Fuel element for nuclear reactor

Claim 1

IN A MULTIREGION FUEL ELEMENT FOR A NUCLEAR REACTOR, SAID FUEL ELEMENT CONSISTING IN LARGE PART OF A FISSILE MATERIAL PRESENT WITHIN AN INNER CORE REGION AND AN OUTER MANTLE REGION, THE FISSILE MATERIAL IN SAID CORE REGION BEING CAPABLE OF WITHSTANDING COMPARATIVELY HIGH TEMPERATURES PREVAILING IN THE CENTRAL PART OF THE FUEL ELEMENT AND THE FISSILE MATERIAL IN THE MANTLE REGION HAVING PHYSICAL PROPERTIES DIFFERENT FROM THE PHYSICAL PROPERTIES OF THE CORE MATERIAL AND HAVING A COMPARATIVELY HIGH HEAT TRANSFER CAPABILITY AND COMPARATIVELY SUPERIOR NUCLEAR PROPERTIES AT A TEMPERATURE DETERMINED SUBSTANTIALLY BY THE THERMAL STABILITY OF THE MATERIAL WHICH IS LOWER THAN THE TEMPERATURE OF THE CORE DURING OPERATION, THE IMPROVEMENT WHEREIN THE INNER CORE REGION IS SEPARATED FROM THE OUTER MANTLE REGION BY A DISTANCE SUFFICIENT TO PROVIDE A SPACE THAT IS FILLED WITH A NON-FISSILE SUBSTANCE THAT HAS LOW NEUTRON ABSORPTION CROSS-SECTION, IS SUBSTANTIALLY CHEMICALLY INERT TO THE MATERIAL OF THE CORE AND THE MANTLE AND FACILITATES REMOVAL AND DISTRIBUTION OF HEAT.