(1) Novel methods to extend lifetime of structural materials in BWR
By Young Kim, GE Global research Center
The author stressed that the risk of IGSCC (inter-granular stress corrosion cracking) in structure materials in BWR can be reduced by reducing the corrosion potential of the environment (ECP) below 230 mV. Two approaches suggested were:
(i) Addition of noble metal (e.g. Pt) followed by an excess H2 (0.20 - 0.40 ppm ) addition in the environment. These noble metals catalyze the reaction of H2 with O2 existing in the environment and thereby reduce the corrosion potential of the environment.
(ii) Second approach is to lower the ECP by coating the surface of the components by dielectric or insulating coating, e.g. TiO2 coating. Significant reduction in iron-oxide deposition on TiO2 coated (using CVD, around 1mm thick) 304 SS surface was observed in the laboratory.
(2) A zirconimum matrix cermet for storage and transmutation of transuranic isotope separated from spent nuclear fuel.
By Sean Mcdeavitt et al., Texas A&M University
The author discussed a processing method to incorporate the TRU bearing solvents into mixed oxides particulates dispersed in a zirconium matrix. This process includes hydriding (operating at ~ 500oC) followed by dehydriding (operating at ~ 900oC) method to recover the nuclear grade zirconium from spent fuel cladding, TRU solvent conversion via sol-gel or denitration processing, and hot extrusion of the final cermet pin ((operating between 600- 1000oC).
(3) Mechanical properties and microstructure of (Zr,Ti)N pellets as a surrogate for (Pu,Zr)N fuel pellets.
By Kirk Wheeler et al., Arizona State University
Alloy (Zr,Ti)N has lattice parameters similar to (Pu,Zr)N in which Zr represents Pu and Ti as Zr. The microstructure of (Zr,Ti)N was studied at various sintering temperature. At 1375oC sintering temperature, a very limited mobility of TiN was observed. An increased TiN mobility/distribution with existence of two different phases was observed at a sintering temperature of 1475oC, whereas, at 1600oC sintering temperature, a single solid solution phase was observed.
(4) Environmental effects on stress corrosion cracking of alloy 22
By Kuang Tsan Chiang et al., Southwest Research Institute
SCC of alloy 22 was studied in simulated concentrated water (SCW, having F-, Cl-, NO3-, SO42- and HCO3-), a representative of yucca mountain environment. A synergistic effect between HCO3- and Cl- ion in promoting SCC of alloy 22 was observed. It was found that at constant HCO3- concentration, susceptibility of alloy 22 to SCC increases with Cl- ion concentration in the solution. The surface morphology of the surface oxide layer was found to be different in a solution of only Cl- ions and a solution having both HCO3- and Cl- ions. A thin oxide layer rich in Cr was observed in a solution containing only Cl-, whereas in (Cl- + HCO3-) solution, this Cr layer was not observed at all. The author believes that in the second solution, Cl- and HCO3- had disrupted the passive Cr-rich oxide film.
(5) Salt fog testing of iron-based amorphous alloy
By Raul Rebak et al., Lawrence Livermore National Laboratory
Alloy 22 and carbon steel 1016 were spray-coated with iron-based amorphous coatings and their corrosion behavior was studied in salt-fog environment (ASTM B 117). The unprotected polycrystalline alloys were found to undergo localized corrosion attacks at grain boundaries, precipitates and edges in a concentrated hot chlorine brines (5M CaCl2 at 1050oC) environment. In the same aggressive environment, the amorphous alloys, in general, were found to have better resistance to localized corrosion and in comparison to polycrystalline material a rather uniform corrosion was observed.
