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Journal Articles

MAAP code analysis for the in-vessel phase of Fukushima-Daiichi Nuclear Power Station Unit 1 and comparison of the results among Units 1 to 3

Sato, Ikken; Yoshikawa, Shinji; Yamashita, Takuya; Shimomura, Kenta; Cibula, M.*; Mizokami, Shinya*

Nuclear Engineering and Design, 422, p.113088_1 - 113088_24, 2024/06

Journal Articles

MAAP code analysis focusing on the fuel debris conditions in the lower head of the pressure vessel in Fukushima-Daiichi Nuclear Power Station Unit 3

Sato, Ikken; Yoshikawa, Shinji; Yamashita, Takuya; Shimomura, Kenta; Cibula, M.*; Mizokami, Shinya*

Nuclear Engineering and Design, 414, p.112574_1 - 112574_20, 2023/12

JAEA Reports

Effect of preparation conditions and storage time on characteristic and rheological properties of carbonate slurries

Kato, Tomoaki; Yamagishi, Isao

JAEA-Technology 2023-018, 53 Pages, 2023/11

JAEA-Technology-2023-018.pdf:2.6MB

In the decommissioning of Fukushima Daiichi Nuclear Power Station, radioactive carbonate slurry waste was generated using the Advanced Liquid Processing System (ALPS) pretreatment and temporarily stored in a high integrity container (HIC). In 2015, overflow of supernatant from HIC estimate as bubble retention in the carbonate slurry was discovered, increasing the need for a safety assessment of the carbonate slurry stored the HIC (HIC slurry). In this study, a carbonate slurry (simulated slurry) was prepared according to the Mg/Ca mass ratio in the ALPS inlet water of the HIC slurry which overflew the HIC. The effects of reaction time during the pretreatment process, suspended solids concentration (SS concentration), and settling time on the particle composition, morphology and rheological properties of the slurry were investigated. Evaluating the effect of reaction time and concentration process on chemical properties in slurry production, the effect of the reaction time was not confirmed in the simulated slurry that had undergone the concentration process, and slurry prepared at SS concentration of 150 g/L was composed of formless particles have a particle diameter of 0.4 $$mu$$m or less. We also investigate the effect of SS concentration on sedimentability, decrease in SS concentration by dilution with processing solution contributed to an increase in the initial slurry settling velocity. Furthermore, two different flow characteristics were observed depending on the settling time, suggesting that the slurry at the initial settling time has non-Bingham flow properties, whereas it changes to Bingham flow properties as the settling time becomes longer. In addition, yield stress was increased with settling time, and this yield stress was found to be exponentially proportional to the density of the slurry. These results provide knowledge to estimate the current state of HIC slurry and are expected to contribute to the safety assessment.

Journal Articles

Radiation imaging of a highly contaminated filter train inside Fukushima Daiichi Nuclear Power Station Unit 2 using an integrated Radiation Imaging System based on a Compton camera

Sato, Yuki; Terasaka, Yuta

Journal of Nuclear Science and Technology, 60(8), p.1013 - 1026, 2023/08

 Times Cited Count:1 Percentile:98.49(Nuclear Science & Technology)

Journal Articles

MAAP code analysis focusing on the fuel debris condition in the lower head of the pressure vessel in Fukushima-Daiichi Nuclear Power Station Unit 2

Sato, Ikken; Yoshikawa, Shinji; Yamashita, Takuya; Cibula, M.*; Mizokami, Shinya*

Nuclear Engineering and Design, 404, p.112205_1 - 112205_21, 2023/04

 Times Cited Count:0 Percentile:75.85(Nuclear Science & Technology)

Based on updated knowledge from plant-internal investigations, experiments and model simulations until now, the in-vessel phase of Fukushima-Daiichi Nuclear Power Station Unit 2 was analyzed using the MAAP code. In Unit 2, it is considered that the core material enthalpy was relatively low when it relocated to the lower plenum of the pressure vessel, then, cooled by the coolant and solidified there. Although the MAAP code tended to underestimate the degree of core-material oxidation during the relocation, this probable underestimation was compensated for by an existing study that was considered more reliable, so that more realistic debris conditions in the lower plenum could be obtained. Basic validity of the former prediction of the Unit 2 accident progression behavior was confirmed and detailed boundary condition for the later phase was provided. This boundary condition should be utilized for future studies addressing debris reheating process leading to lower head failure and debris relocation toward the pedestal.

