ADVANCED TEST REACTOR A winning design Deslonde de Boisblanc and the ATR cloverleaf design In the late 1950s, the Atomic Energy Commission and the Navy invited a number of companies to make proposals for an advanced test reactor that would serve not only the Navy but the AEC’s other test needs for many years to come. Despite study periods of up to three years, none of several responses met the Navy’s demanding requirements within a reasonable cost or time. It appeared that the aluminum-clad/enriched- uranium reactor concept might have reached its limit of performance. The Navy asked Phillips (Petroleum Company) to take two months to review previous proposals and come up, if possible, with a conceptual design. This challenge handed National Reactor Testing Station people a chance to prove they could still produce brilliant ideas. One of them, Deslonde de Boisblanc, a scientist with no doctorate in physics but who nonetheless had a feel for the way neutrons behave, created an elegant design for the reactor core in 1959. The design, named Advanced Test Reactor (ATR), first of all solved the symmetry problem. De Boisblanc described the ATR’s new way of controlling the power level. I tried to avoid a common problem encountered in most other test reactors, where the control elements move up or down. In the ATR, the larger range of control is accomplished by rotating 16 beryllium cylinders with hafnium shells that cover 120° of the outer surface. (Hafnium is a strong neutron absorber.) The cylinders are situated around the core. When rotated singly or in groups, the hafnium moves closer or farther from the core, thereby controlling