Creep-fatigue damage assessment of special type of sodium to air heat exchanger having toroidal shape headers

Abstract

In Prototype Fast Breeder Reactor, which is under construction, a dedicated Safety Grade Decay Heat Removal (SGDHR) is employed for removing decay heat during shut down (in case the normal path is not available). Each SGDHR loop consists of a sodium to sodium heat exchanger (DHX) and sodium to air heat exchanger (AHX). Two types of AHX are employed for diversity and this paper discusses creepfatigue damage evaluation of a special type of sodium to air exchanger. It is a vertical cross flow type heat exchanger with finned tubes connecting two toroidal sodium headers. Five different types of tube configurations, each 50 in numbers (total 250 Nos.) connect both the headers and the entire component is supported through the top header with the bottom outlet header floating. During the normal reactor operating conditions the sodium temperature at the hot end is nearly 823 K. The normal operation, SGDHR operation and shut down condition lead to cyclic thermal stresses. 3-D analyses of the exchanger have been completed for self weight, pressure and thermal loadings. The FEM code CAST-3M, issued by CEA France has been used. The toroidal header has been modeled using shell elements and all the tubes are modeled using pipe elements. The peak stress at the critical junction is 96.4 MPa. The resulting fatigue damage is found to be negligible and the total creep damage is estimated as 0.88 which is conservative, as the stress relaxations are not accounted in the analysis. More details are discussed in the paper.

High Temperature Design and Damage Evaluation of MOD.9Cr-1Mo Steel Heat Exchanger

“…The perforated plate of tubesheet and tubes were modeled with a solid plate having an equivalent Young's modulus and springs in 2D axisymmetric model FE analysis [7]. Other types of 2D FE analysis with shell elements and 2D axisymmetric elements were carried out for the heat exchangers of DHX [8], AHX [9], and the steam generator [10]. In present study, 3D FE analysis with full consideration of tubes, tubesheets, and shells was carried out to evaluate the structural integrity of the DHX component through simulating the DHX component more realistically.…”