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Conference Article: Measurements of temperature coefficient of reactivity of the VHTRC-1 core by the criticality method.

Abstract

Reactivity decrease due to temperature rise of the whole assembly was measured in a pin-in-block HTGR-type critical assembly, VHTRC, by a criticality method, with purpose to verify the calculation accuracy of the design of the High Temperature Engineering Test Reactor (HTTR). The VHTRC was loaded with coated particle fuel rods containing low enriched UO₂, and it was heated up to 200 deg. C by using electric heaters. The measured reactivity decrease was divided by the temperature increment, resulting a temperature coefficient of reactivity, -1.72x10^-4 DELTAk/k/deg. C. The SRAC code system was applied to the calculation of effective multiplication factor at 300 K, 325 K and 500 K where the collision probability method was used in the cell calculation and the three-dimensional, multigroup diffusion model was adopted in the core calculation. The results gave a ratio of the calculated to the measured value of temperature coefficient of reactivity, 0.98. The temperature coefficient of reactivity for a room temperature range was also measured. The result was 30% smaller than that for a room temperature to 200 deg. C range. This tendency is consistent with the result of early work by the authors using the pulsed neutron method. Finally, it is concluded that the calculation of temperature coefficient of reactivity for HTTR by use of SRAC is sufficiently validated by comparing with the experimental data at VHTRC.

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Reference:

Uncertainties in physics calculations for gas cooled reactor cores. Proceedings of a specialist's meeting held in Villigen, Switzerland, 9-11 May 1990

International Atomic Energy Agency, Vienna (Austria). International Working Group on Gas-Cooled Reactors

IWGGCR--24, pp:119-124