Contact Author:
Dr. GEUN IL PARK
ngipark@kaeri.re.kr
P:82-42-868-2290
F:82-42-868-8824
(150-1 Duckjin-Dong), 1045 Daedeokdaero, Yuseong
Daejeon, 305-353
Korea
Fabrication Characteristics of Large Grain DUPIC Pellet using SIMFUEL
Jung Won LEE (KAERI-Korea), Jae Won LEE (KAERI-Korea), Myung Seung YANG (KAERI-Korea), Kee Chan SONG (KAERI-Korea)
Fabrication characteristics to improve the density and grain size of DUPIC fuel with relation to fuel performance is generally carried out using SIMFUEL (SIMulated high burnup FUEL) as a surrogate for actual spent PWR fuel due to the high radioactivity of spent fuel pellet. SIMFUEL with burn-up of 35,000 MWd/tU and 60,000 MWd/tU were used to investigate the influence of fission products contents as impurity on the density and grain size of simulated DUPIC pellet. The fuel powder for fabrication of simulated DUPIC pellet was prepared by attrition milling of the powder obtained by OREOX (Oxidation and Reduction of Oxide fuels) treatment of SIMFUEL pellet. The powder mixture with 0.2 wt.% acrawax powder as a lubricant was pressed into green pellets at 300 MPa and sintered at 1,700oC for 6 hours in an atmosphere of Ar-4%H2. The density of sintered pellets regardless of composition of SIMFUEL were higher than 95% TD (theoretical density) and the average grain size of sintered pellets 7 µm for 35,000 MWd/tU SIMFUEL and 4 µm for 60,000 MWd/tU SIMFUEL, respectively. In order to investigate the influence of impurity groups, the results of pellet fabrication after powder processing of dissolved oxides (SS)-UO2 pellet, oxide precipitates (OP)-UO2 pellet, and metallic precipitates (MP)-UO2 pellet showed that the grain size of pellets were decreased in the order of SS-UO2, OP-UO2, and MP-UO2. Thus, additives of TiO2 and Nb2O5 were used to obtain large grain pellet. The addition of 0.1 wt.% TiO2 and 0.1 wt% Nb2O5 powder for 35,000 MWd/tU SIMFUEL increased significantly the density and grain size of pellet, the average grain size of pellet was 18 µm for TiO2 additions and 15 µm for Nb2O5 addition. For 60,000 MWd/tU SIMFUEL, the density of pellet increased significantly, but the grain size of pellet increased slightly for 8 µm for TiO2 addition and 6 µm for Nb2O5 addition. The averaged grain size of pellets fabricated by addition of 0.2 wt.% TiO2 and 0.2 wt.% Nb2O5 powder for 60,000 MWd/tU SIMFUEL were increased slightly to 12 µm and 8 µm, respectively. The average grain size of pellet fabricated by increasing sintering temperature up to 1,800oC was greatly increased to 16 µm for TiO2 addition and slightly 11 µmfor Nb2O5 addition.