High Burnup Irradiation Research Articles

Evaluation of failure fraction for high burnup High Temperature Gas-cooled Reactor fuel

In high temperature gas-cooled reactors (HTGRs), Tri-isotropic (TRISO)-coated fuel particles are employed as fuel. In the high burnup coated fuel particle, stress due to fission gas pressure and irradiation-induced pyrolytic carbon (PyC) shrinkage is introduced into the coating layers and consequently the stress could cause failure of coating layers under high burnup irradiation condition. A failure model has developed to predict failure fraction of TRISO-coated particle under high burnup irradiation. In the model, failure probability is strongly dependent on the irradiation characteristics of PyC. This paper describes the outline of the failure model and evaluation result of high burnup fuel irradiation experiment by the model.

The modeling and simulation of the thermal conductivity of irradiated U-Mo dispersion fuel: Estimation of the thermal conductivity of the interaction layer

U-Mo dispersion-type fuel is a potential candidate fuel for research and test reactors owing to the relatively stable irradiation performance of U-Mo fuel in comparison with other metallic fuels. However, U-Mo dispersion fuel shows high growth of interaction layers at high burnup irradiation. Although the thermal conductivity of the interaction layer is one of the critical parameters for evaluating U-Mo fuel performance, there have been no studies on the thermal conductivity of the as-irradiated interaction layers based on experimentally measured data. In this study, the thermal conductivities of the as-irradiated interaction layer were estimated using finite element analysis simulation and analytical modeling from the reported thermal conductivities of the fuel meat segments irradiated up to two different fission densities. The thermal conductivities of as-irradiated interaction layer predicted by the analytical modeling and the finite element simulation showed a good agreement when they were estimated by the analytic models considering the interconnected microstructure of the Al matrix.

Physics study of deep-burning of spent fuel transuranics using commercial LWR cores

This paper describes a physics study of the utilization and destruction of the transuranic (TRU) nuclides contained in spent fuel through a high burnup irradiation (Deep Burn) in commercial light water reactors (LWR). The TRU nuclides are contained in the Fully Ceramic Micro-encapsulated (FCM) fuel, comprising of TRISO particles dispersed in a matrix of silicon carbide and manufactured in fuel pellets and fuel pins. This study is performed by using the traditional two-step core design procedure, which consists of fuel assembly calculations and core analysis. The main focus is on the core physics characteristics including safety-related parameters. The target reference core is the YongGwang unit 3, cycle 6 reload core. New fuel assemblies consisting of the conventional UO2 pins and new FCM TRU fuel pins are charged into the cores from cycle 6 to an equilibrium cycle. The results show that the reload cores can be designed to achieve the deep-burning (∼60% burnup) of TRU without adverse changes to the safety-related parameters and the core performance parameters. The equilibrium core has TRU self-recycling capabilities, being able to “deep burn” as much TRU nuclides as it generates.

Verification Program of BWR 9*9 Fuel

The high-burnup BWR 9×9 lead use fuel assemblies (LUAs), which are designed for a maximum assembly burnup of 55 GWd/t in Japan, have been examined after irradiation in a commercial BWR to confirm the reliability of the current safety evaluation methodology and to accumulate data for judging the adequacy of its application to the future higher burnup fuel. The irradiation performance of 9×9 LUAs for two different designs, types A and B, is generally on the extended trend of 8×8 fuel, but some new findings in terms of fuel performance have been addressed after 5 cycle irradiations. Accelerated corrosion of cladding for the corner rods in Type-B fuel assemblies and spacers in both types is observed after 5 cycle irradiations. The increasing trend of high hydrogen concentration seems to be an issue, which should be paid much attention with respect to fuel integrity during high-burnup irradiation. The large difference in fission gas release rate between two types of fuel is confirmed after 3 and 5 cycle irradiations, and the release rate of Al-Si-O doped pellets is particularly higher than the others.

Post-irradiation examinations of Li 4SiO 4 pebbles irradiated in the EXOTIC-8 experiment

In the EXOTIC-8 irradiation experiment in the High Flux Reactor (HFR) in Petten, lithium orthosilicate (OSi) pebbles with 50% 6Li-content were irradiated with the aim at investigating the behaviour of breeder ceramics at DEMO relevant burn-up. Specifically, changes in the mechanical stability as well as in the tritium release properties (in-pile and out-of-pile) had to be studied. After the completion of the irradiation, lithium orthosilicate pebble samples were shipped to the Research Centre of Karlsruhe (FZK) for post-irradiation examinations. The pebbles irradiated up to about 11% 6Li burn-up showed an increase in smaller cracks in the bulk and the presence of larger through-cracks, but the amount of fragments is quite small and the pebbles maintained a very good crush load. On the basis of these results, it can be concluded that the OSi pebbles can withstand high burn-up irradiation without an unduly high fragmentation.

An Investigation of Irradiation Performance of High Burnup HTGR Fuel

In order to investigate fuel behavior under high burnup irradiation condition of high temperature gas-cooled reactor (HTGR), an irradiation test was performed. An irradiation was carried out as a part of a cooperative effort between the US DOE and the Japan Atomic Energy Research Institute. The fuel for the irradiation test was called high burnup fuel, whose target burnup and fast neutron fluence were higher than those of the first-loading fuel of the High Temperature Engineering Test Reactor (HTTR). In order to keep fuel integrity up to high burnup over 5%FIMA (% fission per initial metallic atom), thickness of buffer and SiC layers of fuel particle were increased. This report describes the fuel behavior under high burnup condition in the irradiation test.

