Edgar F. Bennett

The Rice Formulation of Pile Noise

AbstractSpectrum and variance of “pile noise” are discussed according to the formulation of S. O. Rice. It is shown that variance diverges as criticality is approached. A convergent quantity closely related to variance is introduced and observations on this quantity taken with ZPR-IV′, a light water-moderated highly enriched source reactor at Argonne.

Experimental results for Phase II of the JAERI/USDOE collaborative program on fusion blanket neutronics

As the first period of the Phase II series of the JAERI/USDOE collaborative program, neutronic parameters have been measured for a simulated Li 2 O/Be breeder blanket in closed geometry. The experimental system consists of a lithium-oxide test zone and a lithium carbonate enclosure containing a DT neutron source at the Fusion Neutronics Source (FNS) facility at JAERI. Tested blankets were of three 5 cm thick configurations of beryllium neutron multiplier zone. The experiments were performed to examine spatial distributions of reaction rates and the neutron spectrum in the source cavity, and relative profiles of the tritium production rate (TPR), reaction rates, and neutron spectra between the beryllium configurations. A zonal TPR measuring technique, suitable especially for direct comparison with a Monte Carlo method, was applied to a steep gradient distribution. The experimental results of TPRs showed that the beryllium sandwiched system provided the most effective TBR gain (integrated TPR) of about 20% compared with the non-multiplier system. The reaction rate distributions and neutron energy spectra were also provided to test a calculational code system for nuclear design.

Phase III experimental results of JAERI/USDOE collaborative program on fusion neutronics

Abstract A pseudo-line D–T neutron source has been developed with new experimental techniques. This line source was applied in sophisticated neutronics experiments for an annular blanket arrangement simulating the tokamak geometry, as a new series in the JAERI/USDOE collaborative experimental program on fusion neutronics. The source characteristics of the present line source and the measurements for an annular assembly are described. The discussion on the experimental results focuses on the tritium production rate measured in an annular blanket and comparisons were made with the previous point source experiment, and also between the annular blankets with and without an armor reflector of graphite.

Phase-IIB experiment of JAERI/USDOE collaborative program on fusion blanket neutronics

As a part of the Phase-II experimental series of JAERI/USDOE collaborative program on fusion blanket neutronics, the phase-IIB experiment has been performed. The experiment provides information of neutron multiplication and reflection by the inner berryllium layer in a full-coverage blanket geometry. The measurements were carried out at the positions in the test zone on tritium production rate (TPR) using various methods, on reaction rate using foil activation technique and on neutron energy spectrum using NE213 and gas proportional counters. The experimental results showed that the effect of the full-coverage beryllium was a 10% increase for T/sub 7/ (TPR for /sup 7/Li) and a factor of 2-5 increase for T/sub 6/ (TPR for /sup 6/Li). The increase of the integrated TPR for natural lithium (T/sub n/) in the test zone due to the inner beryllium layer was above 60% compared to the non-beryllium system in the Phase-II geometry.

Measurements of the Source Term for Annular Blanket Experiment with a Line Source: Phase IIIA of JAERI/USDOE Collaborative Program on Fusion Neutronics

AbstractA pseudo line DT neutron source has been realized by moving an experimental assembly with respect to a point DT source in the Phase-III experiment of JAERI/USDOE collaborative program on fusion blanket neutronics. In order to examine characteristics of the pseudo-line source made by two types of operational modes, source term experiments were carried out. Neutron flux distribution above 10 MeV was measured by NE213 scintillator with stepwise source mode. The reaction rate distributions were also measured by activation foil technique with continuous source mode. The measured distributions were almost flat over central 1 m region of the simulated line source and agreed relatively with a simple calculation assuming the ideal line source. From these experimental results it was concluded that both modes worked successfully to obtain the pseudo-line source and could simulate well neutron flux distribution emitted from a finite length line source with small influence of reaction kinematics and target str...

Measurement and analysis of low energy neutron spectrum in a large cylindrical iron assembly bombarded by D-T neutrons

Abstract The experimental measurement of low energy neutron spectra in a large iron assembly is essential to examine nuclear data and neutron transport codes for nuclear heating estimations in the superconducting magnet of a fusion reactor as well as shielding design. In-situ neutron spectra between a few keV and 1 MeV in a 0.95 m thick cylindrical iron assembly, bombarded with D-T neutrons, have been measured, using a proton recoil gas proportional counter (PRC). A newly developed data acquisition system for PRC was adopted, where high voltage varies continuously in ramped shape during acquisition. Experimental analyses were performed by the DOT3.5 and MCNP codes with cross section sets based on the JENDL-3 nuclear data library. From the comparison between the measured and calculated neutron spectra, the following facts were obtained. The calculation by DOT3.5 overestimated the experiment by a factor of about 2 for the flux below 500 keV in the front parts of the iron assembly and underestimated by more than a factor of 2 for the flux above 500 keV in the rear parts. The calculation by MCNP gave a general agreement with the measurement, but the discrepancy above 100 keV increased as the detector position moved deeper into the assembly. The calculation above 500 keV underestimated the measured spectrum by more than 30% at the 0.81 m depth.

