But Japanese officials have successfully installed a one-kilometre cable to supply electricity from a Tokyo Electric Power Co (TEPCO) grid to reactor No2 to add power for already existent cooling pumps, taking pressure off the seemingly willy-nilly, desperate attempts to blast and drop water on heating reactors and cooling pools.

The cable should restore power to restart the pumps, which send coolant over the reactor.

“If the restoration work is completed, we will be able to activate various electric pumps and pour water into reactors and pools for spent nuclear fuel,” a TEPCO spokesman told the AFP news agency.

The No. 2 reactor’s containment vessel was partly damaged in its pressure suppression chamber. The reactor building is emitting vapor thought to have originated from spent nuclear fuel’s storage pools into the air.

Diesel power units have also been delivered and can now be operated to supply reactor Nos 5 and 6 alternately to inject water to their used fuel pools. Later, the power will be used to top up water in the reactor vessels.

Workers, who had been reduced to a skeleton crew of 50, down from 800 on Tuesday, received reinforcements and by the end of the day, 322 technicians were on site trying to blast water over exposed nuclear fuel rods to prevent fuel rod melting and leaking lethal radiation.

The 50 technicians that had been working to working to pump tons of water into the plant had to be evacuated early Wednesday when radiation spikes forced them out of the central control room. The were aloud to return some hours later when the radiation subsided.

But the new workers also arrive at the site with new and higher permissible radiation levels in place in which they can work: The cumulative maximum level for nuclear workers was increased to 250 millisieverts from 100 millisieverts by Japan’s health ministry on Tueday.

Levels beside the exposed rods of the reactors that were being inundated would deliver a fatal dose in 16 seconds, said David Lochbaum, a nuclear physicist for the Union of Concerned Scientists and a former U.S. Nuclear Regulatory Commission safety instructor, told Bloomberg.

Harmful radioactive material could be emitted from the rods if attempts to immerse them aren’t successful, said Peter Burns, former chief executive officer of the Australian Radiation Protection and Nuclear Safety Agency.

“The dose rates around the vicinity of the reactor buildings will be so high that the workers will not be able to get in there and do anything,” Burns told reporters on a conference call from Melbourne, according to Bloomberg. “Then you have a more or less cascading situation.”

Six fire engines and a police water cannon were sent in on Thursday evening to spray the plant’s No 3 reactor.

But even with back-up workers on board, radiation levels at plutonium-based fuel burning reactor No 3 continued their increase from 3,700 microsieverts per hour to 4,000 per hour, the Kyodo news agency quoted TEPCO as saying.

The No 3 reactor burns a mix of uranium and plutonium oxide, or MOX, fuel, and releases of plutonium are a source of extreme worry because of plutonium’s longer period of decay and higher potential to cause radiation related diseases.

“Today has seen some good news, but there is still a lot of uncertainty,” said Bellona’s nuclear physicist, Nils Bøhmer.

He had warned earlier in the day that if efforts to cool the fuel storage ponds failed, particularly the pond at the top of reactor No 4, which has suffered two fires, it could lead “to an increased risk of uncontrolled criticality (and uncontrolled chain reaction).

“There has been a lot of progress in getting water into the pumping systems, and some reports are indicating that radiation levels have been reduced by the spent fuel storage ponds,” said Bøhmer.

But Bøhmer aslo raised concern over the overcrowding of fuel rods at six cooling ponds and one common pond at the plant – something TEPCO did intentionally.

Last November, TEPCO released a report detaling how they have managed to store more than 10,000 fuel assemblies at the cooling ponds at Fukushima Daiichi as part of a program to consolidate spent fuel elements before putting them in a prospective interim storage facility in Mutsu, Japan.

The design approach outlined in the report bears comparrison to the way Russia’s Leningrad Nuclear Power Plant introduced the advent of double packing its own spent fuel ponds by creating a spefic apparatus that could hang two spent fuel assemblies instead of just one. The experiment was implemented in leaky ponds. Russia has since gone on to implement the same crowded storage procedure at other of its plants with Chernobyl-design RBMK-1000 reactors.

“But things remain unclear with reactor with Fukushima Daiichi’s Nos 3 and 4 reactors  – radiation is rising even after 30,0000 tons of water has been sprayed into them – it is unclear how much of it hit the fuel pumps,” Bøhmer said.

US Nuclear Regulatory Commission head Greg Jaczko continued to warn on Wednesday that there could be massive emissions of radiation from the spent fuel storage pond, which contains 1000 tonnes of fuel.

Hikaru Kuroda, a Tepco official, said, “We are afraid that the water level at [the No 4 reactor] is the lowest. Because we cannot get near it, the only way to monitor the situation is visually from far away.”

Tepco said a military helicopter crew had seen some water in the No 4 pool but this could not be confirmed, the Guardian said.

US President Barack Obama met at the White House with Jaczko, who said his recommendation was to evacuate Americans within 80 kilometres of the plant, the Associated Press reported.  The US Embassy later released a statement repeating the advice.

The British embassy followed suit with similar advice and asked citizens living in Tokyo and northern Japan to consider leaving, reported the Guardian.

Japan has evacuated 210,000 people from the 20 kilometre radius around the plan, the International Atomic Energy Ageny reported Tuesday, though some 160 elederly and otherwise imobile people have not been able to leave.

During separate testimony on Capitol Hill Wednesday, Jaczko said anyone who gets close to the plant could face potentially lethal doses of radiation.

“We believe radiation levels are extremely high, which could possibly impact the ability to take corrective measures,” Jaczko said, according to AP.

TEPCO’s delay in reconnecting the Fukushima plant to Japan’s national grid has came under fire from Kenneth Bergeron, who has done research on nuclear accident simulation at Sandia national labs in New Mexico, the Guardian reported.

“I am concerned that the management of this accident was left to very local hands for a very long time,” he told the Guardian. “Experience has shown in particular at Three Mile Island that sometimes the managers and operators in place when the accident has taken place are not well qualified. They may have the inability to see the big picture.”

In particular, he faulted the rescue effort for not immediately working to restore the power to the reactors’ cooling systems.

“What was really needed at Fukushima was restoration of the AC power to the emergency cooling system, and instead we saw them running fire hoses from the ocean,” said Bergeron as quoted by the Guardian.

“Time will tell whether that was the only option or not but a jerry-built arrangement like that sounds to me like a move of real desperation,” he said.

But Bellona’s Bøhmer defended TEPCO, saying that, “They’ve been working days to restore power to the cooling pumps since Friday,” when the 9.0 earthquake and 10-metre high tsunamis hit.

“Their work has been  hampered by high radiation levels,” said Bøhmer. “And TEPCO and other rescue workers have been working to install the power line [to the No 2 reactor] since yesterday,” he said, citing Kyodo reports and various others.

Contamination tallies among technicians continue to grow, however. One Tepco worker working within the reactor building of Fukushima Daiichi reactor No 3 during “vent work” was taken to hospital after receiving radiation exposure exceeding 100 milisieverts, a level deemed acceptable in emergency situations by some national nuclear safety regulators, the London-based World Nuclear Association reported.

Another 17 workers – nine Tepco employees and eight subcontract workers – suffered facial exposure to low levels of radiation. They did not require hospital treatment. 

Two policemen were decontaminated after being exposed to radiation, and an unspecified number of firemen who were exposed to radiation are under investigation, the World Nuclear Association reported.