Some 4,600 terabecquerels of radioactive substances were discharged when an explosion ripped through the reactor 1 building March 12, and another 1,060 following an explosion at reactor 3 two days later, according to Tepco’s study of the fallout emitted by the plant’s three crippled units between March 12 and March 31.
The emissions peaked March 15 and 16, possibly because the primary containment vessels of the three reactors degraded due to high temperatures and released massive amounts of fallout and steam from their upper part.
Fukushima radiation release estimates are based upon the primary containment vessels (PCVs) staying intact and emitting only a tiny fraction of the overall radioactivity contained inside. For example:
Major Study: “We [...] assumed a release fraction [...] for the reactor cores [of] less than 1% of the caesium inventory”
More needs to be reported about the ‘degraded’ PCVs, as Tepco is now suggesting their condition had deteriorated to the point of releasing ‘massive amounts of fallout’ from the ‘upper part’.
If the tops were degraded enough to allow for massive radiation releases, what about the bottoms of the PCVs — where the corium is widely reported to be?
Here’s a representative example of how media reports describe the condition of the PCVs: BBC News – How does Fukushima differ from Chernobyl?
Fukushima: Japanese authorities stress that unlike at Chernobyl, the containment vessels at Fukushima remain intact.
Chernobyl: The reactor [...] had no containment structure and nothing stopped the trajectory of radioactive materials into the air.
Published: May 24th, 2012 at 10:48 pm ET
- TEPCO unable to verify water levels at reactors No. 2 and 3 — Suspects water is leaking from damaged containment vessels April 26, 2011
- TEPCO analysis indicates Reactor No. 1 and 2 have breached containment vessels meant to stop radiation from leaking May 25, 2011
- Japan Times: Much of melted fuel is believed to have burned down to bottom of containment vessels — At “last line of defense” January 20, 2012
- Japan Times: Melted fuel burned holes in Fukushima reactors — Explosions cracked containment vessels? March 8, 2013
- Japan Times on Melt Through: “Molten ‘lava’ melted bottom of containment vessel,” says nuclear engineer given access by top official — Huge amounts of fission materials released into environment April 18, 2012