APR: your source for nuclear news and analysis since April 16, 2010

Sunday, March 27, 2011

Some revision by TEPCO... and a better outlook

There is a sliver of evidence this morning (in Tokyo, anyway) that TEPCO thinks that continued fission is NOT occurring above natural decays in the Uranium fuel at Fukushima Daiichi No. 2 plant.

TEPCO made what is widely being reported as a retraction of its earlier statement, but what TEPCO is saying really is not a retraction but a correction. Here is what I can distill out of their releases as given so far....

The water in the basement of No. 2 plant's turbine building is not ten million times the activity found in normal reactor coolant. It's one hundred thousand times the activity found in normal reactor coolant. A major reduction to be sure, but the figure of activity one hundred thousand times that of normal reactor coolant is just as indicative of massive fuel element failure as a figure of ten million times or even ten times that. Or fifty thousand times. The figure changes, but the direct evidence is exactly the same.

The isotope Iodine 134 is now said to have been undetectable when TEPCO reexamined the data taken from the survey. One media outlet is saying that another isotope is indicated; another media outlet provides no further data. This doesn't change the fact that, even in the latest releases of data that TEPCO is still finding a number of other fission products in the water. This MIGHT indicate that the idea of an increased fission rate .. not approaching criticality, indeed, but increased ... is now no longer valid if the very short half life elements aren't being found. It still goes along with the earlier fact to indicate massive fuel damage.

One further piece of information is the fact that the 1000 millisievert reading was obtained with a radiac that "maxed out" or "pegged high".. the operator departed the area without trying a higher range instrument, or resetting his (if it had a higher range.) We might then very safely say that the rad level detected was >1000 mSv/hr.

Now, all of this might seem confusing if you just read the TEPCO data and the press releases but as I've presented it here, it isn't confusing at all. The actual status of the reactor core remains as unknown as it was before, and we have available the official TEPCO press releases stating that, at 10:10 AM Tokyo time, the water injection to the reactor at No. 2 plant was changed from seawater to fresh water with boric acid added. None of the other plants were still receiving boric acid. The reintroduction of this neutron-absorbing substance is odd at this late point, UNLESS the water was supplied from some other location's normal onsite emergency shutdown volume which would naturally be borated. It would not be out of the question. (Plants normally have borated water on hand for shutdown override.)

We will have to wait for further details. Serious core damage, given the new data? Of course. Core melt? Partial melt, very very likely. Full melt, hard to say. Failure of reactor vessel, or a bottom end penetration (for instruments or control rods) or near the support flange by melting? Possible. Primary containment (drywell and suppression chamber) failure? Virtually assured, and TEPCO is saying just exactly that.

We'll keep a close eye on the specific announcements related to the plant, sift them out and present them here with analysis... as has been the convention for a while now.

Further note on the water removal from the turbine buildings: The condenser hotwells at No. 2 and No. 3 plants are already full, so that the water pools building up cannot be pumped into them without emptying them first.

5:10 PM Eastern Sunday 3/27

No comments:

Post a Comment