Summary: Transition boiling data was taken with an improved flow loop, to explore the influence of loop characteristics on rod temperature fluctuations the transition region was found to be much smaller than for comparable conditions with a different loop. Also the amplitude, and frequency of the temperature oscillations, were significantly less than before. These results indicate that loop characteristic and flow disturbance parameters play a prominent part in governing the transition temperature fluctuations. Additional two-rod transition boiling data are presented. The results include data taken at high wall temperature levels during a demonstration test at low steam qualities, and the effect of a change in rod spacing on heat transfer performance.

A research program is being conducted to obtain experimental data in the irradiation of plutonium-enriched fuel to confirm a theoretical model for predicting isotopic composition and reactivity changes in plutonium-enriched, light-water-moderated reactors. Quarterly progress: Project fuel fins irradiated to 1860, 3000, and 5300 MWD/T have been successfully sampled in the Radioactive Materials Laboratory. The samples have been dissolved and aliquots delivered to Chemistry for Mass Spectrometry and burnup determination. The first Stanford Pool Irradiation indicated that there was some inconsistency in the thermal flux and the near thermal epithermal flux. The experiment was repeated, increasing the number of foil wheel positions from two to three. The data from the second measurement are being reduced. The EPITHERMOS code modification has been completed. Comparisons between the results computed by the code and experimental data show much improved agreement. The metallographic photomicrographs of a polished half-pellet from rod F, irradiated to 5000 MWD/T, show structure very similar to that shown by the pellet from rod S, irradiated to 1860 MWD/T.

Abstract: Continued irradiation experience under the AEC - Euratom, UO2 High Performance Program provided five separate and distinct sets of data on UO2 thermal conductivity. Four of these results are expressed in terms of the value of the thermal conductivity. The first two of these measurements were applicable -- strictly -- to poly crystalline UO2. Recently, three additional sets of measurements have been obtained -- all pertinent to UO2 after the formation of large columnar grains. The extent of melting in the experiments on which the results are based ranges from slight, to greater than 70 percent of the fuel cross section. The conclusions from all of these thermal conductivity measurements considered together are: (1) The true value of the UO2 conductivity integral form 0 degrees C to melting (2805 - 15 degrees C) lies in the range from 90 to 96 W/cm. The most probable value is closer to 90 W/cm. To ensure no central melting and the associated clad swelling the maximum thermal performance level for solid pellet, UO2 fuel rods should not exceed 90 W/cm. (2) Any improvement in thermal conductivity due to the formation of large, columnar UO2 grains is small and not detectable within the …

The United States and the European Atomic Energy Community (Euratom), on May 29, and June 18, 1958, signed an agreement which provides a basis for co-operation in programs for the advancement of the peaceful applications of atomic energy. The work described in this report represents the Joint U.S.-Euratom effort. The over-all development program is designed to obtain the test data and operating experience necessary to eventually realize a 50 percent increase in the output of the Garigliano Nuclear Power Station located at Sessa Aurunca (Campania, Italy). One task is in progress: Task I - Data Logging and Computer System. The work on the other tasks is being planned and initiated.