Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Yoshida, Kazuo; Tamaki, Hitoshi; Hiyama, Mina*
JAEA-Research 2023-001, 26 Pages, 2023/05
JAEA-Research-2023-001.pdf:1.61MB
An accident of evaporation to dryness by boiling of high-level radioactive liquid waste (HLLW) is postulated as one of the severe accidents caused by the loss of cooling function at a fuel reprocessing plant. In this case, volatile radioactive materials, such as ruthenium (Ru) are released from the tanks with water and nitric-acid mixed vapor into the atmosphere. Accurate quantitative estimation of released Ru is one of the important issues for risk assessment of those facilities. To resolve this issue, an analytical approach has been developed using computer simulation programs to assess the radioactive source term from those facilities. The proposed approach consists analyses with three computer programs. At first, the simulation of boiling behavior in the HLLW tank is conducted with SHAWED code. Next step, the thermal-hydraulic behavior in the facility building is simulated with MELCOR code based on the results at the first step simulation such as flowed out mixed steam flow rate, temperature and volatilized Ru from the tank. The final analysis step is carried out for estimating amount of released radioactive materials with SCHERN computer code which simulates chemical behaviors of nitric acid, nitrogen oxide and Ru based on the condition also simulated MELCOR. Series of sample simulations of the accident at a hypothetical typical facility are presented with the data transfer between those codes in this report.
Fukaya, Yuji; Maruyama, Takahiro; Goto, Minoru; Ohashi, Hirofumi; Higuchi, Hideaki
JAEA-Research 2023-002, 19 Pages, 2023/06
JAEA-Research-2023-002.pdf:1.48MB
A study on disposal of waste derived from commercial High Temperature Gas-cooled Reactor ("HTGR") has been performed. Because of significant difference between the reprocessing of Light Water Reactor ("LWR") and that of HTGR due to difference in structures of the fuel, adoptability of the laws relating to reprocessing waste disposal, which is enacted for LWR, to HTGR waste should be confirmed. Then, we compared the technologies and waste of reprocessing and evaluated radioactivity concentration in graphite waste by activation and contamination based on whole core burn-up calculation. As a result, it was found that SiC residue waste should be disposed of into a geological repository as 2nd class designated radioactive waste in the Designated Radioactive Waste Final Disposal Act (Act No.117 of 2000), by way of amendment of the applicable order, same as hull and end-piece of LWR, and graphite waste should be shallowly disposed of than geological disposal as 2nd class waste for pit disposal in the Act on the Regulation of Nuclear Source Material, Nuclear Fuel Material and Reactors (Act No.166 of 1957) same as a channel box of LWR.
Koide, Kaoru
JAEA-Research 2023-003, 101 Pages, 2023/06
JAEA-Research-2023-003.pdf:14.08MB
This study developed a geobotanical remote sensing method for estimating high water table areas such as groundwater discharge points using differences in the growth conditions of forest trees induced by moisture supply from groundwater in a humid warm-temperate forest area. A new vegetation index (VI) termed AgbNDVI (Added green band NDVI) was proposed to discriminate the differences. The AgbNDVI proved to be more sensitive to water stress on green vegetation than existing VIs: SAVI and EVI2, and possessed a strong linear correlation with the vegetation fraction. To validate the proposed method, a 23 km
study area was selected in the Tono region of Gifu Prefecture, central Japan. The AgbNDVI values were calculated from atmospheric corrected SPOT HRV data. To correctly detect high VI points, the influence factors on tree growth were identified using the AgbNDVI values, DEM and forest type data; the study area was then divided into 555 segments according to combinations of the influence factors: elevation, slope gradient, slope aspect and forest type. Thresholds for detecting high VI points were defined for each segment based on a histogram of AgbNDVI values. By superimposing the high VI points on topographic and geologic maps, most of the high VI points are clearly located on the concave/convex slopes and near the geologic boundaries prone to groundwater runoff. In addition, field investigations support the correctness of the high VI points, because the growth increments and biomass of trees (
) are greater than at points other than the high VI points, and they are located around known groundwater seeps and in a high water table area. Consequently, the proposed method can be expected to provide useful information for characterizing hydrogeological structures by combining with conventional photo-geological interpretation.
