Specialists' meeting on correlation between material properties and thermohydraulics conditions in LMFRs

In a liquid metal fast reactor (LMFR), temperature fluctuations in the fluid close to a structure occur in many areas: core outlet zone, lower part of hot pool, free surface of pool, IHX outlet, secondary circuit, water steam interface in steam generators. In some conditions, these temperature fluctuations can lead to mechanical damage to structures. Consequently, knowledge of temperature fluctuations and induced thermomechanical damage to structures is essential to support design and maintenance during the plant life-time. In response to a recommendation from the IWGFR, the IAEA convened a Specialist Meeting on 'Correlation between material properties and thermohydraulics conditions in LMFRs' in November 1994. The purpose of the meeting was to exchange information on the state of the art on thermalhydraulic aspects of temperature fluctuations (mixing jet phenomena, temperature gradient fluctuations, transfer of fluctuations from the fluid to the wall), and associated thermomechanical studies (thermal striping, thermal ratchetting, high strain fatigue) as well as design criteria to avoid damage. The main areas discussed by the delegates were: thermalhydraulics and thermomechanics. The objective of thermalhydraulic activities is the characterization of the temperature fluctuations on the wall. Three main items can be identified, for which both the experimental and calculational approaches were considered: identification of the areas where the fluctuations may occur; characterization of the fluctuations in the fluid; and transfer of the fluid fluctuations to the walls. For thermomechanical studies, which cover the effect of the fluctuations in the structures, the following subjects are of great importance: determination of the damage modes induced by thermal loadings in structures (thermal striping, ratchetting, high strain fatigue), and study of all damage modes so as to take them into account in the design criteria and to provide rules for avoiding failure of the structures, crack initiation and limiting damage interaction