Application of 'CANDLE' burnup to LBE cooled fast reactor

A new reactor burnup strategy CANDLE (Constant Axial shape of Neutron flux, nuclide densities and power shape During Life of Energy producing reactor) was proposed, where shapes of neutron flux, nuclide densities and power density distributions remain constant but move along axial direction of the core. The equilibrium state was obtained for a large fast reactor (core radius of 2 m) by using a newly developed direct analysis code. Only natural or depleted uranium is enough to be charged to the core starting from its second sequential lifetime. In other words, if the fuel for the first core is available, neither enrichment nor reprocessing are required further on. In this, the burnup of spent fuel is about 40%. However, it is difficult to apply this burnup strategy to small reactors (core radius of ∼0.8 m). A long-life small fast reactor with nitride fuel and Lead Bismuth Eutectics (LBE) coolant was investigated. In was shown that enriching fuel by 5% of plutonium makes it possible to realize CANDLE burnup for small reactors. The core of 2 to 3 m height can have an operation period of 9 to 28 years with very small reactivity change (less than 0.2%). Though the application of CANDLE burnup strategy to fast reactors will require many changes in their design, CANDLE application to block-type fuel high temperature gas cooled reactor seems to require only few design changes. (author)