Results and Progress of Fundamental Research on FP Chemistry

Transcription

1 Results and Progress of Fundamental Research on FP Chemistry M.Osaka a,*, K.Nakajima a, S. Miwa a, F.G.Di Lemma a, N.Miyahara a, C.Suzuki a, E.Suzuki a, T.Okane a, M.Kobata a a Japan Atomic Energy Agency, Shirakata 2-4, Tokai-mura, Naka-gun, Ibaraki-ken , Japan. Abstract Fundamental research on fission product (FP) chemistry is underway in Japan Atomic Energy Agency. The purpose is to enlarge a FP chemistry database in each location of a LWR under severe accident conditions. Improvement of FP chemical models based on this database is also an important task of the research. Research outputs are reflected to the research and development of decommissioning of Fukushima Daiichi Nuclear Power Station (1F) and the enhancement of LWR safety. Four research items have thus been established considering the specific issues of 1F and the priority in the source term research area, as follows: - Effects of boron (B) release kinetics and thermal-hydraulic conditions on FP behavior, - Cesium (Cs) chemisorption and reactions with structural materials, - Establishment of a thermodynamic and thermophysical properties database for FP compounds, - Development of experimental and analytical techniques for the reproduction of FP release and transport, and for measurement techniques of chemical form of FP compounds. In this paper, results and progress of the research are presented. The main body of the research is reproduction tests for FP release and transport, which aims at acquiring experimental evidences for FP-chemical behavior by direct measurements of chemical forms of FP compounds in deposits and gas-phase samples. Concept and specification of the test facility for the reproduction test is described. A preliminary test result using CsI as surrogate confirmed that the test facility could reproduce the aerosol formation and growth behavior. Another important issue is to obtain basic knowledge on Cs chemisorption onto structural material, specifically stainless steel. It was found that Cs formed Cs-Si-Fe-O compound by the chemisorption. Synthesis of the Cs chemisorbed compounds for the evaluation of basic properties was then carried out and was successfully completed. Keywords: FP-Chemistry, BWR, Boron, Reproduction Test, Chemisorption 1. Introduction A fundamental research program on fission product (FP) chemistry has been conducted in Japan Atomic Energy Agency (JAEA) since 2012 [1]. Basic knowledges of the FP chemistry are expected to be obtained as outcomes of this research. The research aims at contributing to both R&D for decommissioning of Fukushima Daiichi Nuclear Power Station (1F) and the enhancement of LWR safety. It is well known that FP chemistry has a critical impact on FP release and transport under a LWR severe accident (SA). FP chemistry has long been recognized worldwide as an important issue for FP related research. Besides, the 1F accident has recalled the possible chemical effects of BWR control rod materials Boron (B) and atmosphere effects, especially under the steam-starvation atmosphere that could have occurred in the 1F unit-2. In order to correspond to the wide-spreading FP chemical issues, we determined objective of our research to enlarge a FP chemistry database for each location of LWR, i.e. fuel, Reactor Pressure Vessel (RPV), Reactor Cooling System (RCS), Primary Containment Vessel (PCV), Reactor Building (R/B), under a LWR-SA mainly based on experimentally obtained results. Improvement of FP chemical models are also to be conducted based on the FP chemical database. Four research items have thus been determined as follows: (1) Evaluation of effects of B release kinetics and thermal-hydraulic conditions on FP chemical behavior (2) Clarification of cesium (Cs) chemisorption and reaction behaviors on structural materials at relatively high temperatures such as upper head of RPV (3) Enlargement of a database on thermodynamic and thermophysical properties of FP compounds formed within a reactor (4) Development of experimental and analytical techniques for reproduction tests of FP release and transport and of direct measurement methods for chemical form of FP compounds. * Corresponding author address: ohsaka.masahiko@jaea.go.jp (M.Osaka)

