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Kakiuchi, Kazuo; Udagawa, Yutaka; Yamauchi, Akihiro*
JAEA-Research 2022-001, 21 Pages, 2022/06
JAEA-Research-2022-001.pdf:1.84MB
The primary cause of cladding embrittlement during loss-of-cool ant accident (LOCA) is the increase in oxygen concentration in the metallic layer and associated microstructural change due to oxidation. In the case of cladding high temperature rupture, inner surface oxidation by the steam ingress and the consequent increase in hydrogen partial pressure result in hydrogen absorption (secondary hydriding) localized in the axial direction at the distance apart from the rupture opening as is well known from preceding studies. In order to understand the effect of cladding microstructural changes on mechanical property of a fuel rod under LOCA conditions in a more precise and quantitative manner, the nanoindentation method has been applied to evaluation of mechanical properties of a cladding specimen after a LOCA simulated test; results for two samples taken from the rupture opening part and secondary hydriding part were compared with each other. The fraction of plastic work during the indentation was evaluated from the load-displacement curve in addition to hardness and Young's modulus. The plastic work fraction at the secondary hydriding part was found to be clearly lower than that at the rupture opening part and rather close to that in the ZrO
and 
-Zr(O) layers, suggesting the significant ductility reduction of the secondary hydriding part despite its relatively low oxygen concentration.
Hiratsuka, Shinya; Asamori, Koichi; Saiga, Atsushi
JAEA-Research 2022-002, 38 Pages, 2022/06
JAEA-Research-2022-002.pdf:4.49MB
Deep groundwater originates from dehydration of Pacific and Philippine Sea slab subducting beneath Japanese islands, which has characteristics of high temperature and is rich in carbonate species. In this respect, it is very important for geological disposal of high-level radioactive waste to estimate reservoir and migration pathway of deep groundwater. The region where cracks are densely distributed can be regarded as the migration pathway of slab-derived fluid. It is highly probable that the region has strong anisotropy. Shear wave propagating through anisotropic media splits into two mutually orthogonally polarized waves due to shear wave polarization anisotropy. In this report, we applied shear wave splitting analysis to Hongu area of Tanabe City, Wakayama Prefecture and estimated the spatial distribution of leading shear wave polarization direction (LSPD) and arrival time difference between leading and lagging shear waves (dt). Based on comparison with helium isotope ratio of ground water and bubbling gas samples and two-dimensional resistivity structure estimated by previous study, we attempt to estimate migration pathway of slab-derived fluid in Hongu area of Tanabe City, Wakayama Prefecture. The main results are summarized as follows. When helium isotope ratio of groundwater and bubbling gas samples is high, dt value tends to be large. Shear wave propagating through high and low resistivity anomaly zone show small and large dt values, respectively. Previous study suggested that slab-derived fluid migrates from deeper part of western side of Hongu area and wells out in Yunomine and Kawayu hot springs. This is consistent with spatial distribution of dt values estimated by this study.
Miyakawa, Kazuya; Yamamoto, Hajime*
JAEA-Research 2022-003, 40 Pages, 2022/05
JAEA-Research-2022-003.pdf:6.08MB
The excavation of large-scale underground facilities, such as geological disposal of high-level radioactive waste, creates an excavation damaged zone (EDZ) with cracks around the tunnel. In the EDZ, oxygen invades the bedrock through unsaturated cracks and affects environmental conditions for nuclide migration. When a tunnel is excavated in a geological formation containing a high concentration of dissolved CH
, such as the Neogene marine sediments, degassed CH prevents oxygen intrusion. However, it may be promoted through gas-phase diffusion through desaturation. The purpose of this study is to illustrate the method of estimating the spatial distribution of desaturation associated with the construction and operation of underground facilities in a stratum that contains a large amount of dissolved CH. A sequential excavation analysis that reflected the actual process of 10-year excavation of the Horonobe Underground Research Laboratory (URL) was carried out along with gas-water two-phase flow analysis. The analysis results of the amount of groundwater and gas discharged from the URL were about 100 to 300 m
d
and 250 to 350 m d, respectively, as of January 2017. These results showed values close to the observations (100 m d and 300 m d, respectively). The analysis results of the saturation distribution were relatively high around the 250 m gallery and relatively low around the 350 m gallery, confirming that they are consistent with the in-situ observations. Although there were still technical issues of analysis regarding the conditions for groundwater drainage from the tunnel wall and the method of handling grout effects, the numerical calculation was generally appropriate. Although the results of the saturation distribution associated with the excavation were insufficient as the quantitative evaluation, they were almost correct from a qualitative point of view.
