Travel report from the Enlarged Halden Programme Group Meeting at Loen, Norway, 24-28 May, 1999

Generally, the Halden project is very strong considering the fuel pellet-related projects. Very competent researchers are managing these projects, where upon completion the results generated in Halden are compared to open literature data. This comparison significantly increases the value of the Halden generated results. The organisations that benefit the most from these results are the fuel vendors, that are using the results to improve their models in the fuel performance codes. However, the fuel-related problems occurring today in Sweden and in many other countries are almost only related to the Zircaloy cladding performance. Consequently, it would be desirable to increase the focus at Halden on the cladding performance related problems. Halden should also in a much larger degree compare there cladding generated results with open literature data to increase the value of their own data. There are some previous results generated by Halden that contradicted other open literature data and unless no attempt is done to explain the discrepancy in results the Halden data generates more questions than answers. The key conclusions of the Halden presentations are the following: Both UO2 and MOX-fuel behaviour can today already be modelled satisfactory. This situation will make it possible for the fuel vendors to meet the fuel design criteria that ensures that no fuel failures occur during normal operation and anticipated operational occurrences, The risk that liftoff will result in fuel failures in UO2 and MOX-fuel is smaller than previously anticipated, Dry-out tests indicate the pump trip does not significantly impact the fuel performance. During this transient, it is assumed that the maximum cladding temperature is about 700 deg C during a couple of seconds. The tests performed at Halden to study this trip where very conservative, since the maximum cladding temperatures were significantly higher (almost 800 deg C) and lasted for a couple of minutes. Code calculations show that the impact of Anticipated Transient Without Scram, AMS, depends mostly on the assumed heat transfer coefficient between the clad and the coolant, and the average pulse energy. If dryout does not occur during AMS, the impact on the fuel is negligible, MOX-fuel pellets show about the same fission gas release tendency but a somewhat smaller thermal conductivity as compared to UO2 fuel. The anticipated fission gas release will consequently be slightly larger for MOX than for UO2 -fuel, during comparable operating conditions