ANS is committed to advancing, fostering, and promoting the development and application of nuclear sciences and technologies to benefit society.
Explore the many uses for nuclear science and its impact on energy, the environment, healthcare, food, and more.
Explore membership for yourself or for your organization.
Conference Spotlight
Nuclear Energy Conference & Expo (NECX)
September 8–11, 2025
Atlanta, GA|Atlanta Marriott Marquis
Standards Program
The Standards Committee is responsible for the development and maintenance of voluntary consensus standards that address the design, analysis, and operation of components, systems, and facilities related to the application of nuclear science and technology. Find out What’s New, check out the Standards Store, or Get Involved today!
Latest Magazine Issues
Jul 2025
Jan 2025
Latest Journal Issues
Nuclear Science and Engineering
September 2025
Nuclear Technology
August 2025
Fusion Science and Technology
Latest News
Deep Space: The new frontier of radiation controls
In commercial nuclear power, there has always been a deliberate tension between the regulator and the utility owner. The regulator fundamentally exists to protect the worker, and the utility, to make a profit. It is a win-win balance.
From the U.S. nuclear industry has emerged a brilliantly successful occupational nuclear safety record—largely the result of an ALARA (as low as reasonably achievable) process that has driven exposure rates down to what only a decade ago would have been considered unthinkable. In the U.S. nuclear industry, the system has accomplished an excellent, nearly seamless process that succeeds to the benefit of both employee and utility owner.
R. M. Pearce
Nuclear Science and Engineering | Volume 11 | Number 3 | November 1961 | Pages 328-337
Technical Paper | doi.org/10.13182/NSE61-A26012
Articles are hosted by Taylor and Francis Online.
The spatial flux oscillations that may occur in a power reactor as a result of xenon and local temperature effects have been studied on a general-purpose electrical analog computer. The linearized forms of the two-group diffusion equations with xenon-dependent coefficients are solved in one dimension using finite space intervals. The xenon-dependent coefficients are obtained at each space point by solving the linearized forms of the iodine and xenon equations using continuous integration, one second of computer time representing one hour of reactor time. Thus at each space point four operational amplifiers are required—one each for iodine, xenon, fast flux, and slow flux. The present application has ten space points on a radius, or on the half-thickness of a slab, requiring 40 amplifiers and 80 potentiometers. Good agreement is obtained with modal theory for predictions of the threshold fluxes in simple cases. Unlike some applications of modal theory, it is not assumed in the case of a persisting or pure mode that each of the oscillating variables is the product of a real function of space and a function of time. In fact it is found that the space shape changes continually during a cycle of an infinite train of oscillations, this behavior repeating in every cycle. This is partly a result of the xenon's lifetime against burnup varying through the reactor. The change of shape is less marked for the flux and iodine than for the xenon, and is most marked in the case of high equilibrium flux. At a central flux of 2.1 × 1014 cm−2 sec−1, the maxima in the xenon occur 2.5 hr later at the outside of a cylinder or of a slab than at the center. Some examples of two-group mode shapes are also given for reflected and flattened reactors.