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ABSTRACT
A major subject for evaluating the corrosive conditions in the pressurized water reactor (PWR) primary coolant is to determine the optimal hydrogen concentration for mitigating primary water stress corrosion cracking (PWSCC) without adverse effects on major structural materials. An analytical method combining water radiolysis and electrochemical corrosion potential (ECP) analyses was proposed for evaluating the corrosive conditions in PWR primary coolant. These procedures originally developed for boiling water reactors (BWRs) were successfully extended to PWRs with different water chemistry parameters, including pH, temperature, and radiation qualities, after minor changes in the original procedures and major input parameters, such as the inclusion of the effects of alpha radiolysis and Li+ (Na+) and H+ effects for the anodic polarization curve. This study discusses the results of water radiolysis analysis for PWR primary coolant, and the characteristic behavior of hydrogen peroxide (H2O2) as a function of hydrogen inlet concentrations in PWR primary coolant conditions (higher pH and α-ray irradiation). A possible reaction scheme involving eaq– was proposed for H2O2 suppression under alkaline conditions. The corrosive conditions were discussed in the following publication, using ECP as the major index for PWR corrosive conditions.
Nomenclatures
| Cbi, Cbj, Cbm | = | concentration (mol/dm3) [subscript: i, j and m, species; superscript: b, mesh point] |
| gig, gin, gia | = | g-value (mol/J) [superscripts: g, γ rays; n, neutrons; a, alpha rays] |
| [H2] | = | hydrogen concentration (mol/dm3, ppb) |
| [H2O2] | = | hydrogen peroxide concentration (mol/dm3, ppb) |
| kis | = | rate constant for recombination of specie i and s (dm3/mol/s) |
| kimn | = | rate constant for generation of specie i due to reaction between species m and n (dm3/mol/s) |
| kw | = | rate constant near the surface of materials |
| [O2] | = | oxygen concentration (mol/dm3, ppb) |
| [O2]eff | = | effective oxide concentration (mol/dm3, ppb) [[O2]eff=[O2]+1/2[H2O2]] |
| Qg, Qn, Qa | = | absorption dose rate (Gy/s) [superscripts: g, γ rays; n, neutrons; a, alpha rays] |
| T | = | temperature (K) |
| Vb | = | volume (m3) [superscript: b, mesh point] |
| Ginb, Gontb | = | flow velocity (m3/s, kg/s) [subscript: in, flow in; out, flow out; superscript: b, mesh point] |
| = | mixing rate between bulk and surface regions (-) [superscript: b, mesh point] |
Abbreviations
| BWR | = | boiling water reactor |
| ECP | = | electrochemical corrosion potential |
| EDF | = | Electricite de France |
| EPRI | = | Electric Power Research Institute |
| CGR | = | crack growth rate (m/s) |
| HCC | = | hydrogen concentration control |
| INCA loop | = | In-Core Autoclave loop (In pile water chemistry loop at STUDSVIK AB, Sweden) |
| JAEA | = | Japan Atomic Energy Agency |
| MS | = | main steam |
| MSDR | = | main steam dose rate |
| NMCA | = | noble metal chemical addition |
| NPP | = | nuclear power plant |
| pHR | = | room temperature pH |
| pHT | = | high temperature pH |
| PWR | = | pressurized water reactor |
| PWSCC | = | primary water stress corrosion cracking |
| SCC | = | stress corrosion cracking |
| WRAC-J | = | Water radiolysis calculation code – J developed by JAEA |
Acknowledgments
The authors express their sincere thanks to Dr. Hideki Takiguchi, JAPC-retired, for his kind guidance to evaluate PWR water chemistry from the viewpoint of plant utility.
Disclosure statement
No potential conflict of interest was reported by the author(s).