A brief update on the reactor debacle unfolding in Japan:

While two reactors at the Daini complex have restored cooling, the problems @ Daichi are multiplying.

The large General Electric Unit #2 has had two incidents of exposed fuel rods within the reactor core. A hydrogen explosion is likely at this plant like its cousins.

The three reactors are 460mw, 790mw and 790mw respectively.

The problems are unclear but multiplying. There are reported issues with spent fuel ponds, venting valves on containments, inoperable pumps, fire pumps used to provide cooling seawater, along with an inability to overcome steam pressure and hazardous working conditions at the damaged reactors.

Water levels @ various reactors are dropping inexplicably, suggesting leaks. Ditto the waste ponds which are built onto the upper levels of the Daichi containments. It is possible that the twin explosions have damaged the ponds which would allow the spent fuel rod to become exposed and to catch fire.

The explosion @ Unit 3 apparently damaged four out of five pumps (fire trucks?) used to pump seawater and boron into Unit 2. Apparently the core in this reactor was completely exposed for some undetermined period. Adding seawater increased pressure above the ability of the remaining pump (fire truck?) to overcome.

If the pressure in the pressure vessel is relieved the water will flash off as steam exposing the core. Flashing to steam would also cool the core so there is an unknown trade off.

A large and more ominous issue is what would take place should there be a significant release of radiation at one of the three stricken plants. In the event of one meltdown the entire area would be uninhabitable and the two neighboring plants would run away in turn followed by the failure of spent fuel containment.

Good luck all and more on this, later!

UPDATE:

The predictable hydrogen gas/steam explosion took place @ 6:10 am local (Japanese) time within Kurushima Daichi reactor unit #2. Unfortunately, this explosion appears to have damaged the containment structure which surrounds the pressure vessel. How much damage is uncertain but the containment cannot keep radiation out of the environment.

Reports are the plant operator has removed workers from the reactor:

damage was limited and that emergency operations aimed at cooling the nuclear fuel at three stricken reactors with seawater would continue. But industry executives said that in fact the situation had spiraled out of control and that all plant workers needed to leave the plant to avoid excessive exposure to radioactive leaks.

If all workers do in fact leave the plant, the nuclear fuel in all three reactors is likely to melt down, which would lead to wholesale releases of radioactive material — by far the largest accident of its kind since the Chernobyl disaster 25 years ago.

Washington Post notes that fifty operators of the plant remain out of the 1,400 workers prior to the last explosion.

I heard a rumor that diesel generator power had been restored to one of the three reactors but I have not been able to confirm this.

IAEA reports three of the Kurusima Daini reactors are in cold shutdown.

There is an unconfirmed report of a spent fuel fire at an unspecified ‘fourth reactor’. A fire in a spent fuel pond or tank without cooling water would would emit large quantities of radiation, similar to Chernobyl. There are over 1,800 tons of spent fuel @ the three damaged Kurusima Daichi reactors.

Without a cooling loop the only way to keep core temperatures below the melting point of the fuel is to pump water into the cores then bleed off steam and hydrogen gas. There are not likely to be more explosions. Hydrogen had been vented into the ‘attic’ space above the containment structures; to contain gas- borne radiation as long as possible. When the space was filled with gas there was the explosion.

Now, gas is vented straight into the atmosphere carrying some radioactivity.

The drill is to fill the pressure vessel with water then bleed off steam and keep pressures under control. The steam/vent cycling keeps pressures down which cools the core. The energy of the fuel is carried by the steam and hydrogen. The explosions were in fact part of the cooling cycle, dumping energy into the containment and atmosphere.

There are many dangers and hazards.

The operators are exhausted by long shifts and fear. Every possible scenario regarding nuclear station operation exists in highly detailed procedure manuals. The manuals are now useless. Events have outrun them. The operators are being forced to improvise which is easier for some than others. Those who cannot are breaking under the strains of a failure of procedure, the danger and responsibility at hand along with the catastrophe or earthquake and tsunami.

The improvisers are struggling under management culture that resists ‘initiative’.

Like many other disasters, the workers are distracted by uncertainty @ home. Are wives or children safe? Are family members lost or missing?

Like the operators, the equipment is breaking under the strain and ill fitments are beginning to matter. Using fire pumps to flood the reactor cores is a piss- poor expedient. Valves and pumps are failing. A balky valve condemned the core in unit #2 along with a pump that ran out of fuel(!).

Each reactor has its own crew and it is unclear whether any one person is in charge or whether the crew managers are helping each other out.

The explosions have damaged pumps including pumps to push water into the spent fuel tanks located @ the tops of each reactor. The water appears to be boiling out of these tanks which contain many years of spent fuel rods. If the water boils off the rods will catch fire and spew massive amounts of radiation.

There is nothing between the tanks and the great outdoors. The location of these tanks @ the tops of the reactor cores renders them inaccessible to repair techs.

There appears to be water in the suppression pool or ‘basement’ under the pressure vessel in unit #2. If there is a pressure vessel breach or meltdown there will be a steam explosion in the reactor which will push reactive material outside.

This is a reactor schematic from Nuclear Tourist. There are other photos of a boiling water plant similar to the Daichi units at this website.

Reports indicate the explosion in the suppression pool area damaged plumbing which is allowing water in the pressure vessel to flow out.

Right now it appears that the pressure vessels of all three reactors are intact. However, it is impossible for workers to enter the containment or see what is taking place. It is also unknown how much damage the fuel assemblies have sustained.