[en] The use of Th in a pressurized water reactor (PWR) with no modifications in the core lattice parameters, leads to a core design having the following advantages in U utilization and safety over the low enriched U. (a) The U ore demand to support a reactor over its life (30 yr) is reduced by as much as 32% of that of standard PWRs and separative work by 11%. (b) Safety related parameters are generally within the range of values expected for U cycle cores. The consequences of transient and postulated accidents are therefore expected to be no more serious than those for U for which safety requirements have been satisfied. (author)