Further test on pressure vessels at Fukushima Daiichi inconclusive

Readers might recall that, earlier, TEPCO conducted tests at two of the three reactors at Fukushima Daiichi in order to attempt to determine the condition of the bottom heads of the reactor pressure vessels. In that series of tests, TEPCO attempted to test continuity in the rod position indication equipment with the hope that failed areas could be mapped by detection of failed RPI equipment. However, for one or more possible reasons the equipment was deranged enough that no meaningful data were collected. So far as this writer is aware, the test was not even conducted on No. 3 plant because the data were so nebulous on the other two.

Now, it appears that TEPCO has attempted to detect the condition of the pressure vessels at Fukushima Daiichi No. 2 and No. 3 by using sophisticated equipment to detect cable conditions in the core-contained neutron detectors.

These detectors have a continuous cable run from the equipment all the way through the reactor building and dry well (PCV) wall and to the lower head of the pressure vessel, then up to the detectors. Although TEPCO doesn't mention what was used in the tests, this author is somewhat familiar with the use of a TDR or Time Domain Reflectometer for such tests and from memory the test waveforms that TEPCO is showing appear to be the result of using a TDR on the cable runs to detect where they're open or else shorted out.

As with the previous tests using RPI cables, though, TEPCO reports that the new tests are not in any way conclusive. High temperatures and steam exposure for prolonged periods have caused the detector cables to fail such that no realistic mapping of the failed RPV regions are possible using this method.

This is the second round of testing using electric cable runs that TEPCO has attempted in its effort to diagnose the condition of the pressure vessel lower heads. As we all know too well, the condition of the lower heads is not known for certain, although surely they're expected to be found failed when finally viewed (and that first view will almost surely be remote, not the actual eyes of a man) but TEPCO feels that the earlier the actual condition is estimated or described, the easier it will be to plan for defueling the plants. What seems clear now is that, in all likelihood, no sort of indirect testing such as cable continuity is likely to reveal anything about the actual vessel conditions. TEPCO will have to find some other way.

7:15 PM Eastern Wednesday October 19, 2011
ATOMIC POWER REVIEW