– TV: Only ‘some’ of Fukushima melted fuel is now solid — Nuclear Expert: Molten core ‘re-melts’, even with enough cooling water — Japan Engineer: “The Fukushima accident was the first of its kind” (VIDEO) (ENEnews, Jan 29, 2015):
NHK, Jan 27, 2015 (emphasis added): Groundwater entering the facility becomes tainted when it mixes with melted fuel inside the reactor containers. Tepco engineers believe some of the fuel has cooled down and turned into solid debris. But they don’t know the exact situation, so they’re hoping to take a look inside… Scientists have figured out a way of using muons to help them see substances hidden from views — like magma… When particles hit a high-density object like magma, they lose energy or are absorbed… it’s like an x-ray. Researchers are hoping to use the technique to get a better idea of what’s inside the reactors… Engineers will… try and determine the state of the melted fuel… Engineers say knowing what’s inside will help them figure out a way to decommission the plant.
Asahi Shimbun, Jan 24, 2015: [TEPCO] will use cosmic rays… to identify sites with melted fuel… They will first study the No. 1 reactor… by the end of this fiscal year, estimating how much fuel remains in the reactor [and] intend to extract the melted fuel after surrounding it with water… the plant operator will need to repair damaged sections of the containers to prevent water leaks… However… nuclear fuel at the base of the container cannot be seen using the muon technique…
Dr. Ing. Mazzini, Ph.D. Nuclear & Industrial Safety (pdf): Severe Accident Phenomenology… Milestones of Nuclear Safety: 2011 Fukushima Accident (1st for an External Event)
- Ex-Vessel Accident Phenomena:
-> The molten debris falls into the reactor cavity. This produces boiling off of whatever water is there. If sufficient water is present, the core would be cooled and solidify, and would subsequently re-melt.
-> Steam explosions may also occur at this time as the molten fuel falls onto water in the reactor cavity. This can disperse fuel, create radioactive aerosols, and increase the rate of heat transfer to the containment atmosphere.
-> Molten corium attacks the concrete basement, which proceeds to penetrate, and creates a cauldron that releases aerosols and gases [and] containment pressure rises.
DPA, Jan 28 2015: More delays expected in Fukushima nuclear plant clean-up… More delays in treating contaminated water from Japan’s crippled Fukushima nuclear power plant are likely, a senior official of a company involved in the clean-up said Wednesday. “Some schedule(s) would be delayed because the contaminated facility did not operate as planned,” [said] Yoshiki Ogata, director of the global nuclear project department of Mitsubishi… “The situation in the building is not clear,” he told dpa on the sidelines of a nuclear energy conference. Mitsubishi, along with Toshiba and Hitachi, are the three companies helping… Ogata said that the Fukushima accident was the first of its kind so there were a lot of challenges… “So, first stop the underground water from entering and also leakage to the sea…”