Integrated thermal power measurement in the modified STACY for the performance inspections

Araki, Shohei; Aizawa, Eiju; Murakami, Takahiko; Arakaki, Yu; Tada, Yuta; Kamikawa, Yutaka; Hasegawa, Kenta; Yoshikawa, Tomoki; Sumiya, Masato; Seki, Masakazu; et al.

Annals of Nuclear Energy, 217, p.111323_1 - 111323_8, 2025/07

https://doi.org/10.1016/j.anucene.2025.111323

JAEA has modified the STACY from a homogeneous system using solution fuel to a heterogeneous system using fuel rods in order to obtain criticality characteristics of fuel debris. The modification of the STACY was completed in December 2023. A series of performance inspections were conducted for the start of experimental operations. A new thermal power calibration is required for the performance inspections in order to operate at less than 200 W, which is the permitted thermal power. However, the thermal power measurement method and calibration data used in the former STACY is no longer available due to the modification of the modified STACY. We measured the thermal power of the STACY using the activation method that was improved to adapt to the measurement condition and calibrated the power meter system. Since the positions where activation foils could be installed were very limited, the thermal power was evaluated using numerical calculations supplemented by experimental data. Neutron flux data at the positions of the activation foil was measured by the activation method. Neutron distribution in the core was calculated by the Monte Carlo code MVP. A response function of the activation foil was calculated using the PHITS. The uncertainty of the thermal power measurement was conservatively estimated to be about 15%. Four operations were conducted for the thermal power measurement. The power meter was calibrated by using three operational data and tested with the one operational data. It was found that the indicated value of the meter adjusted by the STACY before the modification work would tend to overestimate the actual output by about 40%. In addition, the current calibration was able to calibrate the meter to within 3% accuracy.

Non-condensable gas accumulation and distribution due to condensation in the CIGMA Facility; Implications for Fukushima Daiichi Unit 3 (1F3)

Hamdani, A.; Soma, Shu; Abe, Satoshi; Shibamoto, Yasuteru

Progress in Nuclear Energy, 185, p.105771_1 - 105771_13, 2025/07

https://doi.org/10.1016/j.pnucene.2025.105771

Numerical analysis of a potential Reactor Pressure Vessel (RPV) boundary failure mechanism in Fukushima Daiichi Nuclear Power Station Unit-2

Li, X.; Yamaji, Akifumi*; Sato, Ikken*; Yamashita, Takuya

Annals of Nuclear Energy, 214, p.111217_1 - 111217_13, 2025/05

https://doi.org/10.1016/j.anucene.2025.111217

Role of solute hydrogen on mechanical property enhancement in Fe-24Cr-19Ni austenitic steel; An neutron diffraction study

Ito, Tatsuya; Ogawa, Yuhei*; Gong, W.; Mao, W.*; Kawasaki, Takuro; Okada, Kazuho*; Shibata, Akinobu*; Harjo, S.

Acta Materialia, 287, p.120767_1 - 120767_16, 2025/04

https://doi.org/10.1016/j.actamat.2025.120767

In situ neutron diffraction study of strain evolution and load partitioning during elevated temperature tensile test in HIP-Treated electron beam powder bed fusion manufactured Ti-6Al-4V

Pandian, K.*; Neikter, M.*; Ekh, M.*; Harjo, S.; Kawasaki, Takuro; Woracek, R.*; Hansson, T.*; Pederson, R.*

JOM, 77(4), p.1803 - 1815, 2025/04

https://doi.org/10.1007/s11837-025-07128-1

Crystal structures of ReO under hydrostatic pressure; A Combined neutron, X-ray, Raman, and first-principles calculation study

Efthimiopoulos, I.*; Klotz, S.*; Kunc, K.*; Baptiste, B.*; Chauvigne, P.*; Hattori, Takanori

Physical Review B, 111(13), p.134103_1 - 134103_13, 2025/04

https://doi.org/10.1103/PhysRevB.111.134103

We present a comprehensive study of the high pressure behaviour of ReO using X-ray and neutron diffraction, Raman scattering and first-principles calculations to 15 GPa. We show that the ambient pressure structure converts at 0.7 GPa in a continuous phase transition directly to a cubic phase with space group and rhombohedral structures in this pressure range are an artifact due to an alteration of the sample by high-flux synchrotron X-ray radiation. The structural pressure dependence of the O samples are presented. The data shed light onto the unusual transition and densification mechanism due to progressive tilting of essentially rigid ReO octahedra.

Development of a compact detector for measurement of alpha contamination in piping

Morishita, Yuki; Peschet, L.; Yamada, Tsutomu*; Nakasone, Takamasa*; Kanno, Marina*; Sasaki, Miyuki; Sanada, Yukihisa; Torii, Tatsuo*

Radiation Measurements, 183, p.107414_1 - 107414_6, 2025/04

https://doi.org/10.1016/j.radmeas.2025.107414

In the decommissioning nuclear facilities, it is crucial to inspect piping for contamination to prevent worker exposure to alpha-emitting nuclides. Traditional methods using gamma rays and neutrons are inadequate for detecting small amounts of alpha nuclides due to the short range (approximately 4 cm) of alpha particles in air. To address this, we developed a compact detector capable of distinguishing between alpha particles for direct measurement within pipes. This detector, comprising a ZnS(Ag) scintillator for alpha particles and a plastic scintillator for beta particles (gamma rays), was coupled to a small photomultiplier tube. The system demonstrated high accuracy in differentiating between alpha and beta radiation through pulse shape discrimination (PSD). Monte Carlo simulations and empirical measurements confirmed the detector's effectiveness, achieving a 51.3% detection efficiency for alpha particles with negligible sensitivity to beta and gamma radiation. This innovation presents a significant advancement for direct alpha contamination measurement in environments with high beta and gamma backgrounds, such as the Fukushima Daiichi Nuclear Power Plant decommissioning site.

