Fukushima Daiichi Accident 3 years after, Canadian Nuclear Safety Commission, Ramzi Jammal, Executive Vice-President and Chief Regulatory Operations Officer of the Regulatory Operations Branch, Physics Colloquium at Queen’s University, March 14, 2014:

• Smoke from SFP at Unit 3? Quote from [The National Diet of Japan's report 'Fukushima Nuclear Accident Independent Investigation Commission'] What was the source of the massive amount of heat that caused intermittent water evaporation in the form of white smoke to come out of the pool? If the pool was impacted from the hydrogen explosion, it is probably that the used and unspent fuel assemblies were moved closer together and became compressed against one another, creating a condition of criticality [uncontrolled nuclear chain reaction] inside the pool.
• Comment in the Canadian Nuclear Safety Commission’s presentation: Based on the result of criticality assessment [...] there are no criticality in SFP.

Fukushima Nuclear Accident Independent Investigation Commission, National Diet of Japan (emphasis added): Hydrogen explosion of Unit 3 and heat source within the spent fuel pool. The hydrogen explosion resulted in a plume of white smoke immediately after the explosion, and on the two following days. Observation of the spent fuel pool after the explosion shows the possibility of substantial damage to the fuel. But the dumping of a large amount of water after the explosion might have kept the radioactive material in the pool to be within or around the building, reducing the further spread of radioactive material. It is also possible that rainfall could have caused part of the radioactive material to fall into the ocean. [...] What was the source of the massive amount of heat that caused intermittent water evaporation in the form of white smoke to come out of the pool? The white smoke was generated not only immediately after the hydrogen explosion but on both of the next two days. There was, therefore, the possibility of damaged fuel inside the pool causing temporary massive heat generation. The layout at the Unit 3 spent fuel pool shows that; 1) fifty-two of the unspent fuel assemblies were arranged together in almost one lump, while the surrounding racks were empty, and 2) nearly half of the spent fuel was arranged together in one lump. Therefore, if the pool was impacted from the hydrogen explosion, it is probable that the used and unspent fuel assemblies were moved closer together and became compressed against one another, creating a condition of criticality inside the pool.

Recall this BBC report from March 24, 2011: “Kyodo News [reports] neutron radiation was observed more than a kilometre from reactor buildings [...] Neutrons are emitted during a nuclear chain reaction; so given the context, is Kyodo’s report to be taken as indicating that a chain reaction took place after the reactors shut down? If it is, does that relate to the company’s warning last week that there was a possibility of “re-criticality” in a pool storing fuel rods?”

Watch — Gundersen: Unit 3 started as a hydrogen explosion… but I think it’s more — I actually think it was something called a prompt moderated criticality that was caused by a hydrogen explosion

Published: July 4th, 2014 at 6:11 pm ET By ENENews