G.S. Stanford

Fast-Neutron Hodoscope at TREAT: Methods for Quantitative Determination of Fuel Dispersal

Fuel-motion surveillance using the fast-neutron hodoscope in TREAT experiments has advanced from an initial role of providing time/location/velocity data to that of offering quantitative mass results. The material and radiation surroundings of tha test section contribute to intrinsic and instrumental effects upon hodoscope detectors that require detailed corrections. Depending upon the experiment, count rate compensation is usually required for deadtime, power level, nonlinear response, efficiency, background, and detector calibration. Depending on their magnitude and amenability to analytical and empirical treatment, systematic corrections may be needed for self-shielding, self-multiplication, self-attenuation, flux depression, and other effects. Current verified hodoscope response (for 1- to 7-pin fuel bundles) may be paramatrically characterized under optimum conditions by 1-ms time resolution; 0.25-mm lateral and 5-mm axial-motion displacement resolution; and 50-mg single-pin mass resolution. The experimental and theoretical foundation for this performance is given, with particular emphasis on the geometrical response function and the statistical limits of fuel-motion resolution. Comparisons are made with alternative diagnostic systems.

Fast-Neutron Hodoscope at TREAT: Data Processing, Analysis, and Results

The fast-neutron hodoscope at the Transient Reactor Test Facility is designed for the determination of fuel motion during the course of brief (0.1- to 30-sec) power transients. During the course of a transient test, data must be recorded from each of 334 hodoscope channels at count rates up to 2 million/sec each, down to millisecond time intervals. This is accomplished in a relatively reliable and inexpensive manner by displaying counts from each detector sequentially in binary code on a lamp panel, which is photographed by a high-speed framing camera, producing a film record of the transient test. After chemical development, the film is examined by a computer-controlled flying-spot scanner, and the position and density of candidate lamp images are recorded on magnetic tape. Through further computer processing, these images are sorted and decoded, and the count rate is recovered for each detector at each instant of collection time. A cathode-ray tube and a plotter, both computer controlled, are used to recreate and analyze the fuel motion history of the experiment. Analysis is directed toward fuel distortion or expansion prior to clad failure, slumping, dispersion, amount and rates of movement, post-scram relocation, and ultimate disposition of fuel.

Laser Brightness Verification

Limits on the brightness of ground‐based lasers appear to be straightforward to define and, at high power and with cooperation, to monitor for verification of possible arms‐control treaties. We suggest using potential brightness defined as (beam power)‐ (beam diameter)2/π ‐(wavelength)2 as the appropriate parameter to limit. Actual brightness is quite dependent on atmospheric conditions. The complexities of on‐site monitoring and space‐based lasers are discussed.