Abstract
An evaluation of validity of theoretical pulse models (Fuchs-Hansen and Nordheim-Fuchs model) in reactor pulse modelling was performed by developing so called Improved Pulse Model. The effect of each of the five assumptions on the most important pulse physical parameters, maximal power, total released energy and full width at half maximum was studied. In the Improved Pulse Model the assumptions are disposed out with the improvements, where to account the delayed neutrons the six point kinetic equations are solved, the temperature dependences of the temperature reactivity coefficient of fuel and specific heat are taken into account, also the final ejected time of transient control rod from reactor core, whose value of reactivity varies in height and the heat dissipation from the fuel are considered. It is found that the theoretical models predict a higher maximum power, lower total released energy and full width at half maximum than the Improved Pulse Model.
Highlights
Some reactors and critical assemblies can operate in pulse mode
In the Improved Pulse Model the assumptions are disposed out with the improvements, where to account the delayed neutrons the six point kinetic equations are solved, the temperature dependences of the temperature reactivity coefficient of fuel and specific heat are taken into account, the final ejected time of transient control rod from reactor core, whose value of reactivity varies in height and the heat dissipation from the fuel are considered
In order to asses validity of each approximation, we developed an Improved Pulse Model (IPM) that takes into account delayed neutrons by solving six-group point kinetics equations, the temperature dependence of fuel temperature coefficient of reactivity and the specific heat, a finite time of reactivity insertion and heat removal from the fuel
Summary
The simplest and very common approach to model the reactor pulse is the Fuchs-Hansen (FH) model and the Nordheim-Fuchs (NF) model Both theoretical models are derived from the point kinetics equations on the basis of five assumptions; system is adiabatic, effective temperature reactivity coefficient of fuel is a constant value (i.e. does not depend on temperature), delayed neutron production can be neglected, power of the reactor before the pulse is low or equal zero and that reactivity change is instantaneous. In order to asses validity of each approximation, we developed an Improved Pulse Model (IPM) that takes into account delayed neutrons by solving six-group point kinetics equations, the temperature dependence of fuel temperature coefficient of reactivity and the specific heat, a finite time of reactivity insertion and heat removal from the fuel. A comparison of power versus time and of pulse physical parameters is made, where in all cases the contributions of improvements in IMP model are shown
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