Thermal hydraulic transient analysis of ITER safety-relevant secondary cooling water system

The design of the Chilled Water System (CHWS-1) of ITER (Nuclear Facility INB-174) considers two independent and segregated subsystems, CHWS-1 A & B, which provide cooling water to safety-relevant components in Tokamak and Hot Cell Complexes. CHWS-1 is a Safety Important System needed for the proper functioning of Protection/Safety Important Activities & Components and therefore Single Failure Criterion is included in its design, while physical separation between its trains is maintained as much as possible. However, both CHWS-1 trains are located in the Tokamak Complex Drain Tank Room (DTR) and thus, measures are taken in order to protect them from common causes of failure (i.e. Fire or High Energy Line Break). A failure of a given train in the DTR is investigated in order to analyse the consequences and take required additional measures so as to guarantee full safety cooling to CHWS-1 components outside DTR. A RELAP5 model of CHWS-1B is developed and a pipe break inside the DTR modelled, to perform thermal hydraulic transient analyses of this event. From the results, the transient evolution of the main thermal hydraulic parameters is determined and the required times of intervention evaluated in order to restore the cooling function of the affected CHWS-1 train for its remaining components. Thus, an accident management strategy is included in the analysis effort as well as a definition of CHWS-1 instrumentation and control fulfilling a relevant role in the event detection and mitigation. This paper summarizes the results of this activity.