[en] A difference in the shape of the burnup dependence of the coolant void reactivity (CVR) has been observed between DRAGON and WIMS-AECL calculations. This paper discusses the root cause of the difference and assesses the impact on burnup and full-core reactor calculations. A Fortran procedure has been developed to run WIMS-AECL as necessary in order to mimic DRAGON burnup calculations with leakage effects included. The comparison of standard WIMS-AECL results and simulated DRAGON results demonstrated that the difference is due to different definitions of CVR. If the same CVR definition is used, then the results of both WIMS-AECL and DRAGON analyses are essentially indistinguishable. The discrepancies in the fuel composition and cell-averaged two-group cross sections that are due to differences in WIMS-AECL and DRAGON leakage treatments are insignificant. (author)

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[en] Tests were performed to determine the moderator temperature coefficient of reactivity, the prompt temperature coefficient of reactivity and the power coefficient of reactivity of Mark VII-A charges. This document summarizes the results of the tests and reports values of the coefficients that are commensurate with the test data

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[en] The delayed supercritical process of nuclear reactor with temperature feedback and initial power while inserting small step reactivity (ρ₀<β) is investigated. The effect of initial power in the relation between power and temperature is considered, and the adiabatic model is improved. The variations of the output power and reactivity with time are obtained. The analytic results show the effect of the initial power on the output power and reactivity during the delayed supercritical process is evident. The larger the initial power is, the quicker the reactivity and power respond, and the larger the power varies. (authors)

[en] The flow character in a gap between shroud disc of an impeller and a stator surface (shroud cavity) influences disc friction loss, labyrinth seal loss (parasitic losses) and thrust force. Flow calculations inside the shroud cavity of a model of centrifugal compressor stage and its labyrinth seal in a range of flow rates and axial width and radial gap are presented. The results are presented in terms of non-dimensional coefficients of flow, disc friction and seal leakage losses coefficients and pressure coefficient. The distributions meridional and tangential flow velocities correspond to the continuity and equilibrium equations – flow radial circulation exists in wide cavity and is absent in narrow cavities. The radial pressure distributions as measured and calculated are not fully comparable. The possible reason is that CFD-calculated leakage coefficient is less than calculated by A.Stodola formula. The influence of a cavity width on the losses and the thrust force requires a balanced design. (paper)

[en] The effect of cross-section changes on the moderator temperature coefficient of reactivity of a Calder Hall reactor is investigated at various irradiations and temperatures. The method of calculation uses basic nuclear data and a detailed spectrum model and has been programmed for Mercury (Spectramet). Changes of 1% in certain cross-sections are found to change the moderator coefficient by 0,3 mn/deg C over a wide range of irradiations. Moderator coefficients obtained with Spectramet and Carlson and with different scattering laws are compared and found to be similar. Reasonable agreement is obtained between the calculated results and the measurements on Calder Hall. (author)

[en] Based on the one-delay-group point reactor model, the influence of the transport time delay on the nature of the linear stability of reactor dynamics is studied with the aid of the method of D partitions. From our analysis, the stability domain can be easily determined and plotted in the parametric space. The domain of the linear stability is significantly altered by the delayed temperature feedback. Comparing the stability domain of the one-group model with the effective lifetime model and Welton's criterion, the following conclusions are obtained: (1) the straight line obtained from Welton's criterion is a tangent line of the dynamic stability boundary of the effective lifetime model; and (2) the effective lifetime model is a safe estimation of the linear stability only when the delayed neutron precursor decay constant is greater than the reciprocal time constant for heat removal

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