The wide use of liquid oxygen as an oxidant in rocket engines has resulted in an increased interest in low-temperature heat transfer. Storage tanks for this type of application, being uninsulated, contain a boiling-liquid low-temperature sink, which is susceptible to environmental heat inputs and subsequent liquid loss by vaporization. Such losses are difficult to predict due to the complex combination of ambient conditions which exist, and the lack of knowledge concerning their combined effects. Heat transfer in this field is difficult to analyze primarily because of its transient nature. This is a result of such factors as: (1) the growth of an insulating frost layer on the outer surface of the container, with its accompanying energy transfer to the system; (2) the temperature dependent convective air pattern that surrounds the container, (3) the transfer of radiant energy to the system, and (4) the mechanical failure of the frost itself with subsequent sloughing from the container wall. A lack of knowledge regarding the coefficient of diffusion of water vapor through air and the thermal conductivity of frost in this depressed temperature range further complicates the predictions of heat transfer.

This paper describes the measurement of control rod strength in the PCTR. The first section outlines the theory and method of such a measurement, and the second section presents the results of the measurement of the Experimental Gas Cooled Reactor (EGCR) control rod strength. The reactor parameter actually inferred is the difference in the infinitive multiplication factor for a control rod supercell with and without the control rod in place in the supercell. These measurements are, therefore, very closely related to the measurement of k∞ for an ordinary lattice cell.