An Investigation of Irradiation Performance of High Burnup HTGR Fuel.

In order to investigate fuel behavior under high burnup irradiation condition of high temperature gas-cooled reactor (HTGR), an irradiation test was performed. An irradiation was carried out as a part of a cooperative effort between the US DOE and the Japan Atomic Energy Research Institute. The fuel for the irradiation test was called high burnup fuel, whose target burnup and fast neutron fluence were higher than those of the first-loading fuel of the High Temperature Engineering Test Reactor (HTTR). In order to keep fuel integrity up to high burnup over 5%FIMA (% fission per initial metallic atom), thickness of buffer and SiC layers of fuel particle were increased. This report describes the fuel behavior under high burnup condition in the irradiation test.

Development of a Coated Fuel Particle Failure Model under High Burnup Irradiation

In high temperature gas-cooled reactors (HTGRs), coated particles are used as fuels. For upgrading HTGR technologies, Japan Atomic Energy Research Institute has been developing high burnup Tri-isotropic (TRISO) coated fuel particles. The TRISO coatings consist of a low-density, porous pyrolytic carbon (PyC) buffer layer adjacent to the spherical fuel kernel, follwed by an isotropic PyC layer, a Sic layer and a final PyC layer. In safety design of HTGR fuels, it is important to retain fission products within the particles so that their release to primary coolant does not exceed an acceptable level. Therefore the basic design criteria for the fuel are to minimize the failure fraction of as-fabricated fuel coating layers and to prevent significant additional fuel failures during operation. In the high burnup coated fuel particle, stress due to fission gas pressure and irradiation-induced PyC shrinkage is introduced into the coating layers and consequently the stress could cause failure of coating layers under high burnup irradiation condition. Some models have been developed to evaluate failure fraction of coated fuel particles, however, they are regarded as a guideline for fuel particle design rather than as a predictive tool for coated fuel particle performance. Then the behavior of coated fuel particles has been examined only by many irradiation experiments and development of reliable model has been needed. A failure model is newly developed to predict failure fraction of TRISO-coated particle under high burnup irradiation. In the model, it is assumed that the failure fraction depends not only on failure of the Sic layer but also on that of the PyC layers. The failure fractions of through-coatings failed particles and the Sic-failed particles are calculated based on the failure probability of each coating layer. Based on the model developed here, parameter calculations for the first-loading-fuel of the High Temperature Engineering Test Reactor and for the high burnup fuel were carried out.

Development of a Coated Fuel Particle Failure Model under High Burnup Irradiation.

In high temperature gas-cooled reactors (HTGRs), coated particles are used as fuels. For upgrading HTGR technologies, Japan Atomic Energy Research Institute has been developing high burnup Tri-isotropic (TRISO) coated fuel particles. The TRISO coatings consist of a low-density, porous pyrolytic carbon (PyC) buffer layer adjacent to the spherical fuel kernel, follwed by an isotropic PyC layer, a Sic layer and a final PyC layer. In safety design of HTGR fuels, it is important to retain fission products within the particles so that their release to primary coolant does not exceed an acceptable level. Therefore the basic design criteria for the fuel are to minimize the failure fraction of as-fabricated fuel coating layers and to prevent significant additional fuel failures during operation. In the high burnup coated fuel particle, stress due to fission gas pressure and irradiation-induced PyC shrinkage is introduced into the coating layers and consequently the stress could cause failure of coating layers under high burnup irradiation condition. Some models have been developed to evaluate failure fraction of coated fuel particles, however, they are regarded as a guideline for fuel particle design rather than as a predictive tool for coated fuel particle performance. Then the behavior of coated fuel particles has been examined only by many irradiation experiments and development of reliable model has been needed. A failure model is newly developed to predict failure fraction of TRISO-coated particle under high burnup irradiation. In the model, it is assumed that the failure fraction depends not only on failure of the Sic layer but also on that of the PyC layers. The failure fractions of through-coatings failed particles and the Sic-failed particles are calculated based on the failure probability of each coating layer. Based on the model developed here, parameter calculations for the first-loading-fuel of the High Temperature Engineering Test Reactor and for the high burnup fuel were carried out.

High burnup performance of LMFBR fuel rods—Recent GE experience

A series of tests designed to evaluate the high burnup irradiation performance of mixed oxide fuel rods has acheived substantial burnup in EBR-II without incidence of failure. Several stainless steel cladding alloys and fuel configurations were irradiated over a broad range of operating conditions up to 16.3 at. % burnup, 47 kW/m linear power, and 570°C cladding temperature. Extensive examination showed the rods to be in good condition after extended operation in both loose and tight wire wrap spaced assembly configurations. In fuel rods with typical near-term LMFBR design parameters, cladding inelastic strains in the range from 0.3 to 0.8% were commonly observed at about 10 atom % burnup. The inelastic strain appears to increase with burnup and fluence, with the possibility of threshold values for these variables. Preliminary analyses suggest that the cladding inelastic strain was not entirely caused by pressure from released fission gases. Microstructural examinations indicated good fuel-cladding chemical compatibility and comparable behavior for both physically-mixed and coprecipitated fuel. Significant results include: the observation of negligible fuel-cladding gap in low power fuel at ∼8 atom % burnup, and partial closure of the central void in annular fuel at ∼10 atom % burnup.