Analysis Report) and that there is reasonable assurance that the health and safety of the public will not be endangered by the change.
Accordingly, the Technical Specifications of Facility Opereting License Nc. DPR-2, as amended, are hereby changed as follows:
1.
In Section "D.
Power Operation", delete item 5.b under
" Reactivity Limits" and replace with:
80090 0 h 7 5
2-5.b.
With the reactor in any condition, the follcwing shutdown criterion shall be net:
" Stuck Rod" Criterion:
At every stage during leading and in the fully loaded configuration, the control rods must provide a shutdown control margin of at least 0.01 delta k/k with any rod wholly out of the core and completely unavailable.
2.
In Section "E.
Refueling and Maintenance", delete the second paragraph of item 3 under " Shutdown Margin" and replace with:
The loading procedures shall require verification that the reactor is safely suberitical by withdrawing and re-inserting a control rod in the vicinity of the core position being refueled before and after the addition of each fuel assembly.
A copy of our related Safety Evaluation is enclosed.
Sincerely yours, Peter A. Morris, Director Division of Reactor Licensing
Enclosure:
Safety Evaluation l
i
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S. -.
y
_ SAFETY EVALUATION BY THE DIVISION OF REACTOR LICENSING 4
DOCKET NO. 50-10 COMMONWEALTH EDISON CCMPANY-DRESDEN l' NIT I
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PROPOSED CHANGE NO. 15
.q 9
INTRODUCTI'ON
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- By appli ation dated January 17,' 1968, E he Commonwealth Edison t
Company' has proposed Change No.15. to the Technical Specifications of Facility, License No. DPR-2, as amended, for Dresden Unit I.
The proposed ~ change would elim1nate the' requirement.fer a cocked t
. contro,1, rod during fuel assembly additions, and 16 pose a require-ment to withdtcw and reinsert a control rod in the vicinity of the core position being refueled before and after each fuel assembly is inserted into the core.
13g DISCUSSION The " cocked rod criterion" requires one control rod to be fully withdrawn in the region of core alteration and.available for rapid insertion during fuel additions.
In lieu of maintaining a cocked control rod, Commonwealth Edison proposes to have all control rods fully inserted in the core during refueling operations.
Prior to any refueling of the Dresden I core, each of the "most reactive" regions of the core will be analyzed to determine the reactivity change which will result from addition of the most i-reactive fuel assembly in that region.
The effect of withdrawing the most reactive control rod in each of the 'bost reactive" regions will also be calculated to assure that the control rod will be of greater reactivity worth.than the most. reactive fuel assembly in the~same region.
The calculations wilf be based on.the planned
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refueling scheme.
In ad'dition to these calculations, a requirement to with' draw the mest seactive control rod in the vicinity of the core position being refueled, before and after the insertion of each fuel assembly,will be imposed.
1 EVALUATION The~princ1 pal safety feature of the cocked control rod concept
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used for r~sfueling is the shutdown capability of the withdrawn rod in the event criticality is achieved by the addition of a single L
. e fuel element.
The effectiveness of this procedure depends upon the control room operator's surveillance of source range nuclear instru-mentation, and his early observation of an increased neutron population and immediate insertion of the cocked control rod.
If immediate action is not taken by the operator, the control rod would not be inserted until scra= action occurs.
Maintaining a cocked control rod during refueling is considered of greatest value when the reactivity worths of the fuel assemblies are not accurately known.
The advanta0e of having all control rods fully inserted in the core rather than cocking one rod is increased shutdown margin during fuel insertion.
We believe that Commonwealth Edison has had sufficient experience with the Dresden I core to anticipate and accurately calculate the reactivity changes associated with various core configurations with both old and new fuel assemblies.
Withdrawal and reinsertion of control rods during refueling will verify that a sufficient shutdown margin exists at all times.
If, as the licensee indicates, the reactivity worth of the control rod in any refueling region will be worth more than a single fuel assembly in that region, inadvertent criticality during refueling with the proposed procedure cannot occur.
Furthermorc, withdrawal of a control rod following each fuel addition facilitates identification of approaching critical condition by surveillance of nuclear instrumentation similar to the cocked rod procedure.
CONCLUSION We have exa=ined the implications of climinating the " cocked rod criterion" as described above and we have concluded that the proposed change, with minor modification of the wording for clarification, does not involve significant hazards considertz. ions not described or implicit in the Safety Analysis Report and that there is reasonable assurance that the health and safety of the public vill not be endan-gered by the proposed change.
Therefore, the Technical Specifications of Operating License No.
DP2-2, as amended, may be changed as follous:
1.
In Sectica "D.
Pouer Operation, delete item 5.b. under "Recctivity Limits" and replace with:
's 1
w,
. 5.b.
with the reactor in any condition, the following shutd:vn criterion shall be cet:
" Stuck Rod" Criterion: At every stage during loading and in the fully loaded configuration, the control rods cust provide a shutdown control margin of at least 0.01 delta k/k with any rod wholly out of the core and completely unavailable."
2.
In Section "E.
Refueling and Maintenance", delete the secord paragraph of item 3 under " Shutdown Margin" and replace with:
The loading procedures shall require verification that the reactor is safely suberitical by withdrawing and re-inserting a control rod in *.he.'icinity cf the core position being refueled before and after the addition of each fuel assembly.
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ccf u Donald J kovholt Assistant Director fcr Rea :c: Operations Division of Reactor Licensing Date: May 10, 1968 i