JAEA Reports

Research report on information of the Nuclear Ship "MUTSU" (Contract research)

Aomori Research and Development Center

JAEA-Review 2022-039, 36 Pages, 2023/02

JAEA-Review-2022-039.pdf:4.3MB

In order to use for the consideration of floating nuclear power plant, results of survey about actual process and literature are summarized in this report.

Journal Articles

Radiation imaging using an integrated radiation imaging system based on a compact Compton camera under Unit 1/2 exhaust stack of Fukushima Daiichi Nuclear Power Station

Sato, Yuki; Terasaka, Yuta

Journal of Nuclear Science and Technology, 59(6), p.677 - 687, 2022/06

 Times Cited Count:14 Percentile:95.26(Nuclear Science & Technology)

Journal Articles

Analysis of particles containing alpha-emitters in stagnant water at torus room of Fukushima Dai-ichi Nuclear Power Station's Unit 2 reactor

Yomogida, Takumi; Ouchi, Kazuki; Oka, Toshitaka; Kitatsuji, Yoshihiro; Koma, Yoshikazu; Konno, Katsuhiro*

Scientific Reports (Internet), 12(1), p.7191_1 - 7191_10, 2022/05

 Times Cited Count:3 Percentile:56.75(Multidisciplinary Sciences)

Particles containing alpha ($$alpha$$) nuclides were identified from sediment in stagnant water at the torus room of the Fukushima Dai-ichi Nuclear Power Station (FDiNPS)'s Unit 2 reactor. Several uranium-bearing particles were identified by SEM observation. These particles contained Zr and other elements which constituted fuel cladding and structural materials. The $$^{235}$$U/$$^{238}$$U isotope ratio in the solid fractions that included U particles was consistent with the nuclear fuel in the Unit 2 reactor, which indicated that the U particles had been derived from nuclear fuel. The particles with alpha-emitters detected by alpha track analysis were several tens to several hundred $$mu$$m in size. The EDX spectra showed that these particles mainly comprised iron, which indicated Pu, Am, and Cm were adsorbed on the Fe-baring particles. This study clarifies that the major morphologies of U and other $$alpha$$-nuclides were differed in the sediment of stagnant water in the torus room of FDiNPS's Unit 2 reactor.

JAEA Reports

Preparation of carbonate slurry simulating chemical composition of slurry in overflowed high integrity container and evaluation of its characteristics

