the breeder and light water reactor programs. Negative review At a review meeting with the AEC on 10 November 1954, Nobel Prize winner Hans Bethe and the designer of EPR Walter Zinn disagreed over the outcome of a meltdown in a breeder. Zinn suggested it might cause an explosion while Bethe felt this was extremely unlikely. Everyone agreed that such an explosion, were it to occur, would be small enough to be contained in a suitable building. Shortly after the meeting, Alfred Amorosi was named the technical director of the project. He began an in-depth study of the operations and became concerned about one particular problem. One advantage of the sodium coolant was that it expanded when it got hotter, slowing the reaction speed and cooling the reactor back down. This negative temperature coefficient is highly desirable as it offers passive safety. However, EBR demonstrated a positive temperature coefficient under certain conditions. More disconcerting was that calculations of a second similar effect, the Doppler coefficient, appeared to be positive. In this case additional heat might lead to a runaway condition. Amorosi's work was studied at a 30 June 1955 meeting of the breeder group within the Advisory Committee on Reactor Safeguards, a blue ribbon panel formed by the AEC which is now part of the Nuclear Regulatory Commission. They were concerned that the Doppler coefficient might overwhelm the thermal effect and any automatic systems that were attempting to control it. The team was ambivalent about the concept on a broader sense, raising several potential serious issues and wondering why they were considering moving ahead with a full-scale plant without waiting for results from tests on smaller prototypes. They concluded that "It must be recognized that the assumptions on which these calculations are based have not been established experimentally, and must be so before the operation of such a reactor could possibly be recommended for a site close to a populated area." EBR meltdown To further characterize these effects, in the summer of 1955, EBR began to run experiments to measure the Doppler coefficient. As the effect is more pronounced at higher temperatures, a test was arranged that would run the reactor at , not far below the melting point of the fuel. The reactivity was controlled by a series of motorized control rods that would be slowly extracted to allow the power to rise smoothly. In the case of a