2 The 8 th European Review Meeting on Severe Accident Research - ERMSAR-2017 The mid-term research plan is shown in Figure 1. Basically, the research continues for the enlargement of the fundamental data and knowledge. The immediate milestone is to provide a Cs chemisorption model for the R&D of 1F decommissioning work at the end of 2017, at when the methodology for the debris removal will be decided. Main framework of the research is shown in Figure 2. Reproduction tests by the TeRRa facility (Test bench for FP Release and transport), which will be described later, and chemical reaction kinetic analysis of TeRRa test results are centered in developing the database and improvement of models for FP chemistry. In addition, separate effect tests such as Cs chemisorption and B release kinetics are also performed for detailed mechanistic analysis of the fundamental phenomena. The models and database obtained will then be finally validated by hot tests using a real irradiated fuel sample. This will certify the use of models and database in SA analysis codes and will provide fundamental information for the 1F decommissioning R&D. This paper describes some of recent results and progress for the FP chemistry research. Research items Main outcome Effects of B and thermal-hydraulic conditions 2. Cs chemisorption 3. Thermodynamic /physical properties evaluation 4. Development of exp./anal. techniques Outside 1F sample analysis (under consideration) FP chemical reaction database / model in SA condition Mechanism and process models for Cs chemisorption Thermodynamic/ physical database of FP compounds Establishment of evaluation techniques for FP chemistry Information about FP chemical behavior inside 1F Cs-I-B-Mo-O-H system (Data acquisition of FP chemical form by reproduction tests, analysis of chemical reaction kinetics, V&V of the model by hot tests * ) Analysis of FP chemisorbed material (XPS, raman, ab-initio, etc.), modeling Cs-B-O and Cs-Si-O compounds, etc. (Vapor pressure measurement, phase relation evaluation) Reproduction test (TeRRa), analysis tool, direct measurement for FP chemical speciation (RIMS, HAXPES, TG-DTA-MS) Deposits on lower temperature region, other nuclides (Sr, Te, etc.) Models for SA analysis codes Built-up of HAXPES, analysis of sample outside 1F Sr, Ru, etc. behavior * Hot tests are conducted under a contract with the Nuclear Regulation Authority of Japan. Figure 1 Mid-term plan for the fundamental research on FP chemistry Hot-Cell apparatus Aerosol formation and growth Release from fuel Sorption Desorption Important phenomena V&V Chemical reaction analysis Chemistry database, model Release at MCCI TeRRa facility Steam injection Dissolution Revaporization SIMFuel, B 4 C FP, B Coupons for deposit anlysis Filter, Liq. trap Temperature distribusiton Core RPV RCS, PCV FP/boron release kinetics Filter, Liq. trap Separate effect tests for each stage of SA progression Interaction with structural material in RCS and PCV Thermodynamic / physical property database Development of measurement and analysis techniques for FP chemical behavior Figure 2 Main framework of the fundamental research on FP chemistry 2. Results and progress for the FP chemistry research 2.1. Evaluation of effects of boron release kinetics and thermal-hydraulic conditions on FP chemistry Relatively less knowledge has been obtained so far for the chemical effects of B 4 C control blade material compared with those of the Silver (Ag)-Indium (In)-Cadmium (Cd) used in the control rod of PWR. Boron can alter Cs-I-Mo-O-H chemical system to Cs-I-Mo-B-O-H ones, which could result in altered FP behavior such as

3 The 8 th European Review Meeting on Severe Accident Research -ERMSAR-2017 possible enlargement of gaseous Iodine (I) species. Boron species could be released under a BWR SA from a mixed melts consisted of the control blade materials, B 4 C-stainless steel (SS)-Zircaloy (Zry). However the knowledge on the B release behavior, as well as on the control rod degradation behavior, from the mixed melts is limited and only qualitative [2]. In particular, B release could be suppressed under a steam-starvation atmosphere, which is caused by formation of stable Fe-B compounds. In order to comprehensively understand the effects of B 4 C and atmosphere on FP chemistry, we perform a fundamental study for the effects of B release kinetics and thermal-hydraulic conditions on FP chemistry. Another topic is alteration of release and transport behavior of non- or low-volatile FPs. We noted to nonvolatile Sr as one of such nuclides, since it is reported that Sr release is greatly enhanced under reductive atmosphere. Besides, possible formation of stable Sr chloride having higher vapor pressure [3] is of another