Effectiveness of fused LASSO for prediction of distribution of radioactive materials in reactor buildings

Yamada, Susumu; Yoshida, Toru*; Hasegawa, Yukihiro*; Machida, Masahiko

Proceedings of Waste Management Symposia 2024 (WM2024) (Internet), 15 Pages, 2024/03

In order to safely carry out the decommission of reactor buildings, it is extremely important to identify the radiation source distribution. It has been reported that when the structural model of the building is constructed by uniform cells, the source distribution can be estimated from the measured air dose rates by minimizing an evaluation function using the Least Absolute Shrinkage and Selection Operator (LASSO). Moreover, if cells are non-uniform, we can estimate the distribution using the fused LASSO which minimizes the evaluation function that takes account of the connectivity between the adjacent cells. However, when a group of some cells is considered disconnected from the surrounding ones due to the precision of the measured structural data, the concentration of the group can be singularly high. Therefore, in order to avoid the problem, we propose a new evaluation function that can prevent the singularity. We estimated the distribution for the test model using the proposed evaluation function and confirmed the validity of the function. Moreover, we succeeded in estimating the source distribution in the pool canal circulation system room in JMTR in the Japan Atomic Energy Agency by the fused LASSO for the new function more accurately than previous analysis.

Laboratory experiment on runoff of particles deposited on land surface by rainfall at accidents in the decommissioning stage

Shimada, Taro; Namekawa, Masakazu*; Miwa, Kazuji; Takeda, Seiji

Proceedings of Waste Management Symposia 2023 (WM2023) (Internet), 8 Pages, 2023/02

It is supposed that radioactive dust deposited at the land surface will be moved downstream and concentrated at the depression by overland flow at heavy rain after the accidental release of radioactive dusts accumulated at the filters in the decommissioning stage of nuclear facilities. The authors are developing a calculation code to evaluate distribution changes of radioactivity on the surface and public dose considering the conditions such as rainfall, topography and types of cover surface. It is necessary to construct methods for setting parameter values used for the calculations based on the actual situation. Therefore, the parameter values were obtained by the experiments where FeO powder spread on the cover surface such as smooth and aged-asphalt, concrete and bare soil, was eroded by overland flow and raindrops and they were collected at the lower end of the slope at a minute interval. The collected weights of overland flow and FeO powder were measured. Based on the Manning's roughness coefficient for smooth asphalt already known as a fixed value, the erosion velocity coefficient was evaluated. Then Manning's roughness coefficients for other cover surfaces were obtained using the erosion velocity coefficient. Manning's roughness coefficients were slightly smaller than the range of literature values. In addition, elevations for the cover surface were measured by 3D scanner as point cloud data, and the surface roughness were evaluated. The values of surface roughness and Manning's roughness coefficients had a correlation. It indicated a possibility to utilize the surface roughness to set the Manning's roughness coefficient for the evaluation of radioactivity distribution change by heavy rainfall.

LASSO reconstruction scheme to predict radioactive source distributions inside reactor building rooms; Practical applications

Machida, Masahiko; Shi, W.*; Yamada, Susumu; Miyamura, Hiroko; Yoshida, Toru*; Hasegawa, Yukihiro*; Okamoto, Koji; Aoki, Yuto; Ito, Rintaro; Yamaguchi, Takashi; et al.

Proceedings of Waste Management Symposia 2023 (WM2023) (Internet), 11 Pages, 2023/02

New project on the analysis of contamination mechanisms of concrete at the Fukushima Daiichi Nuclear Power Station

Yamada, Kazuo*; Maruyama, Ippei*; Koma, Yoshikazu; Haga, Kazuko*; Igarashi, Go*; Shibuya, Kazutoshi*; Aihara, Haruka

Proceedings of International Waste Management Symposia 2019 (WM2019) (CD-ROM), 6 Pages, 2019/03

A Multiscale Bayesian data integration approach for mapping air dose rates around the Fukushima Daiichi Nuclear Power Plant

Wainwright, Haruko*; Seki, Akiyuki; Chen, J.*; Saito, Kimiaki

Proceedings of International Waste Management Symposia 2017 (WM2017) (Internet), 8 Pages, 2017/03

We integrate various types of datasets, such as ground-based walk and car surveys, and airborne surveys, all of which have different scales, resolutions, spatial coverage, and accuracy. This method is based on geostatistics to represent spatial heterogeneous structures, and also on Bayesian hierarchical models to integrate multiscale, multitype datasets in a consistent manner. The Bayesian method allows us to quantify the uncertainty in the estimates, and to provide the confidence intervals that are critical for robust decision-making. We showed the demonstration of Bayesian data integration approach for the Fukushima evacuation zones with high air dose rates.

