Uchida, Shunsuke; Karasawa, Hidetoshi; Kino, Chiaki*; Pellegrini, M.*; Naito, Masanori*; Osaka, Masahiko
Nuclear Engineering and Design, 380, p.111256_1 - 111256_19, 2021/08
It is essential to grasp the long-term distributions of FP as well as fuel debris all over the Fukushima Daiichi Nuclear Power Plant (1F) for safe completion of its decommissioning projects. The fuel debris is going to be removed from the plant under the severe conditions of FP being scattered during major decommissioning work, and then, the decommissioning projects are going to be terminated by storing safely the removed debris as recovered fertile materials or as materials for final radioactive disposal. In order to determine the FP distribution in the plant for the long period from the accident occurrence to the termination of the plant decommissioning, procedures for analyzing multi-term FP behaviors were proposed. The proposed procedures should be improved by applying the FP data measured in the plant and validated based on the feedback data. Then, the accuracy-improved procedures should be applied to estimate FP distribution during each period of the decommissioning projects.
Uchida, Shunsuke; Pellegrini, M.*; Naito, Masanori*
Nuclear Engineering and Design, 380, p.111303_1 - 111303_11, 2021/08
Multi-term FP analysis procedures were developed to determine FP distribution all over F1 not only for analyzing accident propagation but also for planning its decommissioning projects. They should be validated based on the measured FP data. One of the useful tools for their validation was application of the dose rate data monitored by the containment atmosphere monitoring system (CAMS). However, in order to compare the data with different characteristics and dimensional units, e.g., FP distribution (kg, Bq) and dose rate (Sv/h), application of the conversion factors bridging them would be effective and useful. In order to prepare speedy, easy-to-handle and tractable procedures to calculate radiation dose rates at the CAMS detector locations, dose rate conversion factors were determined for major source locations and major radionuclides. The dose rates could be easily calculated by multiplying FP amounts obtained with the multiterm FP analysis procedures by the conversion factors.
Genshiryoku No Ima To Ashita, p.63 - 68, 2019/03
The latest situation of contaminated water treatment in Fukushima Daiichi NPP for 8 years after its accident is reviewed. Major subjects, especially tritium treatment, to be solved related to the contaminated water and some proposal for the subjects are introduced.
Uchida, Shunsuke; Chimi, Yasuhiro; Kasahara, Shigeki; Hanawa, Satoshi; Okada, Hidetoshi*; Naito, Masanori*; Kojima, Masayoshi*; Kikura, Hiroshige*; Lister, D. H.*
Nuclear Engineering and Design, 341, p.112 - 123, 2019/01
Improvement of plant reliability based on reliability-centered-maintenance (RCM) is going to be undertaken in NPPs. RCM is supported by risk-based maintenance (RBM). The combination of prediction and inspection is one of the key issues to promote RBM. Early prediction of IGSCC occurrence and its propagation should be confirmed throughout the entire plant systems which should be accomplished by inspections at the target locations followed by timely application of suitable countermeasures. From the inspections, accumulated data will be applied to confirm the accuracy of the code, to tune some uncertainties of the key data for prediction, and then, to increase their accuracy. The synergetic effects of prediction and inspection on application of effective and suitable countermeasures are expected. In the paper, the procedures for the combination of prediction and inspection are introduced.
Uchida, Kenichi*; Daimon, Shunsuke*; Iguchi, Ryo*; Saito, Eiji
Nature, 558(7708), p.95 - 99, 2018/06
Uchida, Shunsuke*; Hanawa, Satoshi; Naito, Masanori*; Okada, Hidetoshi*; Lister, D. H.*
Corrosion Engineering, Science and Technology, 52(8), p.587 - 595, 2017/10
Based on the relationship among ECP, metal surface conditions, exposure time and other environmental conditions, a model to evaluate the ECP and corrosion rate of steel was developed by coupling a static electrochemical analysis and a dynamic oxide layer growth analysis. Major conclusion obtained on the model are as follows. The effect of HO and O concentrations on ECP were successfully explained as the effects of oxide layer growth. Hysteresis of ECP under changes in water chemistry conditions were successfully explained with the model. Decreases in ECP due to neutron exposure were explained well by radiation-induced diffusion in the oxide layers.
Daimon, Shunsuke*; Uchida, Kenichi*; Iguchi, Ryo*; Hioki, Tomosato*; Saito, Eiji
Physical Review B, 96(2), p.024424_1 - 024424_12, 2017/07
Iguchi, Ryo*; Uchida, Kenichi*; Daimon, Shunsuke*; Saito, Eiji
Physical Review B, 95(17), p.174401_1 - 174401_7, 2017/05
Hanawa, Satoshi; Uchida, Shunsuke; Hata, Kuniki; Chimi, Yasuhiro; Kasahara, Shigeki*; Nishiyama, Yutaka
Proceedings of 20th Nuclear Plant Chemistry International Conference (NPC 2016) (USB Flash Drive), 11 Pages, 2016/10
ECP is the exclusive index to evaluate corrosion condition directly at the points of interest in the mixing of neutron and -ray environment. ECP can be calculated through the combination of water radiolysis and ECP model. A water radiolysis model have been applied to experiments performed in in-pile loops in the experimental reactors and applicability was confirmed. An ECP model based on the Butler-Volmer equation was also prepared. ECP of stainless steel was measured under well controlled water chemistry condition in in-pile loop in the Halden reactor, and the model was applied to evaluate ECP measured in the Halden reactor. The measured data were well explained by the water radiolysis calculation and ECP model. Accumulation of in-pile ECP data are expected for further validation of the models.
