抄録
Japan Atomic Energy Agency (JAEA) has promoted the design study of the Accelerator-Driven System (ADS) cooled by lead-bismuth eutectic (LBE) to transmute minor actinide. The structural integrity of the fuel claddings is one of key issues in designing the ADS that tends to have a high power peak around the spallation target. For ADS, frequent beam trips as experienced in existing high power proton accelerators may cause thermal fatigue problems which may lead to degradation of the structural integrity and reduction of the lifetime of the fuel claddings. To estimate the structural integrity of the fuel claddings, at first, the surface temperature and inner pressure of the fuel claddings were estimated considering engineering uncertainties that occurs owing to manufacturing error, estimation error of power distribution and so on. The temperature of the fuel cladding that was the 9Mo-1Cr modified steel was limited below 550℃, which was determined from the mitigation of the corrosion due to LBE. Then, the thermal stress of the fuel cladding was evaluated for following two states: the steady state and the transient state. For the steady-state analysis, the stress was divided into two types: the primary stress and the secondary stress, which were caused by the inner pressure and the thermal load, respectively. These stresses were compared with the design stress limits. As a result, it was confirmed that their structural strength was sufficient under the conditions of design temperature and corrosion environment without irradiation. For the transient-state analysis, the number of acceptable beam trips was evaluated based on the total strain range due to the primary and secondary stress of the fuel cladding. As a result, the number of acceptable beam trips was evaluated to be over 1×10^6 times. If the fuel cladding was replaced once every two years, the acceptable beam-trip frequency was estimated to be greater than 5×10^5 times per year. This acceptable frequency was 20 times greater than the expected beam-trip frequency caused by the accelerator for the JAEA's reference ADS.
