IFPE/IFA-429, Fission Gas Release, Thermal Behaviour UO2 Fuel, Halden Reactor

1 - Description: PWR type fuel rods assembled in three axially separated clusters of six rods were irradiated in the Halden Boiling Water Reactor as IFA-429 from June 1975 to September 1990. The eighteen-rod assembly had been designed to investigate gas absorption, fission gas release (FGR) and thermal behaviour of UO2 fuel during both steady state operation period and rapid power transients. In order to achieve the objectives, two rods were instrumented with fuel centre line thermocouples (TFs) and nine rods were instrumented with null-balance gas pressure transducers (PFs) monitoring rod internal gas pressure. The assembly was instrumented with nine vanadium neutron detectors, one cobalt detector, inlet and outlet coolant thermocouples and an inlet coolant flow turbine as well. This database contains the measured temperature history for one of the middle cluster rods up to the burnup level of 53 MWd/kgUO2 and the measured internal pressure data for three upper and three lower cluster steady-state irradiated fuel rods subjected to rapid power transients. Rationalized power histories are also presented for all the seven rods. In order to study FGR two series of power ramps were induced in August 1985 and in March 1988 by movable neutron absorbing shield surrounding the fuel rod clusters. Manually initiated gas pressure measurements were performed during the testing sequence. The FGR and the gas diffusion coefficients calculated on the basis of the measured rod internal pressure data are tabulated as well. Due to slightly different design characteristics of the six investigated fuel rods, the comparison of FGR data at three different fuel densities (91% TD, 93% TD and 95% TD), at two different grain sizes (6 μm and 17 μm) and at two different fuel-cladding gap sizes (200 μm and 360 μm) are possible. As the null-balance pressure transducers were not part of the automatic data acquisition system the rod internal gas pressure data set is limited. Only the pressure data measured at zero power during the base irradiation period, and the average value of the pressures measured during the two series of rapid power transients are tabulated. Calculated fission gas release (FGR) data are also presented. 2 - Method of solution: As the measured parameters were recorded in every 15. minute of the fifteen-year irradiation time, the huge original test fuel data base is not applicable for model validation without any rationalization. Hence the data were reduced on the basis of power history condensation performed for each rod. For the condensed histories new irradiation time is calculated on the basis of the burnup. However, for the investigation of some phenomena the 15 min. data acquisition frequency is required. Therefore some data from selected irradiation periods are presented without any condensation