Abstract
In the present work, the expansion coefficient due to hydrogen incorporation was measured for the axial direction of a Zircaloy-4 cooling channel, similar to that installed in the Atucha I PHWR, Argentina, trying to simulate the nuclear power reactor operating conditions. As a first step, the solubility curve of hydrogen in Zircloy-4 was determined by two techniques: differential scanning calorimetry and differential dilatometry. The comparison with classical literature curves showed a good agreement with them, although the calorimetric technique proved to be more accurate for these determinations. Dilatometry was able to detect the end of hydride dissolution from concentrations around 60 wppm-H up to 650 wppm-H, where the eutectoid reaction: α + δ→α + β takes place (at 550oC). We assume that this ability is a good indicator of the aptitude of the technique to measure dimensional changes in the given hydrogen concentration range. Then, the expansion of Zircaloy-4 homogeneously hydrided samples was measured at 300oC, the typical operating temperature of a nuclear power reactor, obtaining a relative expansion of 2.21 * 10-4% per wppm-H. Considering the relative expansion observed for Zircaloy-4 at room temperature due to hydriding, starting from a hydrogen free sample, the total relative expansion rate is calculated to be 5.21 * 10-4% per wppm-H.
Highlights
Most of the core structural components of the nuclear power reactors are made of Zicaloy-4, a reference zirconium alloy in many structural nuclear applications
Since the reference is identical to the sample before hydrogen charging, the expansion of the reference compensates and cancels the thermal expansion of the -Zr phase in the hydrided sample
The present work was focused on two main objectives: hydrogen solubility measurements and the determination of the expansion coefficient of Zircaloy-4 for the axial direction of a tube
Summary
Most of the core structural components of the nuclear power reactors are made of Zicaloy-4, a reference zirconium alloy in many structural nuclear applications. The pick up of hydrogen atoms by the metal induces an expansion of its initial length This expansion continues after crossing the solubility limit at the reactor operating temperature, since the hydrogen in excess to that limit precipitates as ZrH1,5+x after some supersaturation in solid solution. Due to the higher specific volume of the zirconium hydride with respect to the zirconium matrix, the onset of precipitation induces an additional dimensional change. This change in length depends on both, the orientation at which the hydrides precipitated in the matrix and the crystalline texture of the component
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