The present report is concerned with the electronic relay which, upon the reaching of a pre-determined value of ionization current in the associated chamber, actuates the safety rod release mechanism. The are here proposed two independent suggestions: (1) An improved trip circuit of such sensitivity and stability as to allow it to be actuated by a signal directly from the chamber without the necessity of interposing intermediate amplifier stages. The value of chamber current at which tripping occurs is stable to +- 0.4%. (2) A triple-wound relay to prevent shut-downs of the pile which would otherwise be caused by development of defects in the safety circuits.

Calculations were made to determine the temperature at various points of a thick disc and cap, on the assumptions that the heat production rate is uniform throughout the slug and that the slug is in perfect thermal contact with the cap. Results obtained by different methods of computation are compared with each other and with results obtained by Drew on the Paschkis electrical network computer at Columbia University.

The resonance absorption of a lump is described in terms of three components. Calculations of resonance absorption are carried out using the model for the resonance spectrum of uranium recently derived; calculations are also made with variations of this model which involve local fluctuations in level strengths. For metal and oxide lumps the agreement with observation is satisfactory. For dilute mixtures, whose resonance activation was measured by Mitchell, computed values fall 20% to 30% above measured ones.

An attempt is made to estimate the influence of operation upon the mechanical properties of tubealloy. It is to be emphasized that the work is highly speculative, being base upon a set of judicious assumptions regarding the transport material within the metal and should not be used as a substitute for a set of well-planned experiments. The two principal effects considered are the hardening which results from the atomic displacement produced by the fission fragments and the changes in mechanical properties arising from the presence of the fission products. The principal conclusion to be drawn is that the disruption of the metal which accompanies operation takes place at at sufficiently high rate that it could readily cause serious changes in the mechanical properties of the slups. the reversal of the disruption resulting from thermal effects probably is sufficiently high to prevent serious embrittlement as a consequence of displacement through most of the volume of the slug if not at the surface. On the other hand, the migration of atoms also appears to be sufficiently high that the rare gas products may have time to diffuse to cracks and produce embrittlement.

The transition region between two parts of a pile which have different compositions is investigated. In the case where the moderator is the same in both parts of the pile, it is found that the diffusion constant times thermal neutron density plus diffusion constant times fast neutron density satisfied the use pile equations everywhere, right to the boundary. More complicated formulae apply in a more general case.