Oxygen potential and self-irradiation effects on fuel temperature in Am-MOX

Ikusawa, Yoshihisa; Hirooka, Shun; Uno, Masayoshi*

2018 GIF Symposium Proceedings (Internet), p.321 - 327, 2020/05

Research and development of Minor actinides (MAs) bearing MOX fuel for fast reactor has been proceeding from the viewpoint of reducing radioactive waste. In order to develop, MA bearing MOX, it is indispensable to clarify the influence of MA addition on irradiation behavior. The addition of Americium (Am) to MOX affects vapor pressure and thermal conductivity, which are important properties from the perspective of evaluating fuel temperature. This is because vapor pressure affects fuel restructuring, and thermal conductivity affects fuel temperature distribution. Focusing on these physical properties, this study evaluates the influence of Am on fuel temperature using irradiation behavior analysis code to contribute to the development of MA-bearing MOX fuel. An increase in Am content decreases the thermal conductivity and increases the oxygen potential of oxide fuel. Because vapor pressure increases with increasing Am content, pore migration is accelerated, and the central void diameter increases with increasing Am content. As a result, after formation of the central void, the influence of Am content on the fuel center temperature is mild. Alpha particles generated by radioactive decay of transuranium elements cause lattice defects in the oxide fuel pellets. It is well known that this phenomenon, which is called self-irradiation, affects thermal conductivity. Since americium is the typical alpha radioactive nucleus, to evaluate fuel temperature of Am-MOX is necessary to take account of the influence of self-irradiation damage on thermal conductivity. Self-irradiation decreases thermal conductivity, and as the Am content increases, the rate of decrease in thermal conductivity is accelerated. Because it recovers with temperature rise, the decrease in thermal conductivity due to self-irradiation damage has very little effect on fuel center temperature. These results suggest that Am-MOX fuel could be irradiated under the same conditions as conventional MOX fuel.

Self-radiation effects and glassy nature of magnetic transition in AmO revealed by O-NMR

Tokunaga, Yo; Nishi, Tsuyoshi; Nakada, Masami; Ito, Akinori*; Sakai, Hironori; Kambe, Shinsaku; Homma, Yoshiya*; Honda, Fuminori*; Aoki, Dai*; Walstedt, R. E.*

Physical Review B, 89(21), p.214416_1 - 214416_8, 2014/06

https://doi.org/10.1103/PhysRevB.89.214416

The magnetic phase transition near K in AmO has been investigated microscopically by means of O NMR. To avoid complexities arising from sample aging associated with the alpha decay of Am, all measurements have been performed within 40 days after sample synthesis. Even during such a short period, however, a rapid change of NMR line shape has been observed at 1.5 K, suggesting that the ground state of AmO is very sensitive to disorder. We have also confirmed the loss of O NMR signal intensity over a wide temperature range below , and more than half of oxygen nuclei are undetectable at 1.5 K. This behavior reveals the persistence of slow and distributed spin fluctuations down to temperatures well below . In the paramagnetic state, strong NMR line broadening and spatially inhomogeneous spin fluctuations have been observed. The results are all indicative of short-range, spin-glass-like character for the magnetic transition in this system.

Evaluation of dose contribution of self-irradiation and cosmic-ray to glass dosemeter for environmental radiation measurement

Sakamoto, Ryuichi; Nagaoka, Toshi; Saito, Kimiaki; Tsutsumi, Masahiro; Moriuchi, Shigeru

JAERI-M 94-060, 21 Pages, 1994/03

JAERI-M-94-060.pdf:0.98MB

no abstracts in English

Self-radiation effects on the electronic ground state of AmO studied by O-NMR

Tokunaga, Yo; Nishi, Tsuyoshi; Nakada, Masami; Ito, Akinori*; Sakai, Hironori; Kambe, Shinsaku; Homma, Yoshiya*; Honda, Fuminori*; Aoki, Dai*; Walstedt, R. E.*

no journal, , 

We will present the result of our recent NMR study performed to elucidate the origin of magnetic phase transition near K in AmO. To avoid complexities arising from sample aging associated with the alpha decay of Am, all measurements have been performed within 40 days after sample synthesis. Even during such a short period, however, a rapid change of NMR line shape has been observed at 1.5 K, suggesting that the ground state of AmO is very sensitive to disorder. We have also confirmed the loss of O NMR signal intensity over a wide temperature range below , and more than half of oxygen nuclei are undetectable at 1.5 K. This behavior reveals the persistence of slow and distributed spin fluctuations down to temperatures well below . The results are all indicative of short-range, spin-glass-like character for the magnetic transition in this system.

Evaluation and formulation of MOX fuel thermal conductivity

Ikusawa, Yoshihisa; Morimoto, Kyoichi; Kato, Masato; Uno, Masayoshi*

no journal, , 

The thermal conductivity of oxide fuel is one of the most important properties, since it affects temperature distribution in fuel during irradiation. It is well known that thermal conductivity strongly depends on the oxide-metal ratio (O/M) and burnup of the oxide fuel, and there have been many studies of UO fuel. On the other hand, the thermal conductivity of uranium-and-plutonium-mixed oxide (MOX) fuel is more complex than UO fuel because it is influenced by plutonium content and alpha damage in addition to the aforementioned factors. We have measured the thermal conductivity of various MOX fuels, such as stored samples, irradiated samples, and, several different plutonium content samples. In addition, plutonium content, alpha damage, and burnup effects on MOX fuel thermal conductivity were investigated from the result of these measurements.

R&D on nitride fuel cycle for MA transmutation to enhance safety and economy, 14; Dimensional recovery of He-accumulated nitride pellet containing Cm by annealing

Takano, Masahide; Takaki, Seiya

no journal, , 

To clarify the influence of high temperature He gas release on the MA transmutation fuel behavior, annealing experiments on a Cm-bearing nitride pellet were carried out after two years of storage at room temperature, and the results were compared with those on the Cm-bearing dioxide. Just before the annealing, the nitride pellet showed the large expansion value of 1.1%, which suggests that vacancies in grains formed voids at room temperature. During the annealing experiments, the gas swelling of the nitride pellet due to He release above 800C was relatively slight. From the microstructure images, smaller grains and higher open-porosity of the nitride pellet resulted in the slight gas swelling. After the annealing at 1300C, the nitride pellet still had expansion value of 0.6%, that should be taken into account when designing the pellet-cladding gap.