Reactivity Effects in Thermal Reactors

Comparison of Experimentally Measured and Analytically Predicted Material Reactivity Worths in the Flexible Critical E3 periment (FCX), V. S. Oblock. S. Salah, W. e Freidhof (W-Astro) 

To validate the analytical methods used nuclear rocket reactor design calculations, dependent materlsd reactivity worths of carl I and polyethylene were measured in the Fiexll Experiment (FCX) reactor at the Westlnghsi nuclear Laboratory. 

Full core length mass changes of U, C, or fwlyethylene were made as a function of radial position. A boron-lined Ion chamber was used to determine the reuctor period (convert to reactivity by use of the inhoir equation) before and after the known mass perturbation to obtain the material reactivity coefficients. The hydrogen worths were obtained by subtracting the carbtm contrlbuUon from the polyethylene. 

For the measurement of the axial worth of polyethylene, 12 two-inch-long rods, each placed at a constant radius from the axial centerline, were remotely moved Internal to the core during slightly supercritical operation. A Face PC-12 analog computer calculated the instantaneous reactivity changes caused by the measured movement of these rods. 

Material reactivity. worths were calculated using the linear first-order perturbation codes, PERT-ilD (modified to Include leakage, corrections for C and H), PERT-2D, and the one-dimensional discrete ordinate transport code ANISN. The radial and axial forward and adjoint angular fluxes used in the PERT-ID and PElftT-2D codes were obtained with ANISN and DOT, respectively. 

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