Niwa, Masakazu; Shimo, Michito*; Shimada, Koji; Goto, Akira
JAEA-Research 2022-004, 38 Pages, 2022/06
JAEA-Research-2022-004.pdf:2.86MB
JAEA-Research-2022-004-appendix(CD-ROM).zip:0.41MB
Methane (CH) seepage to the surface in the early stage of hydrocarbon exploration has attracted increasing attention. Also, detection of CH-rich fluid emission can be applied to reconnaissance surveys for safety management in geological disposal of radioactive waste because high-temperature fluids that come from slab dehydration along a subduction zone are often rich in CH. These fluids likely migrate along faults and fractures. In this study, we employed a portable analyzer that used a wavelength-scanned cavity ring-down spectroscopy (CRDS) with high accuracy (in ppb levels) and short measurement intervals (
1 s). An on-vehicle measurement that employed the CRDS system was performed in the Hongu area in southeast Kii Peninsula, Japan, which included CH-bearing hot springs (Kawayu and Yunomine). The measurement near the hot springs detected a clear CH anomaly (
2 ppm) that exceeded the background concentration. The estimation of CH diffusion in air based on the Gaussian plume model corresponded to the result of the on-vehicle measurement. This study confirmed that the method using the vehicle-mounted CRDS analyzer can help in quickly and easily identifying CH-bearing fluid emissions at the surface. Additionally, directions for use of the analyzer were summarized in this report.
Tetsu, Keiichi*; Takayama, Yusuke; Sawada, Atsushi
JAEA-Research 2022-005, 84 Pages, 2022/08
JAEA-Research-2022-005.pdf:10.32MBJAEA-Research-2022-005-appendix(CD-ROM).zip:35.68MB
Nuclide migration analyses are conducted for the safety assessment in geological disposal system of HLW. Nuclide migration evaluation of fractured host rock mainly uses a model that approximates the fracture with parallel flat plates. However, the actual fractures in the host rock are different from the parallel flat plates, the fractures have complex characteristics such as roughness of fracture surface and the fillings in the fracture. In approximating a fracture model, the methodology development how to set parameter values such as the transmissivity coefficient and the fracture aperture is an issue. One of the issues is to investigate the geometrical features of actual fractures in the host rock. In this study, for the purpose of understanding the geometrical features of fractures including fracture intersection, the internal fracture shape was measured in detail using the method of surface grinding on 50cm scale granodiorite with natural fracture intersection. Thus, the fracture width, fracture aperture, and the shape of the fracture surfaces were obtained. From the obtain data, characteristics such as the average value of the fracture width, the roughness of the fracture surfaces, and the distribution of the fracture aperture were evaluated. As a result, it was confirmed that one of the fractures near the fracture intersection has a particularly large fracture width and fracture aperture as compared with the other part of fractures. Thus, in the granodiorite rock block used in this study, it was inferred that the most permeable path is not the fracture intersection itself, but the particularly large fracture aperture in the vicinity of the fracture intersection.
Kirita, Fumio; Tominaga, Masahiro; Yamazaki, Toshihiko; Seshimo, Kazuyoshi; Uryu, Mitsuru
JAEA-Research 2022-006, 61 Pages, 2023/02
JAEA-Research-2022-006.pdf:6.24MB
Nuclear Fuel Cycle Engineering Laboratories (NCL) has been observing ground motion for a long time. On the border from northern Ibaraki prefecture to Fukushima prefecture, inland crustal earthquakes occur less frequently until the 2011 off the Pacific coast of Tohoku Earthquake (hereinafter referred to as Tohoku Earthquake). After Tohoku Earthquake, aftershocks have become more frequent in this area, and in the Hamadori region of Fukushima earthquake that a remarkable long periodic component was observed in the NCL seismic observation record. Until now there were no such things that long periodic components were observed at the observation points near the epicenter of April 2011 Fukushima earthquake, but it was thought basin structure in deep basement around the NCL affected the propagation process to NCL by reflection survey result. As basement structure of NCL affected the seismic wave propagation process, the seismic wave repeatedly reflects and refracts. For that reason, long periodic components of seismic waves may be possibly amplified. In this study, in order to refine the long periodic ground motion evaluation, using a three dimensional ground structure model (3D model) that can reflect the shape of the deep basement structure around the NCL. When modeling 3D ground structure which has a width of about 80km and a length of about 110km and ranges from the epicenter area of April 2011 Fukushima earthquake to the northern coastal area of Ibaraki prefecture modeled, improved the optimum ground structure model using multiple observation records and performed simulation analysis.
