Hydrogen retention by vanadium-titanium alloys

Abstract

INTRODUCTIONVanadium alloys with the rapid reduction of the induced activity of a V-Ti-Cr system are considered to be promising structural materials for application in future fusion reactors (FRs) of a DEMO type [1][2][3]. There is an interesting idea to use vanadium alloys as a fuel element cladding in fast neutron reactors (FNRs) with sodium cooling, where the required high tem perature strength is provided by a vanadium alloy and required corrosion resistance is provided by clad layers made from ferritic steel [4]. Embrittlement of vana dium alloys during operation can occur in contact with hydrogen isotopes [5][6][7][8][9]. For example,in [7], it is shown that a reduction in the relative elongation of V-Ti-Cr alloys in a hydrogen atmosphere (P ≈ 0.13 kPa) begins at a concentration of 360 wppm H 2 . There are a number of sources where hydrogen penetrates into structural material in FRs and FNRs: the main one is transmutation reactions of type (n, p), (n, d), (n, t), and (n, n I p), which have a threshold (energy) char acter. It should be noted that the amount of hydrogen accumulated in vanadium in FRs significantly exceeds that in FNRs. For example, it was calculated that 20 appm is accumulated in vanadium after 560 days of irradiation in the BN 600, whereas ~680 appm H is accumulated in the DEMO RF [10].Hydrogen can be specifically introduced into a liq uid metal coolant to eliminate oxide deposits. Another source of hydrogen input to the structural materials of the first FR wall is plasma radiation.Vanadium alloys which contain titanium, a strong hydride forming element, are currently considered as structural materials for nuclear reactors [3,11,12]. The most promising alloy for application in FR is the ternary alloy V-4% Ti-4% Cr. This work was aimed at finding the regularities of the retention of hydrogen depending on the titanium content in the V-Ti alloys saturated with hydrogen. EXPERIMENTALThe first stage was to produce the samples of V-Ti alloys, namely, to prepare a master alloy (alloy with a maximum titanium content V-10 wt % Ti) by alloying vanadium with titanium in a MIFI 9 vacuum arc fur nace. Model alloys with 0.5, 1, 5, and 10% Ti additions were prepared by alloying the master alloy with vana dium. The content of titanium was determined using a Camebax SX 50 microanalyzer. Pure vanadium served as a reference. The deviation of alloy composition from the calculated one was not more than 5%.After repeated rolling with intermediate homogeniz ing annealing at 1080 K to a final thickness of ~0.25 mm, the samples with dimensions of 25 × 7 × 0.25 mm 3 were annealed in a vacuum of 10 MPa at 1273 K for 2 h and then cooled together with a furnace. Before hydrogen saturation, the samples were electropolished to a mir ror finish in a solution of H 2 SO 4 (concentrate) + 5% ethanol.Abstract-Hydrogen retention in vanadium and its binary alloys with titanium are investigated by means of hydrogen thermal desorption spectrometry. The samples are saturated with hydrogen for 2000 h at a temper ature of 620 K in an...

Hydrogen Impact: A Review on Diffusibility, Embrittlement Mechanisms, and Characterization

“…With the addition of 0.5% titanium, the amount of trapped hydrogen reduced, whereas with the addition of 1% and 5% titanium, the trapped hydrogen amount increased. However, an addition of 10% titanium predominantly resulted in a decrease in the amount of captured hydrogen [84].…”