Gest-Sip1 Experiments and Post-Test Calculations with the RELAP5 Code

The SIP-1 apparatus (Sistema di Iniezione Passiva) was conceived, designed, numerically simulated and tested by the SIET company as an innovative depressurisation and makeup device for the New Generation LWRs. In particular it is suitable to cope with those accidents where pressure in the circuit must be dumped to allow low pressure injection systems to intervene. The main peculiarity of SIP-1 is the capability of depressurising a system by cold water injection, rather than by discharging mass to the outlet, as in the common depressurisation systems. The water injection is passively actuated on low level occurrence in the Reactor Pressure Vessel or in the Steam Generator secondary side. Moreover the simple geometrical layout of the system, constituted by a limited number of components and pipes, makes it interesting for future applications. ENEA sponsored all the research activity, starting from the SIP-1 design, its numerical simulation with the Relap5 code, the realisation of an experimental facility up to the test execution and post-test calculations. This paper deals with the description of the GEST-SIP1 experimental facility, the SIP-1 operating principles, the most meaningful results of the tests performed in July 2000 the capability of the Relap5 code in reproducing phenomena and events. All results confirm the effectiveness of SIP-1 capabilities to depressurise and refill the system other than its stability during the normal operating conditions of the plant.