For many years effort has been directed toward the development of means for the practical utilization of the heat evolved from the radioactive decay of certain fission and irradiation products. Fission products, in view of their availability in the plentiful, high-level wastes resulting from the processing of irradiated, nuclear reactor fuels have been most intensively studied for applications where their heat of decay might be converted into useful energy such as electricity for the operations of certain devices in place of chemical batteries . In addition other materials having desired radioactive properties may be produced by neutron bombardment of readily available elements.

Sinterability studies on mixtures of UO2 and PuO2 powders have been continued. All of the censities from previous sintering experiments have been recalculated utilizing a somewhat different water immersion technique. Since densities of pellete obtained by physical dimensions are inaccurate due to chipping, and water immersion does not account for the open porosity, the pellets were coated with clear krylon before being immersed in water. This effectively sealed the open pores. Plots of density versus composition still indicate a drastic reduction in UO2 sinterability with even the slightest additions of PuO2 and a rapid increase with PuO2 contents greater than 20 weight percent. The following table compares densities of pure UO2 and PuO2 after an eight hour soak time:

Conceptual design studies conducted at HAPO indicate that the improved thermal efficiencies which can be obtained in a high pressure, high temperature, nuclear-electric power plant might reduce unit power costs substantially. The Plutonium Recycle Test Reactor (PRTR) is designed primarily to investigate various facets of plutonium recycle operation. In order to increases the usefulness of the PRTR as an experimental tool, it is desirable to include facilities for testing materials and fuel concepts under a variety of conditions, including the high temperatures and pressures which may be encountered in future water-cooled power reactors.

Plutonium Oxide Fuels. Mixtures of PWR grade UO2 containing 10, 20, 30, 40, 50, and 60 w/o PuO2 were sintered in hydrogen for 44 hours at 1600 C to get additional data on solubility in this system. Densities of all the pieces were low, approximately 80 percent of theoretical; however, solid solution formation was complete in every case. The low density material should not affect lattice parameter values, but it did slightly reduce the intensity of the reflections.

Plutonium Fuels Development Basic studies. Experiments to determine the effect of plutonium dioxide additions on the sinterability of UO2 have continued. PuO2 has been added to ball milled PWR grade UO2 as a physical mixture, and in the form of the mixed crystal oxide.

The ambient temperature of the Columbia River is of interest to the Aquatic Biology Operation since it provides a basis for controlling the temperatures in various experimental tanks which contain Columbia River organisms and since it provides some indication of whether conditions are favorable for the valuable species of fish living in the river. Since the start-up of the plant, temperatures of the river water have been taken in the several water treatment plants.

Basic Studies. It has been reported previously that mixed crystals of PuO2 and UO2 have a higher sintering rate than UO2 alone. However, results to the contrary were obtained on addition to 1/4, 1/2, 1, 2, 5, and 10 w/o PuO2 to PWR grade UO2. Pellets of the above concentrations were heated for one hour in hydrogen at 100 C intervals from 1000 to 1600C.

Two Zircaloy-clad capsules (GKH-14-19,20) containing two compacts each of high density PuO2-UO2 mixed crystal oxides were shipped to the MTR in December 2, 1958. The compacts contain 0.026 a/o PuO2, have densities of 91 percent of the theoretical value, and will generate the same specific power as an Al-1.8w/o Pu alloy rod of the same diameter would produce. Two capsules (GKH-14-21,22) have been prepared and contain three compacts each of low density, about 65 percent of the theoretical value, PuO2-UO2 mixed crystal oxides. It is tentatively planned to ship the last two capsules during January 1959.

PuO2-UO2 Irradiation Capsules. Four capsules of Zircaloy-clad, sintered PuO2-UO2 mixed crystal oxides in a UO2 matrix are awaiting irradiation in the NTR.

The PRTR pressure loop is an experimental facility to be installed in the Plutonium Recycle Test Reactor, Building 309, for use in testing the feasibility of reactor cooling systems utilizing high pressure water or steam as the coolant. It will furnish operating experience with such systems and serve to test fuel elements and components designed to operate in such environments.

A series of tests conducted in an attempt to reduce the observed O2 content of primary recirculation loop water to a value of <0.14ppm by the current loop method which is a combination of pressurizer degasification and venting flow.

Basic Studies. Sinterability experiments in the system UO2-PuO2 have continued, and data are available at one hour hold times across the UO2-PuO2 composition limits. Sintered densities appear to be markedly dependent on pressed densities with densification occurring very rapidly at higher pressing pressures. The following table illustrates the effect of one hour at temperature on final density for pure plutonium dioxide pressed to both 40 and 60 percent of theoretical density.

On a project of the magnitude and complexity of the Plutonium Recycle Test Reactor is was considered prudent engineering practice to obtain an independant design review by a competent off-site group that had not participated in any way in the development of the design. Accordingly, the Atomic Power Equipment Department of the General Electric Company was requested to make such an engineering review, and an Assistance to Hanford contract authorizing this work was approved by the Atomic Energy Commission in November, 1958.