Neutronic Reaction System

NEUTRONIC REACTION SYSTEM Eugene P. Wigner, Oak Ridge, Tenn., assignor to the... 

FIG. 1 is a diagrammatic view partly in central vertical cross section and partly in elevation of a neutronic reaction system embodying the invention ... 

Neutron generator systems utilising electrostatic acceleration to induce a tritium-deuterium nuclear reaction and specially designed parts (including tubes) thereof. 

During normal operation of the system where the neutronic reaction is controlled only by control rods 179, the slider 184a on the resistor 184, having previously 70 been calibrated in terms of neutron density, is moved to the density position at which the reactor is intended to operate, taking into account the difference in neutron density at the center of the active portion of the reactor... 

To provide a neutronic system wherein the bodies of fissionable material are made available for removal from the system, requiring only a limited period following ces-10 sation of the neutronic reaction for the decay of short-life radioactivity of certain fission products to take place before the removal operation is commenced. 

In order to effect a self-sustaining neutronic reaction 20 at all in a system employing uranium and heavy water, a certain minimum amount of heavy water moderator is required. This minimum quantity is about five tons, provided an c timum arrangement of uranium bodies is used. 

Heavy water, of course, is a liquid and, therefore, must be contained in a tank. This tank may serve as the reactor within which the neutronic reaction takes place. The heat generated during the reaction may be removed by flowing a coolant through the tank necessitating the use of a plurality of tubes in the tank. These tubes pass through the tank walls and are connected to a circulating system. 

Referring now to Figs. 4, 6, 8 and 10, the neutronic reactor is shown at 18 and consists essentially of an elongated horizontally disposed cylindrical tank or shell. The center portion 19 of the reactor is the active part of the system wherein the neutronic reaction takes place and 25 comprises a cylindrical tank 20 containing a quantity of heavy water 21. This tank 20 may be referred to as the reactor tank. 

During the interchange of neutrons in a neutron moderated system of finite size, comprising bodies of any size disposed in a neutron moderator, neutrons may be lost to the chain reaction in four ways by absorption or capture in the uranium content of the bodies without producing fission by absorption or capture in the moderator... 

The neutron detector systems are based on the principle of product registration from nuclear reactions, taking place in the counter volume. Proportional detectors filled by a counting gas containing B or He nuclei are widely used. The following nuclear reactions with neutrons take place ... 

For the BeO systems, since the Be(n, 2n), Be(n, a), and 0(h, a) are all competing fast neutron reactions, the e indicates the net fast multiplication effect of these three reactions therefore, the indicates just the thermal... 

The nanosecond pulsed beam with time gating at the detector and the associated particle method (APM) render the three-dimensional (3D) elemental analysis of solids possible (Overley 1987 Rynes et al. 1999). The APM is based mainly on the D-D and D-T reactions by the detection of He and He particles, respectively, emitted at 180° to the neutron direction. The 4-5 cm/ns travel time of the neutrons allows the imaging of the interrogated volume along the direction of the ns pulsed neutrons with a spatial resolution of 5 cm. Some 2D-3D fast neutron imaging principles and techniques are summarized by Gozani (1994), Mikerov et al. (1998, 2001), and Chen and Lanza (2001), while typical thermal neutron radiography systems are demonstrated by Balasko et al. 1998, 2001) and Shaikh et al. (1998, 2001). 

The basic detection process uses the neutron-alpha reaction in Li. The 4.78-MeV reaction energy produces an easily detected alpha particle with low sensitivity to gamma radiation and good electrical noise immunity. A prototype neutron detection system using a 20-mm gold window surface barrier detector coupled to a LiF foil was tested at the Los Alamos National Laboratory (LANL) Critical Test Facility in the fall of 1968. The detector unit produced an alarm when placed 580 m from a metal assembly producing 5 X 10 fissions in 33 ps. This detector is presently installed in tlie 11 neutron criticality alarm systems at Rocky Flats. 

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