Unified modular reactor plant

Claim 1

A NUCLEAR FISSION REACTOR COMPRISING A PRESSURE VESSEL, A CORE OF FISSIONABLE FUEL ASSEMBLIES MOUNTED WITHIN SAID PRESSURE VESSEL, SAID ASSEMBLIES CONSISTING OF STATIONARY FUEL ASSEMBLIES AND MOVABLE FUEL ASSEMBLIES, EACH OF SAID MOVABLE FUEL ASSEMBLIES CONSISTING OF A LOWER SECTION CONTAINING FUEL ELEMENTS EXTENDING THE LENGTH OF SAID CORE AND AN UPPER SECTION CONTAINING A NEUTRON ABSORBING MATERIAL, ALL OF THE MOVABLE NEUTRON ABSORBING MATERIAL OF SAID REACTOR BEING CONTAINED WITHIN THE UPPER SECTIONS OF SAID FUEL ASSEMBLIES, EACH OF SAID MOVABLE FUEL ASSEMBLIES BEING MOVABLE BETWEEN AN UPPER OPERATING POSITION WHEREIN SAID LOWER SECTION IS LOCATED WITHIN SAID CORE AND THE UPPER SECTON EXTENDS ABOVE SAID CORE TO PERMIT POWER OPERATION OF SAID REACTOR AND A LOWER SHUT DOWN POSITION WHEREIN SAID LOWER SECTION EXTENDS BELOW SAID CORE AND THE UPPER SECTION IS WITHIN SAID CORE TO PREVENT OPERATION OF SAID REACTOR, SAID CORE BEING DIVIDED INTO OUTER AND INNER ZONES OF U235 ENRICHMENT, THE ENRICHMENT RATIO IS BETWEEN THE OUTER ZONE AND INNER ZONE BEING ABOUT 1.6, STEAM GENERATING MEANS LOCATED WITHIN SAID VESSEL OCCUPYING AN ANNULAR SPACE SURROUNDING SAID CORE FOR RECEIVING SECONDARY WATER COOLANT AND PRODUCING SUPERHEATED STEAM, AND MEANS FOR PUMPING PRIMARY WATER COOLANT AND MODERATOR INTO SAID VESSEL AND FORMING A SELF-PRESSURIZED STEAM SPACE IN THE UPPER REGION OF SAID VESSEL, SAID PRIMARY COOLANT BEING CIRCULATED IN TWO PASSES THROUGH SAI CORE AND THROUGH SAID STEAM GENERATING MEANS TO TRANSFER HEAT OF FISSION FROM SAID CORE TO SAID SECONDARY WATER COOLANT, SAID PRIMARY COOLANT MAKING ITS FIRST PASS THROUGH THE OUTER ENRICHMENT ZONE AND ITS SECOND PASS THROUGH THE INNER ENRICHMENT ZONE, THEREBY TENDING TO FLATTEN THE POWER DISTRIBUTION ACROSS SAID CORE, SAID REACTOR DURING NORMAL OPERATION HAVING EACH OF SAID MOVABLE FUEL ASSEMBLIES IN ITS UPPER OPERATING POSITION, SAID REACTOR THEREBY OPERATING NORMALLY WITHOUT THE PRESENCE OF CONTROL RODS IN THE CORE.