Work during this report period includes a continuation of the study of the effect of krypton 85 on the polymerization of styrene; an attempt at evaluation of the polymers produced; and the effect of krypton radiation on the electrical properties of gases, such as the rare gases, and nitrogen, and oxygen. the results obtained are summarized in the report.

The overall scope of the program encompasses both research into the physical parameters involved in the collection of airborne radioactive particles and the development, fabrication and calibration of balloon-borne sampling equipment to enable the precise determination of stratospheric particle concentration and particle size distribution.

Thorium Procedure: As was mentioned in the last report, ammonium nitrate was substituted for ferric nitrate as a salting agent. Also, the acidity of the nitrate solution was reduced from 3.0 molar to 0.5 molar. the revised thorium procedure is described in the report. Radium Procedure: Work has ben initiated on the procedure of Petrow, Nietzel and DeSesa (Winchester Procedure) to determine if the procedure is suitable for very low level concentrations of radium.

Lithium fluoride crystals were quenched into silicone oil from near the melting point. The return to an equilibrium structure during annealing was observed by means of mechanical tests and etching techniques. Crystals containing three levels of impurity, zone refined, commercially pure, and doped with 0.05 mole per cent magnesium, were used in order to separate the effects of foreign ions from those of thermal vacancies. The changes of mechanical properties produced by quenching and by subsequent annealing were generally attributable to point defect-dislocation interactions. Precision density determinations indicated that about 10% of the equilibrium concentration of vacancies at the melting point was retained at room temperature by the quench. The density could be restored to its normal value by annealing. Two important annealing stages were observed. At about 200 deg C the precipitation of impurities retained in solution by the quench caused a sharp increase in the hardness as measured at room temperature. Isothermal annealing revealed the hardening process to have an activation energy of about 0.5 ev which is probably the energy for migration of an associated magnesium ion-lithium vacancy pair. Between 300 and 400 deg C the removal of dislocations and probably vacancy clusters resulting from the quench …

SNAP II is the designation for a nuclear auxiliary power unit, designed primarily for utilization in the WS117L satellite vehicle. The SNAP II system consists of a reactor heat source, a mercury Rankine engine, and an alternator. Dynamic analysis of the power conversion system was conducted utilizing a comprehensive analog computer simulation. Feasibility of a parasitic load control for numerous system disturbances was demonstrated. This analysis was performed under a subcontract to to Atomics International as part of the Atomic Energy Commission Contract No. AT(11-1)-GEN-8.

The development of nuclear reactors and other nuclear particle sources has given the analyst a new analysis method which can be successfully applied to the determination of microgram and submicrogram quantities of many elements. Known as "radioactivation analysis", this method is one in which an "activation" by some type of nuclear reaction is used to produce a radioactive isotope of the element to be determined. Since this radioisotope decays with its own characteristic radiations and half-life, it is possible to make radioactivation analysis a very specific analysis. Chemical separations of the radioisotope are employed whenever necessary and its radioactivity measured by some type of radiation counter.

A helium coolant purification system was designed for the proposed 800 MWT Pebble Bed Reactor. The purification system will operate on a coolant side stream with a flow rate 1% of the total coolant flow and there are provisions for radioactive and non-radioactive contamination removal.

In the Communications of the ACM of April, 1960, p. 240, there appeared two Algol algorithms for the computation of In, the modified Bessel function of the first kind. One of these algorithms uses a convergent series and the other an asymptotic series. Their author, Dorothea S. Clarke, did not give any information with regard to which algorithm is more appropriate in a given situation (a given situation meaning the computation of In (x) for a definite pair of numbers n and x). Such information is necessary, however, if the algorithms are to be useful, particularly since the asymptotic series is in many cases not valid.

The ORNL analog computer was used to examine one aspect of a safety system for the EGCR. The thermal behavior of the fuel as a result of increases in reactivity at various power levels and gas flows was examined. Safety actions initiated by wither a flux-minus-flow signal or a reactor outlet gas temperature signal were included in simulation.

The steady-state radial and axial temperature profiles of an E. G. C. R. 5 1/2" O. D. through tube are determined for the test condition of an attemperated fuel assembly operating at 1500 KW in the loop. The profiles are determined for the case of the central control rod fully inserted and bank insertion to 62 inches (Δk = 0.025). The data are presented in the form of tables and curves.

The thermal-neutron flux prevailing near the upper hole in the HRE-2 core wall was determined from measurements of the induced activity in a specimen cut from the edge of the hole. The specimen was removed following run 21 and was thus exposed to reactor neutrons during runs 13, 14, 16,17, 18. 19, 20, and 21. The neutron flux, calculated for an average core power level of 2 Mw, was 2.8 x10^13 neutrons/cm^2 sec. the core wall area from which the specimen was removed was located approximately 16-in. from the core center.

Multigroup one-dimensional calculations were done recently to obtain estimates of critical masses, power density distributions and fissioning spectra for some homogeneous molten salt reactors having outer reflectors and central "islands," placed inside the currently proposed MSRE vessel. For a 5-inch-thick outer reflector and 1-ft-diamter island, both beryllium, the calculated critical mass is 108 kg; 40 percent of the fissions occur at thermal, and the maximum power density of 3.9 times the core mean power density occurs at the island-salt interface. If the reflector thickness is increased to 10 inches, the critical mass is reduced to 34 kg; 67 percent of the fissions occur at thermal, and the peak power density of twice the core mean again occurs at the core island-salt interface.

The pneumatic temperature probe (PIM) is a device for measuring gas temperatures by utilizing the dependency of the flow of gases through a restriction on the temperature and pressure conditions. The determination is made by measuring critical mass flow across a restrictive element such as a nozzle and by knowing the upstream pressure and other variables pertinent to the critical flow equation, computing the temperature at the entrance to the restrictive element. In practice it has been found useful to use two critical flow nozzles in series and measure the ratio of the pressures at the nozzle inlets, together with the temperature at the downstream nozzle. The limitations of present thermocouple materials for long term use at elevated temperatures makes resort to this device attractive on many installations.

After shutdown heating rates have been calculated for the target, control plates, and the beryllium reflector of the HFIR. Hilvety previously calculated the after shutdown heating rates in the element and his results are reported in ORNL CP-60-4-110. Decay times of 1.0 10, 10^2, 10^3, 10^4, and 10^5 seconds have been considered, and heat fluxes have been computed for all of the mentioned components. The greatest heat fluxes were found to be at the surfaces of the control plates and the permanent beryllium reflector.

The feasibility of improving the mechanical properties at 1700-1800°F of oxidation-resistant Fe-Al-Cr alloys by means of a refractory dispersion has been explored. A literature search was conducted, preliminary experimental determinations of properties of the alloy and its oxides were carried out, and certain mathematical relations between dispersion characteristics and metallurgical variables were derived. The results indicate that the alloys can be strengthened sufficiently by using a dispersion with an interparticle spacing of about 2-3 µ. High-temperature native oxides of the Fe-Al-Cr alloy consist largely of Al2O3 and in theory would serve as a satisfactory second phase.

In a gas-cooled reactor operating at very high power density the thickness of the reflector may be determine by the requirement that the steel pressure vessel be protected from an excessive dose of fast neutrons, rather than by the usual requirements of neutron economy and power distribution. It is important the the reflector not be made thicker than necessary, since an increase in pressure vessel diameter can result in a marked increase in cost, as well as a decrease in the permitted gas pressure level.