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Saturday, April 23, 2011

Memory of Sellafield leak rekindled

Radioactive discharges into Irish Sea in 1970s still monitored; reassurances in Japan similar


By WILLIAM HOLLINGWORTH
Kyodo

LONDON — The release of radioactive materials into the Pacific from the stricken Fukushima No. 1 nuclear plant is being closely monitored by scientists still observing the consequences of a similar incident in Britain more than 36 years ago.

The mid-1970s saw a sharp increase in radioactive matter enter the Irish Sea following problems at the Sellafield nuclear reprocessing facility in northwest England.

Although the releases were authorized, they resulted in a rise of radioactive cesium-137 and iodine-131 in the Irish Sea and the after-effects are still being monitored in the area today.

Scientists claim inquiries have concluded there is no evidence the discharges have adversely affected the health of the local population, but critics of the nuclear industry have cast doubt on these assertions.

Experts in Britain are now turning their attention to the stricken Fukushima plant, which has, until early April, been leaking highly radioactive materials into the sea due to a crack in the structure. In addition, a large volume of low-level waste was deliberately dumped into the ocean to assist the cleanup process.

Bill Camplin, group manager for radiological and chemical risk at the Center for Environment, Fisheries and Aquaculture Science (Cefas), in Lowestoft, said the two incidents are "not grossly dissimilar" in terms of the concentrations reported in the water.

Although Sellafield has been releasing waste into the sea since 1952, the potency of the discharges shot up in the mid-1970s.

Spent fuel rods stored in cooling ponds started to corrode, leading to a significant spike in the radioactive waste flushed out to sea.

As Camplin explained in an interview, at its peak in 1975, Sellafield pumped out 5,000 terabecquerels of cesium-137. By contrast, current discharges are now around 10 terabecquerels per year.

The contamination resulted in seafood caught within 10 km of Sellafield containing "several thousand" becquerels per kilogram of cesium-137. The corresponding seawater concentration around Sellafield was 100 becquerels per liter of cesium-137.

The figures for Fukushima bear some similarities, with water concentrations at about 50 becquerels per liter for cesium-137, and 100 becquerels per liter for iodine-131 in an area 10 km from the release point, according to data supplied to Camplin via the International Atomic Energy Agency in the earlier stages of the crisis. However, the IAEA notes decreasing trends following the plugging of the leak at Fukushima.

Camplin and his team at Cefas agree with the Japanese government's advice not to consume seafood caught close to the Fukushima plant.

In Britain, the authorities would generally intervene when the concentration of cesium-137 reached 1,000 becquerels per kg of seafood and Camplin noted some of the measurements in shellfish caught off Fukushima have been much less than that threshold.

In the 1970s, the British authorities did not impose any restrictions on the consumption of seafood in the Irish Sea despite similar levels.

But, as John Hunt, a consultant to Cefas, explained, "The maximum dose to regular shellfish consumers around Sellafield peaked at 2 millisieverts per year during the mid-1970s. That is more than the current annual dose recommended by the International Commission on Radiological Protection of 1 millisievert, but back then the annual maximum dose was 5 millisieverts. And we are not aware of any health implications as a result of that."

After the spike in radiation, bosses at Sellafield worked hard to bring down the levels.

However, the effects are still present in the sea, particularly in relation to cesium-137, which takes a lot longer to decay than iodine and tends to find its way into the seabed and onto beaches.

Camplin said that if the Japanese authorities haven't done so already, they should be warning people not to spend much time on the beaches near to the plant, as there could be quite high levels of radiation there.

But the good news is the iodine-131 should start to dissipate from the ocean quite rapidly.

Camplin and Hunt both appeared to be satisfied with how the Japanese authorities are coping, but would like to see more marine data and are currently liaising with colleagues in Japan.

Camplin said, "I'm not saying that it hasn't been done, but I would like to see more continuous monitoring. It needs to take into account different radionuclides, marine material and cover a greater area.

"Various institutes are talking about having a collaborative research program into Fukushima. I will expect work to move on to how the ecosystem is reacting to these radioactive inputs."

A millisievert is a measure of the dose of radiation a person can receive. The becquerel is a unit that measures radioactivity and 1 terabecquerel equals 1 trillion becquerels.



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