Kureta, Masatoshi; Yamagata, Yoji*; Miyakoshi, Ken*; Mashii, Tatsuya*; Miura, Yoshiaki*; Takahashi, Kazunori*
JAEA-Research 2022-007, 28 Pages, 2022/09
JAEA-Research-2022-007.pdf:8.17MB
To enhance energy separation in a counter-current Ranque-Hilsch vortex tube, a newly designed hollow helical fin was inserted into the hot tube of the vortex tube. In this study, the effect of the fin on the energy separation was investigated using three types of the vortex tube, and then computational fluid dynamics (CFD) simulation has been conducted to understand the experimental results and discuss the flow structure in the vortex tube with the hollow helical fin. As a result, it was found from the experimental data that the fin effectively enhanced energy separation, and that the tube length could be shorten. When the inlet air pressure was 0.5 MPa, the maximum temperature difference from the inlet to the cold exit was 62.2
C. The CFD code employing the Reynolds Stress Model (RSM) turbulence model was used to analyze the fluid dynamics in the vortex tube. As a result, it was confirmed that the temperature, velocity, and pressure distributions changed significantly at the stagnation point, and that the distributions in the tube with the fin were completely different from those without the fin. It was thought that a strong reversing helical vortex flow with small recirculating vortex structure formed between the fin end and the stagnation point on the cold exit side would enhance energy separation in the vortex tube with the hollow helical fin.
Nagai, Takayuki; Okamoto, Yoshihiro; Yamagishi, Hirona*; Kojima, Kazuo*; Inose, Takehiko*; Sato, Seiichi*; Hatakeyama, Kiyoshi*
JAEA-Research 2022-008, 37 Pages, 2022/10
JAEA-Research-2022-008.pdf:5.27MB
The local structure of glass-forming elements and waste elements in borosilicate glasses varies with its chemical composition. In this study, borosilicate glass frit and simulated waste glass samples were prepared and the chemical state regarding boron (B), silicon (Si) and waste elements of iron (Fe), cesium (Cs) were estimated by using XAFS measurement in soft X-ray region. Following results were obtained by XAFS measurements of simulated waste glass surfaces after immersion test to investigate the long chemical stability. (1) As the leaching time of glass samples in immersion test passed, the Cs M
, M-edge XANES spectra disappeared and the Fe L
, L-edge spectra changed. (2) A new compound was formed on the sample surface after the immersion test, and these changes in the surface state were confirmed by Raman spectroscopy. However, it became difficult to obtain a clear B K-edge XANES spectrum by forming a compound on glass surfaces. The Si K-edge XANES spectra of borosilicate glass frits with different NaO content were measured, and following was confirmed. (1) As the NaO concentration increases in borosilicate glass frit, the K-edge peak of Si shifts to the low energy side. (2) The intensity of the Si K-edge peak is maximum when the NaO content in glass frits was about 7wt%.
Kobayashi, Jun; Aizawa, Kosuke; Ezure, Toshiki; Nagasawa, Kazuyoshi*; Kurihara, Akikazu; Tanaka, Masaaki
JAEA-Research 2022-009, 125 Pages, 2023/01
JAEA-Research-2022-009.pdf:29.22MB
The design studies of an advanced loop-type sodium-cooled fast reactor (Advanced- SFR) have been carried out by the Japan Atomic Energy Agency (JAEA). At the core outlet, temperature fluctuations occur due to mixing of hot sodium from the fuel assembly with cold sodium from the control rod channels and radial blanket assembly. These temperature fluctuations may cause high cycle thermal fatigue around a bottom of Upper Internal Structure (UIS) located above the core. Therefore, we conducted a water experiment using a 1/3 scale 60 degree sector model that simulated the upper plenum of the advanced loop-type sodium-cooled reactor. And we proposed some countermeasures against large temperature fluctuations that occur at the bottom of the UIS. In this report, we have summarized that the effect of the countermeasure structure to mitigate the temperature fluctuation generated at the bottom of UIS is confirmed, and the Reynolds number dependency of the countermeasure structure and the characteristics of the temperature fluctuation on the control rod surface.
