Chemical process for primary system material passivation during hot functional testing of nuclear power plants
The present invention relates to a pre-core hot functional testing (HFT) preconditioning process, which includes the introduction of chemical additives, e.g., zinc, into coolant water that circulates through the primary system of a new nuclear power plant, at various temperatures. The chemical additives contact the primary system surfaces, which results in the formation of a protective zinc-containing oxide film on the fresh surfaces to control corrosion release and deposition during subsequent normal operation of the nuclear power plant. The method includes a series of three chemistry phases to optimize the passivation process: 1) an alkaline-reducing phase, 2) an acid-reducing phase and 3) an acid-oxidizing phase.
1. A method of passivating a metal surface in a primary system of a new nuclear power plant having a nuclear core and coolant water flowing through the primary system, comprising:
heating the primary system to a simulated normal operating temperature prior to an initial loading of fuel in the nuclear core;
initiating an addition of zinc to the coolant water at a temperature greater than or equal to about 350° F. prior to reaching the simulated normal operating temperature;
achieving a target zinc concentration in the coolant water from greater than 40 to 300 ppb at the simulated normal operating temperature;
conducting hot functional testing in the primary system at the target zinc concentration and the simulated normal operating temperature;
allowing the zinc to contact the metal surface in the primary system; and
forming an initial zinc-containing oxide film on the metal surface.
2. The method of claim 1 , wherein the zinc is added in the form of zinc acetate.
3. The method of claim 1 , further comprising adding base to the coolant water.
4. The method of claim 3 , wherein the base is selected from the group consisting of lithium hydroxide, potassium hydroxide and mixtures thereof.
5. The method of claim 4 , wherein the lithium hydroxide has a concentration sufficient for the coolant water to have a pH from 6.9 to 7.4 at the operating temperature or from 9.5 to 10.1 at 25° C.
6. The method of claim 5 , wherein the concentration of lithium in the coolant water is from 0.3 ppm to 2.0 ppm.
7. The method of claim 3 , further comprising adding boric acid to the coolant water.
8. The method of claim 7 , wherein the boric acid is added in an amount to such that there is a concentration of 100 ppm boron or less.
9. The method of claim 3 , further comprising adding hydrogen.
10. The method of claim 9 , wherein a concentration of the hydrogen in the coolant water is selected from a value or a range consisting of at least 4 cc/kg, from 4 to 50 cc/kg, from 4 to 15 cc/kg, from 15 to 30 cc/kg, and 4.5 cc/kg.
11. The method of claim 9 , wherein the adding of the zinc, the lithium hydroxide and the hydrogen is initiated when the coolant water has a temperature of 350° F. or higher and less than the simulated normal operating temperature of the coolant water.
12. A method for passivating a metal surface in a primary system of a new nuclear power plant during pre-core hot functional testing, the nuclear power plant having a nuclear core and coolant water flowing through the primary system, comprising:
heating the primary system to a simulated normal operating temperature prior to an initial loading of fuel in the nuclear core;
achieving an alkaline-reducing phase, comprising:
adding hydroxide in an amount sufficient to maintain the coolant water at an alkaline pH;
initiating an addition of zinc to the coolant water at a temperature greater than or equal to about 350° F. prior to reaching the simulated normal operating temperature;
achieving a target zinc concentration in the coolant water from greater than 40 to 300 ppb at the simulated normal operating temperature;
conducting the pre-core hot functional testing at the target zinc concentration and the simulated normal operating temperature;
allowing the zinc to contact the metal surface in the primary system; and
forming a zinc-containing oxide film on the metal surface;
then initiating an acid-reducing phase, comprising:
borating the coolant water; and
then initiating an acid-oxidizing phase, comprising:
removing hydrogen from the coolant water.
13. The method of claim 12 , further comprising adding an oxygen scavenger to the coolant water prior to initiating the alkaline-reducing phase.
14. A method of controlling the addition of zinc into coolant water flowing through a primary system and a nuclear core of a nuclear power plant during a preconditioning prior to an initial fuel load and normal power operation, comprising:
heating the primary system to a simulated normal operating temperature prior to an initial loading of fuel in the nuclear core;
achieving an alkaline-reducing phase, comprising:
initiating an addition of zinc, hydroxide and hydrogen to the coolant water at a temperature greater than or equal to about 350° F. prior to reaching the simulated normal operating temperature;
achieving a target zinc concentration from greater than 40 to 300 ppb in the coolant water at the simulated normal operating temperature;
establishing a plateau at the simulated normal operating temperature; and
conducting the pre-core hot functional testing at the target zinc concentration during the plateau;
initiating an acid-reducing phase to simulate a plant shutdown chemistry condition, comprising:
adding boric acid to the coolant water; and
initiating an acid-oxidizing phase, comprising:
removing hydrogen from the coolant water.