Status and future plan of decommissioning of the Plutonium Fuel Fabrication Facility

Kuba, Meiji; Watahiki, Masatoshi; Hirano, Hiroshi; Ishikawa, Shinichiro; Sato, Hisato

Proceedings of International Waste Management Symposia 2014 (WM2014) (Internet), 12 Pages, 2014/05

Plutonium Fuel Fabrication Facility is now in a decommissioning phase. In the facility, stabilizing activities of nuclear material residuals remained and the gloveboxes dismantling activities have been carried out simultaneously. Glovebox dismantling activities are performed manually by a worker wearing air-feed suit with mechanical tools in a plastic enclosure which is constructed around the glove boxes for preventing spread of contamination. However, the mental load and physical load of the worker are intensively high. Therefore, worker's safely issue still exists and need to be resolved. Moreover, occupational time for the worker is restricted to only one hour per day, which in turn make shortening schedule and cost savings almost impossible. R&D of new dismantling methods including application of heavy equipment with anti-contamination measure to strengthen the work performance in the plastic enclosures has been started to reduce the above mentioned potential risks and costs.

Adsorption of ruthenium, rhodium and palladium from simulated high-level liquid waste by highly functional xerogel

Onishi, Takashi; Koyama, Shinichi; Mimura, Hitoshi*

Proceedings of International Waste Management Symposia 2013 (WM2013) (CD-ROM), 7 Pages, 2013/02

As part of a development of nuclides separation process by using highly-functional xerogels, xerogels including insoluble ferrocyanide compounds were prepared for separation of Pt group metals. Adsorption and elution behaviors of Pt group metals were investigated in simulated high level radioactive liquid waste. Removal of sulfur from recovered palladium was also conducted by a thermal decomposition and digestion method.

Sensitivity analysis for scenarios relevant to evolution of overpack and buffer material

Takeda, Seiji; Watanabe, Masatoshi; Kimura, Hideo

Proceedings of International Waste Management Symposia 2011 (WM2011) (CD-ROM), 11 Pages, 2011/05

https://www.wmsym.org/archives/2011/papers/11176.pdf

This study focuses on a deterioration of expected barrier functions relevant to evolution of overpack and sand-bentonite buffer material in engineered barrier system in the geological disposal of high-level radioactive waste. Release rates for important radionuclides, Cs-135 and Se-79, were estimated from Monte Carlo-based analysis for the early failure of overpack and the buffer alteration scenarios. One of the possible early failure scenarios is the change of glass dissolution rate, effective diffusion coefficients and distribution coefficients in the buffer material, which are affected by early high temperature in the engineered barrier. The analytical result indicates that this scenario has no detrimental effect on the maximum release rates of these radionuclides. Another scenario is the occurrence of the increase of Se solubility correlated with the enhanced redox potential due to the radiolysis after the early failure of overpack. This scenario allows a conspicuous increase in the maximum release rates of Se-79 from the buffer, which is over one order of magnitude higher than that in the normal scenario. In addition, with the comparison of the maximum release rates between the early failure scenario and the buffer alteration scenario, it is suggested that the effect of the deterioration of the expected barrier functions relevant to the buffer alteration on the release rates is more remarkable than the effect on early failure.

Cement based encapsulation experiments for low-radioactive liquid waste at Tokai Reprocessing Plant

Sugaya, Atsushi; Tanaka, Kenji; Akutsu, Shigeru

Proceedings of International Waste Management Symposia 2011 (WM2011) (CD-ROM), 11 Pages, 2011/02

https://www.wmsym.org/archives/2011/papers/11078.pdf

The main component of the liquid wastes is sodium nitrate. Nitrate ion decomposition technology is under development to conserve a circumference environment of a disposal site. To investigate the methods for decomposing nitrate ion, several small-scale trials were performed using reductants and a catalyst in sodium nitrate solutions. It will be reported that the cement based encapsulation trials to immobilize the sodium carbonate based liquid waste, which was performed under non-radioactive condition at both small and full scale to investigate the optimum cement formulation.

Application of modified truex flowsheet to minor actinide from high level liquid waste

Kawata, Tomio; ; Nomura, Kazunori; ;

WM Symposia, 0 Pages, 1993/00

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