Misono, Toshiharu; Nakanishi, Takahiro; Sanada, Yukihisa; Shiribiki, Takehiko; Urabe, Yoshimi*; Tsuruta, Tadahiko
JAEA-Research 2022-010, 134 Pages, 2023/02
JAEA-Research-2022-010.pdf:8.45MB
An accident occurred at the TEPCO's Fukushima Daiichi Nuclear Power Station (1F) in 2011 and a large amount of radioactive materials were deposited around the 1F. Japan Atomic Energy Agency has continued to conduct research on the dynamics of radioactive materials after the accident. This report summarizes the results of the survey conducted in FY 2021 on the status of marine monitoring survey on radioactive substances. Furthermore, a seabed topography and sediments distribution survey was conducted in the coastal area off the Mano River from the Ohta River to understand the topography and sediment distribution. Furthermore, in order to evaluate the inflow of radioactive Cs from the river, the horizontal distribution of the radioactive Cs concentration on the surface sediment in front of the rivers was measured. As basic information on the effects of radioactive materials on marine products, the distribution status of fish was investigated. In addition, a demonstration test of water sampling and sediment sampling was conducted using an unmanned observation vessel. From these results, we estimated the distribution and its dynamics of radioactive Cs in the sediments in the front area on the 1F.
Yoshida, Kazuo; Tamaki, Hitoshi; Hiyama, Mina*
JAEA-Research 2022-011, 37 Pages, 2022/12
JAEA-Research-2022-011.pdf:2.88MB
An accident of evaporation to dryness by boiling of high level liquid waste (HLLW) is postulated as one of the severe accidents at a fuel reprocessing plant. Two major mechanisms are expected for fission products (FPs) transfer from liquid to vapor phase. One is non-volatiles FPs transfer in the form of mists to the vapor phase in the tank, the other is volatilization of such as Ruthenium. These FPs transferred to the vapor phase in the tank could be released with water and nitric-acid mixed steam and NO gas flow to the environment. NO is generated from denitration of nitrate fission products during dry out phase. These phenomena occurred in this accident originate from the liquid waste boiling in the tank. It is essential for the risk assessment of this accident to simulate thermo-hydraulic and chemical behaviors in the waste tank quantitatively with a versatile computer program. The SHAWED (
imulation of 
igh-level radio
ctive 
aste 
vaporation and 
ryness) has been developed to realize these requirements. In this report, detailed description of major analytical models is explained based on the features of this accident, and some simulation examples are also described for the use in an actual risk assessment.
Lu, K.; Katsuyama, Jinya; Takamizawa, Hisashi; Li, Y.
JAEA-Research 2022-012, 39 Pages, 2023/02
JAEA-Research-2022-012.pdf:1.72MB
For reactor pressure vessels (RPVs) in the light water reactors, the fracture toughness decreases due to the neutron irradiation embrittlement with operating years. In Japan, to prevent RPVs from a nil-ductile fracture, deterministic fracture mechanics methods in accordance with the codes provided by the Japan Electric Association are performed for assessing the structural integrity of RPVs under the pressurized thermal shock (PTS) events by taking the neutron irradiation embrittlement into account. On the other hand, in recent years, probabilistic methodologies for PTS evaluation are introduced into regulations in the United States and some European countries. For example, in the United States, a PTS screening criterion related to the reference temperature based on the probabilistic method is stipulated. If the screening criterion is not satisfied, it is allowable to perform the evaluation based on the probabilistic method by calculating numerical index such as through-wall crack frequency (TWCF). In addition, the reduction of non-destructive examination extent or extension of examination intervals for RPV welds have been discussed based on the probabilistic method. Here, the probabilistic method is a structural integrity assessment method based on probabilistic fracture mechanics (PFM) which is rational in calculating the failure probability of components by considering uncertainties of various factors related to the aged degradation due to the long-term operation. Based on these backgrounds, we developed a PFM analysis code PASCAL and released a guideline on structural integrity assessment based on PFM by reflecting the latest knowledge and expertise in 2017. Here, the main analysis target was the RPV of pressurized water rector considering neutron irradiation embrittlement and PTS events in the structural integrity assessment of RPVs. The objective of the guideline is that persons who have knowledge on the fracture mechanics can carry out the PFM analyses and
Suzuki, Hideaki*; Takayama, Yusuke; Sato, Hisashi*; Watahiki, Takanori*; Sato, Daisuke*
JAEA-Research 2022-013, 41 Pages, 2023/03
JAEA-Research-2022-013.pdf:3.99MB
It is anticipated that the coupled thermal-hydraulic-mechanical and chemical (THMC) processes will occur, involving an interactive process with radioactive decay heat arising from the vitrified waste, infiltration of groundwater from the host rock into the buffer material, swelling pressure of buffer material due to its saturation and chemical reaction between bentonite and pore-water in the near-field of a geological disposal system for high-level radioactive waste repository. In order to evaluate these phenomena in the near-field, the THMC model has been developed. In this study, For the purpose of evaluating the near-field infiltration behavior in seawater-type groundwater environment, a hydraulic model was set in which the permeability of the buffer material change depending on the salt concentration in the pore-water. In order to evaluate the drying phenomenon of the buffer material due to waste heat, a temperature gradient water transfer model was set in consideration of the dependence of temperature and pore-water saturation. The THMC analysis of the in-situ experiment of engineered barrier system (EBS) experiment at the Horonobe Underground Research Laboratory was carried out. The validity of the model was then checked through comparison with measured data.
