O. G. GRIBORIEV, M. P. LEONCHYK, D. E. SKORIKOV, V. V. CHEKUNOV Institute of Physics and Power Engineering, Obninsk, Kuluga Region,

Russian Federation

Abstract

This reactor concept is a development of the well known PIUS reactor.

The main IRIS (Integral Reactor with Inherent Safety) features consist in an integration of all the primary equipment into a pre-stressed concrete reactor vessel (PCRV), natural circulation in the primary circuit and a reactor design with free levels of the coolant and the cold borated water (linked through the gas pressurizer) instead of the upper density lock.

The large volume of the cold borated water in the PCRV provides not only passive shutdown the reactor in emergency (like it is in PIUS), but condensation of the vapor during accidents with the primary coolant boiling. The containment and safety systems may be considerably simplified.

The large scale PCRV makes possible to store inside the vessel all the burnt-up during the reactor lifetime fuel assemblies.

A thick borated water layer between the core and PCRV — walls allows decrease the residual PCRV activity upto an environmentally — acceptable level and to simplify reactor decomissioning.

The high level of safety makes possible siting of this reactor near population centres.

Introduction. The objective of this report is to illustrate conceptual advantages of the integral type PWR, called IRIS (Integral Reactor with Inherent Safety). The reactor concept is a result of development of well — known PIUS project ideas. This innovation establishes some new important properties.

Design features. IRIS design features are: integration of all the primary equipment into a pre-stressed concrete reactor vessel (PCRV); natural circulation in primary circuit; absence of the upper density lock. Principial scheme of the reactor is shown in fig. 1.

Instead of an upper density lock there are communicating vessels with free levels linked through the gas pressurizer and single lower density lock. One of these vessels is the total primary circuit, and another one is a tank with cold borated water. Hence, despite natural circulation in them, this communicating vessels system will support the pure and borated water interface in the density lock inherently.

Only a primary leakage can destroy this interface and cause a proportional flow of borated water into the primary circuit through the density lock.

To exclude the core overheating there are by-pass pipes from the primary circuit volume into the borated water tank. They are arranged above the level of primary coolant. If a coolant overheat was to happen, the level will rise up to the by-pass pipe’s location and come to the borated water tank. Same portion of cold borated water will enter into the core through the density lock.

Therefore, due to the large scale reactor vessel, we have an inherent passive safety system, which is always ready for action, does not impede the normal operation, independent of anybody.