Nagai, Takayuki; Okamoto, Yoshihiro; Yamagishi, Hirona*; Shibata, Daisuke*; Kojima, Kazuo*; Hasegawa, Takehiko*; Sato, Seiichi*; Fukaya, Akane*; Hatakeyama, Kiyoshi*
JAEA-Research 2023-004, 45 Pages, 2023/09
JAEA-Research-2023-004.pdf:6.07MB
The local structure of glass-forming elements and waste elements in borosilicate glasses varies with its chemical composition. In this study, 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. To understand the chemical stability of simulated waste glasses, XANES spectra of B K-edge, Fe L
, L
-edge, and Cs M
, M
-edge were measured on the glass surface exposed to the leachate. As a result, it was found that the glass surface exposed to the leachate was changed and it was difficult to obtain a clear XANES spectrum. From the B K-edge XANES spectra on glass surfaces exposed to the leachate, an increase in three-coordination of B-O (BO) and a decrease in four-coordination of B-O (BO) were observed compared to the glass surfaces before immersion. The XANES spectra of Fe L, L-edge, and Cs M, M-edge show that as the exposure time in the leachate increases, the Cs present on the glass surface dissolves into the leachate. The XANES spectra of Si K-edge were measured on simulated waste glass surfaces before immersion, and it was confirmed that the change in XANES spectra given by NaO concentration had a larger effect than the waste component concentration.
Niwa, Masakazu; Shimada, Koji; Sueoka, Shigeru; Ishihara, Takanori; Ogawa, Hiroki; Hakoiwa, Hiroaki; Watanabe, Tsuyoshi; Nishiyama, Nariaki; Yokoyama, Tatsunori; Ogata, Manabu; et al.
JAEA-Research 2023-005, 78 Pages, 2023/10
JAEA-Research-2023-005.pdf:6.51MB
This annual report documents the progress of research and development (R&D) in the 1st fiscal year of the Japan Atomic Energy Agency 4th Medium- and Long-term Plan (fiscal years 2022-2028) to provide the scientific base for assessing geosphere stability for long-term isolation of high-level radioactive waste. The plan framework is structured into the following categories: (1) Development and systematization of investigation techniques, (2) Development of models for long-term estimation and effective assessment, (3) Development of dating techniques. The current status of R&D activities with previous scientific and technological progress is summarized.
Sugihara, Kenta; Onodera, Naoyuki; Idomura, Yasuhiro; Yamashita, Susumu
JAEA-Research 2023-006, 47 Pages, 2023/10
JAEA-Research-2023-006.pdf:3.28MB
This report presents a new surface capturing method based on the phase field model for gas-liquid two-phase flows simulation. In the conventional phase field model, the interface correction strength parameter was determined from the maximum flow velocity in the computational domain, but because the interface correction was applied uniformly to the entire space, it was also applied to locations that did not require correction. In the new method, the phase field parameter or the intensity of the phase field model is extended to have a spatial distribution, allowing us to set the optimal parameters depending on the local flow velocity fields. We also propose a method to derive the optimal phase field parameter based on systematic parameter scans using error analysis of the interface advection test and bubble rising calculations. Through benchmark tests of gas-liquid two-phase flows, the proposed model is verified, and it is shown that the proposed model has higher accuracy than the conventional phase field model.
Sudo, Ayako; M
sz
ros, B.*; Sato, Takumi; Nagae, Yuji
JAEA-Research 2023-007, 31 Pages, 2023/11
JAEA-Research-2023-007.pdf:3.61MB
For the criticality assessment of fuel debris generated by the accident in Fukushima Daiichi Nuclear Power Station, understanding of the elemental localization in fuel debris is important. Especially, the distribution of Fe and Gd, which may behave as potential neutron absorber materials in the fuel debris, is of particular important from the viewpoint of nuclear criticality safety. To investigate the localization tendency of Gd and Fe in molten core materials during solidification progress, liquefaction/solidification tests on core materials containing UO, ZrO, FeO, GdO, and simulated fission products (MoO, NdO, SrO, and RuO) and concrete (SiO, AlO, and CaO) were performed using cold crucible induction heating technique. During the test, the molten core materials gradually subsided and solidified from the bottom to the top of the melt. Elemental analysis showed that Fe content in the inner region increased approximately up to 3.4 times that in the bottom region. The concentration of Fe into the inner region was observed in all the samples regardless of the initial FeO composition, cooling rates, and phase separation. This suggests that FeO may be concentrated into the low temperature region, where the melt solidified later. In contrast, Gd content in the bottom region increased approximately up to 2.6 times that in the inner region. The concentration of Gd into the bottom region was observed when the initial GdO content was higher than 1 at.%. This suggests that GdO may be concentrated into the earlier solidified region. On the other hand, no significant localization was observed on the simulated fission products.
