Overview and outcomes of the OECD/NEA benchmark study of the accident at the Fukushima Daiichi NPS (BSAF), Phase 2; Results of severe accident analyses for unit 3

Lind, T.*; Pellegrini, M.*; Herranz, L. E.*; Sonnenkalb, M.*; Nishi, Yoshihisa*; Tamaki, Hitoshi; Cousin, F.*; Fernandez Moguel, L.*; Andrews, N.*; Sevon, T.*

Nuclear Engineering and Design, 376, p.111138_1 - 111138_12, 2021/05

https://doi.org/10.1016/j.nucengdes.2021.111138

This is the third part of the three part paper describing the accidents at the FDNPS as analyzed in the Phase 2 of the OECD/NEA project "Benchmark Study of the Accident at the Fukushima Daiichi Nuclear Power Plant" (BSAF). In this paper, we describe the accident progression in unit 3. In the BSAF project, eight organizations from five countries analyzed severe accident scenarios for Unit 3 at the Fukushima Daiichi site using different severe accident codes. The present paper for Unit 3 describes the findings of the comparison of the participants' results against each other and against plant data, the evaluation of the accident progression and the final status inside the reactors. Special focus is on the status of the reactor pressure vessel, melt release and fission product release and transport. Unit 3 specific aspects, e.g., the complicated accident progression following repeated containment venting actuations and attempts at coolant injection at the time of the major core degradation, are highlighted and points of consensus as well as remaining uncertainties and data needs will be summarized. FP transport is analyzed, and the calculation results are compared with dose rate measurements in the containment. The release of I-131 and Cs-137 to the environment is compared with analysis conducted by using WSPEEDI code.

Development of fuel microspheres fabrication by the external gelation process

Tomita, Yutaka; Morihira, Masayuki; Tamaki, Yoshihisa*; Nishimura, Kazuhisa*; Shoji, Shuichi*; Kihara, Yoshiyuki; Kase, Takeshi; Koizumi, Tsutomu

JAEA-Research 2006-088, 95 Pages, 2007/01

JAEA-Research-2006-088.pdf:23.02MB

JAEA has developed sphere-pac fuels in the feasibility study on commercialized FBR cycle systems as one of the candidates for low decontamination TRU fuels. Optimization of the fabrication condition for coarse spheres, development of an improved external gelation process, and examination of peculiar problems for the low decontamination fuel were carried out in Phase II. The results are shown as follows. (1) Fabrication condition of coarse spheres was optimized. (2) Feasibility of the improved external gelation process was confirmed. (3) Rare earth elements did not bring any problem for the characteristic of spheres and fabrication condition. (4) Radiation resistant data of the feed solution was acquired. Results of tests show the feasibility of the external gelation process for the low decontamination TRU fuel microsphere fabrication.

Development of a simple reprocessing process using selective precipitant for uranyl ions; Engineering studies for precipitating and separating systems

Yamasaki, Kazuhiko*; Chikazawa, Takahiro*; Tamaki, Yoshihisa*; Kikuchi, Toshiaki*; Morita, Yasuji; Kawata, Yoshihisa*; Mineo, Hideaki; Koshino, Nobuyoshi*; Asanuma, Noriko*; Harada, Masayuki*; et al.

Proceedings of International Conference on Nuclear Energy System for Future Generation and Global Sustainability (GLOBAL 2005) (CD-ROM), 4 Pages, 2005/10

N-cyclohexyl-2-pyrrolidone (NCP), can selectively precipitate U(VI) ions in aqueous nitric acid solutions. Utilizing this property, we have been developing a simple reprocessing process of spent nuclear fuel based only on precipitation method. In the first precipitation step, only U is separated by precipitation in a yield of about 70%, and in the second precipitation step both U and Pu are recovered and separated from fission products (FP) and other transuranium elements (TRU). In the present study, a precipitator and a precipitate separator were designed and built up, and were tested with aspets of operationability and system performance.

