No abstract

The Mark IIB oscillator rod enables measurement of reactor transfer functions by rotating an absorber material (boron carbide) toward and away from the center of the reactor to perturb reactivity. Its design has eliminated two operating problems encountered with previous EBR-II oscillator rods: bowing and consequent rubbing of the rod in its guide tube, and failure of the seals that prevent air from contacting the sodium coolant. The Mark IIB rod and its drive were installed in EBR-II in April 1971. Both haveperformed satisfactorily since then.

The EBR-II In-core Instrument Test Facility (INCOT) provides the means of inserting instrument sensors into the EBR-II core, exposing them to a fast-neutron flux of 2 x 10 15 nv, and monitoring their performance during their experimental life. The facility includes a thimble assembly that serves as a container for one of three basic types of sensor assemblies, which hold the test sensors during irradiation. The thimble assembly extends from the core, up through the reactor-vessel cover, into the primary-tank sodium, and from there through the small rotating shield plug and onto the operating floor. There it is connected, through a terminal box, to the elevating system that provides the necessary motions to make the facility compatible with reactor fuel-handling operations. Shielded handling containers make it possible to remove individual tests or experiments from the facility and to remove parts of the facility itself. A system for transmitting sensor data carries the sensor signals to the instrument readout and data-logging equipment. This Preliminary System Design Description (PSDD) describes the facility, discusses the principles of operation, and presents pertinent safety precautions.

ThU report wai prepared ai an account of work sponsored by the United States Government. Neither