Nov 14, 2016 - First Progress Report of SPAR IV. Characterization of hydride content as a function of accumulated neutron flux and operating temperature in ...
Gerencia de Ciclo del Combustible Nuclear Departamento de Tecnología de Aleaciones de Circonio First Progress Report of SPAR IV
Final
14/11/16
Characterization of hydride content as a function of accumulated neutron flux and operating temperature in the PCA-S Alloy (Prime Candidate Alloy) Code of the Coordinated Research Project: T13016 Authors: Pablo Vizcaíno, Alejandra Viviana Flores Summary The present report shows the results and analysis of the microstructural evaluation performed to Zircaloy-4 cooling channels removed from the Atucha I reactor at different moments along its time in service. These channels, which remained for different periods in service (full power years in operation) shows the effects of the neutron irradiation in the microstructure of the tubes. The degradation effects are evidenced in different ways. Visual inspection shows an appreciable surface oxide layer but microscopically (OM and SEM) the hydride distribution and hydrogen isotope concentration can be quantified. These parameters converted in [H]eq (equivalent concentration) and oxide layer thickness can be connected, which allows establishing relations between both interconnected processes. Deeper studies performed by TEM and X-ray diffraction show changes in the crystalline structure of the Zr(Fe,Cr)2 second phase particles (amorphisation) and chemical composition. Additionally, the irradiation damage clusters collapsed in dislocation loops can be quantify by these techniques. The present report shows the results obtained from a microstructural evaluation performed to a recently removed channel, a PCA-S (low thin Zircaloy-4) cooling channel removed from central core of the Atucha I reactor in 2012, after 10.6 years at full power operation. The channel was divided into three parts (top, medium and bottom) and samples were cut from each section. The results indicate that the bottom region is the most affected by corrosion, showing a total oxide layer thickness (internal plus external surfaces) of ~262 m (average), being of 153 m the internal and 109 m the external layer. In this section in some points, the oxide thickness of 175 m was measured in the internal surface of the channel, which takes the total oxide layer around ~300 m at these points. This wide layer appears cracked in many of the observed points. The medium section shows an average thickness of ~135 m, being the internal layer of around ~100 m. The top section of the channel shows a significant smaller value, being the total average of ~55 m. As expected, the hydrogen contents determined in each region are compatible with the oxide layer measurements and the average values for these regions are ~350 Heq ppm for the bottom, ~235 Heq-ppm for the medium, and ~180 Heq- ppm for the top. These values are 50% higher respect to the values obtained from a previously removed central channel, another PCA-S channel removed in 2008 after remaining 6.8 years at full power operation. The evaluation indicates an advanced degradation condition similar to the original Zircaloy-4 firstly removed channels in 1989 after 10.3 years at full power operation.