motivation. We have therefore started a preliminary study on the Sr release and transport behavior B release kinetics from Fe-B compounds During a BWR SA, B-containing complex melts (B 4 C-SS-Zry) can be formed due to the interaction of the control rods with the cladding and structural material. B release kinetics can greatly be affected by the formation of stable and less volatile Fe-B (or Zr-B) compounds [4], and could consequently influence the FP behavior. While reliable set of data and models exist for the behavior of B 4 C under SA conditions, those for B 4 C-SS-Zry melts are limited and only qualitative [2]. The aim of our studies is to acquire kinetic data for the B release that is accompanied by oxidation of these complex phases. In this work, the oxidation and vaporization behaviors were investigated using simple representative Fe-B compounds. The B-ReK (Boron Release Kinetics) facility was used for these experiments, which consists of a thermogravimetric analyzer (TGA) connected to a customized steam generator. FeB and Fe 2 B samples were prepared by a powder metallurgy from commercial materials. Weight changes, which were assumed as the oxidation followed by vaporization, were measured by TGA under steam conditions (70 dew point) at several temperatures ( K). The oxidation and vaporization behavior was interpreted based on the characterization of the samples before and after the TGA tests by X-ray diffraction (XRD) measurements. The XRD patterns after the TGA tests at 1173 K showed the possible formation of amorphous B 2 O 3 phase for both FeB and Fe 2 B samples as a broad hump, while B 2 O 3 was completely vaporized at 1373 K. Figure 3 shows the XRD patterns after the TGA tests at 1373 K. Fe 2 O 3 was detected for the FeB sample, while Fe-B-O compounds, possibly as (FeO) 2 FeBO 3, was found for Fe 2 B at 1373 K. As the nominal valence of Fe in this Fe-B- O compounds are less than 3 (the maximum oxidation state of Fe), it implies that Fe is oxidized partially caused by the presence of B. It is considered that the lower weight gain and higher weight loss for FeB respect to Fe 2 B (Figure 4) are mainly related to the higher B/Fe ratio in the Fe-B alloys, which can lead to enhanced formation of B 2 O 3. From these results, it can be inferred that the oxidation and vaporization kinetics of Fe-B compounds can be influenced by the B/Fe ratio, which affects the formation behavior of Fe-B-O compounds that protect B release. Figure 3 X-ray diffraction patterns of the FeB and Fe 2 B samples after the TGA tests at 1373 K

4 The 8 th European Review Meeting on Severe Accident Research - ERMSAR-2017 Figure 4 Mass change in the TGA tests at 1373 K in steam for the FeB and Fe 2 B samples Release and transport behavior of Sr Effects of atmosphere on the Sr vapor species were preliminary investigated. Not only Cs and I but also non- or low-volatile radioactive nuclides such as Sr and U are potentially important in terms of radiological effects. In particular, Sr should be considered as potential radiation source for the debris removal work of 1F. Sr is also important in terms of risk communication to the public considering the similar radiological impacts of Sr to Pu, which retains in the bones of human body for a long term when inhalation occurred. As more release would be expected by the debris leaching in the 1F in views of the long term source term issue, Sr release and transport via aqueous phase should be investigated. On the other hand, Sr release and transport in the reactor during a SA would become of importance considering the fact that Sr release is greatly enhanced under a reductive atmosphere [5]. It is said that a steam-starvation conditions would have occurred in 1F unit-2 by rapid water boiling with depressurization by steam leakage caused by the opening of safety release valve. Therefore some possibility should be considered for the enhanced Sr release and transport in 1F. The investigation was made by a combined calculation of elemental release rate from fuel and chemical equilibrium. Atmospheric dependences of the Sr release kinetics was considered in the elemental release calculation by using the CORSOR-O models [6]. A prototype thermal-hydraulic condition simulating 1F was assumed and released Sr vapor species were calculated by Thermo-Calc software with SGTE database [7]. Results showed that Sr release was greatly enhanced as elemental Sr vapor species under the steam-starvation atmosphere compared with that under steam atmosphere, as shown in Figure 5. Condensation behavior of the released Sr vapor species were also calculated along a downward temperature gradient, which showed the formation of SrO as a major condensate. Figure 5 Calculated released fraction of Sr vapor species just after release; dotted line indicate under steam atmosphere and solid line steam-starvation atmosphere