Nagai, Takayuki
JAEA-Research 2022-014, 84 Pages, 2023/02
JAEA-Research-2022-014.pdf:22.26MB
Most of the simulated waste glasses used for physical property evaluation are processed into a shape suitable for the measurement method from glass gob obtained by slowly cooling molten glass to room temperature. However, the actual vitrified waste glass material is obtained by cooling and being coagulated the glass drained from the bottom of glass melter into the canister. In this study, Raman spectroscopy was performed on the coagulated surface of molten simulated waste glass in the depth direction to evaluate the state of the Si-O bridging structure near the coagulated glass surface. The Raman spectra measured from the surface to the depth direction near the surface of the glasses produced by several melting and coagulation conditions of molten simulated waste glass cullet in the air atmosphere, and it was confirmed that there were changes in these spectra. On the other hand, the raw material glass cullet and the surface of the glass solidified in argon gas atmosphere showed little change in the spectrum in the depth direction, and the Si-O bridging structure near the glass surface was similar. It was also confirmed that the spectrum change in the depth direction measurement was small for the cut surface of the glass, and that the change in the spectrum for the broken glass fracture surface was also small. For glasses with a large change in Raman spectra in the depth direction near the coagulated surface, the molten glass was cooled from the molten state to room temperature in a muffle furnace with air atmosphere. That is, the magnitude of the spectral change with respect to the depth direction depends on the time from the molten state to coagulation. In order to confirm the reason why the number of bridging oxygen in the Si-O bridging structure is small on the coagulated surface of glass, the XANES spectra of Si-K edge and Ce-L3 edge were measured by XAFS on the coagulated surface and the cutting face. As a result, the Si-K edge peak on the coagulated surface is
Shiwaku, Hideaki; Marushita, Motoharu*
JAEA-Research 2022-015, 39 Pages, 2023/05
JAEA-Research-2022-015.pdf:2.74MB
We designed the hard X-ray undulator beamline BL22XU, which is dedicated to Japan Atomic Energy Research Institute (JAERI) at SPring-8 (now Japan Atomic Energy Agency (JAEA)). BL22XU is used for XAFS (X-ray Absorption Fine Structure) analysis experiments to develop separation and extraction materials for radioactive waste treatment and to elucidate their chemical behavior, magnetic research experiments using a diffractometer, and experiments under extreme conditions using a high-pressure press and a diamond anvil cell. The available X-ray energy range was set from 3 to 70 keV. To design the optics of the beamline, the reflectivity of the mirrors, the diffraction width of the monochromatic crystal, and the absorptance of the Be window were calculated. In addition, ray tracing was performed to optimize the materials for optics, dimensions, and location. The delay time of the ADL (Acoustic Delay Line) was also examined to ensure the safety in the use of radioactive materials. The operation of BL22XU "JAEA Actinide Science I" has already started. By collaborating BL22XU and BL23SU "JAEA Actinide Science II," which uses a soft X-ray undulator as a light source, we solve the problems to promote nuclear sciences. Since the monochromator was upgraded in 2018-2019, initial planning and measured data are documented here again.