Yukihiro Murakami

Thermophysical properties of Th1−xUxO2 pellets prepared by spark plasma sintering technique

Th1−x U x O2 solid solutions were synthesized by solid-state reaction and pelletized using the spark plasma sintering (SPS) technique. Pellets with >90% theoretical density were easily obtained within 40 min of sintering without any additive. The thermal conductivity, Youngs modulus, Debye temperature, Vickers hardness, and heat capacity were systematically investigated, and the values for ThO2 agree with the literature data. The thermal conductivity of Th1−x U x O2 decreased with increasing U content up to x =∼0.5. This tendency corresponds to phonon-point defect scattering theory. The Youngs modulus and Debye temperature linearly decreased with increasing U content. The Debye temperature and standard molar entropy derived from the low-temperature heat capacity agree with the reported values.

Feasibility study for the quantification of total protein content by multiple prompt gamma-ray analysis.

Protein is an important nutrient in foods. The classical nitrogen analysis method is the Kjeldahl technique, which is time-consuming and inconvenient. As a convenient method to quantify protein content in biological samples, the feasibility of application of multiple prompt gamma-ray analysis (MPGA) to the quantification was studied. Results for protein content are reported for several reference materials and prove the method to be reliable.

High wettability of liquid caesium iodine with solid uranium dioxide

In March 2011, the Fukushima Daiichi Nuclear Power Plant accident caused nuclear fuel to melt and the release of high-volatility fission products into the environment. Caesium and iodine caused environmental contamination and public exposure. Certain fission-product behaviours remain unclear. We found experimentally that liquid CsI disperses extremely favourably toward solid UO2, exhibiting a contact angle approaching zero. We further observed the presence of CsI several tens of micrometres below the surface of the solid UO2 sample, which would be caused by the infiltration of pores network by liquid CsI. Thus, volatile fission products released from molten nuclear fuels with complex internal composition and external structure migrate or evaporate to varying extents, depending on the nature of the solid–liquid interface and the fuel material surface, which becomes the pathway for the released fission products. Introducing the concept of the wettability of liquid chemical species of fission products in contact with solid fuels enabled developing accurate behavioural assessments of volatile fission products released by nuclear fuel.

Development of thermodynamic databases in the system U–Zr–Ce–Cs–Fe–B–C–I–O–H for application to simulating phase equilibria in severe nuclear accidents

ABSTRACT In case of severe nuclear accidents involving melt down of nuclear fuels at high temperatures, it is of considerable importance to accurately evaluate the highly-volatizing behavior of fission products (FPs) over multicomponent debris. Particularly, cesium (Cs)- and iodine (I)- bearing chemical species are regarded as notable FPs. In the present work, the authors have generated original thermodynamic databases for the system U–Zr–Ce–Cs–Fe–B–C–I–O–H featuring Cs- as well as I-bearing subsystems, which are contained in oxide, iodide, and metal (including borides and carbides) sub-databases. It has been confirmed that the phase diagrams calculated by the present set of the databases reproduce the corresponding literature data well in various kinds of subsystems of the above multicomponent system. The present set of databases has subsequently been applied to simulate phase equilibria and volatizing behavior of Cs- and I-including species, respectively, in multicomponent debris under specific temperature and atmospheric conditions corresponding to severe nuclear accidents.

Wettability of liquid caesium iodine and boron oxide on yttria-stabilized zirconia

ABSTRACT During the Fukushima Daiichi Nuclear Power Plant accident occurred in 2011, volatile fission products (FPs) such as Cs and I had released and caused environmental contamination and public exposure, respectively. However, the release mechanism of these FPs from fuels under the accident is still not completely understood. In recent years, we have focused on the wettability of liquid FPs against solid fuels, because the interface between the fuel surface and the FPs becomes the migration pathway, which might have large influences on the release behaviour of the FPs. Here, we studied the wettability of liquid CsI and B2O3 on yttria-stabilized zirconia (YSZ) solid surface by the sessile drop test, where YSZ is a simulated material of the fuel. It was revealed that liquid CsI exhibited extremely high wettability against the YSZ surface with the contact angle of nearly zero. This high wettability may act to suppress the FPs release. Furthermore, it was confirmed that the crystal orientation and surface roughness of the YSZ solids have large influences on the wettability of liquid B2O3. The present results contribute for deep understanding of the release behaviour of the volatile FPs from fuels.

Spectroscopic study of 63Ni via cold neutron capture reaction: I. Nuclear structure of 63Ni

The γ-radiation has been investigated for 63 Ni produced by cold neutron capture in an enriched 62 Ni sample. The 315 γ-rays produced were placed in a 63 Ni level scheme, in which 272 placements are new. We determined the excitation energies with 0.2–0.8 keV error and the branching ratios of 62 bound levels in 63 Ni, including 30 new levels. The Q -value of the 62 Ni( n ,γ) 63 Ni reaction amounts to 6837.75±0.18 keV. A large-scale shell-model calculation was performed that included the four single-particle orbits of 0 f 7/2 , 1 p 3/2 , 0 f 5/2 , and 1 p 1/2 , assuming an inert 40 Ca core for negative-parity states, and those of 1 p 3/2 , 0 f 5/2 , 1 p 1/2 , and 0 g 9/2 , assuming a 56 Ni core for positive-parity states. The energies of the low-lying 63 Ni states were successfully reproduced. A mean-field statistical-model calculation was also performed by using a self-consistent interaction between the Hartree–Fock + Bardeen–Cooper–Schrieffer method and the statistical calculation. The calculation result ...