Accelerator Driven System target module thermal hydraulics modelling using RELAP5

Accelerator Driven System (ADS) is important due to its ability to transmute radioactive waste and its inherent safety. One of the key components of the ADS is the spallation target module. It constitutes the physical interface between the accelerator and the sub-critical reactor. It is simultaneously subjected to severe thermal-mechanical loads and damage due to high-energy heavy particles. In order to develop ADS system, a basic R and D program has been initiated to study spallation target. For this purpose an experimental LBE target system is currently being developed for coupling to 30 MeV and 500 micro-Ampere proton beam from cyclotron. The incident proton beam deposits approximately 15 kW of heat in the window. The liquid metal LBE (Lead-Bismuth-Eutectic) is circulated to extract the heat from the window. Design of a passive, gas injection-driven enhanced flow system to remove intense heat deposited in the window (thin barrier separating proton beam pipe and circulating LBE) has been studied. To assure the needed heat removal capabilities, the adoption of the air-lift principle is envisaged to enhance coolant circulation by the injection of gas in the riser. Detailed thermal hydraulic analysis of the upcoming experimental ADS facility (at BARC) has been carried out using Reactivity Excursion and Leakage Analysis Program (RELAP5) code. The case study for only buoyancy driven flow is compared with gas driven flow in the target module. Various transient conditions were also considered which are important from the safety point of view. Transient cases considered included Beam shut off, nitrogen injection supply off and loss of cooling. For all the cases analysed, time available for corrective action were predicted. It was found that enough time wise margins are available to prevent undesired accident conditions and window degradation/failure. In the paper details of the modelling and the results obtained will be discussed. (author)