[en] A study has been made of the effects of various arrangements of the transducers and control rods for a height problem. The BASIRA program has been used with a BESM-6 in detailed analysis of the stability of a system with a complicated distribution of the parameters; however, the situation can be analyzed qualitatively without resort to a computer. Here a homogeneous cylindricl reactor of unit radius with zero boundary conditions. 10 refs

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[en] The asymptotic behaviour of a stochastic non-linear nuclear reactor modelled by a master equation is analysed in two different limits: the thermodynamic limit and the zero-neutron-source limit. In the first limit a finite steady neutron density is obtained. The second limit predicts the neutron extinction. The interplay between these two limits is studied for different situations. (author)

[en] Simplification of the computations necessary for the stability analysis of a nonlinear spatially dependent reactor has been achieved for the semigroup method by means of the generalized mean value theorem and a generalization of a classical stability result. Conditions sufficient for asymptotic stability are derived. A simple numerical example and a comparison of this method with previously proven methods indicate that smaller domains of allowable perturbations result, but that the calculational procedure is simplified in that the nonlinear equilibrium problem does not have to be solved

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[en] This report gives an account of the work performed by the Dept. of Nuclear Engineering, Chalmers Univ. of Technology, in the frame of a research contract with the Swedish Radiation Safety Authority (SSM), contract No. SSM 2009/2093. The present report is based on work performed by Imre Pazsit, Victor Dykin, Anders Jonsson and Christophe Demaziere, with Imre Pazsit being the project leader. This report describes the results obtained during Stage 16 of a long-term research and development program concerning the development of diagnostics and monitoring methods for nuclear reactors. The long-term goals are elaborated in more detail in e.g. the Final Reports of Stage 1 and 2 (SKI Report 95:14 and 96:50, Pazsit et al. 1995, 1996). Results up to Stage 15 were reported in (Pazsit et al. 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2003a, 2003b; Demaziere et al, 2004; Sunde et al, 2006; Pazsit et al. 2008, 2009). A brief proposal for the continuation of this program in Stage 17 is also given at the end of the report. The program executed in Stage 16 consists of four parts as follows: - An overview of the present status of experience with BWR stability; - An investigation of the significance of the properties of the noise source for BWR instability; - Study of the dynamics of molten salt systems: construction of the adjoint and calculating the space dependent noise induced by propagating perturbations in the fuel; - A specific study of some novel methods of analysis of non-linear and non-stationary processes

[en] To study instabilities in boiling water reactors (BWRs), the authors recently developed a simple model that can easily be used to obtain the stability boundary for a fixed control rod induced external reactivity ρ_ext. However, due to the linear profiles introduced for the single-phase temperature (enthalpy) and the two-phase quality in the homogeneous equilibrium model (HEM) equations (linear-linear model), the stability boundaries that result are not sufficiently accurate. Thus, better approximations are necessary. In an earlier work on the stability analysis of simple channels heated by fixed heat fluxes (no neutron kinetics feedback), the authors showed that the stability boundaries, obtained using quadratic spatial approximations for these profiles, were far more accurate than those obtained using linear approximations and, in fact, agree quite well with the stability boundaries obtained via the much more complicated exact solution to the HEM equations