Simulating the Behavior of Gaseous Fission Product Bubbles in the Fast Reactor Lead Coolant in the AEROSOL/LM Module of the EUCLID/V2 Integrated Computer Code

Abstract

One of the requirements that have to be met is substantiating the safety of newly designed and constructed lead cooled reactors is to evaluate the consequences from possible escape of fission products from nuclear fuel into the coolant during an accident in which part of fuel pins lose their leak tightness. Hence, it is of relevance to develop a model and a computation module based on this model for simulating the interaction of volatile fission products dissolved in the lead melt (iodine and cesium isotopes, and other radionuclides) with the bubbles of gaseous fission products (xenon and krypton isotopes). The consideration of this process is very important in substantiating the safety of lead cooled reactors, because the interaction of volatile fission products dissolved in the lead melt with the bubbles of gaseous fission products has an effect on the content of dissolved radionuclides in the lead melt and on the release of radionuclides into the gas space above the lead melt. The subsequent migration of radionuclides in the reactor gas circuit results in that the activity of radionuclides becomes redistributed in the circuit. It also facilitates the release of activity, as a consequence of loss of leak tightness of the circuit components, into the reactor rooms and the ventilation system. In addition, the bubbles of gaseous fission products in the lead melt interact with the hydrogen isotopes dissolved in the melt (protium and tritium) and facilitate their escape into the reactor gas circuit. The article presents the results from the development of the model and corresponding software unit, and its incorporation into the AEROSOL/LM module, which is part of the EUCLID/V2 integrated code, for calculating the behavior of inert radioactive gas bubbles, including the interaction of bubbles with the radionuclides dissolved in lead melt and the release of bubbles into the reactor gas space. To check how correctly the models are implemented in the code by means of software, the article presents data on the verification of the developed module based on the results of solving test problems.