HIGH-TEMPERATURE GAS-COOLED REACTOR CRITICAL EXPERIMENT AND ITS APPLICATION

Two types of critical experiments were conducted in support of the 40- Mw(e) Peach Bottom HTGR nucleardesign program. The first was the test-lattice experiment, where detailed measurements of reaction rates were examined in a lattice having a cold neutron spectrum characteristic of the HTGR. This program provided a method for checking the resonance integral of thorium, the Doppler coeificient of thorium, the detailed flux distribution in the lattice, and control-rod effectiveness within a cell. The second experiment was designed as a gross test of the calculational procedures and data. A small critical experiment having a clean geometry and a composition similar to that of the HTGR was constructed. This assembly had approximately one-sixth the volume of the HTGR core and was surrounded on all sides by a 2-ft graphite reflector. Owing to the small core size and the large reflector area, this experiment provided a severe test of the calculational methods. Experiments with this facility encompassed reactivity-coefficient measurements, neutron-flux distributions, effectiveness of groups of control rods, and a measurement of the overall temperature coefficient. (N.W.R.