Criticality problems geometry

Calculations of core cell bum-up in the N2 PWR were performed by the spectral code CETERA [16]. The fission product and actinide activities were estimated using the RECOL [17] library data base, which was generated on the bases of the latest versions of the evaluated nuclear data files, ENDF/B-V, with corrections based on the results of critical experiments [18]. The criticality problem was solved for a realistic 3-D geometry model of a TFC by Monte-Carlo with RECOL and checked with MCNP [19] for fresh fuel load. One-group cross-sections were prepared for bum-up calculation of critical loads of both fresh and spent fuel and input to ORIGEN-2 [20] for detailed radionuclide content calculations. 

The dominant practice in Quantum chemistry is optimization. If the geometry optimization, for instance through analytic gradients, leads to symmetry-broken conformations, we publish and do not examine the departure from symmetry, the way it goes. This is a pity since symmetry breaking is a catastrophe (in the sense of Thom s theory) and the critical region deserves attention. There are trivial problems (the planar three-fold symmetry conformation of NH3 is a saddle point between the two pyramidal equilibrium conformations). Other processes appear as bifurcations for instance in the electron transfer... 

Problem What is the critical weighting i/>dip of the alternative dipolar amide resonance structure in (5.102) that would reverse the preference for pseudo-c/s over pseudo-trans geometry at Cal What are the corresponding bond lengths Rco and Rcn at this critical resonance weighting ... 

The purpose of this brief survey was to demonstrate that, despite the criticisms which may be made of the use of any semi-empirical quantum technique for structural and conformational studies, the CNDO/2 and Extended CNDO/2 formalisms are definitely reliable tools for theoretical conformational analyses in inorganic and coordination chemistry. Moreover, if these tools are combined with the most suitable experimental techniques (i.e. microwave spectroscopy and electron diffraction) in that field, many problems of geometry and conformation can be solved in a way that neither of these approaches could have accomplished alone. 

The work of Calderbank and Rennie (C4) has been criticized by Sargent and Macmillan (S2) on the basis that the liquid flow conditions used by Calderbank and Rennie (C4) are not found in distillation columns. They (S2) consider that cellular foams are formed for dilute aqueous solutions only when low gas flow rates are employed. By using an n-pentane-isopentane system, Macmillan (Ml) found that for all gas flow rates, froths with densities less than 0.15 were formed and the froth densities were independent of the factor vs(pg)112 but dependent on tray geometry. The associated problem of foam stability has also attracted considerable attention (Al, D3, Zl). 

The problem that remains is the study of the interaction of a shock with a matrix of holes in three-dimensional geometry. The basic two-dimensional processes involved in the failure of detonation, the failure diameter of explosives, and the sputtering initiation observed for density discontinuities near the critical size have been described. The three-dimensional study of the interaction of numerous failures and reignited detonations which is necessary for a complete numerical description of these problems must await new computing hardware ... 

To evaluate fission product release in a reactor, it is necessary to supply the appropriate particle geometry, diffusion coefficients, and distribution coefficients. This is a formidable task. To approach this problem, postirradiation fission product release has been studied as a function of temperature. The results of these studies are complex and require considerable interpretation. The SLIDER code without a source term has proved to be of considerable value in this interpretation. Parametric studies have been made of the integrated release of fission products, initially wholly in the fueled region, as a function of the diffusion coefficients and the distribution coefficients. These studies have led to observations of critical features in describing integrated fission product releases. From experimental values associated with these critical features, it is possible to evaluate at least partially diffusion coefficients and distribution coefficients. These experimental values may then be put back into SLIDER with appropriate birth and decay rates to evaluate inreactor particle fission product releases. Figure 11 is a representation of SLIDER simulation of a simplified postirradiation fission product release experiment. Calculations have been made with the following pertinent input data ... 

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