THE OPERATOR OF the troubled Fukushima I nuclear power plant in Japan has disclosed that an explosion at reactor 4 this morning – the cause of a fire in a storage pool for ‘spent’ fuel this morning – has caused the rods there to be exposed to the open air.
Tokyo Electric Power Company (TEPCO) said that the fire at the reactor this morning had been caused by a hydrogen explosion inside the reactor – which had left two holes in its walls, measuring a combined total of eight square metres in size.
Those holes, TEPCO has now confirmed, have left the pool of nuclear fuel – which has been evaporating away, as a cooling failure meant sufficient cooling water could not be supplied – now exposed to the open air, with rods therefore exposed to the atmosphere outside.
TEPCO did not indicate, however, how much radiation the ‘spent’ (used) material was liable to emit.
The worrying admission came after Tepco had confirmed the level of radiation being emitted from the pool was too high to allow staff go about their normal work in the reactor’s control room.
Coolant was being evaporated within the pool quicker than it could be pumped back in, a government spokesman had earlier said.
2,000 times usual annual dose
The UN’s nuclear watchdog, meanwhile, issued a statement saying the level of radioactivity being measured outside the plant had dropped significantly between the hours of 12am and 6am, Irish time.
The International Atomic Energy Agency said the level of radiation being read at the main gate of the station had dropped from 11.9 millisieverts (mSv) at midnight – 9am local time – to 0.6 mSv by 6am (3pm local time).
By way of comparison, the IAEA said the average annual exposure to natural sources of radiation is 2.4 mSv per year – meaning the hourly rate would still accrue, on average, to over 2,000 times the usual dose over the course of a year.
The news at reactor 4 means that all six of the reactors at Fukushima I are now posing significant problems: the containment buildings at reactors 1 and 3 both exploded over the weekend, though the core reactors are not thought to have been damaged.
Reactor 2 exploded overnight, with the core reactor thought to have incurred some moderate damage, while it is now known that the fire at reactor 4 was caused by a hydrogen explosion in the cooling pool for spent nuclear material.
The combined activities at reactors 2 and 4 had led to a confirmed emission of radiation into the atmosphere, authorities confirmed earlier this morning.
Reactors 5 and 6, it had been confirmed earlier, had both seen problems with their backup cooling mechanisms.