Location

Snowmass Village, CO

Start Date

1-1-1995 12:00 AM

Description

The testing of CANDU Zr-Nb pressure tubes for the presence of hydrides is a problem which is of current interest, as the premature replacement of pressure tubes could occur if the estimation of hydride levels is not made correctly. It has been shown that changes in the ultrasonic and thermal expansion properties of the material occur at a particular temperature, known as the terminal solid solubility (TSS) temperature [1]. Here, stable zirconium hydride platelets present at low temperatures dissociate to form free hydrogen on heating, and also reform from free hydrogen on cooling. Note that the TSS temperature is likely to be different for heating and cooling, due to hysteresis and thermodynamic effects, and will be dependent on the heating or cooling rate. The TSS temperature is known to be a function of the concentration of hydrogen present, and in fact follows a well known phase diagram [2], where the two-phase system becomes a single phase plus free hydrogen on heating (see Figure 1). The region of low atomic % is represented at the extreme left of this phase diagram. At a given value of atomic % of hydrogen (or the equivalent in parts per million (ppm)), a phase change will occur on heating from the two phase system containing the hydride to the single phase plus hydrogen. A transition in the reverse direction will occur on cooling. The temperature at which this happens is the TSS temperature, the value of which depends on the % of hydrogen present. Hence, determination of the TSS temperature leads directly to an estimation of hydride content.

Volume

14B

Chapter

Chapter 6: Material Properties

Section

Mostly Metals

Pages

1625-1632

DOI

10.1007/978-1-4615-1987-4_208

Language

en

File Format

application/pdf

Share

COinS
 
Jan 1st, 12:00 AM

High Temperature Non Destructive Evaluation of Hydrided Metal Tubing

Snowmass Village, CO

The testing of CANDU Zr-Nb pressure tubes for the presence of hydrides is a problem which is of current interest, as the premature replacement of pressure tubes could occur if the estimation of hydride levels is not made correctly. It has been shown that changes in the ultrasonic and thermal expansion properties of the material occur at a particular temperature, known as the terminal solid solubility (TSS) temperature [1]. Here, stable zirconium hydride platelets present at low temperatures dissociate to form free hydrogen on heating, and also reform from free hydrogen on cooling. Note that the TSS temperature is likely to be different for heating and cooling, due to hysteresis and thermodynamic effects, and will be dependent on the heating or cooling rate. The TSS temperature is known to be a function of the concentration of hydrogen present, and in fact follows a well known phase diagram [2], where the two-phase system becomes a single phase plus free hydrogen on heating (see Figure 1). The region of low atomic % is represented at the extreme left of this phase diagram. At a given value of atomic % of hydrogen (or the equivalent in parts per million (ppm)), a phase change will occur on heating from the two phase system containing the hydride to the single phase plus hydrogen. A transition in the reverse direction will occur on cooling. The temperature at which this happens is the TSS temperature, the value of which depends on the % of hydrogen present. Hence, determination of the TSS temperature leads directly to an estimation of hydride content.