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Conference Article: Analysis of nuclear graphite core components in HTRs and a critique on conventional approaches

Willaschek, J.G. (Internationale Atomreaktorbau G.m.b.H. (INTERATOM), Bergisch Gladbach (Germany, F.R.))

Abstract

The radial reflector of High Temperature Reactor (HTR) cores is a wall of piled blocks of nuclear graphite surrounding the reactor core. The use of graphite as structural material presents a number of problems especially when the graphite is to be used in a type of HTR being presently developed, a pebble bed reactor with OTTO-fueling load conditions. These load conditions result in a high fluence of fast neutrons - mainly in the upper core range - and lead to material problems related to material properties under HTR environmental conditions. The properties to be considered are irradiation-induced dimensional changes and creep as well as variations of material properties and strength under irradiation. This paper presents an analysis of a radial reflector concept for use in a 300 MWth HTR for process heat production. This concept of a pebble bed reactor (OTTO cycle) requires reflector dimensions and shapes which have previously not been used and which may exceed acceptable stress limits. The calculated reflector element is assumed to lie in the region of peak fast fluence (3.1022 n/cm2 EDN) and low temperature (400oC). Three-dimensional inelastic analysis of a graphite block was performed. The influence of irradiation on dimensional stability and other material properties was taken into account. Numerical results were obtained with the finite-element computer code ADINA. A point of very general interest was to perform a two-dimensional inelastic analysis of the same component to provide a means of comparing the three-dimensional work with a more conventional approach

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key words: damaging neutron fluence; graphite; htgr type reactors; pebble bed reactors; physical radiation effects; shields; stress analysis; thermal stresses; carbon; computer codes; gas cooled reactors; graphite moderated reactors; homogeneous reactors; neutron fluence; radiation effects; reactors; solid homogeneous reactors
Reference:
Specialists meeting on mechanical behaviour of graphite for HTRs, Gif-sur-Yvette, France, 11-13 June 1979.
International Atomic Energy Agency, Vienna (Austria). International Working Group on High-Temperature Reactors.
IWGHTR--3, pp:36-41