Workers in Japan have begun injecting nitrogen into one of the reactors² at the crippled Fukushima Daiichi nuclear plant to prevent more hydrogen blasts.

日本福岛核电站的工人向一座受损的核反应堆注入氮气以防止氢气爆炸。

Explosions caused by a build-up of hydrogen gas happened in three reactors in the aftermath of the 11 March quake.

Earlier, workers succeeded in plugging a gap leaking highly radioactive water from the plant into the Pacific Ocean.

The plant's operator, Tepco (Tokyo Electric Power Co), said it had injected chemical agents to solidify⁴（团结，凝固） soil near a cracked pit of reactor 2 that was the source of the leak.

Since the earthquake knocked out cooling systems, workers have been pumping water into reactors to cool fuel rods, but must now deal with waste water pooling in and below damaged reactor buildings.

Radioactive iodine⁵

Technicians began injecting nitrogen, an inert⁶ gas, at 0131 local time Thursday (1631 GMT Wednesday), said Makoto Watanabe, a spokesman for Japan's nuclear agency.

A Tepco official was quoted by Reuters news agency as saying that it was "necessary to inject nitrogen gas into the containment⁷ vessel⁸ and eliminate the potential for a hydrogen explosion".

The process could take several days, officials said.

The prevention of further hydrogen explosions - like those that had ripped through reactors 1 and 3 - is seen as a priority, because blasts could spew more radiation and damage the reactors.

On Wednesday engineers managed to plug the the leak from the pit in reactor 2. It is thought to have been the source of high levels of radiation found in seawater nearby.

In order to stem the leak, Tepco injected ''water glass'', or sodium⁹ silicate¹⁰（硅酸钠） , and another agent into the pit.

Desperate engineers had also used sawdust（锯屑） , newspapers and concrete in recent days to try to stop the escaping water.

The government's top spokesman said workers could not rule out other leaks at the reactor.

Meanwhile, engineers are continuing to pump some 11,500 tonnes of low-level radioactive seawater into the sea so the more highly contaminated water can be stored in waste buildings.

Officials said this water would not pose a significant threat to human health, but local fishermen have reacted angrily.

In a letter, the largest fisheries group accused the government of an "utterly¹¹ outrageous¹²" action that threatened livelihoods¹³.

On Tuesday, elevated levels of radioactive iodine - about twice the legal limit for vegetables - were found in small fish caught off Ibaraki prefecture（县，辖区） to the south of Fukushima.

The government has promised compensation for the fishing industry and Tepco has already unveiled plans to compensate¹⁴ residents and farmers around the nuclear plant.

The number of people known to have died in the earthquake and tsunami has now reached 12,494, with another 15,107 still missing, according to police.