Investigation into rationalization of low DF pellet fuel fabrication plant configuration Additional Vol. - Study on characteristics evaluation of low DF fuel fabrication systems -

Maekawa, Kazuhiko*; Yoshimura, Tadahiro*; Hoshino, Yasushi*; Munekata, Hideki*; Tamaki, Yoshihisa*

JNC TJ9420 2005-003, 280 Pages, 2005/02

JNC-TJ9420-2005-003.pdf:4.73MB

In feasibility studies on commercialized FBR cycle system, a comprehensive system investigation and properties evaluation for candidate FBR cycle systems has been implemented through view point of safety, economics, environmental burden reduction, non-proliferation resistively, etc. As part of these studies, an investigation into rationalization of low decontamination pellet fuel fabrication plant configuration, and a study on characteristics evaluation techniques which focused on plant operating rate and waste generation was conducted. Until last fiscal year, a characteristics evaluation simulator which calculates plant operating rate and waste generation by input failure frequency data and periodic replacement data of every equipment or component was developed, and characteristics comparison between multiple fuel fabrication systems was done by applying it. Character of each fuel fabrication system, concerning system stability represented by waste generation, was shown and challenges in characteristics evaluation were made clear. In this fiscal year, programs of the simulator were modified to reflect plant designs correctly by describing campaign operation and batch treatment in the plant in order to make more quantitative calculation possible. On the other hand, in response to the challenges in the characteristics evaluation of last fiscal year, the system properties data based on a certain standard were acquired in conceptual design study and database were created with view of inter-system comparison. As the results of comparison between pellet system and sphere-pac system using simulator, it was suggested that system stability of pellet system is higher than sphere-pac system, and pellet system is also better in environmental burden reduction, because waste generation of sphere-pac system is apparently larger than pellet system.

Estimation Tests for Effecting Factor on Decontamination Property in Crystallization Process

Kusama, Makoto*; Chikazawa, Takahiro*; Tamaki, Yoshihisa*

JNC TJ8400 2005-006, 88 Pages, 2005/02

JNC-TJ8400-2005-006.pdf:5.67MB

In crystallization unit, UNH (Uranyl Nitrate Hydrate) crystals are washed by a nitric acid solution to get high decontamination factor, but the data on UNH crystals dissolution by washing procedure is insufficient to evaluate the effectiveness of crystallization unit. So, in this study, the effect of a nitric acid concentration to UNH crystals dissolution and decontamination factor was tested. As results, it was found that UNH-crystals dissolution was suppressed as the nitric acid concentration was higher, for example UNH-crystals dissolution by 1N nitric acid washing becomes half as compared with 8N solution washing. And as for the decontamination factor of UNH crystals, it was found that these values by 1N nitric acid washing raised 2-times as compared with 8N nitric acid washing. It was suggested that the decontamination factor of UNH-crystals have the correlation to UNH-crystals dissolution, and shown that UNH crystals loss by washing is 10~20wt% in this experiment.In addition, the crystallization behavior tests used a simulated spent fuel dissolved solution which was prepared by cold FP elements was carried out in a batch-wise experimental method. As results, it was found that in the condition of the feed solution in process design study, Ba element is crystallized with UNH, but other elements were remained in mother liquid. Besides, in the condition of the feed solution contained extreme quantity of Cs than process design concentration, it was found that Cs element was crystallized with UNH. On the other hand, the decontamination factor of other elements except Ba and Cs was about 10 after crystal-liquid separation by filtration, and then increased about 100 after crystal washing. It was confirmed that UNH crystal purity was increased by crystal-liquid separation and washing procedure.

Study on characteristics evaluation techniques of low DF fuel fabrication systems (3)

Tanimoto, Ryoji*; Yoshimura, Tadahiro*; Hoshino, Yasushi*; Munekata, Hideki*; Tamaki, Yoshihisa*

JNC TJ9420 2004-003, 212 Pages, 2004/02

JNC-TJ9420-2004-003.pdf:117.29MB

Comparative evaluation of system characteristics such as system safety, economics, environmental burden reduction, etc. concerning candidate fuel fabrication systems are carrying out in the feasibility study on commercialized FBR cycle systems. In its phase II study, a study on characteristics evaluation techniques which focused attention on operating rate of the plant and waste generation started. In last fiscal year, the relationship between operating rate of the plant and waste generation amount was investigated in consideration of failure frequency and periodic replacement of equipments, and perspectives of characteristics comparison between multiple fuel fabrication systems were made clear. In this fiscal year, system characteristics evaluation of each low DF fuel fabrication system was conducted and characteristics comparison between those systems was carried out on the bases of perspectives which made clear last fiscal year. Plant design data obtained for each characteristics evaluation were linked to a database in order to make use of future system design investigation. In addition, system safety represented by operating rate and environmental burden reduction represented by waste generation were chosen as the intended characteristics in this study. In addition to this, programs of the characteristics evaluation simulator which designed until last fiscal year were modified in order to make more accurate calculation possible.

