Japan’s nuclear clean-up nears its deadliest phase
TOKYO: The operator of Japan’s crippled Fukushima nuclear plant is preparing to remove 400 tons of highly irradiated spent fuel from a damaged reactor building, a dangerous operation that has not been attempted before on this scale.
Containing radiation equivalent to 14 000 times the amount released in the atomic bomb attack on Hiroshima 68 years ago, more than 1 300 used fuel rod assemblies packed tightly together need to be removed from a building that is vulnerable to collapse should another large earthquake hit the area.
Tokyo Electric Power Co (Tepco) is already in a losing battle to stop radioactive water overflowing from another part of the facility, and experts question whether it will be able to pull off the removal of all the assemblies successfully.
“They are going to have difficulty in removing a significant number of the rods,” said Arnie Gundersen, a veteran US nuclear engineer and director of Fairewinds Energy Education.
The operation, beginning in November at the plant’s Reactor No 4, is fraught with danger, including the possibility of a large release of radiation if a fuel assembly breaks, gets stuck or gets too close to an adjacent bundle, say Gundersen and other nuclear experts.
That could lead to a worse disaster than the March 2011 nuclear crisis at the Fukushima plant, the world’s most serious since Chernobyl in 1986.
No one knows how bad it can get, but independent consultants Mycle Schneider and Antony Froggatt said recently in their World Nuclear Industry Status Report 2013: “Full release from the Unit-4 spent fuel pool, without any containment or control, could cause by far the most serious radiological disaster to date.”
Tepco has already removed two unused fuel assemblies from the pool in a test operation last year, but these rods are less dangerous than the spent bundles. Extracting spent fuel is a normal part of operations, but safely plucking them from a badly damaged reactor is unprecedented.
The utility says it recognises the operation will be difficult but believes it can carry it out safely.
Nonetheless, Tepco inspires little confidence. Sharply criticised for failing to protect the Fukushima plant against natural disasters, its handling of the crisis since then has also been lambasted.
Last week, Prime Minister Shinzo Abe ordered the government to take a more active role in controlling the overflow of radioactive water being flushed over the melted reactors in units 1, 2 and 3.
The fuel assemblies are in the cooling pool of the No 4 reactor, and Tepco has erected
The amount of caesium 137 in the pool is equal to 14 000 Hiroshima atomic bombs
a giant steel frame over the top of the building after removing debris left by an explosion during the 2011 disaster.
The structure will house the cranes that will carry out the delicate task of extracting fuel assemblies that may be damaged by the quake, the explosion or corrosion from saltwater that was poured into the pool when fresh supplies ran out during the crisis.
Tepco expects to take about a year removing the assemblies, spokesman Yoshikazu Nagai said.
It’s just one instalment in the decommissioning process which is forecast to take about 40 years and cost $11 billion (R109bn).
Each fuel rod assembly weighs about 300kg. There are 1 331 of the spent fuel assemblies and a further 202 unused assemblies are also stored in the pool, Nagai said.
Almost 550 assemblies had been removed from the reactor core just before the crisis. These are the most dangerous because they have only been cooling since then.
“The No 4 unit was not operating at the time of the accident, so its fuel had been moved to the pool from the reactor, and if you calculate the amount of caesium 137 in the pool, the amount is equivalent to 14 000 Hiroshima atomic bombs,” said Hiroaki Koide, assistant professor at Kyoto University Research Reactor Institute.
Spent fuel rods also contain plutonium, one of the most toxic substances in the universe.
Gundersen said there was a risk of an atomic chain reaction that left unchecked could result in a large release of radi- ation and heat that the fuel pool cooling system isn’t designed to absorb.
The rods were also vulnerable to fire should they be exposed to air.
The pool was exposed to the air after an explosion a few days after the quake and tsunami blew off the roof. The cranes and equipment usually used to extract used fuel were also destroyed.
Tepco has shored up the building, which was bulging after the explosion, a source of global concern that has been raised in the US Congress.
The utility says the building can withstand shaking similar to the quake in 2011, and that it carries out regular structural checks, but the company has a credibility problem. Last month it admitted that contaminated water was leaking into the Pacific Ocean after months of denial.
The operation to remove all the fuel would normally take about 100 days. Tepco initially planned to take two years before reducing the schedule to one year in recognition of the urgency. But that may be an optimistic estimate.