J. van de Laar

The radial distribution of plutonium in high burnup UO2 fuels

Abstract A new model (TUBRNP) is described which predicts the radial power density distribution as a function of burnup (and hence the radial burnup profile as a function of time) together with the radial profile of uranium and plutonium isotopes. Comparisons between measurements and the predictions of the TUBRNP model are made on fuels with enrichments in the range 2.9 to 8.25% and with burnups between 21000 and 64000 MWd/t. It is shown to be in excellent agreement with experimental measurements and is a marked improvement on earlier versions.

Modelling the high burnup UO2 structure in LWR fuel

The concept of a burnup threshold for the formation of the high burnup UO2 structure (HBS) is supported by experimental data, which also reveal that a transition zone exists between the normal UO2 structure and the fully developed HBS. From the analysis of radial xenon profiles measured by EPMA a threshold burnup is obtained in the range 60–75 GW d/t U. The lower value is considered to be the threshold for the onset of the HBS and the higher value the threshold for the fully developed HBS. Xenon depletion in the transition zone and the fully developed HBS can be described by a simple model. At local burnups above 120 GW d/t U the xenon generated is in equilibrium with the xenon lost to the fission gas pores and the concentration does not fall below 0.25 wt%. The TRANSURANUS burnup model TUBRNP predicts reasonably well the penetration of the HBS and the associated xenon depletion up to a cross section average burnup of approximately 70 GW d/t U.

Extension of the TRANSURANUS burnup model to heavy water reactor conditions

Abstract The extension of the light water reactor burnup equations of the TRANSURANUS code to heavy water reactor conditions is described. Existing models for the fission of 235 U and the buildup of plutonium in a heavy water reactor are evaluated. In order to overcome the limitations of the frequently used RADAR model at high burnup, a new model is presented. After verification against data for the radial distributions of Xe, Cs, Nd and Pu from electron probe microanalysis, the model is used to analyse the formation of the high burnup structure in a heavy water reactor. The new model allows the analysis of light water reactor fuel rod designs at high burnup in the OECD Halden Heavy Water Reactor.

Swelling analysis of highly-rated MX-type LMFBR fuels: II. Microsopic swelling behaviour☆

Abstract Microscopic swelling has been investigated by electron microscopy in several MX-type fuels, irradiated in fast and thermal flux. The results show that fission gas bubbles in these compounds grow to large sizes if the in-pile temperature rises above a critical value (swelling critical temperature T c ). A comparison has been made of the swelling rates in fuels of different composition, showing that T c increases from carbides to nitrides. In fuels subjected to in-pile restructuring (highly rated He-bonded pins) microscopic swelling is affected by pore and grain boundary migration. The influence of these phenomena on the fuel swelling performance has been discussed.