Boric Acid Corrosion And PbSCC Behaviors Of Structure Alloys In PWR Nuclear Power Plant

The low alloy high strength steel,stainless steel,nickel alloy and Fe-Ni base alloy are the main structural materials of PWR nuclear power plant.The corrosion failure of these materials will pose serious challenges to the safety and economy of nuclear power operation.Boric acid corrosion of low alloy high strength steel is the common form in primary coolant of PWR nuclear power plant.Lead-induced stress corrosion of stainless steel,Fe-Ni base alloy and nickel alloy are partial corrosion that threaten the steam generator.Therefore,that's theoretically significant to study the boric acid corrosion of strength steel and lead-induced stress corrosion of stainless steel and nickel alloy,meanwhile,the research will bring application value for understanding the mechanism of corrosion,preventing the occurrence of these corrosion,ensuring the safe and economic operation of nuclear power plant.The research status of boric acid corrosion and lead-induced stress corrosion in nuclear power plants are summarized in this paper,as well as the occurrence situation of boric acid corrosion in reactor primary system.The main factors that affect the boric acid corrosion,the research status of lead-induced stress corrosion mechanism of stainless steel and nickel alloy are discussed.The thesis systematically studied the boric acid corrosion behavior of A508-3 low-alloy high-strength steel in the primary loop coolant of a simulated pressurized water reactor.The study showed that in this type of concentrated solution,the corrosion rate of A508-3 low-alloy high-strength steel would be accompanied by the concentration of the solution.As the temperature increases,the corrosion rate first increases and then decreases,and the corrosion rate is the fastest at 90?;the negative and anode reaction transfer coefficient a of the boric acid corrosion reaction of A508-3 low-alloy high-strength steel It is almost equal to ?,which is obviously different from a and ? in deionized water,indicating that the corrosion reaction of A508-3 low alloy high strength steel is different in deionized water and in the simulated primary circuit coolant;A508-3 low alloy The surface film of high-strength steel corrosion at 50? in the simulated primary circuit coolant is denser than the surface film produced by corrosion at 170?.The thesis systematically studied the open circuit potential change of 304L stainless steel in different concentrations of boric acid solution and the composition and morphology of the surface products.The study showed that at 50?,the higher the concentration of boric acid,the higher the open circuit potential;In comparison,the open circuit potential of 304L stainless steel is more affected by changes in the concentration of boric acid;the corrosion products of 304L stainless steel after being placed in solutions of various concentrations at 185? are mainly iron compounds,and the specific gravity of oxygen in the product will change.As the concentration of boric acid increases,it decreases.The thesis studied the galvanic corrosion behavior of a galvanic pair composed of A508-3 low-alloy steel and 304L stainless steel in the primary circuit coolant of a simulated pressurized water reactor and its concentrated solution.The study found that in the galvanic corrosion,the concentration of the solution varies with the Increase or temperature increase,the corrosion rate of the A508-3 low-alloy high-strength steel anode in the galvanic pair increases;the cathode-to-anode area ratio in the galvanic pair has no significant effect on the galvanic voltage and galvanic current,indicating that A508-3 The galvanic pair composed of low-alloy high-strength steel and 304L stainless steel simulates galvanic corrosion in the primary circuit coolant,and the cathode process is a speed control process.The galvanic couple composed of A508-3 low-alloy high-strength steel and 304L stainless steel at 90? contains 1200-2400ppm boron in the simulated primary circuit coolant and deionized water.The main component of the corrosion products is Fe3O4,in the simulated primary circuit containing 6000ppm boron.The main component of the corrosion products generated in the coolant is FeOOH.The effect of trace lead ion on the corrosion behavior of 304L stainless steel in simulated PWR primary coolant with high temperature and pressure water was studied.It was found that the addition of trace lead increased the thickness of oxide film and accelerated the corrosion rate of 304L stainless steel in high temperature water.Compared with no lead,the content of Fe and Ni decreases in oxide film on the surface of 304L stainless steel in high temperature water with trace lead.Meanwhile,the electron binding energy of Fe2p?Cr2p and O1s decreases in the oxidation film formed on stainless steel surface in high temperature water with trace lead.The reason for the increase of corrosion rate of 304L in high temperature water is the addition of trace lead,which is also the fundamental reason for stress corrosion of stainless steel and nickel alloy caused by lead.The research results reveal the mechanism of boric acid corrosion reaction and galvanic corrosion of A508-3 steel in simulated PWR primary coolant containing concentrated solution;From the perspective that influence of lead on the electronic binding energy of metal elements in oxide film,the root reason of lead-induced stress corrosion of stainless steel and nickel alloy are explained in detail,which will deepen the understanding of lead-induced stress corrosion mechanism.