Thermal property change of MOX and UO(2) irradiated up to high burnup of 74 GWd/t

Thermal property is important because it controls fuel behavior under irradiation. The thermal property change at high burnup of more than 70 GWd/t is examined. Two kinds of MOX fuel rods, which were fabricated by MIMAS and SBR methods, and one referenced UO(2) fuel rod were used in the experiment....

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Bibliographic Details
Published in:Journal of nuclear materials 2013-01, Vol.440 (1-3), p.515-523
Main Authors: Nakae, Nobuo, Akiyama, Hidetoshi, Miura, Hiromichi, Baba, Toshikazu, Kamimura, Katsuichiro, Kurematsu, Shigeru, Kosaka, Yuji, Yoshino, Aya, Kitagawa, Takaaki
Format: Article
Language:English
Subjects:
Fuels
Heat transfer
Irradiation
MOX
Rods
Scattering
Thermal conductivity
Thermal properties
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Summary:Thermal property is important because it controls fuel behavior under irradiation. The thermal property change at high burnup of more than 70 GWd/t is examined. Two kinds of MOX fuel rods, which were fabricated by MIMAS and SBR methods, and one referenced UO(2) fuel rod were used in the experiment. These rods were taken from the pre-irradiated rods (IFA 609/626, of which irradiation test were carried out by Japanese PWR group) and re-fabricated and re-irradiated in HBWR as IFA 702 by JNES. The specification of fuel corresponds to that of 17 x 17 PWR type fuel and the axially averaged linear heat rates (LHR) of MOX rods are 25 kW/m (BOL of IFA 702) and 20 kW/m (EOL of IFA 702). The axial peak burnups achieved are about 74 GWd/t for both of MOX and UO(2). Center-line temperature and plenum gas pressure were measured in situ during irradiation. The measured centerline temperature is plotted against LHR at the position where thermocouples are fixed. The slopes of MOX are corresponded to each other, but that of UO(2) is higher than those of MOX. This implies that the thermal conductivity of MOX is higher than that of UO(2) at high burnup under the condition that the pellet-cladding gap is closed during irradiation. Gap closure is confirmed by the metallography of the postirradiation examinations. It is understood that thermal conductivity of MOX is lower than that of UO(2) before irradiation since phonon scattering with plutonium in MOX becomes remarkable. A phonon scattering with plutonium decreases in MOX when burnup proceeds. Thus, thermal conductivity of MOX becomes close to that of UO(2). A reverse phenomenon is observed at high burnup region. The phonon scattering with fission products such as Nd and Zr causes a degradation of thermal conductivity of burnt fuel. It might be speculated that this scattering effect causes the phenomenon and the mechanism is discussed here.
ISSN:0022-3115