The IRIS pressurizer: Simulation of out-surge transients and optimization procedure to design scaled experiments

Abstract

Numeric models of the IRIS reactor pressurizer having either two or three volumes were employed to simulate a typical out-surge transient. The vapor volume may contain liquid drops. Vapor bubbles can be generated in the liquid volume. The mass, the energy, the constitutive, and the state equations, represent all relevant phenomena. A pressure equation is derived by the substitution of the mass and energy equations onto the pressurizer volume constraint, assuming that the instantaneous pressure is the same in all volumes. The pressurizer experimental data of a loss of load transient in the Shippingport reactor are used to validate these pressurizer models. These models are also employed to verify the capacity of the thermal power controller to restore the pressure in the IRIS out-surge transient. The preliminary validation, using the Shippingport experimental data, and the close agreement reached by all the developed software, for the IRIS out-surge transient, recommends further validation of these models for the test evaluation and the design of scaled experiments for the IRIS pressurizer. The proper choice of the pressure number was employed to obtain the best form of the non-dimensional conservation equations for a two-volume pressurizer. This form and the non-dimensional constitutive models, define the similarity numbers of scaled systems similar to the IRIS reactor pressurizer. The similarity numbers represent the scaled transport of mass and energy, and of the local rainout, flashing, and wall condensation mass and energy transport. The genetic algorithm (GA) search variables of scaled models are the geometric sizes, the surge mass flow rate, and the heater power needed to control the pressure. The similarity numbers are used to define a “fitness function” to evaluate the quality of the defined variables. The operation of the systems is verified using a two-volume transient model to simulate a typical out-surge transient. The agreement of the non-dimensional pressure as the model pressure increases, and the good agreement of the non-dimensional volumes of different scaled systems recommends this non-dimensional formalism, the GA optimization, and the numeric simulation of a surge transient, to design scaled experiments for modeling the IRIS pressurizer.