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Conference Article: An analytical study on porosity changes of nuclear graphites under high temperature irradiations

Arai, T. (Japan Atomic Energy Research Inst., Ibaraki (Japan). Dept. of High Temperature Engineering)

Abstract

A quantitative description of the changing pore structure, based on some radiation damage mechanisms, may introduce a physically appropriate method for lifetime assessment of graphite fuel and moderator components. Recently Brocklehurst and Kelly have analyzed well-characterized data on dimensional changes of UK reactor graphites to quantify volumetric and linear pore generation terms. The analysis (B/K theory) has demonstrated that a crystal strain parameter XT, depending on irradiation temperature and fluence, is suitable for defining structure factors, which relate changes in microstructure with those in macroscopic properties of a family of nuclear graphites. Graphite components in high temperature reactors are subjected to higher temperatures well above 1000 deg. C, which accelerate pore generation. Their mechanical integrity will suffer from the deterioration, resulting in a reduced lifetime. Previous design considerations on the dimensional change behavior have been based on an empirical approach using measured data obtained in a number of irradiation experiments. A large variety of experimental data have been utilized to develop a general phenomenological model(Graphite Damage Model, GDM) for predicting engineering properties of nuclear graphites. The present study tries to combine the B/K theory with the GDM prediction with a view to characterizing porosity changes at high temperatures of some graphites from different manufacturing routes. The dimensional change data in the literature are analyzed by the GDM to obtain their analytical presentation as a function of temperature and fluence. The results are used to derive an XT function and pore volume change as a function of XT for each grade of graphite. The resulting porosity changes are compared between different kinds of graphites.

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key words: Gas Cooled Reactor, Nuclear Technology
Reference:
Specialists meeting on graphite moderator lifecycle behaviour. Bath (United Kingdom). 24-27 Sep 1995.
International Atomic Energy Agency, Vienna (Austria)
IAEA-TECDOC--901, pp:225-237