5 Temp. ( o C) The 8 th European Review Meeting on Severe Accident Research -ERMSAR Fundamental study on the Cs chemisorption behavior Chemisorption is of importance during a SA, as it can influence FP retention especially in the RPV and thus the amount of radioactive materials released to the environment [8]. However shortage of knowledge and data for the chemisorption make construction of detailed models difficult. The detailed model that incorporates chemical process of the chemisorption behavior is believed to be required for the effective prediction of Cs deposits in 1F that experienced various chemical conditions during SA from unit to unit. We have therefore performed fundamental studies for a deep understanding of this phenomena and its modelling for SA codes [8,9]. Moreover, as information on the distribution, composition and properties of such chemisorbed deposits can have significant impact on the decommissioning of reactor, they could also be useful for the 1F decommissioning practice. The experimental study so far has given us several important knowledges. Our experimental studies for CsOH chemisorption is made on two different SS samples (SS316, which contains several percent of Mo, and SS304 including no-mo) used as simulants of reactor structural materials. A series of chemisorption tests has been carried out under conditions at 1073 K or 1273 K in Ar-5%H 2 O-5%H 2 atmosphere. The Cs deposits onto SS samples were analyzed after the chemisorption tests by various analytical techniques (Scanning Electron Microscope /Energy Dispersive X-ray spectroscopy (SEM/EDX), Raman spectroscopy, XRD, ICP-MS) for the characterization of deposited compounds. An example of elemental distribution on the surface of SS304 exposed to CsOH vapor is shown in Figure 6. The chemisorbed compound was revealed to be CsFeSiO 4 for both SS304 and SS316 samples. Besides, a small amount of Cs-Mo-O compounds were observed on the SS316 sample surfaces. The CsFeSiO 4 compound was observed not only on the sample surface but also in the depth of the sample. We investigated the re-vaporization behavior of these chemisorbed compounds, which resulted in the greater stability of CsFeSiO 4 than that of Cs-Mo-O compounds. In order to deeply see the vaporization behavior, pure CsFeSiO 4 and Cs 2 MoO 4 samples were synthesized for a TG-DTA. Figure 7 shows TG-DTA curves of the synthesized samples. It is clearly seen that Cs 2 MoO 4 vaporize much faster than CsFeSiO 4. Figure 6 Elemental distribution on the surface of stainless steel exposed to CsOH vapor at 1073 K; congruent distribution of Cs and Si implies the formation of Cs-Si-O compounds Δw/w i _CsFeSiO Temperature Δw/w i _Cs 2 MoO Time (min.) Δw/w i Figure 7 TG-DTA curves for Cs 2 MoO 4 and CsFeSiO 4 samples

6 Intensity (ab. Units) The 8 th European Review Meeting on Severe Accident Research - ERMSAR Enlargement of a database on thermodynamic and thermophysical properties of FP compounds Cesium forms various kinds of complex compounds under every situations due to its active chemical affinity to other elements. Thermodynamic evaluation are of useful for the various prediction of material chemical behavior, such as a preliminary prediction of chemical species formed, interpretation of chemical analysis results and so on. We have thus been preparing thermodynamic database for the Cs compounds mainly by means of high temperature mass spectrometry Cs-B-O system Cesium metaborate, CsBO 2, has been said to be a main compound among Cs-B-O system having various chemical compositions [10]. On the other hand, according to Girault and Payot [11] who investigated B effects on FP transport and deposition behaviors in the Phebus-FPT tests, the thermodynamic calculations show only a limited impact of B on Cs chemistry. This discrepancy might be caused by a lack of accurate thermodynamic data for various cesium borates. Thermodynamic properties are only available for CsBO 2, although many other ternary compounds exist such as Cs 2 B 4 O 7 and CsB 3 O 5. The first target to be investigated in our study is CsB 3 O 5, since it has the highest melting temperature and is therefore expected to