Horita, Takuma; Yamagishi, Isao; Nagaishi, Ryuji; Kashiwaya, Ryunosuke*

JAEA-Technology 2021-012, 34 Pages, 2021/07

JAEA-Technology-2021-012.pdf:2.1MB
JAEA-Technology-2021-012(errata).pdf:0.18MB

Waste mainly consisting of carbonate precipitates (carbonate slurry) from the Advanced Liquid Processing System (ALPS) and the improved ALPS at the Fukushima Daiichi Nuclear Power Station of Tokyo Electric Power Holdings, Inc. have been storing in the High Integrity Container (HIC). The supernatant solution of carbonate slurry contained in some of HICs were overflowed in April of 2015. The all of level of liquid in the HICs were investigated; however, almost of the HICs were under the level of overflow. The mechanism of overflow suggested to be depending on the difference of the properties of the carbonate slurry such as the retention/release characteristics of the bubbles. Therefore, in order to clarify the mechanism of leakage, the repeatability experiment was carried out by using simulated carbonate slurry. The simulated carbonate slurry was perpetrated by using the same cross-flow filter system of the actual ALPS. Moreover, the preparative conditions for the simulated carbonate slurry were the same as Mg/Ca concentration ratio in inlet water of the ALPS (raw water) and the ALPS operating conditions. The chemical characteristics of simulated carbonate slurries were revealed by ICP-AES, pH meter, etc. The density of the settled slurry layer tended to increase depending on the calcium concentration in the raw water. The bubble injection test was conducted in order to investigate the bubble retention/release behavior in the simulated carbonate slurry layer. The simulated carbonate slurry with high settling density, which was generated by high calcium concentration solution was revealed to retain the injected bubbles. Since the ratio of concentration calcium and magnesium during the carbonate slurry generation is assumed to affect the retention of bubbles in the slurry layer, the information on the composition of raw water is one of important factor for overflow of HICs.

Oral presentation

Analysis of alpha radionuclide in the contaminated water at the torus room of unit #2 reactor of Fukushima Daiichi NPS, 2; Analysis of alpha-emitting nuclides of solid components by ICP-MS

Ouchi, Kazuki; Yomogida, Takumi; Oka, Toshitaka; Kitatsuji, Yoshihiro; Koma, Yoshikazu; Konno, Katsuhiro*

no journal, , 

In order to grasp the existence state of $$alpha$$-nuclides contained as particulate solids in the contaminated water, $$alpha$$-nuclide concentrations in the solids and the filtrate which classified according to particle size using filters with pore sizes of 10, 1, 0.1 and 0.02 $$mu$$m were quantitatively analyzed by ICP-MS. Reactor-derived U was detected in the particulate solids in the contaminated water, and most of them settled deeply as coarse particles of $$>$$10 $$mu$$m. U existing in the water as fine particles and ions was also confirmed.

Oral presentation

Analysis of alpha radionuclide in the contaminated water at the torus room of unit #2 reactor of Fukushima Daiichi NPS, 4; Detection of fine particle containing $$alpha$$-emitters by SEM-EDX and alpha track

Yomogida, Takumi; Ouchi, Kazuki; Oka, Toshitaka; Kitatsuji, Yoshihiro; Koma, Yoshikazu; Konno, Katsuhiro*

no journal, , 

It has been revealed from the analysis results of ICP-MS and $$alpha$$-ray spectrometry that the contaminated water at the torus room of Unit 2 reactor contains $$alpha$$-nuclides which were derived from nuclear fuels. To investigate the morphology of these $$alpha$$-nuclides, we tried to detect particles containing $$alpha$$-nuclides by scanning electron microscopy-X-ray detection (SEM-EDX) and the alpha track method. As a result of SEM-EDX observation, several sub-$$mu$$m to several $$mu$$m size particles containing U were identified. These particles contain elements derived from fuel cladding materials such as Zr, suggesting the possibility that these particles are fine fuel debris. The particles containing alpha emitters were identified by alpha-track method. These particles with few hundred $$mu$$m in diameter were mainly composed of iron oxide, which suggest Pu, Am, Cm were attached to the surface of these particles. These results indicated that the forms of U and other $$alpha$$-nuclides were different.

Oral presentation

Analysis of alpha radionuclide in the contaminated water at the torus room of unit #2 reactor of Fukushima Daiichi NPS, 1; Outline of the state analysis of alpha radionuclides containing in the solid component

Kitatsuji, Yoshihiro; Ouchi, Kazuki; Yomogida, Takumi; Oka, Toshitaka; Nitta, Ayako; Hinai, Hiroshi; Koma, Yoshikazu; Konno, Katsuhiro*

no journal, , 

In order to clarify the chemical species of alpha nuclides in the contaminated water of the Fukushima Daiichi Nuclear Power Station, sludge was classified by particle size. The concentration of alpha radioisotope was measured and the particles were investigated. Most alpha particles were larger than 10 micrometers and settled at the bottom of the torus chamber.

