HTGR-UNDERLYING PRINCIPLES AND DESIGN

Abstract

The ultimate goal in developing the High-temperature, Gas-cooled, Graphite-moderated Reactor (HTGR) is to combine in one reactor the high temperature potentialities of gas cooling with high power density and a fuel capable of high burnup. It is believed that the proposed concepted helium- cooled, solid-homogeneous type reactor, in which carbides of fuel and fertilc material are dispersed in graphite-offers the best prospects of realizing these objectives. Some heat transfer characteristics of the proposed reactor are discussed and compared with a Calder Hall reactor. The proposed reactor outlet gas temperatures are of the order of 1,380 deg F, whereas in presently operating gas-cooled reactors the coolant temperature is limited between 650 and 750 deg F. In the proposed design steam may be produced at 1,450 psi and 1,000 deg F, with a thermal efficiency of about 40%, without resorting to re-heat or dual-pressure cycles. The fuel element consists of a graphite sleeve with end fittings which contain the fuel compacts and both top and bottom reflectors. The fuel compact consists of U/sup 235/ and Th/sup 232/ in the form of carbides dispersed in a graphite matrix (1U/sup 235/: 10Th:700C atom ratio). At the operating temperatures (i.e., approximately 2,000 and 3,000 degmore » F for element-surface and centerline temperatures, respectively) of the fuel these carbides are thermodynamically stable. Fission-product control starts in the fuel compacts where roughly one-half of the fission-prcduct elements formed can be expected to remain fixed, either because of their own nonvolatility or because of their formation of stable, nonvolatile carbides. The escaping fission-products are carried to an external trapping system by a helium purge stream that flows between the compact and the outer sleeve. (B.O.G.)« less