ammonia by pump means pa 1a 1s and is connected to the urea recovery section dist through conduit 108 advantageously the reactor rot is of the 34 once through 34 high yield type with partial removal of the reaction heat the 34 once through 34 reactor rot comprises two parts a primary section r 1 of the so called 34 kettle 34 type with reaction heat removal and a secondary section r 2 of conventional type the urea recovery section dist preferably comprises at least two carbamate decomposers e 1 and e 2 connected in series through conduit means 110 most advantageously the first carbamate decomposer e 1 operates at a pressure substantially equal to that of the existing stripper 201 c while the second carbamate decomposer e 2 operates at approximately 10 bar abs according to an aspect of the present invention a first stream leaving carbamate decomposer e 1 including unreacted ammonia and carbon dioxide vapors is directly recycled to the carbamate condenser 202 c operating at the same pressure through conduit 111 a second stream including unreacted ammonia and carbon dioxide vapors which leaves the top of carbamate decomposer e 2 is first condensed in e 3 and then recycled to the carbamate condenser 202 c through conduit means 112 and pump 301 j js from the bottom of carbamate decomposer e 2 a purified urea solution is obtained which may be either fed through conduit 113 to the low pressure distiller 301 c of the urea recovery section 104 or directly collected to storage tank 302 f trough conduit m in the first instance the urea solution leaving the carbamate decomposer e 2 is further treated.