Long game at Japan nuclear plant

We are now in a long game at the stricken Fukushima Daiichi nuclear power plant in Japan.

Two-and-a-half weeks on from the colossal Tohoku quake and its associated tsunami, engineers are working tirelessly to regain full control of the facility.

The past week has seen major gains in getting on top of the crisis, but difficulties and frustrations continue to hamper progress.

The major concern right now would appear to be the second reactor unit at the six-unit plant.

High levels of radiation have been found in waters in the basement of the building.

Doses at 1,000 millisieverts per hour have been measured – the highest readings recorded in the crisis so far.

Just 15 minutes exposure to this water would result in emergency workers at Daiichi reaching their permitted annual limit of 250 millisieverts.

Radioactive-contaminated water has also almost completely filled a tunnel system leading from the Unit 2 building.

Efforts are ongoing to ensure none of it floods out and into the ocean some 50m away.

Why the water is so contaminated is not completely clear, but the suspicion is that it has at some stage come into contact with nuclear fuel fragments from inside the reactor or from fuel rods stored in a cooling pond just outside it.

It may be the reactor’s pressure and containment vessels or the pipework that feeds them has been compromised in some way. There is no definitive information on this.

“Together with the fact that the water found outside is highly radioactive, I think it can be said that this is proof that the fuel rod has melted a bit and this is a very serious thing,” said Japan’s Chief Cabinet Secretary, Yukio Edano. “We are doing our best to make sure we can stop (the further spreading of radioactivity) and contain the situation.”

It is now a balancing act, Yukio Edano added. Water must be pumped continuously into the Number Two reactor to keep it cool, while at the same time not putting too much pressure on the system in case leakages of further radioactive water result.

“If the infrastructure doesn’t deteriorate at Fukushima, the reactors are kept cold and the radiation is kept localised – then the level of radioactivity has to fall away naturally because the reactors are switched off,” observed Paddy Regan, a British professor of nuclear physics at the University of Surrey.

“They seem to me to be doing exactly the right thing. Their protocol is to do whatever has to be done to keep the fuel rods cool. If they’re not cooled there’s still residual heat in them, called decay heat, and if the coolant evaporates and they’re exposed to air then a combination of the heat and the fact they’re exposed to air means you can have reactions on the zirconium cladding on the rods, and that is what releases the fission fragments.”