ML19274F809
| ML19274F809 | |
| Person / Time | |
|---|---|
| Issue date: | 06/05/1979 |
| From: | Richings H Office of Nuclear Reactor Regulation |
| To: | Mattson R Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19207A182 | List: |
| References | |
| NUDOCS 7908060458 | |
| Download: ML19274F809 (3) | |
Text
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June 5, 1979 MEMORANDUM FOR:
Roger J. Mattson, Director Division of Systems Safety FROM:
Howard J. Richings, Reactor Physics Section Core Performance Branch, DSS
SUBJECT:
DECAY HEAT AND IS0 TOPES FOR TMI-2 FROM EXTENDED OPERATION This is a response to the question of how much the decay heat would increase during the shutdown time for which there was potential for fuel damage and relt in THI-2 if the ooerating history of TMI-2 had been extended to maxi-rize fission product buildup.
Isotope buildup is also discussed.
The accompanying table gives the decay heat (in percent of full power for T'1I-2) for the TMI-2 operating history and for several assumed operating histories.
The shutdown times examined bracket the times during which fuel damage may have occurred (about 2 to 15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br /> after shutdown).
The primary damage is presently thought to have occurred near 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> after
- hutdown.
The entries in the table are as follows:
1.
The decay heat for the actual TMI-2 operating history (see attached memo describing this history).
2.
Decay heat assuming operation at full (TMI-2) power for an infinite time and with all fissions fron U235.
3.
Decay heat from infinite operation with all fissions from Pu239.
It may be noted that decay heat from Pu239 is less than from U235, thus buildup of Pu from operation tends to reduce the decay heat total.
(Pu239 and U235 bracket as well as dominate contributions fre other fissile isotopes and thus others need not be considered in these con-parisons.)
4.
Decay heat fror U235 assuming finite (but continuous) full power operation for 2 years, a burnup of about 24,000 MUD /T.
Tnis is generally in excess of tne average burnup which will exist in the reactor.
It is also the maximum for peak power density fuel.
It represents e maxinum operating history for reactor decay heat cal-culations.
Real histories would produce less decay heat since the varicus real shutdcwn and reduced power operations would extend tne oserating tire (rot the integrated burnup) and reduce the fissior pre:uct inventcry.
790806045i
Roger J. Mattson 5.
Decay heat for 2 years operation with Pu239.
E.
Secay heat assuming that at 2 years operation the ratio of fission p.er from U235 and Pu239 is one.
This is a reasonable but conservative approximation for this maximum history.
For the shutdown times of in-terest it is also a reasonable approximation to assume the final fission ratio has occured throughout the operating history.
The overall effect of this fissile inventory approximation is conservative relative to a real inventory, largely because the Pu239 power fraction assumption at two years is low.
7.
The ratio of the decay heats for the maximum operating history and for TMI-2.
- is concluded that if a maximum operating history had preceded the TMI-2 event, tne oower level during shutdown times of importance to fuel melting c-damage would have increased about 10%, with the increase during the most significant tine frame (about 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />) about 6%.
This increase would not copear to have a significant effect on the iikelihood of fuel melt.
In acdition to tne increase in decay heat there is also a potential for in-c ease ir. in:'ividual isotope inventory from extended operation.
For those isotcpes which were (could be) " volatile" during the event there might be an increase in contribution to doses from this extended operation.
There aapears to be only a few significant isotopes for which this is the case.
A,cnc the obvious " volatiles" (the noble gases and halogens) only Kr 85 (ground state), and among isotopes with boiling points less than that c: curring in tne event (about 2000 C) only Cs 137 and Sr 90, appear to be significant isotopes with half lives long compared to the TMI-2 effective coe-atior tire.
For the extended history previously aiscussed, the inventory c# these isoto:es would be increased Ly about an order of magnitude (i.e.,
71C) over that existing for TMI-2.
The other volatile " dose" isotopes v.aulc not be increased significantly.
None of the three isotopes appear to tave prir.ary factors in TMI-2 dose observations, and thus the increase would rat appear to be hignly significant.
p Howard J.' Richings' Reactor Physics Section Core Performance Branch Division of Systems Safety c::
l Stel'o K. Kniel
- - 50 r:e:e-J. Voglewede t 'e: esc:
J. Crutchfield
- 3. rien:
E n c '. c s u re :
"s : fr F.J. Richings to Karl Kniel re:
Decay hea for TMI-2, 5/9/79
Decay Heat - Percent of Full Power 4
Shutdown time (seconds) 103 10,
105 (hours) 0.28 2.8 27.8 (1) TMI-2 1,92 0.918 0.433 (2)
U235(infinite) 2.13 1.095 0.58 5 (3)
Pu239 (infinite) 1,92 0.968 0.550 (4)
U235 (2 years) 2.07 1.030 0.520 (5)
Pu239 (2 years) 1.87 0.915 0.497 (6) 50% (4) + 50% (5) 1.97 0.973 0.509 (7)
Ratio (6)/(1) 1.03 1.06 1.12 All values include actinide contribution from " infinite" operation.
.