Precise Evaluation of Corrosion Environments of Structural Materials under Complex Water Flow Condition, (I): Estimation of Corrosion Potentials in Reactor Pressure Vessel Bottom of BWRs

Abstract

To estimate the corrosion potentials of structural materials under complex water flow condition, such as reactor pressure vessel (RPV) bottom region of Boiling Water Reactors (BWRs), a method was newly developed. Threedimensional water flow analysis was performed and corrosion potentials of structural materials were calculated on the basis of the flow analysis results. Water flow analysis showed the velocities in the RPV bottom region varied from about 0.1 ms −1 to 4.5 ms −1. From the corrosion potential estimation under hydrogen water chemistry (HWC) condition, at the jet pump outlet and shroud support leg, a rather large amount of hydrogen had to be added to reduce the potential because of high flow velocity condition. Conversely, a small amount of hydrogen was sufficient in the case of the stub tube of the control rod drive (CRD) guide tubing located in the center of the bottom region.

Evaluation Methods for Corrosion Damage of Components in Cooling Systems of Nuclear Power Plants by Coupling Analysis of Corrosion and Flow Dynamics (I)

“…The calculated acceleration patterns agreed with the measured ones, though absolute acceleration values should be improved to match the measured ones. 17) (2) Stress Corrosion Cracking (SCC) Several computational models for water radiolysis have been successfully applied to evaluate corrosive conditions in the BWR primary cooling system [18][19][20][21] and a few have been improved for application to evaluation of PWR primary coolant corrosive conditions. 22) The model newly developed in the project has basically the same functions for water ) radiolysis analysis but it will be modified for application to evaluation of corrosive conditions in the PWR secondary cooling system.…”

Verification and validation procedures of calculation codes for determining corrosive conditions in the BWR primary cooling system based on water radiolysis and mixed potential models

“…The water radiolysis codes have been composed based on nonlinear rate equations for mass balances of radiolytic species in the cooling water, where their generation reactions due to radiation-induced decomposition of H 2 O molecules, their reactions for generating other species, and reactions for their disappearance and their transfer between liquid and gaseous phases are expressed ( Figure 4 and Table 1) [5][6][7][8][9][10].…”

“…In order to calculate the concentrations of radiolytic species, plant parameters, e.g., pipe diameters and lengths, components, flow rate, temperature, spatial distributions of neutrons and gamma rays, and steam quality in the cooling water, should also be prepared ( Table 3) [5][6][7][8][9][10][11].…”

“…Basic constants for the calculations are generation of major radiolytic species due to radiation-induced decomposition of H 2 O molecules (g-values) and reaction rate constants at elevated temperature, which are shown in Tables 4 and 5 [5][6][7][8][9]. …”

“…In order to evaluate IGSCC crack growth rate in the BWR primary system, the relationship between stress intensity factor and crack growth rate for two kinds of austenitic stainless steels, i.e., the normal one and a low carbon containing one, has been proposed as the guideline by the Japan Society of Mechanical Engineers (JSME) as well as the American Society of Mechanical Engineers (ASME) and this guideline has been accepted by the Japanese government [3,4]. The relationship has been prepared for two values of electrochemical corrosion potential (ECP), i.e., normal water chemistry There are several sets of calculation codes for determining corrosive conditions that basically depend on the same theoretical basis but their numerical treatments, major calculation constants, and input data taken from plant operational features are not the same [5][6][7][8][9][10]. A trio of authorized procedures for crack growth rates, corrosive conditions, and stress intensity factors should be set and then all the procedures for the evaluation of reliabilities of major components could be accepted by the government and the public.…”