Comparison of Performance and Oxidation of Nitronic-50 and Stainless Steel 316 in Subcritical and Supercritical Water En
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INTRODUCTION
INCREASED thermodynamic efficiency can greatly benefit any form of power production.[1] Thermal reactors, both coal and the proposed Gen IV nuclear reactors, attempt to realize this goal through the use of increased operating temperatures and pressures, and as such require the utilization of materials capable of withstanding these extreme conditions.[2] One proposed method of attaining increased thermodynamic efficiency is through the use of supercritical water (SCW), water above the critical point of 647 K (374 C) and 22.1 MPa, as the heat transfer medium between the power source and the steam generating system.[2,3] Despite the advantages of using SCW, numerous material challenges stem from its usage because in addition to the degrading high temperatures and pressures encountered in these systems, SCW is also highly oxidizing.[4–6] Therefore, in order to achieve the benefits of the use of SCW, an understanding of the alteration of mechanical and corrosion characteristics of materials upon exposure to SCW is needed to determine the viability of these proposed materials.[5] Operating at a core inlet temperature of 553 K (280 C) and an outlet temperature of 823 K (550 C), SCWRs are capable of increasing efficiency by ~40 pct compared to current reactors.[7–9] The high operating temperatures of SCWRs necessitate high operating pressures of ~25 MPa to maintain the supercritical fluid state.[2,9,10]
ZACHARY KARMIOL, Graduate Student, and DEV CHIDAMBARAM,Associate Professor, are with the Materials Science and Engineering Department, University of Nevada, Reno, Reno, NV 89557-0388. Contact e-mail: [email protected] Manuscript submitted January 30, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS A
The following technology gaps for the SCWR have been identified,
SCWR materials and structures, including – – – –
Corrosion and stress corrosion cracking (SCC), Radiolysis and water chemistry, Dimensional and microstructural stability, and Strength, embrittlement, and creep resistance;
SCWR safety, including power-flow stability during operation; and
SCWR plant design.[2] Structural material concerns are of great importance for the SCWR. In addition to the mechanical strength constraints, SCW is extremely oxidizing which can lead to corrosion of key components.[2,5] These simultaneous requirements make materials research investigating mechanical properties as well as corrosion resistance upon exposure to SCW, imperative. Three classes of materials have been primarily investigated for use as structural materials in SCWRs, ferritic/martensitic steels, nickel-based alloys, and austenitic steels.[5] Ferritic/Martensitic (F/M) steels have been observed to have desirable irradiation swelling properties, a rate of ~1 pct/dpa with exhibited evidence of a saturation of 10 pct, and are thus attractive for potential high fluence applications in SCWRs.[5,11–21] However, F/M steels have poor creep resistance at high temperatures, and are observed to undergo severe weight gains in corrosion testing of the proposed structural alloys
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