Advanced Alloy Development for Pb-Bi Cooled Reactor Systems

The use of lead or lead-bismuth eutectic (LBE) as a coolant for advanced lead-cooled fast reactor systems and transmutation designs has been limited by the corrosive nature of the coolant on fuel cladding and structural materials. The existing upper limit of approximately 550°C for operation of LBE systems (slightly higher for Pb) is insufficient for economic viability of the Pb-cooled system. Increasing the operating temperature limit and expanding the chemical potential window (controlled by the oxygen potential) would represent enabling technology for the Pb-cooled system. A recent development effort has made very significant progress in this area by combining a newly developed Fe-12Cr-2Si alloy with a high strength steel (T91/F91) in a functionally graded composite (FGC). The new system is designed to provide both a multi-layer protective film (Fe-Oxide/Cr-Oxide/Si-Oxide) over a wide range of oxygen potentials and, at the same time, provide minimal solubility in liquid Pb or LBE at very low oxygen potentials, which may occur in crevices or other oxygen-depleted areas. The new FGC has demonstrated excellent resistance to corrosion in Pb/LBE that suggest that corrosion will not be an issue for operation of materials at temperatures up to 700°C. Moreover, the FGC has been commercially produced in product forms that include piping, with a 5.18 cm OD and Fe-12Cr-2Si cladding on the ID, and a fuel cladding product pre-form, which is clad on the OD. Commercial fabricability has also been demonstrated-at least for the coolant piping product. The latest corrosion data for 1000 hour exposure @ 650C in LBE indicate extreme resistance. If the initial results can be confirmed, this product represents enabling technology for the Pb-Bi cooled reactor for both structural and cladding materials.The purposes of this project is to take the next step in the FGC development effort. Viability/Success will be defined as: (1) Corrosion rate of less than 20m/yr at an operating temperature of 650C and a flow velocity of >3 m/sec. (2) Dilution of the corrosion resistant layer to no less than 1.25 wt. % Si for the expected operating lifetime (25,000 hours for fuel cladding, 40 years for structural materials) including the effects of radiation damage. (3) Acceptable susceptibility to LME (essentially none). (4) Adequate mechanical properties that comply with ASME Section II limits for the structural material. (5) Adequate FGC performance under irradiation to high dose.