Science: Fukushima far more damaged than first thought
May 18, 2011
In the absence of consistent, credible, on the scene reports from the Fukushima site, observers are forced to go to a wide range of news sources and try to tease out the real truth from the subtle differences in reporting. So far, the situation has repeatedly shown itself worse than the reporting and official press releases have let on. Suggestion: watch the vids above, and below, compare to print sources here, find a way to split the differences.
TOKYO—Over the last several days, evidence has emerged indicating that the situation at the Fukushima Daiichi Nuclear Power Plant was far more dire than previously recognized. The main evidence is extensive—rather than partial—melting of the nuclear fuel in three reactors in the hours after the 11 March earthquake and tsunami. Despite that bad news, however, today plant owner Tokyo Electric Power Co. pledged it would still meet the target set 17 April to stabilize the situation by January 2012 so 100,000 residents evacuated from around the plant can return to their homes and the decade-long process of demolishing the reactors can get started.
At first, analysts from Tokyo Electric and the government believed there was only limited damage to the fuel cores. But over the last week, a combination of robotic and human inspections has led to the conclusion that the fuel assemblies in units 1, 2, and 3 were completely exposed to the air for from over 6 hours to over 14 hours and that melting was extensive if not complete. Much of the fuel is now likely at the bottom of the reactor pressure vessels.
Despite extensive melting of the fuel, “we do not believe there is massive damage to the reactor pressure vessel,” Sakae Muto, Tokyo Electric’s chief nuclear officer told reporters this evening. Last week workers found that an estimated 3000 tons of water has leaked from the unit 1 containment vessel into a basement. In its 17 April roadmap, Tokyo Electric envisioned flooding the containment vessel and building a new cooling system to lower the temperature of the core. But the containment vessel now appears to be too leaky for that scheme to work. Instead they will collect water from the basement, purify it, and inject it back into the reactor pressure vessel, from where it will leak back into the basement. It is simpler than a new cooling system, but it will also require additional measures to watch for and counter leaks of contaminated water into the environment, Muto said. They may still build new cooling systems to supplement or replace the water injection scheme.
In recent days the plant’s operator has revealed that the damage sustained by the reactors immediately after the magnitude-9.0 earthquake and tsunami was far more severe than initially thought.
Officials from the Tokyo Electric Power Company (Tepco) say fuel rods at the plant began to melt down as early as six hours after the 11 March tsunami knocked out vital cooling systems.
Within 16 hours most of the fuel in reactor 1 had melted to the floor of the pressurised chamber housing the reactor, creating a hole that allowed 3,000 tonnes of contaminated water to leak into the basement of the building.
Officials said the fuel in reactors number 2 and 3 was also exposed to the air and might have largely melted too.