Fission Product Release Under Supercritical Water-Cooled Reactor Conditions

Most supercritical water-cooled reactor (SCWR) concepts being considered as part of the Generation IV initiative are direct cycle. In the event of a fuel defect, the coolant will contact the fuel pellet, potentially releasing fission products and actinides into the coolant and transporting them to the turbines. At the high pressure (25 MPa) in an SCWR, the coolant does not undergo a phase change as it passes through the critical temperature in the core, and nongaseous species may be transported out of the core and deposited on out-of-core components, leading to increased worker dose. It is therefore important to identify species with a high risk of release and develop models of their transport and deposition behavior. This paper presents the results of preliminary leaching tests in SCW of U-Th simulated fuel pellets prepared from natural U and Th containing representative concentrations of the (inactive) oxides of fission products corresponding to a fuel burnup of 60 GWd=ton. The results show that Sr and Ba are released at relatively high concentrations at 400°C and 500°C

Stability and Hydrolyzation of Metal Organic Frameworks with Paddle-Wheel SBUs upon Hydration

Instability of most prototypical metal organic frameworks (MOFs) in the presence of moisture is always a limita- tion for industrial scale development. In this work, we examine the dissociation mechanism of microporous paddle wheel frameworks M(bdc)(ted)0.5 [M=Cu, Zn, Ni, Co; bdc= 1,4-benzenedicarboxylate; ted= triethylenediamine] in controlled humidity environments. Combined in-situ IR spectroscopy, Raman, and Powder x-ray diffraction measurements show that the stability and modification of isostructual M(bdc)(ted)0.5 compounds upon exposure to water vapor critically depend on the central metal ion. A hydrolysis reaction of water molecules with Cu-O-C is observed in the case of Cu(bdc)(ted)0.5. Displacement reactions of ted linkers by water molecules are identified with Zn(bdc)(ted)0.5 and Co(bdc)(ted)0.5. In contrast,. Ni(bdc)(ted)0.5 is less suscept- ible to reaction with water vapors than the other three compounds. In addition, the condensation of water vapors into the framework is necessary to initiate the dissociation reaction. These findings, supported by supported by first principles theoretical van der Waals density functional (vdW-DF) calculations of overall reaction enthalpies, provide the necessary information for de- termining operation conditions of this class of MOFs with paddle wheel secondary building units and guidance for developing more robust units

Performance of chemical vapor deposition and plasma spray-coated stainless steel 310 in supercritical water

In this study, aluminized and NiCrAlY plasma-sprayed AISI 310 stainless steel samples were tested in supercritical water (SCW) at 500°C. The microstructure after SCW exposure was analyzed using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD). Weight measurements were taken before and after exposure to provide quantitative comparison of the two coatings on AISI 310 base metal. The results showed that aluminized and bare 310 stainless steel experienced similar weight gain, in the range of 0.02-0.08 mg/cm2 after 1550 hr. The aluminized sample had a slight weight decrease as exposure progressed. Oxide formation, in the forms of Al2O3 and (Fe; Cr)2O3, was found on the aluminized surface along with surface cracking after 1550 hr testing in SCW. NiCrAlY-coated 310, however, had the most consistent weight increase and oxide formation (mainly Al2O3) on the surface. Based on the results from this study, the aluminized coating has limitations in providing surface protection due to surface cracking and weight loss. The NiCrAlY plasma-sprayed coating with alumina formation on the surface has the potential to provide long-term surface protection to the substrate material in SCW