be the most thermodynamically stable among the cesium borates. First, phase relations of Cs-B-O system around CsB 3 O 5 at high temperatures is investigated by XRD and TG-DTA, since the phase diagrams reported in the past do not agree with each other [12,13]. The investigated region for B 2 O 3 to Cs 2 O ratio is from 2 to 3. From our analyses we observed that two phases exist at room temperature, Cs 2 B 4 O 7 and CsB 3 O 5, while no Cs 3 B 7 O 12 was found as shown in Figure 8. The last phase was previously reported to be present as one of the largest structures known in an anhydrous inorganic material [14]. Further, TG-DTA curves suggested existence of a high temperature phase which was previously indicated in phase diagrams [12]. This phase is inferred to be Cs 3 B 7 O 12, considering the analogue to Rb 3 B 7 O 12 [15]. * the JCPDS-ICDD card number Figure 8 X-Ray diffraction patterns of synthesized Cs 2 B 4 O 7 and CsB 3 O 5 at room temperature Cs-Si-O system Although CsFeSiO 4 and Cs-Si-O in the Cs chemisorbed deposit were expected, only a few thermodynamic and thermophysical properties are available for Cs-Si-O system. Besides, only crystal structure data of CsFeSiO 4 have been reported in the past [16]. Therefore, we have prepared these compounds in order to experimentally clarify their thermodynamic and thermophysical properties. Figure 9 shows the XRD patterns of Cs-Si-O prepared by a powder metallurgical techniques. Cs 2 Si 2 O 5 was synthesized at 1123 K in air, while CsFeSiO 4 was synthesized at 1273 K. As shown in this figure, the samples of Cs 2 Si 2 O 5 and CsFeSiO 4 seem to be successfully prepared.

7 Intensity (ab. Units) The 8 th European Review Meeting on Severe Accident Research -ERMSAR-2017 * the JCPDS-ICDD card number Figure 9 X-ray diffraction patterns of synthesized Cs 2 Si 2 O 5 and CsFeSiO Development of reproduction test technology for FP release and transport A test facility for the reproduction of FP release and transport under a SA condition is being developed. The name of the test facility is TeRRa (Test bench for FP Release and transport). The TeRRa has a simple path of a straight pipe for FP migration in order to minimize the thermal-hydraulic influences. Figure 10 shows the appearance of and FP flow in the TeRRa facility. Basic specification of the TeRRa facility is shown in Table 1. The evaporated FPs at the core part are transported to the Thermal Gradient Tube (TGT) part having linear temperature gradient from K to 400 K. Airborne aerosols can be extracted at each 100 K of the temperature range of the TGT, and their size distribution can be measured by both a cascade impactor and an on-line aerosol spectrometer. Small coupons made of various materials are also set in desired parts in the tube, which can collect the FP deposits and/or chemically absorbed FP compounds. These trapped and deposited samples can be then subjected to various off-line analyses by SEM-EDX, XRD, Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS), and so on. These analyses can give essential information about the FP chemistry at different temperatures and chemical conditions, which can help us identify the main chemical reactions occurred under the RCS or PCV conditions, in order to construct the FP chemical database. Although a part of the TeRRa design referred to the CHIP facility in IRSN [17] and EXSI-PC in VTT [18], usage of solid samples in the higher temperature up to fuel melting and the on-line aerosol size measurements are unique characteristics of the TeRRa. The first performance test of the TeRRa was conducted using a CsI compound. This test was expected to show that the TeRRa could control the temperature from fuel to PCV as expected and reproduce basic FP release and transport behavior such as aerosol formation, growth and deposition. It was confirmed that nearly linear temperature gradient from K to 400 K was obtained in the TGT. Aerosol growth behavior was also estimated by vaporization of CsI at K part of TGT. The formed aerosol was measured by aerosol spectrometer with the effective measurement range of µm. Aerosol size distribution was obtained those sampled from 400 K as shown in Figure 11. This results show that CsI aerosols had grown and have a size distribution through the transportation from K to 400 K. Number of reproduction tests using simulated fuels containing representative elements such as Cs, I, B will be conducted to acquire basic data for FP chemistry and aerosol size distribution for B containing system.

