nuclear-news

“They have to remove the fuel as early as possible – the risk from major structural failure leading to pool collapse is a greater threat than leaving the fuel in situ.”.

Radiation levels in those reactors are still too high for humans to enter, and attempts to use robots to determine the exact location of the melted fuel have failed. Instead, officials are placing their faith in the law of gravity, assuming only that the highly hazardous material lies somewhere deep inside the reactor basements.

Fukushima nuclear cleanup enters critical phase Tokyo Electric Power to begin removing more than 1,500 fuel assemblies from spent fuel pool in unprecedented operation Justin McCurry in Fukushima The Guardian, Friday 8 November 2013 Gazing down at the glassy surface of the spent fuel pool inside the No 4 reactor building at Fukushima Daiichi, it is easy to underestimate the danger posed by the highly toxic contents of its murky depths.

But this lofty, isolated corner of the wrecked nuclear power plant is now the focus of global attention as Japan enters the most critical stage yet in its attempt to clean up after the worst nuclear accident in the country’s history.

Later this month the plant’s operator, Tokyo Electric Power (Tepco), will begin removing more than 1,500 fuel assemblies from the pool, the first step in a decommissioning process expected to last at least three decades.

On Thursday, the Guardian witnessed Tepco’s preparations for an unprecedented operation that the utility’s critics claim has the potential to end in disaster.

The risk posed to the reactor by earthquakes and other natural catastrophes has made removal of the fuel – 1,331 spent assemblies and 202 fresh ones – a matter of urgency. An event similar to the 9.0 magnitude quake that crippled the plant on 11 March 2011 could collapse the fuel pool altogether, some observers say, leading to the leaking of huge quantities of radiation into the atmosphere. Tepco, however, insists the structure could withstand such a quake.

Reactor No 4 had been shut down for maintenance checks when the quake and subsequent tsunami struck, but a hydrogen explosion days later blew off its roof and exposed the fuel pool, located 100 feet above ground, to the elements.

In the 32 months since the disaster, workers have reinforced the reactor building and covered it with a huge steel canopy. Tepco officials conceded, however, that the fuel removal carries significant risks, particularly if the assemblies collide or are exposed.

“If, for some reason, the water levels dropped, the fuel would quickly heat up,” said Takashi Hara, a Tepco employee in charge of fuel removal.

There are fears, too, that some of the uranium pellets inside the fuel rods may have been damaged, although Tepco says it has found no evidence of this……

A newly built crane that will manoeuvre the fuel must be operated manually, rather than automatically, because the assemblies are not exactly where they should be; and the pool is still littered with tiny pieces of debris caused by the blast.

Each batch of fuel rods will be placed into dry casks, which will then be lowered to ground level and transported to a safer storage site nearby…….

Shaun Burnie, a nuclear consultant, said Tepco had “clearly demonstrated its inability” to manage the cleanup…….

“They have to remove the fuel as early as possible – the risk from major structural failure leading to pool collapse is a greater threat than leaving the fuel in situ.”…..

Even if all goes to plan, Tepco officials concede that securing reactor No 4 is only a first step: work to remove molten fuel from three neighbouring reactors that suffered meltdown won’t begin for at least another six years.

Radiation levels in those reactors are still too high for humans to enter, and attempts to use robots to determine the exact location of the melted fuel have failed. Instead, officials are placing their faith in the law of gravity, assuming only that the highly hazardous material lies somewhere deep inside the reactor basements. ….http://www.theguardian.com/environment/2013/nov/07/fukushima-nuclear-cleanup-spent-fuel