HTGR Knowledge Base

Conference Article: Nuclear Graphite for High Temperature Reactors

B.J. Marsden, AEA Technology Risley, Warrington Cheshire, WA3 6AT, UK

Abstract

The cores and reflectors in modern High Temperature Gas Cooled Reactors (HTRs) are constructed from graphite components. There are two main designs; the Pebble Bed design and the Prism design, see Table 1. In both of these designs the graphite not only acts as a moderator, but is also a major structural component that may provide channels for the fuel and coolant gas, channels for control and safety shut off devices and provide thermal and neutron shielding. In addition, graphite components may act as a heat sink or conduction path during reactor trips and transients.
During reactor operation, many of the graphite component physical properties are significantly changed by irradiation. These changes lead to the generation of significant internal shrinkage stresses and thermal shut down stresses that could lead to component failure. In addition, if the graphite is irradiated to a very high irradiation dose, irradiation swelling can lead to a rapid reduction in modulus and strength, making the component friable.
The irradiation behaviour of graphite is strongly dependent on its virgin microstructure, which is determined by the manufacturing route. Nevertheless, there are available, irradiation data on many obsolete graphites of known microstructures. There is also a well-developed physical understanding of the process of irradiation damage in graphite. This paper proposes a specification for graphite suitable for modern HTRs.

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key words: Gas Cooled Reactor, Nuclear Technology
Reference:
IAEA Technical Committee Meeting on “Gas Turbine Power Conversion Systems for Modular HTGRs”, held from 14-16 November 2000 in Palo Alto, California
International Atomic Energy Agency, Vienna (Austria). Technical Working Group on Gas-Cooled Reactors
IAEA-TECDOC--1238, pp:174-189