INTRODUCTIONShut Down System-2 (SDS-2) in advanced vertical pressure tube type reactor, provides rapid reactor shutdown by high pressure injection of a neutron absorbing liquid called poison, into the moderator in the calandria. Poison inside the calandria is distributed by poison jets issued from holes provided in the injection tubes. In this study, a transient one-dimensional (1-D) hydraulic code, COPJET is developed, to predict the performance of system by predicting poison jet length with time. Validation of the COPJET is done with the data available in literature. Thereafter, it is applied for poison jet length prediction of advanced vertical pressure type reactor.
DEVELOPMENT OF ANALYTICAL MODELIn SDS-2, poison injection in calandria takes place in a very short span of time to shut down the reactor. Unlike in steady state flow condition, inlet flow condition for injection tube changes with time and inertia has to be considered in momentum equation.Transient 1-D hydraulic code, COPJET for liquid poison injection is developed which consists of four modules. These modules are gas expansion, system piping, injection tube and poison jet length. In first module gas expansion is modelled. In second and third module, transient momentum and continuity equations are modelled. In fourth module semi-empirical formula is used, which is developed from experimental data of . Thermal hydraulics of the flow is simplified based on the assumption of isothermal 1-D flow throughout the transient.COPJET is validated for the lateral flow distribution and jet front length with the data given in literature. The validated computer code, COPJET was used to simulate the SDS-2 poison injection behaviour in advanced vertical pressure tube type reactor. Different parameters like mass flow rate, gas tank pressure, dead time for different holes in injection tube, non-uniformity in injection tube and poison jet length are predicted using COPJET.
CONCLUSIONSAn analytical model, COPJET is developed for predicting liquid poison injection behaviour in the pressure tube type reactors. In this model, a semi-empirical equation in non-dimensional form is incorporated for modelling jet injection in to the moderator. The code is used to simulate the jet growth of poison injected for advanced vertical pressure tube type reactor.
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