Oral presentation

Development of the decommissioning research infrastructure database (debrisWiki)

Yamashita, Takuya

no journal, , 

no abstracts in English

Oral presentation

Examine on preparation of alpha-ray measurement samples by cerium hydroxide coprecipitation method for rapid bioassay method

Maehara, Yushi; Nagaoka, Mika; Nihei, Hidekazu*; Fujita, Hiroki; Ono, Masako*

no journal, , 

no abstracts in English

Oral presentation

Detection and analysis of particles containing alpha-emitters in stagnant water at torus room of Fukushima Dai-ichi Nuclear Power Station's Unit 2 reactor

Yomogida, Takumi; Ouchi, Kazuki; Oka, Toshitaka; Kitatsuji, Yoshihiro; Koma, Yoshikazu; Konno, Katsuhiro*

no journal, , 

As part of the decommissioning work of the Fukushima Daiichi Nuclear Power Plant (1F), disposal of stagnant water existing in the basement of the turbine building is underway. Higher concentrations of alpha nuclides have been detected in the stagnant water in the reactor building than in the downstream buildings. It is necessary to consider technology to effectively remove $$alpha$$-nuclides to proceed with the disposal of the stagnant water in the reactor buildings. We focused on particulate $$alpha$$-nuclides in the stagnant water in the torus room of Unit 2, and analyzed and investigated their particle size, chemical form, etc to understand morphology of $$alpha$$-nuclides. We detected particles containing $$alpha$$-nuclides by SEM-EDX and alpha-track detection. The results showed that U is in particle form, ranging from a few hundred nm to a few $$mu$$m. Other $$alpha$$-nuclides (Pu, Am, and Cm) were distributed on iron oxide particles.

Oral presentation

In-vessel phase MAAP analysis based on the latest findings on Fukushima Daiichi Nuclear Power Station in JFY2021, 1; Overview and Unit 2 analysis results

Sato, Ikken; Yamashita, Takuya; Yoshikawa, Shinji; Cibula, M.*; Mizokami, Shinya*

no journal, , 

no abstracts in English

Oral presentation

In-vessel phase MAAP analysis based on the latest findings on Fukushima Daiichi Nuclear Power Station in JFY2021, 2; Unit 3 Analysis results and use for future studies

Yamashita, Takuya; Sato, Ikken; Yoshikawa, Shinji; Cibula, M.*; Mizokami, Shinya*

no journal, , 

no abstracts in English

Oral presentation

Analysis for investigation of sludge observed in the storage tank of Fukushima Daiichi Nuclear Power Station

Yamaguchi, Yukako; Sekio, Yoshihiro; Maeda, Koji; Koma, Yoshikazu; Fujiya, Akihiko*

no journal, , 

no abstracts in English

Oral presentation

$$alpha$$-emitting nuclides analysis of the stagnant water including sediments in Fukushima Daiichi NPS, 1; $$alpha$$-emitting nuclides in the stagnant water at the unit 3 reactor of Fukushima Dai-ichi NPS

Ouchi, Kazuki; Oka, Toshitaka; Yomogida, Takumi; Morii, Shiori; Kitatsuji, Yoshihiro; Koma, Yoshikazu; Konno, Katsuhiro*

no journal, , 

To understand the existence of $$alpha$$-nuclides in the particulate solids contained in the stagnant water in the unit 3 reactor of Fukushima Daiichi Nuclear Power Station, the stagnant water was classified by particle size using filters with pore diameters of 10, 1, 0.1, and 0.02~$$mu$$m, and U and Np concentrations in the solid fraction and filtrate were investigated using ICP-MS. Both nuclides were present in large particles larger than 10~$$mu$$m, and some were present in the stagnant water on fine particles or ions smaller than 0.02~$$mu$$m.

25 (Records 1-20 displayed on this page)