Hanawa, Satoshi; Uchida, Shunsuke; Hata, Kuniki; Chimi, Yasuhiro; Kasahara, Shigeki*; Nishiyama, Yutaka
Proceedings of 20th Nuclear Plant Chemistry International Conference (NPC 2016) (USB Flash Drive), 10 Pages, 2016/10
The authors proposed and ECP evaluation model introducing irradiation-induced diffusion in the oxide layer to simulate neutron irradiation effect, and predicted with this model that ECP is started to depress from the neutron flux of about ten to the fourteenth per square meter. As the JMTR has in-pile loops applicable to water chemistry experiments, degree of irradiation effect on ECP appears in the in-pile loop was estimated by the model. Under oxygen injected condition, ECP in a capsule becomes constant along the vertical direction due to the presence of high amount of oxygen and hydrogen peroxide in a capsule. However, if neutron irradiation depress ECP, ECP in a capsule along vertical direction wouldn't become constant, and the degree to the decrement is detectable by experiments.
Kikkawa, Takashi*; Uchida, Kenichi*; Daimon, Shunsuke*; Saito, Eiji
Journal of the Physical Society of Japan, 85(6), p.065003_1 - 065003_2, 2016/06
Uchida, Shunsuke; Hanawa, Satoshi; Kysela, J.*; Lister, D. H.*
Power Plant Chemistry, 18(1), p.6 - 17, 2016/01
In order to establish reliable NPP operation, each plant requires its own unique optimal water chemistry control based on careful consideration of its system, materials and operational history. Electrochemistry is one of key issues that determine corrosion related problems, e.g., FAC. Based on the relationships among ECP, metal surface conditions and exposure time, a model to evaluate ECP and corrosion rate of steel was developed by coupling an electrochemical model and an oxide layer growth model. Major conclusions are as follows. (1) The effects of water chemistry improvement and mass transfer coefficients due to local flow velocity on FAC wall thinning rate and ECP could be evaluated with the proposed model. (2) The effects of HO and O concentrations on ECP were evaluated with the model. Exposure time dependent ECPs were also explained as the effects of oxide film growth on the specimens. (3) Decreases in ECP due to neutron exposure were explained by radiation-induced diffusion in the oxide layers.
Uchida, Shunsuke; Hanawa, Satoshi; Lister, D. H.*
Power Plant Chemistry, 17(6), p.328 - 339, 2015/12
In nuclear power plants, radiation makes the relationship between structural materials and water chemistry much more complex than that in fossil fueled power plants. It is difficult to maintain safer and more reliable plant operation by controlling water chemistry based on only a restricted number of measured data. It is often required to control water chemistry with suitable assistance from computer models, which can extrapolate measured water chemistry parameters to those at the required locations and predict future trends of the interactions between structural materials and water chemistry. In the paper, water chemistry control based on parameters determined with plant simulation models and major computational models to be applied for water chemistry control are discussed.
Kikkawa, Takashi*; Uchida, Kenichi*; Daimon, Shunsuke*; Qiu, Z.*; Shiomi, Yuki*; Saito, Eiji
Physical Review B, 92(6), p.064413_1 - 064413_9, 2015/08
Uchida, Kenichi*; Oe, Junichiro*; Kikkawa, Takashi*; Daimon, Shunsuke*; Hou, D.*; Qiu, Z.*; Saito, Eiji
Physical Review B, 92(1), p.014415_1 - 014415_8, 2015/07
Lister, D. H.*; Uchida, Shunsuke
Journal of Nuclear Science and Technology, 52(4), p.451 - 466, 2015/04
The chemistry of the process and coolant systems in water-cooled nuclear reactors is tightly controlled to minimise materials degradation and, for some systems, to regulate reactor power. Tight control entails monitoring the systems and making appropriate adjustments. On-line monitoring can be utilised where instruments are available but otherwise samples must be taken and measurements made off-line. This paper reviews the current technologies for monitoring and sampling.
Daimon, Shunsuke*; Iguchi, Ryo*; Uchida, Kenichi*; Saito, Eiji
Journal of Physics D; Applied Physics, 48(16), p.164014_1 - 164014_4, 2015/04
Schreier, M.*; Bauer, G. E. W.*; Vasyuchka, V.*; Flipse, J.*; Uchida, Kenichi*; Lotze, J.*; Lauer, V.*; Chumak, A.*; Serga, A.*; Daimon, Shunsuke*; et al.
Journal of Physics D; Applied Physics, 48(2), p.025001_1 - 025001_5, 2015/01
Uchida, Shunsuke*; Wada, Yoichi*; Yamamoto, Seiji*; Takagi, Junichi*; Hisamune, Kenji*
Journal of Nuclear Science and Technology, 51(1), p.24 - 36, 2014/01
ECP in the BWR primary cooling system can be measured only in the restricted region. In order to determine ECP at any location, ECP should be evaluated by computer simulation codes consisting of water radiolysis models to determine the concentrations of corrosive radiolytic species and mixed potential models to determine ECP based on corrosive species. Mitigation of SCC crack growth rate due to decreasing ECP can be authorized by the JSME Standards, while mitigation of ECP due to hydrogen addition has not been authorized yet. In the paper, standard procedures to authorize the computer simulation codes based on the verification and validation method are proposed. The numerical justification of every code applied as a standard code should be verified and its accuracy and applicability for plant analysis should be validated. Benchmark problems for verification processes are proposed and comparison of the calculated results with the measured ones for the plant of evaluation is required.