CALIBAN and Godiva-IV measurements using helium-3 detector systems

CALIBAN and Godiva-IV are both fast burst reactors with HEU cores. A description and comparison of the two assemblies is presented. Joint LANL and CEA measurements were conducted to measure configurations on the CALIBAN and Godiva assemblies using He-3 detector systems. Measured configurations included many subcritical configurations at various reactivity states as well as configurations at and above delayed critical. The subcritical and delayed critical measurements were analyzed using the Hage-Cifarelli formalism of the Feynman Variance-to-Mean method. This analysis can be used to calculate the multiplication of each configuration, from which the multiplication factor and reactivity are determined. These results are compared to the reactivity states based upon control rod worth curves and MCNP simulations. For each delayed critical configuration an estimate of the delayed neutron fraction is also calculated. Traditionally subcritical neutron noise methods have not been used on systems at, near, or above delayed critical. This work discusses the use and problems encountered of such methods in this regime. Count rate measurements from the positive period configurations were also very accurate but correlated neutron analysis for these configurations was not successful. Very few data sets which can be analyzed using neutron multiplicity analysis exist over such a large range of reactivity values (-$20 to +$0.14). (author)