THE SODIUM REACTOR EXPERIMENT FABRICATION

e [Music] in mid 19 1954 the atomic energy commission and atomics international entered into a program to study and improve the technology associated with the Sodium graphite type of nuclear reactors the technical feasibility of this approach to economical nuclear power is experimentally demonstrated through the construction and operation of the Sodium Reactor experiment the facility is located in the Santa Susanna mountains 30 m Northwest of downtown Los [Music] Angeles it incorporates a 20,000 thermal kilowatt reactor having the basic design features of a fullscale Central Station sodium graphite reactor liquid sodium serves as the coolant and heat transfer medium graphite is used as moderator the arrangement of major reactor components is shown by illustration the stainless steel core tank is 19 ft deep and 11 ft in diameter it is located beneath ground level surrounding the core tank is a cast steel thermal Neutron Shield a secondary tank to maintain the sodium level above the fuel elements in the event of a core tank rupture thermal insul I a Steel Vault liner and a concrete Vault an overhead view shows the graphite moderator and reflector units which are contained in 119 canned assemblies the inner 55 are pierced axially by coolant channels within which the fuel elements may be suspended liquid sodium coolant flows into the reactor at the bottom of the core tank from there it flows past the hot fuel elements to an upper pool to remove this heat the radioactive coolant is pumped through a primary Loop and returned to the core tank for recirculation the heat from the sodium in the primary Loop is transferred by a heat exchanger to a secondary Loop which is non radi active the heat from the secondary Loop can be exhausted to the Atmosphere by a sodium to a heat exchanger or it can be utilized in a steam generator the steam drives a conventional turbo generator for the production of electricity output capacity is rated at 7,500 electrical Kow a closely packed array of hexagonal graphite blocks pandon zirconium forms the reactor moderator fabrication of the moderator units will be shown in detail the blocks were machined from 300 lb log they were first rough cut then smooth finish each operation required a single pass under the cutter tolerance across the flats was held to 1,000 of an inch this graphite exceeds the extremely high Purity standards established for reactor application no impurities of any significance can be measured by the conventional chemical or spectrographic methods Personnel working with the graphite wore uniforms and gloves which were laundered in a boron-free soap and all tools gauges and fixtures were washed with alcohol as insurance against contamination the graphite was stored at all times in aluminum foil the zirconium cans which enclosed the graphite moderator blocks were fabricated from six separate longitudinal panels the formation of each panel was completed in a single brake operation this is a 60° bent the formed panels were machined to the specified width this operation was critical since it determined the Tolerance on the completed moderator can tolerance across the flats was 125,000 of an inch after machine cing the panels were cleaned by micro sand blasting the final step before assembly a helar welding state was employed for longitudinal welding the seams were fused together without the use of filler rods this assured neater joints with a minimum of contamination dimples which were rolled into the panels during fabrication ensure a thin flat Channel between adjacent can walls this space permits heat removal by the circulating reactor coolant the bottom end caps were helar welded in place argon Under Pressure within the central tube provided an inert atmosphere behind the weld moderator C end cap welds were investigated through mid 1955 10in sections of the cans were prepared for these tests the object was to study the possibility of buckling or cracking of the head welds due to Thermal stress which might be encountered during reactor shutdown the thermal stress was simulated in this test by mechanical cycling the can was immersed in sodium and evacuated sodium temperature was maintained at 950° fah any break in the wells would be detected by a sodium leak indicator early failures were observed which led to an improvement in head design later heads have survived cycling tests equivalent to nearly 8 years of operation in the Sodium Reactor experiment the main purpose of the moderator can is to isolate the graphite from the sodium coolant a leaking can would allow absorption of sodium by the graphite causing excessive Neutron losses each can was sealed evacuated and all Wells helium leak tested the wells were also x-rayed to check for paracity and contamination any faulty portions were marked rewelded and x-rayed again a horizontal graphite loading jig facilitates final assembly of the the moderator elements three graphite