PRECISION LIMITATIONS IN THE MEASUREMENT OF SMALL REACTIVITY CHANGES

Expected errors in reactivity measurements made with a servo control are discussed and compared with observation. The influence upon measurement statistics of a residual spurious reactivity drift, of variable detector efficiency, and of servo control parameters was examined and compared with results using a thermal reactor at 72 watts. Power limited precision is shown to be obtainable with a servo control over a broad range of operating configurations and with good discrimination against incoherent residual reactivity drift. (auth)

Characteristics of a Deuterium-Tritium Fusion Source on a Rotating Target Used in Simulated Fusion Blanket Experiments

The neutron source characteristics of the Japan Atomic Energy Research Institute (JAERI)/U.S. Department of Energy collaborative program on fusion neutronics Phase-IIA and -IIB experiments are determined by measuring neutron spectra and various activation rates in the cavity and on the inner surface of the enclosure and the test regions. The analyses are performed by both JAERI and the United States using individual nuclear data and transport codes. The neutron spectra are generally well predicted by both Monte Carlo and S{sub n} calculations in the energy range of 15 MeV to a few kilo-electron-volts, except for energies 10 to 1 MeV. The discrepancies between the measured and the calculated activation rates are within {+-}10% when recently evaluated nuclear data are used. Through the present investigation, the characteristics of incident neutrons in the test region can be satisfactorily predicted. 10 refs., 22 figs., 1 tab.

Japan Atomic Energy Research Institute/United States Integral Neutronics Experiments and Analyses for tritium breeding, nuclear heating, and induced radioactivity

A large number of integral experiments for fusion blanket neutronics were performed using deuterium-tritium (D-T) neutrons at the Fusion Neutronics Source facility as part of a 10-yr collaborative program between the Japan Atomic Energy Research Institute and the United States. A series of experiments was conducted using blanket assemblies that contained Li 2 O, beryllium, steel, and water-coolant channels with a point neutron source in a closed geometry that simulated well the neutron spectra in fusion systems. Another series of experiments was conducted using a novel approach in which the point source simulated a pseudo-line source inside a movable annular blanket test assembly, thus providing a better simulation of the angular flux distribution of the 14-MeV neutrons incident on the first wall of a tokamak system. A number of measurement techniques were developed for tritium production, induced radioactivity, and nuclear heating. Transport calculations were performed using three-dimensional Monte Carlo and two-dimensional discrete ordinates codes and the latest nuclear data libraries in Japan and the United States. Significant differences among measurement techniques and calculation methods were found. To assure a 90% confidence level for tritium breeding calculations not to exceed measurements, designers should use a safety factor >1.1 to 1.2, depending on the calculation method. Such a safety factor may not be affordable with most candidate blanket designs. Therefore, demonstration of tritium self-sufficiency is recommended as a high priority for testing in near-term fusion facilities such as the International Thermonuclear Experimental Reactor (ITER). The radioactivity measurements were performed for >20 materials with the focus on gamma emitters with half-lives <5 yr. The ratio of the calculated-to-experimental (C/E) values ranged between 0.5 and 1.5, but it deviated greatly from unity for some materials with some cases exceeding 5 and others falling below 0.1. Most discrepancies were attributed directly to deficiencies in the activation libraries, particularly errors in cross sections for certain reactions. A microcalorimetric technique was vastly improved, and it allowed measurements of the total nuclear heating with a temperature rise as low as 1 μK/s. The C/E ratio for nuclear heating deviated from 1 by as much as 70% for some materials but by only a few percent for others.

Design and techniques for fusion blanket neutronics experiments using an accelerator-based deuterium-tritium neutron source

The experiments performed in the Japan Atomic Energy Research Institute/U.S. Department of Energy collaborative program on fusion blanket neutronics are designed with consideration of geometrical and material configurations. The general guide that is used to design the engineering-oriented neutronics experiment, which uses an accelerator-based 14-MeV neutron source, is discussed and compared with neutronics characteristics of the reactor models. Preparation of the experimental assembly, blanket materials, and the neutron source is described. A variety of techniques for measuring the nuclear parameters such as the tritium production rate are developed or introduced through the collaboration as a basis of the neutronics experiments. The features of these techniques are discussed with the experimental error and compared with each other. 25 refs., 15 figs., 4 tabs.