DEVELOPMENT OF APPROXIMATION METHOD TO EVALUATE ISOTOPIC COMPOSITION OF DEPLETED FUEL, S .Aleshin, A. Shcherenko,
23rd Symposium of AER on VVER Reactor Physics and Reactor Safety (2013, Štrbské Pleso, Slovakia)
Advances in spectral and core calculation methods
Abstract
DEVELOPMENT OF APPROXIMATION METHOD TO EVALUATE ISOTOPIC
COMPOSITION OF BURNT FUEL
Aleshin S.S, Shcherenko A.I.
Russia, Moscow, NRC ?Kurchatov Institute?
ABSTRUCT
Fuel rods within FA burn out in different conditions in the process of operation due
to the presence of water cavities, absorber and etc. Therefore, the accumulation of isotopes in
different fuel rods goes on in different manner even with identical values of fuel burn-up. The
behavior of isotopic composition can be described in detail by variation spectral code.
However, a full-size core calculation takes much running time, so, it is impractical to realize
the calculation within the framework of design or in-process calculations. In order to take into
account spectral differences during fuel rod operation, it is reasonable to work out an accurate
and fast-operating approximation method to evaluate isotopic composition of burnt fuel.
The paper discusses the method based on spectral functionality – a nonassemptotic
factor which allows to take into account the conditions and history of exposure. The paper
outlines a code based n this method. The method accuracy is determined by comparing the
data by this method against the data obtained by a spectral code.
On this basis of the comparison data, the paper draws a conclusion about the
possibility of using the method to evaluate the isotopic composition of burnt WWER fuel
rods.
INTRODUCTION
The idea of this work was led from (urgency of this work is) the necessity to solve
following problems:
1)
The account of the fissile material in the burnt fuel.
In present time there is planned to repair fuel assemblies by removing the damaged
fuel rods. On this issue we need to have the means to calculate nuclides content in single fuel
rods.
2)
To verify the accuracy of engineering codes.
One way to determine the accuracy of engineering codes is to compare results of
these programs calculation with ones, obtained by the precision software such as MCU, using
the minimum number of approximations (compared with engineering codes).
In that way the main aim of this work is to develop a tool to evaluate the isotopic
content in the burnt fuel rods of WWER reactor core.
There are two different approaches to get the isotopic composition in the fuel rods: to
solve a system of equations for the fuel burn-up cycle or take advantage of approximation
methods.
In this paper, there will be presented a method to obtain the isotopic composition of
the fuel in the cells of WWER using the approximation method that takes into account the
history of fuel depletion by two functional verification – a spectrum nonassemptotic factor and
fuel burn-up.