ML19323H264
| ML19323H264 | |
| Person / Time | |
|---|---|
| Issue date: | 04/25/1980 |
| From: | Catton I Advisory Committee on Reactor Safeguards |
| To: | Okrent D Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-CT-1237, NUDOCS 8006120295 | |
| Download: ML19323H264 (2) | |
Text
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67-4?37 t
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April 25. 1980 y,t;EWO
% > 35 TO:
D. Okrent
-l '.U.; 9 FROM:
I. Catton
SUBJECT:
Breac'h of Containment by a Core Melt gt b
REFERENCE:
Letter from Ivan Catton to David Okrent dated 6 March 1980
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,J-The question posed is whether or not it is feasible and practical to It is my opinion that l design a containment that.c.an withstand a core melt.Of course there will be a number to do so is both feasible and practical.
I will attempt to substan-or hurdles to overcome in arriving at a design.
tiate my opinion in the following paragraphs by first addressing existing pla ts and then give my ideas about new plants.
Before discussing LWRs, however, I would like to call your attentioh Designs for core catchers were to hrevious work in this area for LMFBR's.A number of crucible materials we proposed for FFTF and CRBR.
The Gennan and both passive (time delay) and active systems were considered.
reactor SNR 300 will have an actively cooTed crucible using depleted UO2 as Several ideas fer core retention have come out of a sacrificial material.
A fim in Germany was found that efforts of the GE advanced reactor group.
for what I remember to would make standard size bricks out of depleted UO2 was needed to absorb the th 2
be a reasonable cost.
The depleted U0 from the melt and protect the active cooling system. The designs were not When one considers fully evaluated but had potential for being successful.that the fuel melt fro magnitude greater than an LWR one sees t' hat the design of a core catcher for a LWR will be less difficult.
A number of aspects of a : ore melt accident were discussed in the above They : are repeated referenced letter, which dealt with Indian Point and Zion.
here in part.
Steam exolosions will probably not occur in-vessel if the pressure 1.
Even if a steam explcsion were to occur in-vessel, is above 7-10 bars.
recent SANDIA work shows that there is little chance of a missle that could The only missile that might be of concern was the penetrate the containment.Some plants have missile shields for.this already and control rod drive.
An ex-vessel steam explosion will only plants without could install one.
occur if water is in the reagtor cavity before the vessel is penetrated or enters shortly thereafter (before the molten pool solidifies and while gas is still being generated by concrete decomposition). The ex-vessel steam explosion will probably not do much damage and it appears that acceleration Further con-of missiles that will penetrate the containment is unlikely.
firmation of this opinion is needed to assure that damaging the shield wall, moving the vessel or some other aspect will not lead to containment penetra-High steam generation rate will occur if water precedes the melt and tion.
the resultant high steam generation rate needs to be a factor considered in seeking mitigation measures.
8006120275
In-vnssol core coolability is presently not well enough und:rstood 2.
to fully describe the ccre meltdown process. programs presently und;;rway in Germany and the US may yield sufficient information at some time in.the future At this time one can only bound the problem and must to describe the piocess.
It should assume that penetration of the vessel occurs early in the worst way.For example be mentioned that it is not really clear what the worst way is.
a jet of fuel resulting from a hole in the bottom of the vessel might erode j
a hole in the base mat with subse uent erosion of the hole being greater than i
if the entire vessel lower dome failed dumping all the alten fuel at one time.
Ex-vessel core debris coolability will depend strongly on whether 3.
If water is in the cavity in sufficient quan-
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or not water is in the cavity.
tify before the vessel is penetrated, the core debris will be quenched as it t
A sufficient quantity of water is a pool deep enough to prevent erosion cnters.
/of the base mat.
It is not clear how deep this is. SANDIA programs under-tray, however, could help answer this question.
If a reflux path is available This opinion is based the gore debris will probably not dry out and re-melt.
en past work at TREAT, UCLA, ANL and SANDIA that shows that c.= 0.45 is a[ reasonable void fraction and that an average particle size of 500 pm is For c =.45 and 500 pm particle sizes the entire core and to be expected.
a gfeat deal of steel (125 tons of fuel and steel) will remain coolable.
i If vessel penetration occurs when no water is in the reactor cavity, a The amount of penetra-great deal of penetration of the base mat may occur.
tion occurring during the period when the core debris is molten is predictable.
Once ft freezes a complicated process occurs and the amount of penetration Again, studies are undemay in Germany (their strong is not predictable.
interest results because they do not allow water into the reactor cavity)
Use of a that will answer this question within the.next couple of years.
liner in the cavity could buy time for plant personnel to get water into the cavity.
The debris could enter the dry cavity and become particulates. The gas flow from the decomposing concrete might block water added later from entering the bed.
It is not known whether the cooling by the gases from the decomposing gases will be sufficient to preclude re-melting. This sequence needs further study if it cannot be shown that water will always precede the melt.
To sur:rnarize, in existing plants where water precedes the melt in suf-
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ficient quantities and can be resupplied, penetration of the base mat will Under these conditions an ex-vessel steam explosion most likely not occur.
will probably take place with the possibility of a great deal of stean gene-ration that must be accommodated. The possibility of damage of the biological shield or shifting of NSSS components leading to containment damage needs to be further assessed. When water is not available, the chances of base mat The conclusion is that a water supply needs penetration are much greater.
to be assured. A cavity liner of depleted U0, Al 0, Mg0 or some similar 2
23 refractory or sacrificial material should be considered.
A containment building could be designed based on present information to preclude molten core penetration. A conceptual design that has redundant cooling capability as well could include the following features:
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te that cininizes gas generation on decomposition and has tne uu3i.
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Conc po.ssible refractory characteristics. bricks actively cooled at th Several cour'ses of depleted UObrick interface similar to the SNR 300 co 2
2.
UO2 could be an existing plarit system.
bricks.
A steel liner to protect the U02 ht A caviky flooding capability and a method of refluxing to insure t a 3.
4.
the cavity stays flooded.
w research.
Such a system requ' ires very little new technology and depends on no at It;s, hould also be relatively inexpensive.
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