Research plan on geosphere stability for long-term isolation of radioactive waste (Scientific program for fiscal year 2023)

Niwa, Masakazu; Shimada, Koji; Sueoka, Shigeru; Fujita, Natsuko; Yokoyama, Tatsunori; Ogita, Yasuhiro; Fukuda, Shoma; Nakajima, Toru; Kagami, Saya; Ogata, Manabu; et al.

JAEA-Review 2023-017, 27 Pages, 2023/10

JAEA-Review-2023-017.pdf:0.94MB

This report is a plan of research and development (R&D) on geosphere stability for long-term isolation of high-level radioactive waste (HLW) in Japan Atomic Energy Agency (JAEA), in fiscal year 2023. The objectives and contents in fiscal year 2023 are described in detail based on the JAEA 4th Medium- and Long-term Plan (fiscal years 2022-2028). In addition, the background of this research is described from the necessity and the significance for site investigation and safety assessment, and the past progress. 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.

Measurement of angular dependent neutron production from thick target bombarded with 140-MeV protons

Iwamoto, Yosuke; Satoh, Daiki; Hagiwara, Masayuki*; Iwase, Hiroshi*; Kirihara, Yoichi*; Yashima, Hiroshi*; Nakane, Yoshihiro; Nakashima, Hiroshi; Nakamura, Takashi*; Tamii, Atsushi*; et al.

Nuclear Technology, 168(2), p.340 - 344, 2009/11

https://doi.org/10.13182/NT09-A9205

It is important to calculate neutron production from thick targets at forward angle near 0 degree and backward angle near 180 degree for the shielding design of proton accelerator facilities, and the accuracy should be determined by experimental data. There are, however, few experimental data near 0 degree, and no data near 180 degree in the energy region above 100 MeV. Neutron energy spectra at 0, 90 and 180 degrees produced from thick graphite and iron targets by 140 MeV protons were measured. It was found that the calculation with JENDL-HE was more suitable for the shielding design of proton accelerator facilities in the forward direction.

Effect of high-velocity friction on ESR signal in quartz

Tanaka, Kiriha*; Muto, Jun*; Takahashi, Miki*; Oka, Toshitaka; Nagahama, Hiroyuki*

no journal, , 

A fault dating using electron spin resonance (ESR) is a method to estimate the age of the last seismic fault activity. This method assumes that natural radiation-induced ESR intensity, which is proportional to trapped charge concentration in the interseismic period, was annihilated by fracture, stress, and frictional heating during the fault slip. However, the sensitivity of ESR can be reduced by high-dielectric materials, we have re-examined the zeroing by seismic fault slips near the surface by performing high-velocity friction experiments and ESR measurements for simulated-fault gouges. Although the decreasing effect of frictional heating on the E centre is expected, grain fracture affected the centre enough to surpass it, resulting in the increase in the centre with displacements. On the contrary to previous consensus, this implies that seismic fault slips near the surface can increase the E centre due to grain fracture.

Supporting the surface charging mechanism of seismic-electromagnetic phenomena by the direct measurements of the electron and hole trapping centers

Tanaka, Kiriha*; Nagahama, Hiroyuki*; Muto, Jun*; Oka, Toshitaka; Yabe, Yasuo*

no journal, , 

The mechanisms of the seismic-electromagnetic phenomena attracted as precursors of short-term earthquake forecast have been suggested, however, it is still incompletely understood. Our results showed that the fracture by fault motions could produce the surface charges on the fault. It proves that the electromagnetic abnormalities by the fault motions may also be observed through the surface charging mechanism. Therefore, our study supports that the surface charging mechanism is plausible.

Dependencies of ESR intensities for trapped charges in quartz on depth from outcrop surface