Feasibility investigation of a denitration/conversion equipment concept (2)

Tanimoto, Ryoji*; Yoshimura, Tadahiro*; Hoshino, Yasushi*; Munekata, Hideki*; Tamaki, Yoshihisa*

JNC TJ9400 2004-002, 58 Pages, 2004/02

JNC-TJ9400-2004-002.pdf:1.39MB

In this investigation, ceramics denitration containers with ball valve units were manufactured and preliminary tests of microwave denitration, calcination and reduction were carried out in last fiscal year. In this fiscal year, a small scale denitration /conversion apparatus with turntable system was designed and manufactured, then a series of microwave denitration/conversion tests was conducted. Feasibility of the denitration/conversion apparatus with turntable system was evaluated by checking powder properties and soundness of apparatus through the series of tests. The summary of the results are as follows;(1).By the series of microwave denitration, calcination, and reduction tests using small scale denitration/conversion apparatus with turntable system manufactured, it is confirmed that there are no critical problem in the apparatus.(2).Checking the powder properties after grinding, it is confirmed that the powder is equivalent of one obtained by conventional microwave denitration /conversion facility.(3).Reduced powder was grinded and pressed to several pellets, then sintered. It was confirmed that high density pellet fuel can be obtained.(4).Studying the test results from the viewpoint of feasibility of denitration/conversion facility with turntable system, the R&D issues were made clear.

Investigation of low decontamination pellet fuel manufacture line composition

*; *; *; Tamaki, Yoshihisa*; *

JNC TJ9420 2003-003, 133 Pages, 2003/02

JNC-TJ9420-2003-003.pdf:4.79MB

As 2nd fiscal year of phase II of FBR cycle utilization strategy investigation research, following on the denitration conversion process 1ast year, the apparatus design in consideration of remote automation, line composition, and the arrangement design in a cell were performed, and the following result was obtained in this examination about each equipment from pelletizing process to former part of fuel element assembling process of a low decontamination pellet manufacture plant. (1)The outline structure design of each equipment based on remote automatic operation and the conceptual design of a process were performed, and technical formation nature was checked. (2)The formation nature of a maintenance system which conveys the units to maintenance area and repairs was checked at the time of a trouble. (3)The information about failure of the units of each equipment was examined, and operating ratio was evaluated using the plant characteristic simulator which took the throughput and buffer capacity for every process as parameters. (4)About the arrangement plan of equipments in a building, reexamination the arrangement plan of phase I by reflecting the design progress result of each equipment was performed, and accuracy was raised.

Ther study of characteristic evaluation techniques about nuclear fuel pellet manufacturing system (2)

*; *; *; Tamaki, Yoshihisa*; *

JNC TJ9400 2003-010, 66 Pages, 2003/02

JNC-TJ9400-2003-010.pdf:4.03MB

In this study, while examining the operating ratio which took into consideration the operation characteristics of apparatus for the low decontamination pelltizing method, and apparatus exchange frequency as the 2nd fiscal year of phase II of FBR cycle utilization strategy investigation research, the system characteristics evaluation simmulator was modified to able to calculate waste amount generated by fixed exchange of the parts. A comparison study of the operating ratio in a few other fabrication system was also performed by applying the simulator to them, and the following result was obtained. (1)While arranging the setting plan of operation characteristics of apparatus in connection with the apparatus operating ratio, optimization of the buffer capacity, throughput, and the number which improve operating ratio was performed. (2)The calculation program of waste amount generated which can respond to the case of fixed exchange of the parts, and the case parts of exchange at the time of failure was made. (3)The comparison method of the system characteristics among fabrication systems was considered, and comparison examination of operating ratio was performed by applying to the other fuel fabrication systems. (4)The simpler method for data input of the characteristic evaluation simulator manufactured in the last fiscal year was examined, and the simulator modification was carried out.

The Study to wash UNH crystals in the reprocessing process

Yamasaki, Kazuhiko*; *; Tamaki, Yoshihisa*

JNC TJ8400 2003-016, 40 Pages, 2003/02

JNC-TJ8400-2003-016.pdf:0.9MB

Crystallization procedure is considered to have an adaptability to new reprocessing process based on the PUREX process because it has an advantage in recovering rather pure uranium from contaminated uranium solution without any reagents. Up to now, a small-scale uranium test has been performed to confirm an applicability of crystallization. We focus on the decontamination factor (DF) of FP in the crystallization procedure. Some mock experiments have been also performed and suggested that most of FP is on the surface of crystals in mother liquor. We expected that the content of the mother liquor decreases with increasing of the size of crystals. Consequently it is possible that the DF increases with increasing of the size of crystals. In this study, we performed the experiment to estimate the DF of Ce (ⅵ) of various size of UNH crystals. And our expectation is confirmed.