A method is described whereby many types of flaws lying close to the surface of a metal can be ultrasonically detected, regardless of the time duration of the interrogating pulses. Lamb waves are established in the metal between a flaw and the surface by an ultrasonic beam which impinges at the proper angle of incidence. A suitably positioned receiver transducer picks up the waves to reveal the flaw. In this method the usually troublesome surface echo is eliminated from the receiver by an acoustic barrier, making it well suited for routine and automatic testing. Results of applying the technique to several testing problems are discussed.

It has been suggested by many workers in the power reactor field that a more efficient utilization of natural uranium may be obtained in thermal reactors if the Pu produced in a fuel cycle were used to enrich a subsequent cycle in which the irradiation-depleted-uranium would be reirradiated. The work described here was done for the purpose of evaluating the reactivity value of the Pu enrichment under the assumption that all plutonium produced is, after chemical separation, fabricated into separate fuel elements and not alloyed with recycled uranium. It has been suggested that the reactivity value of the Pu decreases with exposure to such an extent that highly burned plutonium should be discarded. We, therefore, wish to look at two of the variables affecting the limiting exposure: the reactivity value of the fuel as a function of exposure and temperature and the fraction of potential fissions which would be discarded as a function of exposure. Though the residence time of the Pu fuel before reprocessing, refabrication, and recycling depends upon the relative decrease in specific power, decrease in reactivity due to fission product build-up, the lifetime of the fuel elements before failure, and the cost of reprocessing, only the first …

Neutron attenuation in the old pile shields is dependent more and more on the slowing down characteristics of the iron as the hydrogen is baked out of the masonite. For neutrons above 1 or 2 Mev, iron does a good job by inelastic scattering. However, below this energy attenuation can be done only by the gradual moderation by elastic scattering to thermal energies with subsequent capture in the iron. Since iron is heavy and thus a poor moderator, there is a good possibility that many neutrons of intermediate energy will leak out of a burned out shield. Also, iron has a large dip in its cross section at 25 Kev which might allow a large burst of neutrons at this energy to leak out. Measurements using a lucite moderator with gold foil detectors indicate a large leakage of neutrons of intermediate energy, but interpretation of these measurements is difficult. These considerations prompted an attempt to get a rough idea of the energy distribution of the leakage neutrons through pure iron using a simple qualitative theory.

Average coefficients of thermal expansion of the temperature range 25 C to approximately 425 C are reported for numerous types of graphite. The dependence of thermal expansion on crystal orientation and crystallite size and the effects of oxidation and cold test hole irradiation are discussed. An empirical relationship between thermal expansion and the initial rate of physical expansion under cold test hole irradiation is formulated.