As you may have read in the press, the Japanese earthquake caused the Fukushima Nuclear plants to shutdown and emergency power failed, causing a failure of emergency cooling systems in Fukushima 1. as a result of the failure of the cooling systems, the containment was pressurizing. The press was breathlessly anticipating a Chernobyl style meltdown. While the loss of cooling is certainly serious, comparisons to Chernobyl are significantly overblown. Fukushima 1 is a BWR , which has a robust containment structure to contain any radioactivity released from core damage. The latest reliable information I have from NEI’s website is that as of 5 pm EST, Tokyo Electric Powr Co had delivered 3 of 4 mobile power units to the site and engineers were connecting the units. Containment pressures had increased, but were well within enginering design limits. If pressure continued to rise, vepor could be vented through filtered vent systems to prevent overpressurization of the containment and contain any released radioactivity.
Significant diffeences betwen Fukushima and Chernobyl are:
Chernobyl had no containment structue – Fukushima 1 has a robust engneered steel and concrete containment.
Chernobyl had a graphite moderated core that caught fire spreading radioactivity as a result of the fire. Fukushima has a water moderated and cooled core. There would be no fire. The core might be damaged, but even if water levels within the vessel fell below the top of active fuel, significant steam cooling would still occur. As I mentioned earlier, even without cooling water, containment pressure can still be controlled through controlled filtered venting. Therefore a significant uncontrolled release of radioactivity is extremely unlikely, even if the core is damaged.
Even though Japanese authorities have ordered the evacuation of residents within a 3 km radius, this does not mean that an uncontrolled release of radioactivity is imminent. Nuclear plant emergency planns are extremely conservative and forward looking. In US nuclear plats, evidence of potential fuel damage would be enough to trigger emergency evacuations without any expectation that containment structure failure was imminent.
This accident is serious but it won’t be another Chernobyl.