Study on the radionuclide contamination mechanisms of concrete and the estimation of distribution of radionuclides, 23; Penetration of alpha nuclides into hardened cement pastes simulating cracking

Aihara, Haruka   ; Hinai, Hiroshi; Koma, Yoshikazu  ; Tomita, Sayuri*; Maruyama, Ippei*

At the Fukushima Daiichi Nuclear Power Plant, contaminated water has remained in the buildings, and alpha nuclides such as plutonium have been detected. Analysis results of contaminated water indicate that plutonium concentration is decreasing downstream, therefore there is concern that plutonium is remaining in the reactor buildings. To evaluate the depth of penetration of -nuclides into the wall surface of the building contacted with contaminated water, a sample consisting of two cement paste test pieces was immersed in simulated contaminated water. When the crack width was less than 0.1 mm, the penetration depth of -nuclides did not increase due to cracking and remained within 2 mm from the surface layer. On the other hand, the penetration of -nuclides increased significantly when the crack width was 0.5 mm or more, suggesting that the effect of cracks of about 0.1 mm, which is expected in normal operation, is small, whereas the formation of large cracks during an accident may result in the penetration of -nuclides.