Tanaka, Kiriha; Ogata, Manabu; Tsukahara, Yuzuko; Nishiyama, Nariaki

no journal, , 

Electron spin resonance (ESR) dating of a quaternary sediment is a technology with the potential to directly determine the age of the last sedimentation. This method assumes that charges trapped in defects (trapped charges) in quartz in a sediment have been released by sunlight exposure (optically bleaching) during processes of erosion, transportation, and/or sedimentation, then trapped charges are accumulated by natural radiation during a process of burial. A sediment which has exposed to sunlight during a burial process must avoid being used for ESR dating, because its depositional age is underestimated. Thus, sediment under cm depth from an outcrop surface in strike direction, which is not exposed to sunlight, is conventionally used for ESR dating. However, the correct depth to be remove is not clearly demonstrated and unchecked each time. Therefore, it is crucial to reveal the effect of sunlight exposure on trapped charges detected by ESR measurements in a surface layer of an outcrop. In this study, silty aeolian loam and silt to fine marine sand samples were collected with poly vinyl chloride pipes with a diameter of 4 cm and a length of 35 cm from a terrace deposit located at the altitude of 30-33 m in Nanao-shi, Ishikawa prefecture. The loam and marine sand samples were cut into three and seven pieces, respectively. Quartz grains isolated by chemical processing were used for ESR measurements. For the loam sample, ESR intensity for the E' center remained constant regardless of depth in the strike direction. Whereas ESR intensities for the Al and Ti center at depths of 20 and 30 cm were greater than that at a depth of 10 cm, respectively. For the marine sand sample, ESR intensities for all the trapped charges at depths of 3-14, and 33 cm were approximately equal, whereas the intensities were greater than those at depth of 20-30 cm.

Potential for ESR signal zeroing of the E' center by experimental fault slips

Tanaka, Kiriha; Ohashi, Kiyokazu*; Muto, Jun*; Oka, Toshitaka

no journal, , 

Electron spin resonance (ESR) dating of a fault assumes that charge trapping centers in quartz in a fault material have been completely annihilated by the seismic fault slip (ESR signal zeroing). There is little understanding of the relationship between the signal zeroing and fault parameters. The previous high-velocity friction (HVF) experiments have implied that the E' center in quartz could be correlated with frictional power density and begin to decrease at a power density of 0.60.9 MW/m. However, the data was lacking to confirm the signal zeroing at higher power density. We performed HVF experiments for simulated quartz gouges with a slip rate of 1 m/s, a displacement of 10 m, and normal stresses of 1.02.5 MPa. ESR measurements were conducted for gouges before and after experiments. The peak-to-peak height of the E' center calibrated by that of the standard material was calculated as the ESR intensity (ESR intensity ratio) of the E' center. The ESR intensity ratio of the E' center decreased with increasing frictional power density of 0.961.4 MW/m. The maximum temperatures near the sliding surface were 260C at 0.96 MW/m, 600C at 1.0 MW/m, and 480C at 1.6 MW/m. The E' center is thermally unstable at 300C and more unstable at higher temperatures. Hence, the ESR intensity ratio might decrease due to larger frictional heating with increasing power density. Comparing our results with those in the previous study, the ESR intensity ratio clearly decreased with increasing power densities of 0.61.4 MW/m. HVF experiments mimic seismic fault slips of earthquakes with a moment magnitude of 89 at shallow depths of 100 m. Seismic fault slip of an earthquake at a depth of at least one hundred meters under the earth's surface can be required for ESR signal zeroing of the E' center.

Host rock thermal properties on behavior of trapped charges during coseismic fault slip

Tanaka, Kiriha; Ohashi, Kiyokazu*; Muto, Jun*; Oka, Toshitaka

no journal, , 

Electron spin resonance (ESR) dating of a fault is a developing method to estimate the age of the last seismic slip assuming that trapped charges in minerals were completely released during the last coseismic slip (zeroing). However, behaviors of the trapped charges during coseismic slips are poorly understood. According to previous studies, frictional heating is a key factor in zeroing. This study investigated the effect of the rock thermal properties linked to frictional heating on the behaviors of the trapped charges during coseismic slips. To investigate the effect of the rock properties, two series of high-velocity friction (HVF) experiments were conducted on artificial quartz grains using mullite (HVF I) and titanium alloy (HVF II) host cylinders. The experiments were designed to reproduce coseismic slips in different levels of frictional power density (FPD) in HVF I and II. ESR measurements and grain characterizations were conducted for the initial quartz grains and simulated-gouges to investigate the change in the number of a fundamental trapped charge and its associated mechanism. The trapped charge was produced in all of the HVF experiments. Although the FPD ranges differed between HVF I and II, the productions decreased monotonically to a similar value with increasing FPD. On the other hand, the productions decreased with increasing the maximum temperature observed on a gouge regardless of the FPD ranges. Thermal conductivities of the mullite and titanium alloy are 4.2 and 7.5 W/m/K, respectively. Thus, mullite retains heat more easily than titanium alloy. It indicates that frictional heating could more effectively release the trapped charges in HVF I than in HVF II, resulting in the production decreases described above. This study suggests that thermal properties of a host rock can be a key factor in controlling the effect of frictional heating on trapped charges, namely, zeroing.