The Experimental Breeder Reactor I (EBR-I) Mark III

[Music] argonne national laboratories idaho division located at the national reactor testing station operates the experimental breeder reactor one experience gained since 1951 in the operation of this reactor forms the foundation for fast power reactor development this is the first reactor to employ sodium potassium alloy as a coolant and to utilize the direct current electromagnetic pump during this time the reactor performed satisfactorily as a steady power source demonstrated the breeding concept generated the world's first electricity from nuclear power and served its primary function in providing fundamental fast reactor information when ebr-1 was operated at power to flow ratios one and one-half times the design ratio some undesirable dynamic characteristics were observed these were a prompt positive temperature coefficient and a tendency toward spontaneous oscillation of power it was believed these characteristics were related and that the cause of the prompt positive temperature coefficient was either the doppler effect which increases the effective fissioning cross-section due to heating enriched uranium or to mechanical motion of the fuel elements enriched uranium in the form of the helix was prepared for measurement of the doppler effect in fast reactors this experiment was performed in the laboratory's critical assembly facility zpr-3 the helical form was adopted to minimize motion due to heating which could produce undesirable side reactivity effects positioned within an assembled ebr-1 core mock-up the helix was periodically heated then cooled on a 20-second cycle time careful measurement of the power oscillations resulting from the cycling made it fairly certain the doppler effect was much too small to have been the primary cause of the prompt temperature coefficient observed in the reactor concluding that the primary problem was mechanical motion it was decided to investigate ebr1 performance as part of an overall program to study reactor dynamics a rigid core assembly to restrict mechanical motion was designed for ebr one designated mark iii the core structure consisting of laminated steel disks was machined and assembled by the laboratory central shops the inside hexagonal surface fits the outer perimeter of the blanket sub-assemblies these discs are held and aligned with tie rods paralleling the assembly of the core structure fabrication of mark iii fuel was underway by the metallurgy division the fuel for the mark iii core is uranium enriched to 93 percent the blanket is normal uranium both blanket and core uranium are alloyed with two weight percent zirconium clad with zircolloy2 they are co-extruded into the form of a rod the rough cores for the blanket extrusion billets are produced by casting in a multi-cavity graphite mold the enriched uranium is melted in a five kilogram batch and cast in a single cavity mold a graphite crucible coated with ceramic wash is charged with the uranium biscuit and zirconium sponge for the blanket alloy melting and alloying is done by induction heating in a vacuum of 10 microns or less after alloying the metal is bottom poured into the mold by lifting a stopper rod these castings after machining are tested for homogeneity by a non-destructive method a sound transmission principle is utilized five mega cycle ultrasonic waves are generated by means of a quartz transducer and sent through the metal the quality of the casting is graphically recorded on a strip of electro sensitive paper the casting after further machining yields two extrusion billet cores these cores assembled with copper nickel end plugs are encased in a sleeve of zircoloy ii a copper jacket is added to prevent contamination of the billet components during heating and to provide lubrication during extrusion by heliarc welding the assembled billet is then evacuated outgassed and sealed the billets are co-extruded by nuclear metals incorporated to rods of one half inch diameter upon return they are inspected pickled to remove the copper and swage to a specified diameter heat treated for stabilization the rods are cut to appropriate fuel and blanket lengths and the cladding thickness measured to join the sections of either type rod a commercial glass lathe was specifically adapted at argonne for tungsten arc butt welding this welding operation is extremely precise because of the difficulty of fusing the high melting zerkloy without excessive melting of the uranium a 10 mil zirconium spacer disc separates the enriched and blanket sections on each fuel rod chill and gas retainers surround the electrode and weld area welding is purposely limited to the 20 mil zerkeloy cladding and is made in a double pass each pass requiring a different welding current a section bond is made at each weld by fusing the metal in a small zone to add mechanical strength the cladding is protected against oxidation by passing a stream of helium through the vicor ii after heat treatment planting thickness is measured by an eddy current method any currents are induced in the circular cladding by means of a point probe the apparent impedance of the probe is influenced by the cladding thickness the bond on the rods is then scanned by the ultrasonic transmission technique non-destructive testing methods help to ensure the quality of the completed fuel and blanket rods zirconium ribs are spot welded to rods ground to their finish diameter these will provide accurate spacing of the tightly clustered rods in their final geometry the welding operation is performed automatically on a specially designed condenser discharge type spot welder welds are placed at one quarter inch intervals along each of the three ribs a total of 240 welds per rod machining operations complete the fuel and blanket rod fabrication the completed core structure ready for installation in the reactor tank has a total height of nine feet and five inches the reduced diameter at the bottom will receive the core and inner blanket rods the structure rests on this shoulder with the inlet plenum chamber located just above the upper blanket this plenum chamber contains four two-way inlet valves for switching from series to parallel flow the up position of the valves permits series flow through the inner blanket and core while the down position allows parallel flow the plate above the inlet plenum chamber has seal rings to prevent bypass leakage between the inlet and outlet plenum chambers this seal plate also contains two flow control valves for throttling the exit flow from the inner blanket under parallel flow conditions under series flow conditions these valves are closed additional rigidity is obtained by an arrangement of clamps around fuel and blanket sub-assemblies at the core center line and at the seal plate the upper part of the structure is primarily shielding with an overflow plenum chamber near the top the top plate holds the actuators and position indicators for the various valves and clamps in the structure the core structure is installed in the same reactor tank that house the ebr-1 mark 1 and mark two cores fuel and blanket rods with their attached extensions for handling are positioned within a hexagonal can complete sub-assemblies within the hex can contain 36 rods and depending upon location within the structure will consist of fuel and or blanket material a tightening rod is located at the center of each sub-assembly and when expanded provides additional rigidity the thorough temperature instrumentation of mark iii includes thermocouples in the plenum chamber structure fuel rods blanket rods and coolant passages the complete mark iii loading contains 19 sub-assemblies seven enriched sub-assemblies comprise the core these are surrounded by a ring of twelve inner blanket sub-assemblies criticality was achieved on november 11 1957. it was determined to be 47 and 4 10 kilograms of uranium-235 within two percent of the critical mass determined from the mock-up of the core on the zero power reactor three operating test data indicates that mark three would be stable at several times design power and the unstability apparent in mark ii was due to mechanical design and is not inherent in fast reactors this investigation of reactor dynamics is continuing and will establish parameters affecting the stability of fast reactors [Music] you

Channel: Nuclear Engineering at Argonne

Views: 16,068

Keywords: nuclear, reactor, EBR-I

Id: KX1ruVBq9ag

Length: 13min 28sec (808 seconds)

Published: Tue May 08 2018