Abstract
Usually the synthesis of two-dimensional and one-dimensional discrete ordinate calculations is used to evaluate neutron fluence on VVER-1000 reactor pressure vessel (RPV) for prognosis of radiation embrittlement. But there are some cases when this approach is not applicable. For example the latest projects of VVER-1000 have upgraded surveillance program. Containers with surveillance specimens are located on the inner surface of RPV with fast neutron flux maximum. Therefore, the synthesis approach is not suitable enough for calculation of local disturbance of neutron field in RPV inner surface behind the surveillance specimens because of their complicated and heterogeneous structure. In some cases the VVER-1000 core loading consists of fuel assemblies with different fuel height and the applicability of synthesis approach is also ambiguous for these fuel cycles. Also, the synthesis approach is not enough correct for the neutron fluence estimation at the RPV area above core top. Because of these reasons only the 3D neutron transport codes seem to be satisfactory for calculation of neutron fluence on the VVER-1000 RPV. The direct 3D calculations are also recommended by modern regulations.
Highlights
In this paper the 3D discrete ordinate code KATRIN [1, 2] is tested for calculation of fast neutron fluence on VVER-1000 Reactor Pressure Vessel (RPV) by discrete ordinate method
KATRIN calculations have been compared with ex-vessel measurements at VVER-1000 and with the experimental results obtained for the first time in the surveillance assemblies irradiated close to inner surface of VVER-1000 reactor pressure vessel (RPV)
This value is comparable to 2 error limits of dosimeters measurements and is much less than theoretical uncertainty of fast neutron fluence calculation [10]
Summary
In this paper the 3D discrete ordinate code KATRIN [1, 2] is tested for calculation of fast neutron fluence on VVER-1000 Reactor Pressure Vessel (RPV) by discrete ordinate method. The code KATRIN solves the multigroup transport equation for neutrons, photons and charged particles in 3D x,y,z and r, ,z geometries. The AWDD scheme is used for approximation of the continuous slowing-down term in solving the charged particle transport problems. Calculation of the scattering integral is parallelized in circular variable The code works both with symmetrical and asymmetrical angular meshes, a module that generates suitable quadrature meshes (ESn type [5], Gauss-Chebychev and composite Sn type (the last quadrature can be used in the case when it is necessary to give more nodes in the desirable angular direction)) is included in KATRIN. Testing of Russian 3D Code KATRIN for Fast Neutron Fluence Calculation on RPV of VVER-1000
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