Where the Breach(es) May Be

News reports now seem to confirm 2 potential breaches which might allow release of dangerous amounts of radioactive material.

a) the Unit 2 Reactor may have developed a breach in the containment vessel as described here.

From World Nuclear News:

Confirmation of loud sounds at unit 2 this morning came from the Nuclear and Industrial Safety Agency (NISA). It noted that “the suppression chamber may be damaged.” It is not clear that the sounds were explosions in the usual sense.

Also known as the torus, this large doughnut-shaped structure sits in the centre of the reactor building at a lower level than the reactor. It contains a very large body of water to which steam can be directed in emergency situations. The steam then condenses and reduces pressure in the reactor system. One effect of this is that the water and steam in the torus will exist alongside a range of gases produced by the nuclear processes in the reactor

The pressure in the pool was seen to decrease from three atmospheres to one atmosphere after the noise, suggesting possible damage. Radiation levels on the edge of the plant compound briefly spiked at 8217 microsieverts per hour but later fell to about a third that.

In line with the theory that non-condensed gases in the torus will be released fairly promptly and not replenished at the same rate, it is possible that the radiation release – at least via this route – will diminish and stabilise.

Nuclear Energy Institute reports:

UPDATE AS OF 9:15 A.M. EDT, TUESDAY, MARCH 15:
Fukushima Daiichi
Units 1 and 3 at Fukushima Daiichi are stable and cooling is being maintained through seawater injection. Primary containment integrity has been maintained on both reactors.

The Japan Atomic Energy Agency (JAEA) reported an explosion in the suppression pool at Fukushima Daiichi Unit 2, at 7:14 p.m. EDT on March 14. Reactor water level was reported to be at 2.7 meters below the top of the fuel. The pressure in the suppression pool decreased from 3 atmospheres to 1 atmosphere. Radiation readings at the site increased to 96 millirem per hour.

Another view of the suppression pool (doughnut shaped torus at the bottom):

b) the Unit 4 Reactor, which was not in use during the accident, has apparently suffered overheating in a spent fuel pool, a subsequent fire, and explosion which may have opened the secondary containment, and allows a path for waste products to escape if the spent fuel continues to overheat.