Patchy nuclear chain reactions

Stochastic fluctuations of the neutron population within a nuclear reactor are typically prevented by operating the core at a sufficient power, since a deterministic (i.e., exactly predictable) behavior of the neutron population is required by automatic safety systems to detect unwanted power excursions. In order to characterize the reactor operating conditions at which the fluctuations vanish, an experiment was designed and took place in 2017 at the Rensselaer Polytechnic Institute Reactor Critical Facility. This experiment however revealed persisting fluctuations and striking patchy spatial patterns in neutron spatial distributions. Here we report these experimental findings, interpret them by a stochastic modeling based on branching random walks, and extend them using a “numerical twin” of the reactor core. Consequences on nuclear safety will be discussed.

50 Years of Nuclear Power

This article highlights the Atomic Age that announced itself to the world with the destruction of two Japanese cities in 1945. After the first bomb fell, on Hiroshima in August, mankind suddenly realized that it possessed a new technology of unprecedented destructive power. In 1948, Untermyer transferred to the Argonne National Laboratory near Chicago. The lab traced its origins to Enrico Fermi, who with Leo Szilard had been first to demonstrate a nuclear chain reaction only six years earlier. Argonne was the first national laboratory with the mission of developing nuclear power for peaceful purposes. Untermyer left General Electric (GE) in 1964 to find the National Nuclear Equipment Corp. to design and manufacture equipment for the nuclear industry. He was awarded several more patents. GE’s Economic Simplified Boiling Water Reactor also makes use of passive systems. According to GE, the reactor has more than 72 hours of passive running capability, and its simplified systems make it cheaper to build and run.