perceptions_now wrote on May 2^nd, 2011 at 4:37pm:


Well the limit for radiation workers in Australia is as low as possible, but no more than 50mSV in a year. There are also limits for 5 years.

Well, the risk of raising the exposure limit to 250 mSv has been quantified. This ISCORS publication provides some cancer risk rates for exposure to different substances:
http://www.iscors.org/doc/RiskTEDE.pdf

The question is whether it's acceptable or not.

As a ballpark figure, the morbidity risk is about 0.02 per Sievert. At one Sievert exposure, one in every 50 people would contract cancer as a result of the exposure.  At  0.25 Sv, it would be about 1 in 200.

Please note that I'm not defending the decision - just providing some information that might be useful.

Japan's stricken nuclear plant has new leak

By North Asia correspondent Mark Willacy and wires

Updated 4 hours 6 minutes ago

The operator of Japan's crippled Fukushima nuclear plant says rods inside one of the reactors have most likely melted after being fully exposed.

The Tokyo Electric Power Company (TEPCO) has reported a leak from the reactor vessel and another spill of contaminated water into the ocean.

The company says the water level inside reactor No. 1 was much lower than it thought, exposing about 1.5 metres of the fuel rods.

It says the rods have likely melted and workers are still trying to cool them in water at the bottom of the pressure vessel.

The company believes that about half the reactor core in reactor No. 1 has been damaged and has been pumping in up to eight tonnes of water an hour into the pressure vessel to try to keep the rods cool.

The update comes as emergency crews battle to bring the tsunami-hit and radiation-leaking plant into stable "cold shutdown" sometime between October and January.

The giant ocean wave triggered by the magnitude-9.0 quake on March 11 knocked out the plant's water cooling systems, leading fuel rods inside several of the reactor cores to partially melt down.

TEPCO says new measurements taken this week, after workers in protective suits fixed gauges in the badly hit reactor No. 1 building, indicate that water pumped into the pressure vessel had quickly leaked out.

The water level inside had fallen below the bottom of the four-metre-long fuel rods, suggesting they had been exposed to the air, increasing the risk of a dangerous full meltdown.

However, the vessel's relatively low outside temperature of 100-120 degrees Celsius indicated that the rods had dropped to the bottom of the vessel and were under water there, TEPCO said.

The dousing operations - in which tens of thousands of tonnes of water have been injected with fire trucks, concrete boom pumps and other pumping systems - have created massive amounts of highly contaminated run-off water.

TEPCO has struggled to stop spills into the Pacific Ocean and has now reported another, saying water had leaked into the sea from a concrete pit near reactor No. 3, one of the plant's six units.

Samples of seawater taken near the plant contained caesium-134 at a concentration 18,000 times the permitted level, the company said, adding that the spill had been stopped by filling the pit with concrete.

"We have continued to investigate the route of the leakage into sea and why it happened," TEPCO spokesman Yoshinori Mori said.

Top government spokesman Yukio Edano called the leak "deplorable" and apologised to the fishing industry and to neighbouring countries.

- ABC/AFP

Japan extends the exclusion zone around Fukushima

Mark Willacy reported this story on Monday, May 16, 2011 08:11:00

PETER CAVE: Japan has begun evacuating people from outside the official exclusion zone around the crippled Fukushima nuclear plant.

With radiation levels remaining high, small children and pregnant women were the first to be moved with thousands more to be shifted into shelters and temporary housing.

As the evacuation zone widened more details have emerged about the meltdown in Fukushima's reactor number one, with revelations the fuel rods probably melted in the hours after the magnitude nine earthquake in March - a fact not discovered until last week.

North Asia correspondent Mark Willacy reports from Tokyo.

(Sound of a man speaking Japanese)

MARK WILLACY: It was the news the people of Iitate village had been dreading. A touch over 30 kilometres from the Fukushima nuclear plant Iitate is outside the evacuation zone, or it was until now.

[...]

About 8,000 residents of Iitate and the nearby village of Kawamata are being asked to move, joining the tens of thousands who've already been forced out of their homes by the nuclear crisis at the Fukushima plant.

These people will be put up in hotels, public housing and evacuation shelters. No-one knows when they'll be allowed to return.

[...]

Because of wind patterns Iitate and nearby communities have been swathed in high radiation and authorities aren't willing to let people stay any longer.

As these new evacuations began, more news filtered out about the meltdown of fuel rods at Fukushima's reactor number one.

It appears that the rods melted just hours after the earthquake and tsunami struck two months ago. The melted material then dropped to the bottom of the pressure vessel at the core.

Authorities now believe the fuel rods could have been exposed to the air for as long as 14 hours.

After the operator of the plant, TEPCO, told the Japanese people that things were stabilising at Fukushima, it's now clear they knew far less about the situation than they were willing to admit.

This is Mark Willacy in Tokyo for AM.