A transfer function is a very convenient mathematical description of the dynamic behavior of a complex system because all pertinent parameters are contained within it.For this reason transfer functions are widely applied in the field of reactor dynamics. Only linear systems or linear approximations to nonlinear systems are amenable to analysis by methods of complex plane transformations.The thermal properties of a re ac tor (e.g. the specific heat capacity, the thermal conductivity of the fuel and the heat transfer coefficient of the gap between the fuel and the coolant) however are functions of the temperature, leading to nonlinearities in the system. As long as only relatively small oscillations are considered it seems reasonable to use constant values for these properties l corresponding to an average power and temperature level.It will be shown that this simple linearization process .is only partially correct and may lead~o considerable errors even for small temperature vari~tions. Therefore a new linearization method has been developed by properly modifying the transfer functions and by introducing additional parameters which are functions of the s~eady state conditions. Temperature transients in nuclear reactors are usually treated by applying the "lumped model" which does not take into ac count any he at propagation effect.Because it has been shown that these effects are not always negligible /1,2/, space and time dependent equations for the heat transfer-and.transport equations have been used.

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