[en] This publication reports on the outcome of a technical meeting on high burnup fuel experience and economics, held in Buenos Aires, Argentina in 2013. The purpose of the meeting was to revisit and update the current operational experience and economic conditions associated with high burnup fuel. International experts with significant experience in experimental programmes on high burnup fuel discussed and evaluated physical limitations at pellet, cladding and structural component levels, with a wide focus including fabrication, core behaviour, transport and intermediate storage for most types of commercial nuclear power plants

[en] In the presentation will be disseminated the information about experience of the Bulgarian Nuclear Regulatory agency collected during licensing activities taken in relation of transition to the fuel with high burnup. Will be put in attention such problems as a compatibility of nuclear fuel during transitional cycles, neutron-physical characteristics of the core loaded with new fuel and necessity of further analysis, safety analyses for the particular unit (reactivity accidents, accidents with a large loss of coolant, etc.), characteristics of the fuel and unit’s specification, as well as input data for accidents. (author)

[en] Fragmentation and relocation of the high burnup fuel pellets was observed in Halden LOCA tests and in Studsvik hot cell experiments. A simple model has been developed for the analysis of the mechanical behaviour of the fuel pellet to explain the fragmentation mechanism. High pore pressure and porosity can cause such stresses in high burnup fuel pellet that can lead to fragmentation of UO_2. (author)

[en] Atucha I NPP started its operation on June 1974 using natural uranium fuel and since 1995 the core has been converted to SEU (U 0.85% enrichment). Moreover, in the recent years CNEA Fuel Engineering has developed a program to increase the U mass that involves a new structural design of the fuel element (FE), in order to achieve a higher burn up and reduce the frequency of on-line refuelling. According to these developments a number of activities were planned for the follow-up and periodic control of the FEs in service. In this presentation the poolside facilities to perform visual inspection and fuel rod metrology are described, in special the applied techniques for the measurement of the axial growth at burn ups higher than those for the original FE designs. Contribution of these results to this program is also presented. (author)

[en] If CNEA wants to handle the fuel elements technology for reactors of Generation III (high bum-up and cooling water at higher temperature and pH) must access to the technology of zirconium alloys low in Nb and free of tin. This paper present a roadmap to achieve, as semi-finished product, strips of Zr-le-O alloy of about 27 mm wide and 1 mm thick which must reach the standards for the yield stress and creep resistance of the commercially available French M5"T"M alloy or Russian E110 alloy. (author)

[en] The BaCo code was developed to simulate the nuclear fuel rods behaviour under irradiation. BaCo has good compatibility with PHWR, PWR, VVER, among others type of fuels (commercial, experimental or prototypes). The code includes additional extensions for 3D calculations, statistical analysis, fuel design, a full core analysis and accident conditions - at work. Research on new fuels and cladding materials properties based on ab initio and multiscale modelling of materials (M"3) are currently under development to be included in the BaCo code modelling. Examples of the code by using the cases of the CRP FUMEX of IAEA, new fuel conditions, such as fuel burnup extension, dry storage and an approach of new materials, and an overview of our present results of M"3 will be presented. (author)

[en] The version 2.0 of the DIONISIO code has been recently developed with the purpose of improving the accuracy of the simulation of the whole fuel rod. To this end, the rod is divided into a number of axial segments. The local values of linear power and coolant temperature are given as input data to DIONISIO 1.0 which is executed in each segment obtaining as outputs the local values of temperature, stress, strain, among other physical variables. Then, the general rod parameters (internal rod pressure, amount of fission gas released, pellet stack elongation, etc.) are evaluated at the end of every time step, conveniently combining the results of all the axial segments. The new code architecture allows taking into account the axial variation of the linear power and, consequently, evaluating the dependence of all the significant rod parameters with the longitudinal coordinate. Moreover, new calculation tools designed to extend the application range of the code to high burn up have also been incorporated to DIONISIO 2.0 in recent times and are the subject of other presentation. With these improvements, the code results are compared with some experiments published in the IAEA data base, covering more than 380 fuel rods irradiated up to average burnup levels of 40-60 MWd/ng. The results of these comparisons, which are presented here, reveal the good quality of the simulations. (author)

[en] Indian Pressurised Heavy Water Reactors (PHWR) have been operated over the years using natural UO_2 bundles. Recently high burn up fuels have drawn the attention. As part of the High burn up fuel experimental irradiation, AFFF (Advanced fuel fabrication facility) has taken up the fabrication of MOX fuel for PHWRs. The MOX fuel pellets containing 0.4 wt % of PuO_2 have been used for this purpose. The PHWR MOX bundles consist of two inner rings of MOX fuel pins and an outer ring of 12 Nat UO_2 fuel pins. This paper describes fabrication and quality and process control of MOX for PHWR along with the design changes made in fuel element. TIG welding has been chosen instead of resistance for end plug joint. Advantages associated with the changes have also been described. Fuel economics have also been presented regarding the burn-up and residence time. (author)

[en] Slovenske elektrarne operate four units of VVER 440 V213 type. Nuclear fuel cycle is being continuously modified in order to satisfy current operational requirements as well as to optimize nuclear fuel cycle costs. These trends caused that fuel type has been modified practically every couple of years during the last decade, based on the fuel portfolio offered by the producer - TVEL. The latest fuel type, first time loaded into the reactor core in 2011, is designed to reach relatively high burnup values up to 72,5 MWd/ng for fuel rod or up to 65 MWd/ng for fuel assembly in six year fuel cycle. These values are substantially higher than previously reached values and are therefore subject to detail safety assessment during the licensing phase. In order to obtain license for the nominal design burnup values, Slovenske elektrarne had to launch a new initiative in order to summarise an adequate safety case. At the moment the licences are still limited for four years of operation only and utility is working on relevant documentation to be submitted to NRA for approval. The paper describes main technical issues and overall strategy selected in order to fulfill its licensing intent. (author)

[en] Nuclear energy is currently facing challenges regarding its competitiveness. In order to stay at current position, one of the methods is to reduce the fuel cycle costs. Increasing burnup is one of the technique that can be used to meet this goal, with enhanced safety features. However there is a number of fuel failure causes related to increased burnup, as follows. 1) Effect of increased burnup on fuel cladding corrosion and water chemistry parameters that accelerates the corrosion rate. 2) Effect of hydrogen pickup and stresses, as it effects mechanical properties of cladding. 3) Mechanical and chemical interactions between pellet and cladding. 4) Internal pressure of fuel rod. 5) LOCA impact of increased burnup. It is believed that failure tendency may increase with increased burnup due to the embrittlement of the cladding. However, at the same time one has to keep in mind that the reactivity of the fuel decreases with burnup. Higher failure rate at higher burnup is caused by mechanical and chemical degradation of cladding material. In this paper current and potential mechanisms related to fuel failure are discussed. (author)