High radiation levels from concrete in new apartment building

On January 15, the Cabinet Office’s Nuclear Emergency Response Headquarters and the Nihonmatsu City Council in Fukushima Prefecture announced that radiation levels of 1.24 microsieverts/hour were detected in a brand new 3-storey apartment building in the city. The levels exceed the radiation levels found outdoors and residents from the 1st floor of the building have been advised to move elsewhere.

According to the Cabinet Office, the concrete used in the construction of the building was made from stones from a quarry in Namie Town, just 10 km from the Daiichi Nuclear Plant. Construction materials such as stone and gravel have not been required to be tested for radiation. An investigation has started into the possible spread of contaminated construction materials.

It is now thought that contaminated gravel has been used in over 1000 different construction projects, including:
– roads and residential driveways in Kawamata Town
– road repairs near a school in Nihonmatsu City
– earthquake-retrofitting on two schools

The apartment building is located in Wakamiya-ku, Nihonmatsu City, and is 70km west of the nuclear plant. Construction was completed in July, 2011, and 12 apartments are occupied. A female junior high school student who is living on the 1st floor had been measuring her personal exposure using a dosimeter and confirmed that her accumulated radiation dose over three months was 1.62 millisieverts. When officials investigated the building they found that the outdoor radiation levels were 0.7 ~ 1.0 microsieverts/hour, and the indoor area on the 1st floor of the building were 0.9 ~ 1.24 microsieverts/hour. The indoor radiation levels on the 2nd and 3rd floors were 0.1 ~ 0.38 microsieverts/hour.

The Cabinet Office said that the radiation levels are below the levels that call for evacuation and they pose no immediate risks to health. Meanwhile, the City has offered to assist the 1st floor residents to find new accommodation should they want to move. A total of 9 of the 12 households have expressed their desire to move out.

The contractors for the building had used the same concrete in farming irrigation channels in the city which had also tested high for radiation. Although the stones were dug out of the quarry prior to the nuclear disaster, they had been stored outside and were processed into concrete on April 11, 2011. The City is investigating into the possibility that the materials have been contaminated with radioactive cesium. The concrete floor of the 1st floor was poured in April.

The company in charge of the Namie quarry said that up until April 22, 2011, they had sold 5200 tons of quarry stones and gravel to twenty construction companies within Fukushima Prefecture. On a  report aired on the TBS program “Mino Monta no Asa Zuba,” newscaster, Kunihiko Okudaira, visited the quarry with a geiger counter and measured radiation levels of 14.5 microsievert/hr in the air, which increased to 20 microsievert/hr as he approached a pile of rocks, and 65 microsievert/hr from the surface of the pile of rocks.

The Ministry of Economy, Trade and Industry (METI) and the Ministry of Land, Infrastructure, Transport and Tourism (MLIT) are now trying to track the whereabouts of the quarry materials that were sold. They are also investigating six other quarry sites within the same area.

Although there are regulations to limit the reuse and recycling of dirt and rubble following the nuclear disaster, no restrictions were set for quarry materials that are used in concrete. This is the first discovered case were radioactive construction materials have caused residents to move-out.

Ten of the twelve households in the apartment building were former evacuees who moved into the building after the March 11 disaster. Some were from the forced evacuation zones around the nuclear plant.

Sources:
The Mainichi Shimbun, January 15, 2012.
NHK, January 15, 2012.
J Cast, January 17, 2012.