Investigation of stratification effects on the surge line of a pressurized water reactor

Abstract

During the regular start-up procedure of a pressurized water reactor temperature stratification effects may occur especially in the horizontal parts of the surge line. Corresponding measurements in German plants have shown that temperature differences of up to 150 K can be expected in the horizontal section. The stratification effect causes additional deformation as well as bending moments, which are assessed by finite element calculations. For this purpose two types of finite element models are used. One is built up with pipe elements and consists of steam generator, pressurizer, surge line and the hot leg of the primary coolant line. The second model consists of surge line and pressurizer. Isoparametric solid elements with 20 nodes each are used in this case. In the paper the two models are described as well as loading and boundary conditions and the elastic-plastic temperature dependent material data used. Results are presented for calculations with several temperature variations with or without stratification.