Annals of Nuclear Energy, Apr 2016 (emphasis added): The importance of severe accident research has been again seen after [Fukushima]… As the accident analysis showed, it seems that in the Daichi Unit 3 a steam explosion occurred… A steam explosion… is an energetic fuel coolant interaction (FCI) process, which may occur during a severe accident when the hot reactor core melt comes into contact with the coolant water… Steam explosions… potentially jeopardize the primary system and the containment integrity…
Korea Electric Power Corporation, Sep 2013: Steam explosion is a phenomenon that… results in explosive dynamic pressure… In the accidents, reactor fuel and materials melts due to the lack of adequate cooling capability as observed in Fukushima accident… In the actions of mitigating… severe accident progression, cold water supplies to cool the corium by any means. In this process, molten corium contacts water, resulting steam explosions that may provide mechanical and functional damages to the surrounding structures…
- A postulated full core meltdown… possibly causing a steam explosion was reportedly averted by judicious supplemental cooling.
- [H]eat signature in unit 3 may suggest a possible ejection of the concrete shield plug by the observed hydrogen or possibly steam explosion.
- Unit 3 was the only unit… that uses… MOX fuel… A reported long vertical crack running down the side of the containment vessel implies the possible occurrence of a steam explosion.
- Hydrogen or steam explosion tore out the upper part of the containment… smoke emanating from possible burning of the UO2 fuel.
- Lateral horizontally propagating hydrogen explosion at second chimney from the right preceded the vertical suspected steam explosion at unit 3.
- Figure 58. Sequence of vertical steam explosion following the horizontal hydrogen explosion at unit 3.
- Highly energetic vertically propagating hydrogen or possibly steam explosion at the Fukushima Daichi unit 3… was followed by a fire and reactor fuel damage. Heavy debris… was vertically ejected and is seen falling back down in the photograph… It bears some analogy to the complex aerodynamics of an “exploding vortex ring.”… Exploding vortices suggest a steam explosion occurrence at unit 3.
- The ejection of fuel parts from unit 3 would imply a more serious event than a hydrogen explosion in the form of a criticality excursion and a steam explosion…
Why is a steam explosion — rather than the reported hydrogen explosion — such a big deal?
US Nuclear Regulatory Commission – transcript excerpts (pdf), Mar 18, 2011:
- CHAIRMAN JACZKO: So I think we really should produce a source term that is truly what I would call a worst-case but a possible scenario…
- TRISH HOLAHAN: We’ve also been asked to look at the MOX capability… in Reactor 3…
- JACZKO: I have to believe that there is no possibility… to reject an entire core. I mean, that’s basically steam explosion; isn’t it?
- HOLAHAN: Yes…
- JACZKO: I think we’ve ruled that, as an agency, we’ve ruled that out…
Published: May 11th, 2016 at 10:36 am ET
- Nuclear Professor: Blast at Fukushima Reactor 3 was like “exploding vortex ring” — Ejection of nuclear fuel implies there was a “criticality excursion” and steam explosion — Black smoke may have been burning MOX and uranium (PHOTOS) September 25, 2014
- NBC: US officials “hid concerns… as Fukushima melted’ — CIA told nuclear regulator that blast was hydrogen, experts then noted “no evidence to support” this theory March 11, 2014
- Engineer: 6 experts say nuclear explosion at reactor is possible — NRC: Fukushima Unit 3 explosion had 3 loud bangs, much larger than Unit 1 blast — Tokyo professor’s presentation adds question mark: “Hydrogen explosion of Reactor #3?” (VIDEO) December 28, 2013
- Video: “Purple cloud” seen by engineer after Fukushima explosion… “I took a photo” — Former Prime Minister: Smoke from reactor blast had different color than officials claim; Steel appears to have melted on top of Unit 3; Suggests possible nuclear explosion October 30, 2014
- Nuclear Engineer: New cover on Unit 4 can trap hydrogen gas during criticality in fuel pool — Blast would be close to a nuclear explosion, from a practical standpoint (AUDIO) November 22, 2013