日本提高福島核污水泄漏事故級別

日本原子能規制委員會日前將福島核電站核污水泄漏事故級別從一級提高至三級，形容其爲“嚴重事件”，並對東電公司應對這一事故的能力表示擔心。國際核輻射事件分級表根據泄漏事件嚴重程度將其分成0至7級，7級爲最嚴重。本週一，東電公司發現福島核電站一處高輻射性污水儲罐發生泄漏，預計已有300噸高輻射性污水泄漏。東電公司最近的一份報告顯示，部分污水已滲入地表，部分或已流入附近的太平洋海域。東電檢測發現，已泄露污水每小時的輻射釋放量爲100毫希沃特，這意味着，按照國際安全標準，如果一個人站在那裏一小時內所受的輻射量將是核電作業人員一年內所能承受輻射上限的5倍。

2011年地震海嘯使福島核電站三處核反應堆冷卻系統失靈，需要將水泵入反應堆幫助其冷卻，同時也需要大量的儲罐來存儲這些帶有高輻射性的污水。此前也發生過核污水泄漏事故，但此次泄漏事件是至今爲止最嚴重的一次。

Japan's nuclear agency has upgraded the severity level of a radioactive water leak at the Fukushima plant from one to three on an international scale.

Highly radioactive water was found to be leaking from a storage tank into the ground at the plant on Monday.

It was first classified as a level one incident on the International Nuclear and Radiological Event Scale (Ines).

But Japan's Nuclear Regulation Authority proposes elevating it to level three on the seven-point scale.

Japanese reports say it is a provisional move that had to be confirmed with the IAEA, the UN's nuclear agency.

This week is the first time that Japan has declared an event on the Ines scale since the 2011 earthquake and tsunami.

The move was announced in a document on the agency's website and was subsequently approved at a weekly meeting of the regulatory body.

The March 2011 tsunami knocked out cooling systems to the reactors at the plant, three of which melted down.

Water is now being pumped in to cool the reactors but this means that a large amount of contaminated water has to be stored on site.

There have been leaks of water in the past but this one is being seen as the most serious to date, because of the volume - 300 tons of radioactive water, according to Tepco - and high levels of radioactivity in the water.

Japan's Nuclear Regulation Authority (NRA) said it feared the disaster was "in some respects" beyond Tepco's ability to cope.

"We should assume that what has happened once could happen again, and prepare for more," watchdog chairman Shunichi Tanaka told a news conference. "We are in a situation where there is no time to waste."

He said Tepco had failed to spot the leak for days - maybe weeks - despite patrols that are supposed to check each storage tank twice every day. Workers had also left a tap open in the safety barrier that surrounds the base of the leaking storage tank.

That had allowed highly toxic water to trickle away into the ground. Latest reports from the plant suggest some of it may already have reached the nearby Pacific Ocean.

A puddle of the contaminated water was emitting 100 millisieverts an hour of radiation, Kyodo news agency said earlier this week.

Teams of workers at the plant have surrounded the leaking tank with sandbags and have been attempting to suck up large puddles of radioactive water.

But it is a difficult and dangerous job. The water is so radioactive that teams must be constantly rotated and it is clear that most of the toxic water has already disappeared into the ground.

Under the Ines, events have seven categories starting with Level 0 ("without safety significance") and Levels 1-3 denoting "incidents" while Levels 4-7 denote "accidents".

The triple meltdown at Fukushima two years ago was classed as a level 7 incident, one of only two nuclear events ever rated that highly - along with the 1986 Chernobyl disaster in the former Soviet Union.