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Fundamental Nuclear Processes: Scattering, Fission, and Absorption
Published in Robert E. Masterson, Nuclear Engineering Fundamentals, 2017
Delayed neutrons play an important role in the time dependent reactor behavior because they are produced slowly enough to make it possible for the reactor control system to respond to changes in the neutron population before too many neutrons or too few neutrons are produced. In other words, delayed neutrons are what allow the nuclear chain reaction to be controlled. Without delayed neutrons, commercial power reactors would be almost impossible to control. The study of delayed neutrons is part of the field of reactor kinetics, which is discussed in more detail in our companion book.* The delayed neutron fraction also appears in a famous reactor kinetics equation called the Inhour equation. Among other things, the Inhour equation can be used to predict how the core-wide neutron population increases or decreases with time.
Benchmark of the Kilowatt Reactor Using Stirling TechnologY (KRUSTY) Component Critical Configurations
Published in Nuclear Technology, 2022
Kristin N. Stolte, Jeffrey A. Favorite, George E. McKenzie, Theresa E. Cutler, Jesson D. Hutchinson, Nicholas W. Thompson, Rene G. Sanchez
The five configurations evaluated in the benchmark differed in the reflecting material at the bottom of the central core column and the height of the BeO reflector ring. Two configurations also had an AmBe neutron source in the middle of the fuel. The full breakdown of the experimental configurations as well as the date they were performed and the measured reactor period are presented in Table I. The reported reactor period measurements are the average of three compensated ion chambers (referred to as linears since they display data on a linear scale), each located at least 3 m from the assembly, and the reactivity was calculated based on the Inhour equation, the delayed neutron data for 235U fast fission as given by Keepin,19 and the measured prompt neutron decay constant.20 A lengthy discussion regarding the applicability and associated uncertainty analysis of using Keepin’s delayed neutron data can be found in Sec. 2.1 of the KRUSTY benchmark evaluation.15
A New Era of Nuclear Criticality Experiments: The First 10 Years of Godiva IV Operations at NCERC
Published in Nuclear Science and Engineering, 2021
Joetta Goda, Caiser Bravo, Theresa Cutler, Travis Grove, David Hayes, Jesson Hutchinson, George McKenzie, Alexander McSpaden, William Myers, Rene Sanchez, Jessie Walker
Another method to measure burst size is to use gamma detectors such as photomultiplier tubes (PMTs) and photodiodes. The rate of gamma production is proportional to the rate of neutron production. The signal from the PMT is recorded on an oscilloscope, and the data are fit to an exponential to determine the initial period of the burst. Again, using the Inhour equation, the period is converted to reactivity. The signal from the photodiodes, also recorded on the oscilloscope, can be used to determine the FWHM of the burst. The PMTs and photodiodes from TA-18 were moved with Godiva. In 2015, an additional photodiode was installed. Data from the new detector for three bursts in January of 2021 are shown in Fig. 15.
Transient Reactor Test (TREAT) Facility Restart Heat Balance Calibration and Rod Worth Measurements
Published in Nuclear Technology, 2019
Daniel T. Willcox, James R. Parry
To accurately measure the reactivity of the control rods, a power increase is initiated by an incremental rod manipulation. As power increases, the time required to increase power by a factor of e, the exponential, was recorded. For a particular segment of a control rod, the observed average period is then used to determine the reactivity associated with the segment. Using the Inhour equation, a reactivity value can be determined based on the recorded period. This process is repeated for ten different increments covering the full length of the rods for each of the rod groups. These ten differential worth values are then used to calculate a fitted rod worth curve for each of the rod groups.