Methods and apparatus for inspecting reactor pressure tubes
View Patent ↗An apparatus and method for determining terminal solid solubility temperature in materials capable of forming hydrides, such as reactor pressure tubes. An inspection device is positioned within the reactor pressure tube under test and a pair of annular seals are radially deployed to seal a section of the pressure tube. Any water within the sealed section is displaced through the injection of gas and the heating of the sealed section to dry the tube and the device. A probe assembly on the device is deployed to contact the interior surface of the pressure tube and measure resistivity changes in the pressure tube wall as a function of temperature. The probe assembly includes a thermocouple probe for measuring temperature and transmit and receive coils for inducing eddy currents within the pressure tube wall. The pressure tube is allowed to cool at a predetermined rate, is reheated at a predetermined rate, and is allowed to cool again. Discontinuities within the temperature coefficient of resistivity indicate terminal solid solubility temperatures of precipitation or dissolution, which may be used to determine the hydrogen concentration of the sealed section of reactor pressure tube.
1. A method of inspecting reactor pressure tubes, comprising the steps of:
(a) sealing a section of the reactor pressure tube;
(b) initiating a temperature change within the reactor pressure tube at a predetermined rate;
(c) measuring changes in the electrical resistivity of the reactor pressure tube in relation to the temperature change; and
(d) determining a terminal solid solubility temperature of the reactor pressure tube from the measured changes in the electrical resistivity.
2. The method claimed in claim 1 , further including a step of preconditioning the reactor pressure tube prior to said step of initiating, said step of preconditioning including heating said sealed section of reactor pressure tube.
3. The method claimed in claim 2 , wherein said step of preconditioning includes injecting inert gas into said sealed section of reactor pressure tube to flush any fluids from said sealed section prior to said step of heating.
4. The method claimed in claim 1 , wherein said step of initiating a temperature change includes cooling said sealed section of the reactor pressure tube at a first predetermined rate.
5. The method claimed in claim 4 , wherein said step of initiating includes a subsequent step of re-heating said sealed section of the reactor pressure tube at a second predetermined rate.
6. The method claimed in claim 5 , wherein said step of initiating includes a further subsequent step of re-cooling said sealed section of the reactor pressure tube at a third predetermined rate.
7. The method claimed in claim 4 , wherein said first predetermined rate is 10 degrees Celsius per minute.
8. The method claimed in claim 5 , wherein said second predetermined rate is 10 degrees Celsius per minute.
9. The method claimed in claim 1 , wherein said step of measuring includes inducing eddy currents in the reactor pressure tube.
10. The method claimed in claim 1 , wherein said step of determining further includes determining a hydrogen concentration from said terminal solid solubility temperature using an appropriate Arrhenius relationship.
11. The method claimed in claim 1 , wherein said terminal solid solubility temperature includes a terminal solid solubility temperature of precipitation.
12. The method claimed in claim 1 , wherein said terminal solid solubility temperature includes a terminal solid solubility temperature of dissolution.
13. The method claimed in claim 1 , wherein said step of determining a terminal solid solubility temperature includes identifying a discontinuity in a temperature coefficient of resistivity from said measured changes in resistivity.