IncreasedfuelburnupinaCANDUthoriumreactorusingweapongradeplutoniumOriginalResearchArticle

WeapongradeplutoniumisusedasaboosterfissilefuelmaterialintheformofmixedThO2/PuO2fuelinaCanadaDeuteriumUranium(CANDU)fuelbundleinordertoassuretheinitialcriticalityatstartup. Twodifferentfuelcompositionshavebeenused:(1)97%thoria(ThO2)+3%PuO2and(2)92%ThO2+5%UO2+3%PuO2.Thelatterisusedtodenaturizethenew233Ufuelwith238U.Thetemporalvariationofthecriticalityk∞andtheburn-upvaluesofthereactorhavebeencalculatedbyfullpoweroperationforaperiodof20years.Thecriticalitystartsbyk∞=∼1.48forbothfuelcompositions.Asharpdecreaseofthecriticalityhasbeenobservedinthefirstyearasaconsequenceofrapidplutoniumburnout.Thecriticalitybecomesquasiconstantafterthesecondyearandremainsabovek∞>1.06for∼20years.Afterthesecondyear,theCANDUreactorbeginstooperatepracticallyasathoriumburner. Veryhighburnupcouldbeachievedwiththesamefuelmaterial(upto500,000MW·D/T),providedthatthefuelrodcladdingswouldbereplacedperiodically(afterevery50,000or100,000MW·D/T).Thereactorcriticalitywillbesufficientuntilagreatfractionofthethoriumfuelisburntup.Thiswouldreducefuelfabricationcostsandnuclearwastemassforfinaldisposalperunitenergydrastically.