8 The 8 th European Review Meeting on Severe Accident Research - ERMSAR-2017 Core part TGT part Figure 10 Appearance of TeRRa facility Figure 11 An example of performance test results of TeRRa; measurement result of CsI aerosol size distribution by the aerosol spectrometer Table 1 Basic specifications of TeRRa Size Whole facility (app.) 3 m(l) x 1 m(w) x 2 m(h) Temperature gradient tube 39.4 mmφ(i.d.) x 1300 mm Temperature Maximum at core part 2,500 K Temperature gradient tube 400 K On-line aerosol spectrometer Particle size measurement range µm µm µm Atmosphere Carrier gas Ar Gas flow rate 1 5 L/min Off-line analyses Steam condition (maximum dew point) 80 SEM-EDX XRD Raman spectroscopy X-ray Photoelectron Spectroscopy (XPS) ICP-MS

9 3. Expected outcomes The 8 th European Review Meeting on Severe Accident Research -ERMSAR-2017 Outcome of the present FP chemistry research is the FP chemical database and improved elemental models, as already mentione in Chapter 1. Basic framework of the database is expected to be that as shown in Figure 12. The database would consist of mainly two parts, experimental data and chemical reaction expected. Lots of the experimental results for FP release and transport tests including those by TeRRa will be gathered and shown as functions of vaious experimental conditions such as temperature, atmosphere (H 2 O/H 2 ratio), gas composition, fluid conditions, coupon material, and so on. The sample condition, i.e. sample specification and heating pattern, is also included. Not only FP deposit amount but also various analytical results such as microstructure, crystal structure, chemical states and so on would also be included. The other part, the chemical reaction part, is main chemical reactions expected to occurr with kinetic reaction constants evaluated by the analysis using chemical kinetics analysis tool. At the present, the followings are considered as the target models to be improved/constructed based on the FP chemistry database: - The chemisorption model, which implements chemical species of Cs-Si-O and Cs-Mo-O with their revaporization. - Representative fractions of FP chemical species and major chemical reactions considering their chemical kinetic reaction constants at each region of the reactor - B release model from complex melts of B 4 C-SS-Zry - Changes of liquid properties (such as ph) at PCV - Pool scrubbing efficiency with imporved FP solubility considering FP chemical compositons/states - FP sorption fractions onto wall and floor of reactor building and inner surface of PCV annulas Experimental data: TeRRa FP chemical Condition forms and their Deposits amount at various Vapor/aerosol Condition Deposits Vapor/aerosol Condition temperature D.P. Deposits FP and atmosphere Vapor/aerosol FP Condition Temp D.P. Deposits Chemical temp amount FP Vapor/aerosol Chemical amount FP Condition Temp [K] D.P. Chemical [ o form Chemical Temp temp Deposits form C] amount FP [K] [mg] Chemical Vapor/aerosol amount FP D.P. temp [mg] [ o C] amount FP form [mg] amount FP Chemical Temp form [K] D.P. temp [mg] [ o C] amount FP Chemical form [mg] amount FP Chemical form Temp [K] Chemical B: 0 I [mg] 2 Cs: 50 Cs [ o form Chemical tempc] amount [mg] B: I: 010 I amount