Mechanical energy generation during high burnup fuel failure under reactivity initiated accident conditions

The dominant factor of mechanical energy generation during high burnup fuel failure under reactivity initiated accident (RIA) conditions is discussed on the basis of results from recent two RIA-simulating tests with burnup fu el rods and separate-effect tests with powder fuels. When cladding failed d uring the RTA conditions, solid fuel fragments were dispersed into the cool ant water. The results from the recent two burnup fuel experiments indicate d that the dominant factor of mechanical energy generation was thermal inte raction of dispersed fuel fragments with the coolant water. To eliminate th e effect of gas release from the fuel rod, and to evaluate the potential of the thermal interaction; powder fuel experiments were also performed as se parate-effect tests. The results showed consistency in the mechanical energ y generation process between the burnup fuel experiments and the powder fue l experiments. Accordingly, thermal interaction should be the dominant fact or of the mechanical energy generation. Concerning the conversion ratio fro m thermal to mechanical energy, the finer fuel particles generated more mec hanical energy at the same energy deposition level.