Control rod drive

Claim 1

IN A NUCLEAR REACTOR, A REACTOR VESSEL HAVING A COOLING FLUID UNDER PRESSURE THEREWITHIN, A CONTROL ROD DRIVE ASSEMBLY INCLUDING A HOLLOW CYLINDRICAL HOUSING EXTENDING OUTWARDLY FROM AND OPEN INTO SAID VESSEL, A FIRST PISTON HAVING A PASSAGEWAY EXTENDING THERETHROUGH TO FORM A HOLLOW SLEEVE COAXIAL WITH AND SLIDABLY RECEIVED IN SAID HOUSING AND FORMING WITH THE HOUSING AN ANNULAR FIRST CHAMBER, AN EXPANDED SECTION ON THE OUTER EDGE OF SAID FIRST PISTON MAKING SLIDABLE CONTACT WITH THE INSIDE SURFACE OF SAID HOUSING, AN ANNULAR SHOULDER ON THE INSIDE OF SAID CYLINDRICAL HOUSING MAKING SLIDABLE CONTACT WITH THE OUTSIDE SURFACE OF SAID FIRST PISTON, SAID ANNULAR CHAMBER BEING BOUNDED ON ITS OUTER END BY SAID PISTON EXPANDED SECTION AND ON ITS INNER END BY SAID HOUSING ANNULAR SHOULDER, A HOLLOW SLEEVE TELESCOPING INTO THE OUTER END OF THE FIRST PISTON IN SPACED RELATION THEREWITH AND SECURED TO THE HOUSING IN A FLUID-TIGHT MANNER OUTWARDLY OF SAID AN ANNULAR ABUTMENT ON THE INSIDE WALL OF SAID FIRST PISTON AND LOCATED INWARDLY OF SAID SECOND PISTON, SAID SECOND PISTON ARRANGED FOR ABUTTING ENGAGEMENT WITH SAID ABUTMENT AND HAVING A CYLINDRICAL WALL EXTENDING OUTWARDLY EFFECTIVELY FORMING OUTWARDLY OF SAID SECOND PISTON A SECOND CHAMBER, THE EFFECTIVE PRESSURE BEARING AREA OF SAID SECOND PISTON EXPOSED TO SAID SECOND CHAMBER BEING EQUAL TO THE AREA OF SAID FIRST PISTON THAT BOUNDS THE OUTER END OF SAID ANNULAR FIRST CHAMBER AND FACING OPPOSITELY, A SOURCE OF FLUID OUTSIDE OF SAID REACTOR AND UNDER A PRESSURE GREATER THAN THAT OF THE REACTOR COOLING FLUID, AND MEANS CONVEYING THE SAME TO SAID CHAMBERS WHEREBY EQUAL FORCES ARE CREATED URGING THE PISTONS INTO SAID ENGAGEMENT IN SAID HOUSING, SAID PISTONS EACH HAVING EQUAL AND OPPOSITELY DISPOSED SURFACES BEARING THE PRESSURE OF THE REACTOR COOLING FLUID, EACH SAID OPPOSITELY DISPOSED SURFACE BEING ALSO OPPOSITE TO A CORRESPONDING PISTON AREA BEARING THE PRESSURE OF SAID FLUID SOURCE, THE PRESSURE ON THE OPPOSITELY DISPOSED SURFACES AND AREAS NORMALLY MAINTAINING SAID PISTONS IN ENGAGEMENT, MOTOR MEANS OPERATIVE TO MOVE SAID SECOND PISTON AXIALLY OF THE HOUSING THEREBY ACCURATELY POSITIONING BOTH SAID PISTONS MOVABLY TOGETHER, AND CONTROL MEANS FOR INDEPENDENTLY RELEASING THE FLUID PRESSURE FROM SAID ANNULAR FIRST CHAMBER THEREBY RELEASING SAID FIRST PISTON FROM ENGAGEMENT WITH SAID SECOND PISTON.