NISA instructs TEPCO to demonstrate dry well flooding is safe from seismic

Will Davis examines the NISA letter to TEPCO, dated April 30, 2011.

NISA, or for those who are recently joined readers, the Nuclear and Industrial Safety Agency, has instructed TEPCO (Tokyo Electric Power Company) to make a very thorough analysis of various parameters relative to TEPCO’s plan to flood the dry well of Fukushima Daiichi No. 1 to a level above that of the active fuel region inside the pressure vessel.

It is beginning to look as if NISA seriously questions this move… not in terms of restoration of core cooling, but rather in terms of building safety and more importantly (and directly) reactor safety in the event of a further earthquake, taking into consideration the large increase in mass that this much water will add to the dry well structure.

This is perhaps one of those watershed moments, because if TEPCO finds that this plan is not safe in this seismic environment (or if NISA doesn’t like TEPCO’s answer and stops the plan anyway) then this will entirely derail TEPCO’s sole plan to restore core cooling in a timely manner.


Read the whole thing — it’s a bit complicated. If NISA concludes the flooding strategy is not prudent, I do not know what the fallback will be. Will Davis concludes with this:

This is a pivotal report for the movement of plant recovery forward, so we will be watching for the response and have it up here as soon as we see it.