form [K] HBO 2 [mg] Cs: 2 I: Cs [ I 2 form form C] [mg] B: I: 0 10 I HBO 2 [mg] Cs: 2 I: Cs I 2 FP release and transport test B: I: 010 I Cs: 18 HBO 2 Cs: 2 I: Cs Cs:50 I 2 Cs 900 B: 80I: 010 I Cs: CsI I: 18 HBO 2 2 Cs: I: Cs 20 Cs:50 I TeRRa: steam 2 CsI I:70 Cs I: 10Cs: I I: 18 HBO 20 2 I: 50Cs:50 I CsI I:70 2 Cs FP-Chem: hydrogen Cs: I 2 80 I: 1820 Cs: I:70 Cs CsI I 2 VERDON: hot test Cs: FP-Chem I: 1820 Cs:50 I:70 Cs 900 I 2 80 CsI I: 20 I:70 I 2 RPV: > K RCS: 400 K Cs + I CsI CsI CsI(s) FP release and transport analysis ANSYS-FLUENT-CHEMKIN software CsI + H 2 O CsOH + HI CsOH CsOH(s) Benchmark analysis with THALES-2, ASTEC, SAMPSON. 2CsOH + MoO 3 Cs 2 MoO 4 (s) CsI + HBO 2 CsBO 2 (s) + HI CsI + HBO 2 CsBO 2 (s) + HI FP chemistry database: Dominant chemical reaction equations and their reaction kinetics coefficients at each stage of LWR with major chemical behavior Figure 12 Images of enlargement of FP chemistry database 4. Summary and prospect The recent results and progress of fundamental research on FP chemistry were reported. The research has progressed as planned and has continuously provided fundamental data and knowledge towards the construction of the FP chemistry database. The research shall continue towards the goal of contributing to both the 1F decommissioning R&D and the enhancement of LWR safety. In addition to the concrete promotion of research, the following points should be taken into consideration for more effective promotion of the research. - The construction of a Japanese FP research platform is considered essential [19], especially for fundamental research. The platform is expected to attract and interact with oversea researchers, by providing knowledges on FP behavior and accepting researchers. It will also be effective for the promotion

10 The 8 th European Review Meeting on Severe Accident Research - ERMSAR-2017 of the FP-related research in Japan since such fundamental research basis of FP is currently insufficient in Japan. - A methodology for elucidating in-reactor FP behavior from the analysis results of samples outside 1F units is interesting approach and a related study should start from a trial step. Such methodology construction could also contribute to the planning of 1F debris sample analyses. - Results should continuously be reflected to the research on LWR safety enhancement. For instance, evaluation of FP behavior at the boundary region between in-reactor and outside-reactor, i.e. PCV, S/C, filtered venting system, could be useful. Other issues having large uncertainty should be considered, such as FP release behavior at a re-flooding to the degraded core, sea-water effect on the FP chemistry, behavior of semi-volatile FPs that would be important for 1F issue, steep depressurization effects on the FP behavior and so on. [1] M. Osaka, S. Miwa, K. Nakajima, F.G.DiLemma, C. Suzuki, N. Miyahara, M. Kobata, T. Okane and E. Suzuki, "Results and Progress of Fundamental Research on Fission Product Chemistry - Progress Report in ", JAEA-Review , Japan Atomic Energy Agency, [2] F. G. Di Lemma, S. Miwa and M. Osaka, "Boron Release Kinetics from Mixed Melts of Boron Carbide, Stainless Steel and Zircaloy - A Literature Review on the Behavior of Control