Tokyo Electric Power Co. engineers tried to stabilize three nuclear reactors damaged by the biggest earthquake in Japan's history after the plant was struck by a second explosion and as water levels dropped at one reactor, exposing fuel rods and increasing the threat of a meltdown.

The cooling system failed at the Dai-Ichi No. 2 reactor today, said Tokyo Electric, which runs the Fukushima nuclear plant 220 kilometers (135 miles) north of the nation's capital. Fuel rods at the reactor may have melted after becoming fully exposed, Chief Cabinet Secretary Yukio Edano told reporters.

A hydrogen explosion occurred at the No. 3 reactor today, following a similar blast on March 12 at the No. 1 reactor that destroyed the walls of its building. The utility has been flooding the three reactors with water and boric acid to reduce the potential for a large release of radiation into the atmosphere following the March 11 earthquake-generated tsunami that smashed into the plant, disabling electricity supply and backup generators.

"They are managing the situation, they have very qualified personnel there," Gennady Pshakin, a nuclear expert based in Obninsk, Russia, said by telephone. "We will have a week or 10 days of this uncertainty, but the situation should normalize. What we need is for the water supply to be constant."

David Fuller's view How this tense situation plays out over the next few days, or perhaps weeks, will obviously have a profound and lasting influence on public attitudes towards nuclear power. This will inevitably have important consequences for the industry.

A favourable result, in which no one is seriously harmed by nuclear radiation from Japan's reactors, despite an almost unimaginable assault on them from one of the world's largest recorded earthquakes and a devastating tsunami, should reassure most people.

Conversely, if the health of any workers at Japan's Fukushima nuclear power plants is seriously compromised by radiation, and if the risk is considered too dangerous for the emergency exclusion zone applying to residents living a few kilometres away to be lifted in the next few weeks, then public opinion regarding nuclear power will become less favourable.