Evaluation of THTR-300 commissioning data for application to the follow-on HTR systems. Partial project 2.3

Operation of the fuel element loading system in the THTR-300 so far has shown that damaged fuel elements may lead to operating disturbances, the main causes being fuel elements that got stuck in the pebble fuelling channel or in the helical debris removal section. The formation of such pebble jams has been studied and clarified in a 1:1 scale model, where experiments have also been made for determining ways and means of removing such jams by avoiding disassembly of the helical section. These experiments have been successful to a certain extent, but have shown that the current design of the THTR fuel elemenmt discharge system does not allow really satisfactory solutions of this problem. It could be demonstrated, however, that fuel element jams can be removed without disassembly of the helical section, by means of remote handling equipment, within a range of about 10 m, providing for the required design modifications to be done in the current fuel discharge section. Tests have been done in addition to the above experiments in order to detect any possible early signs of a coming jam (as e.g. reduced conveying capacity, change of the torque, faulty system operation), so as to be able to determine appropriate countermeasures in time. (orig