Nagai, Takayuki; Hasegawa, Takehiko*
JAEA-Research 2023-008, 41 Pages, 2023/12
JAEA-Research-2023-008.pdf:7.52MB
To reduce the risks posed by stored the high-level radioactive liquid waste (HAW), Tokai Vitrification Facility (TVF) is working to produce the HAW into vitrified bodies. With the aim of steady vitrification of HAW in TVF, the vitrification technology section has manufactured a new 3rd melter with an improved bottom structure and is working to verify the performance of this melter. In this study, solidified glass samples were taken from simulated vitrified bodies produced by flowing molten glass during the bottom drain-out test in the operation confirmation of the TVF 3rd melter. And the properties of the surface layer and fracture surface of the vitrified bodies were evaluated by using Raman spectroscopy, synchrotron radiation XAFS measurement, and laser ablation inductively coupled plasma atomic emission spectroscopy (LA ICP-AES) analysis. As a result of measuring the surface layer and fracture surface of the solidified samples produced on an actual scale, a slight difference was confirmed between the properties of the surface layer and those of the fracture surface. Since the chemical composition of these simulated vitrified bodies does not contain platinum group elements, it is expected that the glass structure of solidified glass samples is different from that of the actual vitrified body. However, this sample measuring was a valuable opportunity to evaluate samples produced by using the direct energized joule heating method. The properties of cullet used the operation confirmation of the TVF 3rd melter and the cullet of another production lot were measured and analyzed in the same manner under the measuring conditions of solidified glass samples. As a result, it was confirmed that cullet with different producing histories have different glass structures even with the same chemical composition, and that differences in glass structures remain in the glass samples after melting these cullet.
Hirouchi, Jun; Charnock, T.*
JAEA-Research 2023-009, 47 Pages, 2023/10
JAEA-Research-2023-009.pdf:1.65MB
In Decision making during the recovery phase of a radiation emergency, it is important to provide predicted doses to those implementing the recovery strategy for different options, costs, effort, amount of waste and radioactive concentration of that waste for different options. The European Model for Inhabited Areas (ERMIN) can provide the information. The Waste Estimation Support Tool (WEST), which was developed by the US Environmental Protection Agency, is focussed on estimating the potential volume and radioactivity levels of waste generated by a radiological incident and subsequent decontamination efforts. This study shows an exercise to compare the waste calculation approaches of the ERMIN and WEST in order to inform further development of the ERMIN tool. From the comparison between ERMIN and WEST, following potential improvements in ERMIN have been suggested: 1) Develop a better representation of interiors to allow for decontamination options for walls and ceilings to be evaluated; 2) Subdivide waste endpoints into liquid and solid components; 3) Addition of high-pressure washing and firehosing on concrete surfaces; and 4) Addition of various building coverage ratio for different building environments.
Hokama, Tomonori; Kimura, Masanori; Togawa, Orihiko
JAEA-Research 2023-010, 57 Pages, 2024/02
JAEA-Research-2023-010.pdf:3.29MB
In the case of a nuclear accident, itis planned to perform simple measurement of radioactive iodine radioactivity in the thyroid of residents. The screening level for simple measurement is set at 0.20 
Sv/h as a reference, and it is required to be reviewed appropriately according to the situation such as a nuclear accident. However, a specific method for reviewing the screening level is not shown. When reviewing the screening level, it is important to take into account factors related to the feasibility of simple measurement, such as the judgment level for internal exposure dose of the thyroid and the duration of the measurement period. In this study, we organized the derivation process of 0.20 Sv/h, which was set as the reference for screening level, and considered the feasibility of the reviewing of screening level. We calculated the relationship between the judgment level and the duration of simple measurement for each screening level, ranging from 0.025 to 0.50 Sv/h. Then, the feasibility of the reviewing of screening level was considered. It was found that reviewing the screening level is technically feasible, provided that the judgment level and the duration of simple measurement are appropriate. However, assuming that simple measurement will be performed in an actual nuclear accident, we assessed that it would be reasonable to review the screening level within the range of 0.030 to 0.20 Sv/h, in a situation where the duration of simple measurement must be extended.
