Events at the Fukushima Daiichi nuclear powerplant in Japan continue to unfold, with workers there steadily restoring redundancy and containment measures across the site. It remains highly unlikely that the workers themselves will suffer any measurable health consequences from radiation, and – continued media scaremongering notwithstanding – effects on the public look set to be nil.
Operations at the plant itself continued yesterday, with powerful mobile pumping equipment set up at both the No 3 and No 4 reactors there to refill the spent-fuel pools at those buildings.
Water levels in those pools were thought to be at low levels last week, raising the possibility of damage to the spent rods from their own internal heating – though this is hugely less than that present in a reactor core, and experts have differed on the point of whether such damage would actually be significant. All sides agree, however, that with the three damaged cores effectively stabilised using seawater cooling the pools had become the greatest potential source of radiation at the site. Efforts to restore a deep layer of water over the spent rods have been the main focus of operations at Fukushima Daiichi since the middle of last week.
Both pools are now being continually topped up using mobile vehicles capable of squirting large amounts of water into the pools from 20m+ heights, the vehicles left running unattended to reduce the radiation doses sustained by their operators. At first a vehicle (and mobile Super Pump Trucks) supplied by Tokyo fire department's elite Hyper Rescue unit was employed, but some reports indicate that this was damaged by being left running for 13 hours at the weekend. Additional vehicles normally used to pump concrete at high-rise construction sites are now in play and cooling of the pools continues.
Personnel were briefly evacuated from the area of No 3 during the afternoon yesterday (UK time), when white smoke was seen coming from the reactor building. This could have been a sign of hydrogen being emitted, presaging a hydrogen explosion of the sort which wracked the site in the days following the quake. However the smoke – which could equally have been steam resulting from pool cooling water pouring down through the building – then declined. Radiation levels and pressure/temperature readings from the No 3 core remained steady and workers returned to No 3 as the smoke emissions ceased.
Meanwhile efforts to restore grid power from off site continued, with power provided at all reactors as of the latest reports. Nos 5 and 6 are now considered fully safe, with cores at cold shutdown status and spent-fuel pools running normally. Engineers are still restoring services including instruments and cooling at 1 and 2: it has been reported that the spent-fuel pool at No 2 is now being topped up using water from a fire engine connected to its usual cooling pipework. External power lines have been connected to switching equipment serving Nos 3 and 4 but plant operator TEPCO doesn't expect to fully restore power there until later in the week.
Radiation levels measured inside the plant continue to be such as to require workers there to carefully manage their dose rates, but not such as to mean any long-term health worries. Workers are permitted to sustain a total annual dose of 250 millisievert before being withdrawn from the operation, which is not such as to cause them or their families any concern. As only small numbers of personnel are involved, and cancer is a very common cause of death, future investigations decades from now will almost certainly not be able to attribute any cases of cancer among the workers to service during the current incident.