ML20037B643
| ML20037B643 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 07/20/1962 |
| From: | Wade I COMMONWEALTH EDISON CO. |
| To: | Lowenstein R US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 8010270587 | |
| Download: ML20037B643 (4) | |
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e6LsNose July 20, 1962
.9 Mr. Robert Lowenstein, Director
'0i Division of Licensing and Hegulation
';t U. 3. Atomic Energy Commission Washington 25, D. C.
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Dear Mr. Lowenstein:
In an application dated January 27, 1961, Co=monwealth Edison Company proposed a number of changes to License DPH-2.
One of these was a request for a ocange in Appendix
'A", Section E, paragraph 5(e) 83eactivi:7 L1=its'.
Due to the urgency of other items in the application this request was never acted upon.
We now wish to reinstate that request and to revise it so that the former paragraph 5(e) of Section E (redesignated as Section D pursuant to Amendment No. 4 of the application dated January 5, 1962) will read in its entirety as follows:
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he moders;or ;an,:s:u;ure
_9 ffi:13nt hring un11:r heating of the core shall be limited so that the potential =aximum reactivity addition available from nuclear heating of the moderator will always be less than 0 7Mf.
The maximum moderator temperature at which the ocefficient ceases to be positive will be less than 550 P.*
Appendix A attached to this application contains technical information relative to operation with a positive temperature coefficient and the hazards evaluation on which our request is based
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COMM0hMTH EDISON COMPANT
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TECHNICAL INFORMATION ON REVISION TO MODERATOR TEMPERATURE COEFFICIENT IN DEESDEN LICENSE --g)A~.
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A.
License Reauirements L. -
The Dresden operating license DPH-2, as amended, specifies the following requirement:
"The moderator temperature coefficient of reactivity will change from positive to negative at a temperature below the maximum reactor temperature that can be obtained under atnospherio condifions.
Measurements will be made to confirm this.'
In view of the considerations in the following paragraphs, it is necessary that the above specification be revised in order to preclude the eventuality of not being able to start up the Dresden reactor following a shutdown because of the rostriction which limits the positive temperature ccefficient to the range below 212 F.
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3 T?seere:ure Coefficient Data The =oderstor temperature coefficient of reactivity for the Dresden reactor has been measured during reactor startups over its entire period of operation.
Prior to the June 25., 1962 startup, the data indicated that the temperature coefficient was becoming less negative with increase in fuel exposure.
However, ;aese.2easurenen;a J,1d not in. iia,;.;a faa; the cceffi: lent would become positive at temperatures above 0
212 F before the reactor would be shut down for refueling.
During the reactor startup of June 25, 1962, the temperature coefficient was measured over three different temperature ranges between 2500F and 4400F.
All values were I
negative and ranged from -o.7 x 10-547 / F at 270 F to 0
-1 9 x 10-5 q/oF at 430 F.
Measurements were not made at A
temperatures below 212 F due to considerations of potential 0
cavitation in the recirculating pumps.
Extrapolation of l
this data indicated that the ocefficient was negative or 0
too small to measure at 212 F.
Based on this and the earlier measurements of the temperature coefficient, it is currently expected that the coeffiolent may also become positive over i
0 a large portion of the reactor temperature range above 212 F, l
before the reactor is refueled.
C.
Operatina Considerations A positive moderator temperature will not create any signifloant operating difficulties.
The manner of operation during startup and heating will be similar to that previously employed except that the positive temperature coefficient behavier will extend to higher temperatures than
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.2-before.
As the toeperature increases it will be necessary to slowly insert control rods rather than continuing to withdraw them as was the case over the negative temperature coefficient range.
This method of startup operation is similar to that necessary to compensate for xenon transients following shortuiuration shutdowns.
It will continue to be teoessary to withdraw control rods to increase primary steam flow rate because ths void coefficient of reactivity is negative.
D.
Fa*aMs Evaluation From a safety standpoint, it is not particularly sig.:Lificant whether the sign of the tecperature coefficient is positive or negative as long as the total reactivity change due to temperature change is less than.7%AQ when critical.
This is due to the fact that during an increase in power, re M,ess of rate, the negative Doppler coefficient e
acts promptly to reduce reactivity and terminate the increase.
If the power increase is slow enough, the heat transferred from the fuel will heat the water inside the channels and tend to create volds.
This effect 13 also negative.
Positive reactivity is added only when the water in the water gaps between channels is heated.
Since this water is heated primarily by increasing the temperature of the inlet plenum, the reactivity additions from this nechanism are necessarily slow.
W1:h fu total reactivity :hr.3 Ocn be id2:d b,- in-creasing the moderator temperatuM due to nuclear heating limited to less than 0 7% M, even if it were possible to add all of this reactivity.".'.pidly, the reactor fuel would not be damaged.
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