Japan has promised to overhaul nuclear safety standards once it regains control of the wrecked Fukushima complex, admitting its current safeguards were not enough.
The struggle to contain radiation at the complex has unfolded with near-constant setbacks - including two workers drenched today with radioactive water despite wearing supposedly waterproof suits.
The unfolding drama has drawn increasing criticism of the company that owns the plant as well as scrutiny of Japan's readiness for nuclear crises.
"Our preparedness was not sufficient," chief cabinet secretary Yukio Edano admitted. "When the current crisis is over, we must examine the accident closely and thoroughly review" safety standards.
The Tokyo Electric Power Company had dismissed scientific evidence and geological history that indicated that a massive earthquake - and subsequent tsunami - was far more likely than they believed.
That left the complex with nowhere near enough protection against the March 11 tsunami triggered by the massive offshore earthquake.
The mission to stabilise the power plant has been fraught, as emergency workers have dealt with fires, explosions and radiation scares in the frantic bid to prevent a complete meltdown.
The plant has been leaking radiation that has made its way into vegetables, raw milk and tap water as far away as Tokyo. Residents within 12 miles have been ordered to leave and some nations have banned the imports of food products from the Fukushima region.
Highly toxic plutonium was the latest contaminant found seeping into the soil outside the plant.
Safety officials said the amounts did not pose a risk to humans, but the finding supports suspicions that dangerously radioactive water is leaking from damaged nuclear fuel rods.
"The situation is very grave," Mr Edano said.
Workers succeeded last week in reconnecting some parts of the plant to the power grid. But as they pumped in water to cool the reactors and nuclear fuel, they discovered numerous pools of radioactive water, including in the basements of several buildings and in trenches outside of them.
The contaminated water has been emitting four times as much radiation as the government considers safe for workers. It must be pumped out before electricity can be restored and the regular cooling systems powered up.
That has left officials struggling with two crucial but contradictory efforts: pumping in water to keep the fuel rods cool and pumping out contaminated water.
Officials are hoping tanks at the complex will be able to hold the water, or that new tanks can be trucked in.
Today the Nuclear Safety Commission, an expert panel of nuclear watchdogs, said other possibilities include digging a storage pit for the contaminated water, recycling it back into the reactors or even pumping it to an offshore tanker.
The latest mishap came, when three workers trying to connect a pump outside the Unit 3 reactor were splashed by radioactive water from a pipe. Although they were wearing suits meant to be waterproof and protect against high levels of radiation, they were soaked to their underwear with the contaminated water.
They quickly washed it off and were not injured, officials said.
Last week, two workers were taken to hospital with burns after they were issued ankle-high protective boots to walk into highly radioactive knee-high water.
Such incidents have led to increased criticism of the utility company.
Nikkei, Japan's top business newspaper, called it "outrageous" that Tepco had been slow to release information about trenches outside the reactors filled with contaminated water.
Prime Minister Naoto Kan, meanwhile, reiterated in a speech to parliament that Japan was grappling with its worst problems since the Second World War.
"This quake, tsunami and the nuclear accident are the biggest crises for Japan" in decades, said Mr Kan. He said the crises remained unpredictable, but added: "We will continue to handle it in a state of maximum alert."
Mr Kan has faced increasing criticism from opposition MPs over the handling of a nuclear disaster stretching into a third week.
"We cannot let you handle the crisis," one said in parliament. "We cannot let you be in charge of Japan's crisis management."Reuse content