They believe their FTBR is one such 'candidate' reactor that can produce energy from these two fertile materials with some help from fissile plutonium as a 'seed' to start the fire.
By using a judicious mix of 'seed' plutonium and fertile zones inside the core, the scientists show theoretically that their design can breed not one but two nuclear fuels - U-233 from thorium and plutonium from depleted uranium - within the same reactor.
This totally novel concept of fertile-to-fissile conversion has prompted its designers to christen their baby the Fast 'Twin' Breeder Reactor.
Their calculations show the sodium-cooled FTBR, while consuming 10.96 tonnes of plutonium to generate 1,000 MW of power, breeds 11.44 tonnes of plutonium and 0.88 tonnes of U-233 in a cycle length of two years.
'At present, there are no internal fertile blankets or fissile breeding zones in power reactors operating in the world,' the paper claims.
The concept has won praise from nuclear experts elsewhere. 'Core heterogeneity is the best way to help high conversion,' says Alexis Nuttin, a French nuclear scientist at the LPSC Reactor Physics Group in Grenoble.
Thorium-based fuels and fuel cycles have been used in the past and are being developed in a few countries but are yet to be commercialised.
France is also studying a concept of 'molten salt reactor' where the fuel is in liquid form, while the US is considering a gas-cooled reactor using thorium. McLean, Virginia-based Thorium Power Ltd of the US, has been working with nuclear engineers and scientists of the Kurchatov Institute in Moscow for over a decade to develop designs that can be commercialised.
India does not have sufficient uranium to build enough thermal reactors to produce the plutonium needed for more FBRs of the Kalpakkam type.
'Jagannathan's design is one way of utilising thorium and circumventing the delays in building plutonium-based FBRs,' says former BARC director P.K. Iyengar.