This report is a working document of the UB AEC Nuclear Cross Sections Advisory Group and is issued about twice a year for the purpose of stimulating important cross section measurements. The requests listed in this report have originated from various Atomic Energy Commission contractors, the Advisory Committee on Reactor Physics, and the Nuclear Cross Sections Advisory Group. The distribution is limited to members of the US Nuclear Cross Sections Advisory Group (NCSAG), the US Advisory Committee on Reactor Physics (ACRP), the Tripartite Nuclear Cross Sections Committee (TNCC), the European-American Nuclear Data Committee (EANDC), to US AEC off-site contractors, and to the requestors and measurers of the cross sections listed in this report. The contents of this document are not to be republished in part or in full without special permission of the chairman of the NCSAG, The unpublished data which appear in this report must not be quoted in publications without permission of the experimenter.

The calculation of concentration transients caused by mixing in the interconnected three-body system of the fuel dump tanks, core and blanket has been coded for the IBM-704. The system of equations includes material balances, the dependence of critical temperature on core and blanket concentrations, and the effect of temperature (density) changes on flow rates. The controllable flow rates, the fuel dump tank weight and the initial conditions are input variables. Outputs include core and blanket concentrations, critical temperature, concentration ratio and power ratio. The code has been used to compute transients during a number of operating situations.

An experiment was performed at the ORR in order to find a good fission chamber location. Two locations on the pool side of the reactor tank were explored with a one inch diameter fission chamber. The thermal neutron flux attention was found to vary nearly exponentially with distance, and no shadowing effect could be seen during a reactor startup. The fission products high gamma flux could be discriminated without difficulties. Both positions seem to be adequate to locate a reactor control fission channel.

Experimental determination of heat-transfer coefficients, burnout heat fluxes, and friction factors have been made for swirl flow of low-and moderate-pressure water through electrically heated aluminum, nickel, and copper tubes containing full-length Inconel twisted tapes. For nonboiling conditions, swirl-flow heat-transfer coefficient were successfully correlated with both the Froude modulus (the ratio of inertial to centrifugal forces) and a grouping of the Grashof and Reynolds moduli (ratio of buoyant to inertial forces).

A generalization of Wigner's simple model for the distribution of nuclear level spacings is studied. It is based on a stochastic process which reproduces the correct joing probability distribution of N enerfy levels for small spacings. The case N=3, which includes the effect of the correlation between adjacent spacings, is discussed in detail. The resulting distribution and the correlation coefficient are compared with experimental data. No definite conclusion can be drawn except to say that the effect of the correlations on the spacing distributions on the spacing distribution is very small.