Study on IR drop control of high-impedance pure water systems in nuclear power field
[Objective]Deviations caused by current(I)and resistance(R),known as IR drops,are prevalent in various engineering and industrial applications,such as cathodic protection of buried pipelines,electrocatalytic CO2 reduction reaction,and water electrolysis.These IR drops substantially affect the field of electrochemical characterization.During the evaluation of the performance and service life of engineering materials,IR drops are an influential factor.This is especially crucial in high-impedance pure water systems used in nuclear power,in which the resistance of the pure water solution amplifies the impact of IR drops.[Methods]We constructed an electrochemical three-electrode system to study IR drops and utilized well-polished samples of nuclear-grade 304L stainless steel and pure water as the working electrode and cell electrolytes.Before the electrochemical tests,conventional X-ray diffraction(XRD)measurement was utilized to analyze the phase of the matrix composition of the nuclear-grade 304L stainless steel samples.Then,grazing incidence X-ray diffraction(GIXRD)was employed to investigate the passive film phase on the surface of these samples.Subsequently,a series of electrochemical tests,including electrochemical impedance spectroscopy(EIS)and polarization curve tests,were carried out.[Results]XRD characterization results showed that the matrix of the nuclear-grade 304L stainless steel sample mainly comprised the austenite phase with a small amount of ferrite phase.The GIXRD results revealed a passivation film on the sample surface composed of multivalent oxides such as Cr2O2.4,Cr3O,FeCr,and FeO,in addition to a matrix austenite phase.This passivation film was considered while selecting the electrochemical fitting circuit.Based on the GIXRD phase analysis,a reasonable equivalent circuit shaped as"R(RQ)(RQ)(RQ)"in the series mode was selected to fit the EIS spectroscopy data for nuclear-grade 304L stainless steel in pure water solution.Electrochemical parameters were obtained from this model,with the resistance Rs of the pure water solution measured at 3.319 × 104 Q.This value could easily be confused with the passivation film resistance and charge transfer resistance.To verify whether the 3.319 × 104 Ω value was indeed the solution resistance,we assumed that the high-impedance pure water solution behaved like a"pure water coating"with a response of the parallel plate capacitor.By analyzing and comparing the theoretically calculated capacitance value of this"pure water coating"with the actual measured values,we validated the proposed hypothesis.This promoted further research on IR drop control in high-impedance pure water systems within the nuclear power field.The IR drop compensation calculation for the polarization curve further confirmed the presence of solution resistance for the"pure water coating"and ensured the accuracy of related measurements.[Conclusions]For high-impedance pure water systems in the nuclear power field,the"pure water coating"exhibited characteristics akin to a flat plate capacitor response.After the IR drop compensation,the polarization curve of the nuclear-grade 304L stainless steel in a pure water system accurately reflects the actual conditions.Therefore,timely IR drop compensation is crucial for electrochemical systems with high solution resistance.
high-impedance pure water systemnuclear-grade 304L stainless steelpolarization curveelectrochemical impedance spectroscopyIR drop
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