There is also a theory that filling the drywell with water in reactor 1 is an attempt to 'wet vent' the radiation and therefore minimize the release of radiation into the air. (http://ex-skf.blogspot.com/2011/05/fukushima-i-nuke-plant-may-8-release-of.html) "This journalist (link is in Japanese) says one of his friends who used to work at Fukushima I Nuke Plant as an engineer thinks the main purpose of filling the Containment Vessel with water is "wet vent". If the release of radioactive materials in large amount is expected on May 8, the reason why TEPCO is pouring more water into the Containment Vessel is to do the "wet vent" that will reduce the amount of radioactive materials coming out of the Pressure Vessel by having them go through water."
TEPCO workers face a long and difficult task. One that’s not going to be made any easier by the constant instrusion and criticism of those with little to no experience in nuclear operations.
My experience is ephemeral, amounting to perhaps a thousand or so hours in operating plants, and none at all with TEPCO’s units. From what I’ve read, I expect they’re trying to clean up containment in order to set interior control points and ventilation that will minimize uncontrolled environment discharge of radiation. Doing so may mean some short-term increases. >PS