Highly Radioactive Sludge Found At Sewage Plants In Fukushima Prefecture

Sewage plants in Fukushima perplexed over how to dispose of highly radioactive sludge (Mainichi Daily News):

Highly radioactive sludge found at sewage plants in Fukushima Prefecture will be temporarily kept at those plants, the central government has announced.

The move came after high levels of radioactive cesium were detected in sludge and other waste material at sewage plants in Fukushima Prefecture — home to the disaster-crippled Fukushima No. 1 Nuclear Power Plant.

On May 12, the government announced that highly radioactive sludge will be tentatively kept at sewage plants in the prefecture, while sludge with relatively low-level radiation could be recycled into cement and other material.

While highly-radioactive sludge will be treated in the same way as radioactive waste for the time being, no plans for the final disposal of such sludge were presented. It will also be difficult to promote the recycling of sludge with high-level radiation contamination. Since relevant laws and regulations do not cover highly-radioactive sludge at sewage plants, the government faces serious challenges in handling the issue.

According to the announcement, sludge with radioactivity levels of over 100,000 becquerels per kilogram should preferably be incinerated and melted in Fukushima Prefecture before being kept at sewage plants. Ash generated through sludge incineration should be contained in metal barrels to prevent it from scattering. Sludge with radioactivity levels of under 100,000 becquerels per kilogram can be temporarily kept at sewage plants and controlled disposal sites, with radioactivity monitoring required.

“Radioactive sludge should be treated in the same way as radioactive waste,” said an official with the Cabinet Office’s Nuclear Disaster Countermeasures Headquarters, adding, “We will look into how to ultimately dispose of it later.”

Sludge with radioactivity levels of under 1,000 becquerels per kilogram can be recycled into cement and other material if the levels can be reduced to under 100 becquerels through mixture with other materials and dilution.

“The volume of radioactive sludge should be reduced as much as possible through recycling,” said an official with the Ministry of Land, Infrastructure, Transport and Tourism, adding that the recycling of such sludge into fertilizer should be withheld for the time being.

The government also announced that safety standards for workers at sewage plants should be applied in accordance with the Ordinance on the Prevention of Ionizing Radiation Hazards, which is administered by the Ministry of Health, Labor and Welfare.

The ordinance mandates operators to set up controlled areas and control radiation doses if radiation levels in the air at workplaces are expected to exceed 1.3 millisieverts in three months. However, since the ordinance does not presume cases in which private operators transport radioactive sludge, the government cannot obligate forwarding agents to take the abovementioned measures.

On May 1, the Fukushima Prefectural Government announced that 334,000 becquerels per kilogram of radioactive cesium was detected in molten slag after sludge was processed with high heat at a purification center in Koriyama, Fukushima Prefecture. The finding was followed by the detection of radioactive cesium in sludge at 15 other sewage plants in the prefecture, as well as at one sewage treatment facility in Tochigi Prefecture, one in Ibaraki Prefecture, three in Gunma Prefecture and one in Niigata Prefecture. The Kanagawa Prefectural Government announced on May 12 that cesium was detected in sludge at four sewage plants in the prefecture, while the Tokyo Metropolitan Government disclosed the same day that up to 24,000 becquerels of radioactivity was detected in sludge incineration ash at three sewage plants in the capital.

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