TRANSIENT ANALYSIS OF THE ASTRID DEMONSTRATOR INCLUDING A GAS NITROGEN POWER CONVERSION SYSTEM WITH THE CATHARE2 CODE

摘要

The present paper is dedicated to preliminary transient studies carried out for the analysis of the overall system behavior of the ASTRID (Advanced Sodium Technological Reactor for Industrial Demonstration) demonstrator developed in France by CEA and its industrial partners. ASTRID is foreseen to demonstrate the progress made in SFR technology at an industrial scale by qualifying innovative options, some of which still remain open in the areas requiring improvements, especially safety and operability. Among the options investigated, two various power conversion systems (PCS) are studied. On the one hand, a classical water/steam Rankine cycle has been considered, on the other hand, a gas Brayton cycle has also been preliminarily designed in order to assess its figure of merits in terms of safety. In this latter innovative PCS, the working gas is nitrogen whose flow rate delivers power to a turbine driving with the same shaft two compressors (low and high pressure) separated by an intercooler. The other part of the work delivered by the gas is used to drive the alternator that produces electricity. The main objective of such a PCS consists in avoiding physically the possibility of a sodium/water reaction with the secondary circuit but the impact of this PCS on the control of the accidents is still under assessment. The main purpose of the studies presented in the paper is to assess the dynamic behavior of ASTRID including a gas PCS with the CATHARE2 code for typical transients. Two families of initiating events affecting the PCS are investigated: a loss of power supply and the spurious opening of the turbine by-pass valve. Regarding this last transient, sensitivity studies have shown that an adequate design of the turbomachine by-pass lines allow a control of the event without shutdown. Moreover, regulating actions following the scram are also investigated in order to take benefit of the PCS in order to remove the decay heat.