Changes to Irradiation Conditions of VVER-1000 Surveillance Specimens Resulting from Fuel Assemblies with Greater Fuel Height

Pavel Panferov,Denis Makhotin,Andrey Timofeev,Dmitry Erak,Alexandr Reshetnikov,Viacheslav Kochkin,A Lyoussi

doi:10.1051/epjconf/201610602013

Abstract

The goal of the work was to obtain experimental data on the influence of newtype fuel assemblies with higher fuel rods on the irradiation conditions of surveillance specimens installed on the baﬀe of VVER-1000. For this purpose, two surveillance sets with container assemblies of the same design irradiated in reactors with different fuel assemblies in the core were investigated. Measurements of neutron dosimeters from these sets and retrospective measurements of 54 Mn activity accumulated in each irradiated specimen allow a detailed distribution of the fast neutron flux in the containers to be obtained. Neutron calculations have been done using 3D discrete ordinate code KATRIN. On the basis of the obtained results, a change of the lead factor due to newtype fuel assemblies was evaluated for all types of VVER-1000 container assemblies.

Highlights

VVER-1000 reactors are equipped with surveillance specimens which are irradiated in container assemblies (CA)
The comparison of calculated and measured dosimeter activities (C/E) in the containers of surveillance sets 6L and 1L is shown in Figs. 5, 6
The comparison of C/E values shows that the difference between calculated and experimental absolute 54Mn activity is acceptable being within ±15%

Summary

Introduction

VVER-1000 reactors are equipped with surveillance specimens which are irradiated in container assemblies (CA). Each container assembly contains one or several specimen containers and has one or two levels. Container assemblies are located on the baffle above the upper boundary of the core. The fast neutron flux on surveillance specimens depends strongly on the distance between the upper fuel boundary and the specimen containers. There are two pairs of symmetrical positions: L1, L5 and L2, L4. Position L3 is the farthest from fuel assemblies and specimens in this position are irradiated with the lowest flux. The fast neutron flux in positions L1 and L5 is approximately two times higher than that in position L3

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Conclusion