b'P ROVING THE P RINCIPLEs u fficiently low, that the AEC deemed or was planning. Reactors were to be The SL-1 was the first of three antici-such a feature unnecessary. 3 stationary, portable, or mobile, pated Army experiments at the NRTS.depending on the intended field appli- The other two were intended to perfectInside, the plant was arranged like a cation, and rated for low, medium, a mobile reactor so miniaturized thatthree-layer cake. In the bottom third, or high power. 5 it would fit on a truck and move when-native stone and gravel shielded the ever a field station moved. As of 1958pressure vessel containing the reactor. The IDO opened up an Army Reactor all the reactors built in the UnitedThe middle third was the operating Experimental Area (AREA) about a States had been cooled with water orlevel, giving the crew access to the top half mile north of State Highway 20 liquid metal. But gas was a coolant pos-of the reactor, the turbine generator, and and ten miles east of Central Facilities. sibility and the Army chose to explorecontrol rod machinery. On top, a fan it for mobile reactors. Ultimately, thefloor attic contained equipment to con- Army hoped ordinary air could be used,dense and cool the recirculating water. further simplifying the power plant andA weather-protected stairway snaked up eliminating more weight. The Armythe side of the cylinder to connect the contracted Aerojet General Corporationadjacent control building to the operat- to design a Gas Cooled Reactoring floor level. 4 Experiment (GCRE) and do for the gas-cooled concept what BORAX, SPERT,After Argonne handed over the finished and TREAT had done for the other con-plant to the Armys operating contrac- cepts: determine its safe operating para-tor, Combustion Engineering (CE), the meters and select the best fuel. ThatArmy named the reactor Stationary done, the Army would use the remote-Low-Power Reactor Number One, or ness of the NRTS to field-test a proto-SL-1. This name distinguished the reac- type for the Mobile Low-Powertor from a whole family of other small Reactor, or ML-1. 6reactors that the Army already had builtINEEL 59-4018 The IDO reserved sites for the threereactors at half mile intervals along anaccess road it named Fillmore Avenue.The GCRE, a water-moderated reactorsituated in a swimming pool pitbelow the floor, went critical in 1959,and the ML-1 was expected to arrivesometime in 1961. 7Above. Cadremen at SL-1 control panel. Left.Operators make adjustments in GCRE reactor pit.INEEL 63-44541 4 0'