Abstract: (1) Grain growth in UO2 pellets was studies between 100 C and 2600 C. The pellets were encapsulated in small vacuum-tight tungsten containers in an argon atmosphere. (2) The grain size-time relationship could be expressed by an equation. A low exponent, m>_ 1/3, was found in those experiments and is related to the type of UO2 investigated. An activation energy of 65 kcal/mole was obtained for the grain growth process. The time exponent, m, increased with increasing temperature if the pellets were not contained in closed capsules bu heated under an argon pressure of 1.5 atm. (3) An interaction between tungsten and UO2 could be observed at a a temperature of 2600 C after prolonged heat treatment.

Summary: The Mixed Spectrum Superheater (MSSR) is an integral superheater reactor in which boiling occurs in an annular Boiling Water Reactor section and steam in superheated in an unmoderated fast section in the center. A Mixed Spectrum Critical Assembly (MSCA) to be operated at the Vallecitos Atomic Laboratory has been designed to mock up a 75-150 MWe prototype MSSR. The principal experimental measurements aimed at proving the feasibility of the MSSR concept include power distribution, Doppler effect, flooding effects, distribution of reactivity, control rod worths, and the effect of the control system on the power distribution.

Introduction: The purpose of this technical report is to review the water chemistry methods and equipment developed for use with the Maritime Loop Irradiation Program conducted in the General Electric Test Reactor (GETR) from December 2, 1960 to July 19, 1962. Special emphasis is given to areas having general application to other high purity water systems. The Appendix includes a discussion of specific conductivity and pH in high purity water systems. A major section of this report is devoted to a review of gross activity levels on coupons of two different surface finishes exposed in the loop coolant system for various time intervals. A major objective of the chemistry program was to select or develop analytical methods such that the analyses could be performed at the loop location by technical personnel who normally operate the loop. By this means, frequent samples were obtained and analyzed directly thus providing close monitoring and control of the loop water chemistry at minimum expense.