Calculation method improvement of the original one-dimensional code GENGTC

Fuyushima, Takumi; Sayato, Natsuki; Otsuka, Kaoru; Endo, Yasuichi; Tobita, Masahiro*; Takemoto, Noriyuki

JAEA-Testing 2024-008, 38 Pages, 2025/03

JAEA-Testing-2024-008.pdf:2.37MB

In Japan Materials Testing Reactor (JMTR), irradiation tests had been conducted by loading specimens into capsules for irradiating fuels and materials. The thermal design calculation of capsules is significant to irradiate various types of specimens at the target temperature. The decommissioning plan of JMTR was approved in March 2021, and the Department of Waste Management and Decommissioning Technology Development is currently working on irradiation plans by foreign testing reactors as an alternative for JMTR. A one-dimensional thermal calculation code "GENGTC", which was developed at the Oak Ridge National Laboratory in U.S., is used for capsule design and irradiation tests. GENGTC has been repeatedly improved as improvements of computer performance, but there were some defects in calculation function. Therefore, we investigated the cause of the problem and changed the program from the currently used FORTRAN77 language program to a Visual Basic language program that uses the macro calculation function of Excel. In addition, the program was improved to make it easier to use the calculation code.

Experimental verification of operational conditions for the 3rd glass melter in TVF

Asahi, Yoshimitsu; Fukuda, Shigeki; Shiramizu, Daiki; Miyata, Koshi; Tone, Masaya; Katsuoka, Nanako; Maeda, Yuta; Aoyama, Yusuke; Niitsuma, Koichi; Kobayashi, Hidekazu; et al.

JAEA-Technology 2024-024, 271 Pages, 2025/03

JAEA-Technology-2024-024.pdf:33.98MB
JAEA-Technology-2024-024-hyperlink.zip:31.96MB

A glass melter for the vitrification process of highly active liquid waste in the Tokai Reprocessing Plant, TVF's 3rd melter, was built, and the glass of 18 vitrified waste canisters in weight was melted and poured through a cold test operation. The molten glass surface was covered by a cold cap from feeding fiberglass cartridges saturated with non-radioactive simulant liquid waste as raw material, whose components are equivalent to actual waste. Differences in inherent characteristics of the thermal behavior between the 2nd and the 3rd melter due to the difference in design were considered to establish the procedure to control the new melter. The melter's condition was stabilized at a higher glass temperature and the cooling of 1 kW less in each of the two main electrodes, compared to the 2nd one. Under 39 kW joule heating of the main electrodes with 26 Nm3/h coolant flow rate, it showed the capability to finish heating the bottom furnace in 5 hours before pouring, 2 hours shorter than the 2nd melter. Measurements of the temperature distributions in molten glass and casing surface yielded data that is efficient for developing a simulation model. After Platinum Group Elements (PGE) concentration saturates in the molten glass, feeding raw material and discharging glass were suspended to examine a holding state, indicating PGE settling could retard. During the holding test, observation of the melting process of the cold cap declared that the surface was covered by a thin layer with almost non-fluidity. It will be a reason for choosing the no-slip condition of a fluid calculation, even in the hot-top condition. The investigation of PGE discharging behavior by analyzing the elemental composition of poured glass showed the accumulated PGE amount in the 3rd melter is small compared to the 2nd melter. Inspection of the melter inside after draining out concluded that there were neither significant residual glass nor refractory fragments.

Background aerial monitoring and UAV radiation monitoring technology development for emergency response and preparedness in fiscal year 2023 (Contract research)

Futemma, Akira; Sanada, Yukihisa; Nakama, Shigeo; Sasaki, Miyuki; Ochi, Kotaro; Sawahata, Yoshiro*; Kawasaki, Yoshiharu*; Iwai, Takeyuki*; Hiraga, Shogo*; Haginoya, Masashi*; et al.

JAEA-Technology 2024-022, 170 Pages, 2025/03

JAEA-Technology-2024-022.pdf:15.09MB

On March 11, 2011, the 2011 off the Pacific coast of Tohoku Earthquake caused a tsunami that led to the Fukushima Daiichi Nuclear Power Station accident, releasing radioactive material into the environment. Since then, Aerial Radiation Monitoring (ARM) using manned helicopters has been employed to measure radiation distribution. As a commissioned project from the Nuclear Regulation Authority, the Japan Atomic Energy Agency (JAEA) utilizes this technology for emergency monitoring during nuclear facility accidents, aiming to provide prompt results by pre-arranging information on background radiation, topography, and control airspaces around nuclear power plants nationwide. In fiscal year 2023, the commissioned project included conducting ARM around the Sendai Nuclear Power Station and preparing related information. To enhance effectiveness during emergencies, ARM and the first domestic training flight of Unmanned Aerial Vehicles (UAVs) were conducted during the FY2023 Nuclear Energy Disaster Prevention Drill. Furthermore, UAVs radiation monitoring technology was advanced by selecting UAVs and investigating their performance. This report summarizes the results and technical issues identified providing insights to improve emergency preparedness.