ORNL measurements at Hanford Waste Tank TX-118

A program of measurements and calculations to develop a method of measuring the fissionable material content of the large waste storage tanks at the Hanford, Washington, site is described in this report. These tanks contain radioactive waste from the processing of irradiated fuel elements from the plutonium-producing nuclear reactors at the Hanford site. Time correlation and noise analysis techniques, similar to those developed for and used in the Nuclear Weapons Identification System at the Y-12 Plant in Oak Ridge, Tennessee, will be used at the Hanford site. Both ``passive`` techniques to detect the neutrons emitted spontaneously from the waste in the tank and ``active`` techniques using AmBe and {sup 252}Cf neutron sources to induce fissions will be used. This work is divided into three major tasks: (1) development of high-sensitivity neutron detectors that can selectively count only neutrons in the high {gamma} radiation fields in the tanks, (2) Monte Carlo neutron transport calculations using both the KENO and MCNP codes to plan and analyze the measurements, and (3) the measurement of time-correlated neutrons by time and frequency analysis to distinguish spontaneous fission from sources inside the tanks. This report describes the development of the detector and its testing in radiation fields at the Radiation Calibration Facility at Oak Ridge National Laboratory and in tank TX-118 at the 200 W area at Westinghouse Hanford Company