HTGR Knowledge Base

Topical Article 5: Graphite Material Technology

The core, surrounding neutron reflector, and thermal and radiation shielding of a modular HTGR is constructed of ceramic materials capable of withstanding very high temperatures. This capability is an essential property for the passive heat removal feature of the modular HTGR designs. Graphite, the predominant ceramic material, serves as an effective neutron moderator with low neutron absorption properties. The long-term behaviour of graphite under the temperature and irradiation conditions representative of the designs is a complex function of the initial material properties and service conditions.

Extensive experience with graphite behaviour under irradiation has been obtained through experimental testing as well as operation of HTGR plants. In addition, a large body of experience is available from the operation of the carbon dioxide cooled reactors (Magnox and AGRs) developed in the UK. Important aspects of this experience is documented in the proceedings of IAEA meetings on the status of graphite development for gas cooled reactors [TECDOC 690], and on graphite moderator lifecycle behaviour [TECDOC 901]. A report on Irradiation Damage in Graphite due to Fast Neutrons in Fission and Fusion Systems [TECDOC 1154] summarises the vast amount of information that has been accumulated and the understanding that has been gained for the use of those concerned with graphite materials in the future.

The IAEA is supporting the development of a database on irradiated graphite properties, with the comprehensive data available to participating organisations from an Agency web site, and more limited data generally available.