Togawa, Orihiko; Hokama, Tomonori; Hiraoka, Hirokazu; Saito, Shota
JAEA-Research 2023-011, 78 Pages, 2024/03
JAEA-Research-2023-011.pdf:2.09MB
When radionuclides are released into the atmospheric environment at a nuclear emergency, protective measures such as evacuation and temporal relocation are carried out using motor vehicles such as private cars and buses to reduce radiation exposure to residents. To confirm conditions of contamination for the evacuated/relocated residents and the used motor vehicles, contamination inspection is conducted in the middle of the route from border areas of Nuclear Emergency Planning Zone to evacuation shelters. In the present inspection in Japan, a value of OIL4 = 40,000 cpm is used as decontamination criteria. For the details and derivation methods of the value, however, no official documents are found which give systematically detailed descriptions and explanation. It is also recognized that even few experts on nuclear emergencies can explain these subjects in detail as a whole. In order to explain scientifically and technically the OIL4 value of decontamination criteria used in contamination inspection in Japan, this report aims at investigating and estimating the deviation methods of OIL4, and examining and considering these results. To achieve the objectives, we show the bases for decontamination criteria, and investigate and estimate the derivation methods for limits of a surface contamination density corresponding to the generic criteria for each exposure pathway. Moreover, we give the OIL4 value some consideration and suggestions from a viewpoint of positioning and feature of OIL4 in Japan, and cautionary points at revising the value.
Nakanishi, Chika*; Ota, Masakazu; Hirouchi, Jun; Takahara, Shogo
JAEA-Research 2023-012, 29 Pages, 2024/02
JAEA-Research-2023-012.pdf:6.05MB
The OSCAAR program is a probabilistic risk assessment program for reactor accidents developed by Japan Atomic Energy Agency. To improve the model included in the OSCAAR program, which is about long-term exposure caused by the resuspension of radioactive materials deposited on soil surfaces, we calculated resuspension factors for Cs-137. The one- dimensional atmosphere-SOiL-VEGetation model, SOLVEG-R was utilized to compute resuspension factor. The wind velocity was kept constant in this study since it significantly affects particle resuspension behavior. Our calculations indicate that wind velocities below 6 m s
resulted in little variation in the annual mean resuspension factor at a height of 1 m. However, as wind velocities increased above 6 m s, the resuspension factor significantly increased. The resuspension factors ranged from 10
to 10
m for wind velocities ranging from 1 m s to 7 m s.
Hirouchi, Jun; Charnock, T.*
JAEA-Research 2023-013, 57 Pages, 2023/12
JAEA-Research-2023-013.pdf:2.28MB
The recent ICRP publication of dose coefficients for external exposures to environmental sources, ICRP Publ. 144, provided an opportunity to evaluate and improve the dose coefficients and dose conversion factors used by the European Model for Inhabited Areas (ERMIN). ERMIN contains several idealised built environments with the "open area" environment being very similar to the ICRP Publ. 144 "planar sources on and within the ground" situation. The study compares the values given in ERMIN with those derived from ICRP Publ. 144 for the external gamma dose coefficients, the dose conversion factors to convert from air kerma to effective dose and the beta dose coefficients. This study has enabled ERMIN to be improved in several ways. A new "open area" environment was developed based on ICRP Publ. 144. New dose conversion factors were developed moving from a single radionuclide specific one to nine that account for depth in the soil. The dose coefficients for Cs-137, Pr-143, Pr-144, Ru-106, Sr-89, Sr-90, Y-90, and Y-91 were significantly different between ERMIN and ICRP Publ. 144 because bremsstrahlung was not considered in ERMIN. 144, dose coefficients considering bremsstrahlung were developed using correction coefficients based on ICRP Publ. 144.