The Pebble-Bed Reactor Experiment (PBRE) was designed to advance the pebble-bed concept by providing a test of characteristic features and make contriliutions to the general development of all-ceramic gas-cooled reactors. The following objectives were established for the reactor experiment: to investigate key features of the pebble-bed concept, including on-stream fuel handling, movement of fuel through bed, and performance of core; to obtain operation and maintenance experience with a system contaminated with fission- product activity; and to investigate the behavior of graphite fuel elements. A fourth objective, study of the behavior of core materials at conditions occurring with exit gas temperatures in the range 2000 to 2500 deg F, was tentatively included. The preliminary design oE a 5-Mw(t) reactor for achieving these objectives was prepared. The core of the PBRE is a 2 1/2-ft-diam, 4-ft-tall cylinder containing approximately 12,000 spherical graphite fuel elements 1 1/2 in. in diameter. Fuel spheres are added to and removed from the core by gravity flow, and these operations are performed while the reactor is at power by using pairs of valves for passage of elements into and out of the high-pressure system. Exposed fuel can be recycled to the top of the core. Helium coolant at 500 psia enters the bottom of the core at 550 deg F and emerges from the top at 1250 deg F. Concentric ducting connects the reactor to a single heat exchanger, which is located sufficiently high above the core that natural circulation will suffice to remove afterheat in the event the blower ceases to function. The coolant flow path is such that the entire pressure envelope is swept with helium at the temperature at which it emerges from the heat exchanger. Provision for semi- remote maintenance of contaminated components is emphasized in the layout, and most of the equipment in the primary and auxiliary systems is accessible from above by the removal of modular shielding units. Thc design permits replacement of the entire core graphite structure, The reactor can be adapted for testing core materials at high temperature by attemperation of the hot helium emerging from the core wwiih cool gas in a plenum in the upper graphite structure. Location of the PBRE at the site of the HRE-2 facility is proposed to take advantage of available buildings and services, but the reactor and auxiliary equipment will be contained in a completely new vessel located adjacent to the existing building. The design and direct construction cost of the reactor plant is estimated to be 958,000, allowance for contingencies, overhead, and escalation brings the total to ,260,000. High-temperature operation can be achieved when desired for an additional expenditure of less than 0,000. (auth)
