Fuel Rod Assemblies Research Articles

A computation method for the steady state thermohydraulic analysis of fuel rod bundles with single phase cooling

A detailed description is given of a thermohydraulic subchannel analysis of multirod fuel bundles with single phase cooling. Both grid spacers and helical wire spacers are considered. An analytical mathematical approach has been adopted for computing the axial distribution of subchannel coolant temperatures. The computation method has been applied to fast reactor fuel elements with liquid metal cooling. Intersubchannel heat transport mechanisms are discussed in detail. Numerical results centre on the effect a lateral power gradient has on the temperature field in a hexagonal fast reactor fuel rod assembly. An important result obtained, is that for large hexagonal fuel rod assemblies intersubchannel heat transport does not contribute to the attenuation of circumferential flow duct temperature differences. This holds both for assemblies with grid spacers and those with helical wire spacers.

Dynamic response of fast-reactor core subassemblies

A program for predicting the behavior of the hexagonal fuel assembly duct when subjected to internally generated pressures in the LMFBR is described. To a large extent, studies have been made with two-dimensional models of the hexcan. In these problems, the loadings must be restricted to line loads of sufficient length so that axial effects can be neglected. The finite element models range from a single hexcan to models which include both the loaded hexcan, two adjacent rows of hexcans, the coolant layers between hexcans, and the fuel rod assemblies. A nonlinear, transient finite element program called STRAW is used for the analyses. The program accounts for both geometric and material nonlinearities, and has special features for treating the coolant layer between hexcans by a quasi-Eulerian description and vertical flow in the hexcans and layer so that motions of the coolant can be accurately analyzed. The model has been used with loadings ranging from 500 psi to the kilobar range, and has yielded significant results on damage in adjacent assemblies and the restraining effects of the coolant. For example, preliminary results have shown that deformations of the loaded hexcan are reduced by 25 to 50% when the role of the coolant is included and that corner ductility has very large effects on hexcan response.

Forced-flow interchannel mixing model for fuel rod assemblies utilizing a helical wire-wrap spacer system

A forced-flow interchannel mixing model is presented which is applicable to LMFBR fuel assemblies containing helical-wire spacer systems. The model accounts for the directional nature of the interchannel mixing mechanism, and can be incorporated into the COBRA-II and COBRA-III B lumped-parameter computer codes. Predictions based on this model are compared with available experimental data, and with results computed using turbulent mixing models. Recommendations are made for designing future mixing experiments in rod-bundles containing helical-wire spacer systems.

Theoretical Heat Transfer Predictions for Finite Nuclear Fuel Rod Assemblies

Temperature distributions in an idealized nuclear fuel assembly were computed and studied parametrically. The assembly, which consists of a square array of spacer-free fuel elements, is bounded by ...

Vibration of the fuel assembly of a marine reactor

Experimental and theoretical investigations on the lateral vibration of a fuel rod assembly of a light water ship propulsion reactor in air and water medium. This study of the dynamic behaviour of the fuel assembly yielded design information needed for avoiding resonance vibration which could be induced by vibrations of the hull of the ship.

Identification of Products in the Radiolysis of Liquid Benzene

Liquid benzene was irradiated by Co/sup 60/ gammas in a cell which continuously extracted the non-volatile fractions during the irradiation as weil as in a static cell irradiated by the radiations from spent fuel rod assemblies. The noncondensable products were found to contain a C/sub 12/ fraction containing biphenyl, phenylcyclohexadiene, phenylcyclohexene and bicyclic compcunds in which neither ring is aromatic. A C/sub 18/ fraction containing hydrogenated terphenyls as well as a higher molecular weight fraction were also found. No evidence was found for cyclic compounds with non-cyclic substituents. The results are explained in terms of a fixed fraction of excited benzene reacting with benzene to form two of the major products as well as to form bicyclic radicals which further react with benzene and other radicals. (auth)