[en] The problem of estimating the time-varying net reactivity from flux measurements is solved for a point reactor kinetics model using a linear filtering technique in an H_∞ settings. In order to sue this technique, an appropriate dynamical model of the reactivity is constructed that can be embedded into the reactor model as one of its variables. A filter, which minimizes the H_∞ norm of the estimation error power spectrum, operates on neutron density measurements corrupted by noise and provides an estimate of the dynamic net reactivity. Computer simulations are performed to reveal the basic characteristics of the H_∞ optimal filter. The results of the simulation indicate that the filter can be used to determine the time-varying reactivity from neutron density measurements that have been corrupted by noise

[en] Some imprecisions are pointed out in the derivation by a previous author of a correction for the neutron flux in a heterogeneous lattice cell. In particular, the equation which is basic to the mathematical formulation does not properly take into account the lethargy and energy variables. It is shown that this and other errors in the derivation lead to an overestimation of the proposed correction. (UK)

[en] Requirements on detector and cable are defined, tests are described, and rules for the physical design of the measuring system are stated. The standard has to be equivalently applied to other instrumentations if used in place of the neutron fluence rate for determination of the power density or the power density distribution. (orig./HP)

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[en] The present paper deals with the statistical errors affecting the reactivity estimate in rod-drop and rod-jerk experiments. Within the framework of the one-velocity point-reactor model with delayed neutrons and using the Kolmogorov theory of the branching stochastic processes, expressions for the mean values and the covariance matrix of the counts taken in such measurements were obtained. Various experiments were simulated and then analysed with a simple classical model here revisited. In all cases the estimated reactivities were in very good agreement with the 'true' ones. The importance of using the correct covariance matrix was then checked by treating the pseudo-experimental counts as if they were Poissonian. In the case considered here it turned out that this simple assumption, while yielding acceptable point estimates for the reactivities, delivers unreliable values for their standard deviations, thus possibly inducing the assessment of non-existent discrepancies. (author)

[en] The new primary state standard in the field of neutron measurements has been developed. The complex of measuring means forming a part of the standard provides a reproduction of the neutron flux unit within the range of 10³ up to 10⁹ s^-1 at neutron energy from 4x10^-21 up 2.4x10^-12 g (0.025 eV-10 MeV). To increase the accuracy of neutron flux measurements three independent techniques have been conducted: recording of accompaining particles ³He and ⁴He from the T(α, n)⁴He and D(de n)³He reactions, manganese activation in aqueous solution of manganese sulfate and activation of gold foils in water

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