Remediation strategy, capping construction and ongoing monitoring for the mill tailings pond, Ningyo-toge Uranium Mine, Japan

Saito, Hiroshi; Taki, Tomihiro

Proceedings of 15th International Conference on Environmental Remediation and Radioactive Waste Management (ICEM 2013) (CD-ROM), 4 Pages, 2013/09

Ningyo-toge Environmental Engineering Center has been managing the Ningyo-toge Uranium Mine. The Mine is subject to environmental remediation to ensure the radiation protection from the exposure pathways to humans in future, and to prevent occurrence of mining pollution. The Yotsugi Mill Tailings Pond is considered as the highest prioritized facility. So far, capping is put on the stable upstream part of the Pond to reduce dose rate, radon exhalation and rainwater precipitation. Prior to its construction, it was decided that the capping are to be multi-layered and natural materials are to be used, and the capping specifications were decided. Also, drainage channels and gabion work are constructed around the capping and at the foot of capping slope, respectively. Monitoring, which will continue for years, has started to confirm the effectiveness of the capping and the data will be utilized for the future remediation of the downstream of the Pond.

Demonstration test results of organic materials' volumetric reduction using bio-ethanol, thermal decomposition and burning

Tagawa, Akihiro; Watanabe, Masahisa

Proceedings of 15th International Conference on Environmental Remediation and Radioactive Waste Management (ICEM 2013) (CD-ROM), 6 Pages, 2013/09

Behaviour of IPG waste forms bearing BaSO as the dominant sludge constituent generated from the treatment of water used for cooling the stricken power reactors

Amamoto, Ippei; Kobayashi, Hidekazu; Yokozawa, Takuma; Yamashita, Teruo; Nagai, Takayuki; Kitamura, Naoto*; Takebe, Hiromichi*; Mitamura, Naoki*; Tsuzuki, Tatsuya*

Proceedings of 15th International Conference on Environmental Remediation and Radioactive Waste Management (ICEM 2013) (CD-ROM), 8 Pages, 2013/09

The great amount of water used for cooling the stricken power reactors at Fukushima Dai-ichi has resulted in accumulation of "remaining water". As the remaining water is subsequently contaminated by FPs, etc., it is necessary to decontaminate it in order to reduce the volume of liquid radioactive waste and to reuse it again for cooling the reactors. Various techniques are being applied to remove FP, etc. and to make stable waste forms. One of the methods using the iron phosphate glass as a medium is being developed to stabilize the strontium-bearing sludge whose main component is BaSO. From the results hitherto, the iron phosphate glass is regarded as a potential medium for the target sludge.

Distribution of radioactive cesium in trees and effect of decontamination of forest contaminated by the Fukushima nuclear accident

Iijima, Kazuki; Funaki, Hironori; Tokizawa, Takayuki; Nakayama, Shinichi

Proceedings of 15th International Conference on Environmental Remediation and Radioactive Waste Management (ICEM 2013) (CD-ROM), 6 Pages, 2013/09

In decontamination pilot projects conducted by Japan Atomic Energy Agency (JAEA), many different techniques were tested to determine their applicability to remediate areas evacuated after the Fukushima Daiichi nuclear accident. The projects evaluated the radioactive contamination of trees and the effectiveness of decontaminating a highly contaminated evergreen forest. As the first step, three Japanese cedar trees and three fir trees were cut down and the distributions of radioactive cesium (Cs) were measured in each. The total concentrations of Cs and Cs in the leaves and branches were about 1 MBq/kg for both cedar and fir trees, and were appreciably higher than in the bark for cedar. The concentrations in the outer part of the trunks (under the bark) were lower, on the order of 10 kBq/kg, and those in the core of the trunks were lower than 1 kBq/kg for both kinds of trees. The observation that the Cs concentrations are higher in the outer part of trees, is compatible with the assumption that radio-Cs was mostly adsorbed on the surface of trees and partly penetrated into the trunks through the bark. Evolution of air dose rates in a 10060 m pasture adjacent to the forest was monitored during decontamination of the forest and of the pasture itself. The dose rates in the pasture decreased drastically after stripping contaminated topsoil from the pasture and decreased slightly more after stripping contaminated topsoil of the forest floor and pruning the trees. Cutting down and removing 84 trees in the outermost area (10-m width) of the forest also slightly decreased these dose rates. After decontamination, the residual dose rates around the highly contaminated forest were mostly attributed to radioactive Cs existing in or on trees and topsoil in the untouched forest beyond the decontaminated area.