[Professor S]

http://bravenewclimate.com/2011/03/1...march-summary/

During March 12 and 13, there were serious issues with providing sufficient cooling to units 1 and 3 after the tsunami had caused damage to the diesel backup generators and compromised the emergency cooling water supply. This resulted in a decision to use sea water injection to keep the reactors cool — a process that is ongoing. Steam was regularly vented as part of the effort to relieve steam pressure within the reactor vessels, but this also led to an accumulation of hydrogen gas within the secondary buildings that house the reactor units. Possible sources for the hydrogen are discussed here. Unfortunately, this hydrogen could not be vented sufficiently quickly, resulting in chemical explosions (hydrogen-oxygen interactions) within the two reactor housing buildings of both unit 1 and unit 2 during March 12-13.

The roof and part of the side walls of both buildings were severely damaged as a result. After the first hydrogen explosion there is no longer a roof on the building, so there is little chance of any large buildup of hydrogen or further explosions at these units. [In restrospect, the designers (40 years ago) perhaps should have more carefully considered the implications of the decision to vent the pressure suppression torus to the reactor building space]. Although hydrogen recombiners are a standard feature of that design, they unfortunately lost all AC power, and then the batteries were run down. Containment (the robust concrete shell and 18 inch thick steel reactor vessel within it), however, remained intact. This was verified by monitoring levels of radiation surrounding the units — if there had been any containment breach, levels would have jumped...

Regarding radiation levels: It is very important to distinguish between doses from the venting of noble-gas fission products, which rapidly dissipate and cause no long-term contamination or ingestion hazard, and aerosols of other fission products including cesium and iodine...

Japan suffered an earthquake and tsunami of unprecedented proportion that has caused unbelievable damage to every part of their infrastructure, and death of very large numbers of people. The media have chosen to report the damage to a nuclear plant which was, and still is, unlikely to harm anyone. We won’t know for sure, of course, until the last measure to assure cooling is put in place, but that’s the likely outcome. You’d never know it from the parade of interested anti-nuclear activists identified as “nuclear experts” on TV.