Sodium cooled fast reactors development and operating experience: lessons learned in the past and challenges for the future

Excellent thermophysical properties of sodium were demonstrated at the first test facilities as early as in the 1950s, and promised its large-scale application in the power area. During the period 1958-1963, design studies were made on the use of sodium as a coolant of traditional boilers: sodium heated by burning fossil fuel in the furnace was used to transport heat to the steam generator (SG), located in the vicinity of the turbine. This resulted in considerable decrease the length of steam/water pipelines. However, this option was abandoned because of complicated sodium handling for traditional power engineering. The mentioned issues, as well as fast reactor development declined, have forced researchers to complete the knowledge on fast reactor technology with alternative coolants: gas (He and CO2), steam and heavy liquid metals15 (lead-bismuth and lead). Less imminent requirements to the breeding capability have made it possible to expand the range of coolants under study, since one of advantages achieved by sodium, i.e. high power densities of cores assuring effective fuel breeding was no longer so important. Of course, some sodium cooled fast reactors had faced operating and technological issues, but it should be noted that this would be true for any other reactor line at the initial stage of development, as this type of reactors is. Full industrial development of fast reactors has not been completed yet. It is simply too early at the prototype stage of development to more general view of sodium cooled fast reactor technology. Other reactor technologies, including water cooled reactors, achieved high reliability when their respective large scale introduction had taken place. We cannot say that this will not happen in the case of LMFR. In this context, sodium?s attractive properties should be recalled, namely: compatibility with traditional structural materials and all fuel compounds up to high temperatures owing to its corrosion inertness and pressure close to atmospheric value, excellent thermohydraulic characteristics, thus assuring effective heat removal under conditions of either nominal flow rate or natural circulation flow rate at the reactor. Therefore, on condition of proper design and manufacture of components, there are no physical factors provoking failures. Consequently, in most countries involved in fast reactors R and D activities, sodium cooled reactor line is considered showing promise