blocks comprise the moderator element for each can a graphite indexing plug at the junction of adjacent blocks prevents rotation the total weight that the complete canned moderator assembly is about 760 lb after loading the top cap was welded in place and X-ray and the complete moderator unit given a final leak test there are four control elements in the core located as shown diagrammatically in this overhead view each element is self-contained in a sealed thimble assembly which extends from the top of the upper Shield to a point just below the core the poison column is made up of a series of 18 Boron nickel alloy Rings suspended on a pole tube the pole tube is raised and lowered by a motor drive system located just above the top Shield studies were made to determine the optimum clearance between control rod rings and the tube within which they operate an electrically heated graphite coil was employed to bring the test rings to s re operating temperatures various ring sizes were tested to establish the best size for free movement and disspation of the expected heat load these Rings were thermal cycled in another series of tests to investigate physical changes which might occur under operating temperatures they were cycled 500 times for a maximum of 1500° f down to 700° with a gradient across the rings of 300 to 400° these tests indicated that the changes in size would be well within acceptance limits a grid plate near the bottom of the core tank supports and locates the moderator assemblies it was fabricated from type 304 stainless steel and is 1 and 1/2 in thick the smooth finishing of the moderator can spacer holes is shown here a pedestal at the bottom of each moderator can fits into these holes to support the can and position it precisely these holes face the lower ends of moderator cans and fuel elements on an 11-in triangular lattice the core tank is 19 ft deep and 11 ft in diameter made of 304 stainless steel it has a wall thickness of an inch and a half the bottom head was formed cold and specially heat treated to maintain the required close tolerances prior to fabrication all material was ultrasonically inspected for internal laminations and voids the sides of the tank were built of three ring sections each welded in place all welds were given die penetrant and x-ray inspection surrounding the core tank is the thermal Shield its function is to absorb most of the heat due to gamma rays and neutrons and to protect the concrete shield from thermal damage it was fabricated from 1030 carbon steel melted in an electric steel furnace the complete Shield was made up of seven individually cast rings each ring was fully annealed to remove stresses in the casting and then was machined to to the specified 5 1/2 in thickness the top ring is 29 in high the remaining rings are reach 35 in high outside diameter is 12 1/2 ft with the tolerance held to a plus or minus 132 of an inch on both inside and outside diameters to allow free expansion and contraction during reactor shutdown these rings are not welded to each other stainless steel Bellows seal the tops of the core tank and outer tank they permit vertical expansion of the tanks but prevent Escape of sodium vapor and helium from the core area total weight with concrete and plugs is 75 tons the sodium pumps are modified hot oil pumps designed for high temperature service in oil refineries the principal modifications consist of vertical mounting and the addition of Frozen sodium seals at the shaft and at The Capes this pump will deliver 1,285 Gall a minute against a 130 ft sodium head the intermediate Heat exch Changers employ a shell and Tube counterflow Arrangement designed in a u-shape this configuration conserves space and minimizes thermal stresses all components requiring special cooling are served by a system which circulates liquid tetralin a material which does not chemically react with sodium the cold traps sodium pump seals top Shield concrete cavity liner and fuel storage cells are a few of the components serviced by the tetralin coolant system a leak test is conducted on coolant piping a fuel handling Cask is provided for loading and unloading fuel elements from the core an attached control panel showing here as it is being wired permits the operator to position The Cask over the specified plugs for fuel loading and unloading a fullscale mockup of the fuel handling system excluding the lead shielding has been checked out on the test Tower the fuel hoist and electrical interlocks were operated through a series of tests in which fuel elements were raised and lowered an equivalent length of the core shown in this film was the fabrication and testing of major components for the Sodium Reactor experiment it is anticipated that the experience gained from this fabrication assembly and operation will permit major improvements in reactor technology this information will be incorporated into improved design for full scale sodium graphite power plants