Rod Materials under Severe Accidents-", JAEA-Review , Japan Atomic Energy Agency, [3] M. Kurata, N. Shirasu and T. Ogawa, Thermodynamic Evaluation on Effect of Sea Water to Degraded Nuclear Fuel in Severe Accident of LWR, Trans. Atomic Energy Soc. Jpn. 12, , [4] S. Miwa, S. Yamashita and M. Osaka, Prediction of the effects of boron release kinetics on the vapor species of cesium and iodine fission products, Prog. Nucl. Energy 95, 254, [5] S. Miwa, G. Ducros, E. Hanus, P. D. W. Bottomley and S. Van Winckel, "Upgrading the experimental database of fission products and actinides release behaviour in the VERCORS program through chemical analysis, Proc. 7th European Review Meeting on Severe Accident Research (ERMSAR 2015), Marseille, France, [6] R. A. Bream and M. E Osborne, "A Summary of ORNL Fission Product Release Tests With Recommanded Release Rates and Diffusion Coefficients", NUREG/CR-6261, [7] A. T. Dinsdale, SGTE data for pure elements, CALPHAD 15, 317, [8] F. G. Di Lemma, K. Nakajima, S. Yamashita and M. Osaka, Surface analyses of cesium hydroxide chemisorbed onto type 304 stainless steel, Nucl. Eng. Design 305, 411, [9] F. G. Di Lemma, K. Nakajima, S. Yamashita and M. Osaka, Experimental investigation of the influence of Mo contained in stainless steel on Cs chemisorption behavior, J. Nucl. Mater. 484, 174, [10] K. Minato, Thermodynamic analysis of cesium and iodine behavior in severe light water reactor accidents, J. Nucl. Mater. 185, 154, [11] N. Girault and F. Payot, Insights into iodine behaviour and speciation in the Phebus primary circuit, Annals Nucl. Energy 61, 143, [12] A. B. Kaplun and A. B. Meshalkin, Phase equilibria in the binary systems Li 2 O B 2 O 3 and Cs 2 O B 2 O 3, J. Cryst. Growth 209, 890, [13] N. Penin, M. Touboul and G. Nowogrocki, New form of the Cs 2 O B 2 O 3 phase diagram, J. Cryst. Growth 256, 334, 2003.

11 The 8 th European Review Meeting on Severe Accident Research -ERMSAR-2017 [14] G. Nowogrocki, N. Penin and M. Touboul, Crystal structure of Cs 3 B 7 O 12 containing a new large polyanion with 63 boron atoms, Solid State Sci. 5, 795, [15] R. S. Bubnova, S. V. Krivovichev, I. P. Shakhverdova, S. K. Filatov, P. C. Burns, M. G. Krzhizhanovskaya and I. G. Polyakova, Synthesis, crystal structure and thermal behavior of Rb 3 B 7 O 12, a new compound, Solid State Sci. 4, 985, [16] R. G. J. Ball, B. R. Bowsher, E. H. P. Cordfunke, S. Dickinson and R. J. M. Konings, Thermochemistry of selected fission product compounds, J. Nucl. Mater. 201, 81, [17] B. Clement, "Towards reducing the uncertainities on Source Term Evaluations: an IRSN/CEA/EDF R&D programme", Proceedings of EUROSAFE2004, Berlin, Germany, November 8-9, [18] P.D.W. Bottomley, K. Knebel, S. Van Winckel, T. Haste, S.M.O. Souvi, A. Auvinen, J. Kalilainen, and T. Kärkelä, Revaporisation of fission product deposits in the primary circuit and its impact on accident source term, Annals Nucl Energy 74, 2014, 208. [19] Research Team for Fission Product Behavior, "Significance of international cooperative research on fission product behavior towards decommissioning of Fukushima Daiichi Nuclear Power Station; Review of the CLADS International Workshop", JAEA-Review , Japan Atomic Energy Agency, 2016.