Inhibition of radioactive cobalt deposition in water-cooled nuclear reactors

• US 4,950,449 A
• Filed: 02/26/1988
• Issued: 08/21/1990
• Est. Priority Date: 08/27/1986
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Marble, William J., Gordon, Gerald M., Petersen, George E., Robinson, Randall N., Gordon, Barry M., Ruiz, Carl P.
• Primary Examiner(s): Jordan, Charles T.
• Assistant Examiner(s): Eldred, J. Woodrow
• Application Number:
  US07/160,725
• Time in Patent Office: 907 Days
• Field of Search: 376/306, 376/904
• US Class Current: 376/306
• CPC Class Codes: G21C 17/0225 Chemical surface treatment, e.g. corrosion corrosion prevention in presence of water from scale removal or by modification of the properties of the liquid C02F5/00; inhibiting corrosion by adding corrosion inhibitors C23F11/00
• CPC Class Codes: G21C 19/28 Arrangements for introducing fluent material into the reactor core; Arrangements for removing fluent material from the reactor core pumping coolant G21D
• CPC Class Codes: Y02E 30/30 Nuclear fission reactors
• CPC Class Codes: Y10S 376/904 Moderator, reflector, or coolant materials

Abstract

Deposition of radioactive cobalt on the interior surfaces of a water-cooled nuclear reactor and intergranular stress corrosion cracking are inhibited or substantially prevented by the continuous injection of zinc oxide to the reactor water. The zinc oxide may be prepared in the form of a paste, a slurry, or a preformed aqueous solution.

Claims

1. A method for inhibiting intergranular stress corrosion cracking and the deposition of radioactive cobalt in a water-bearing vessel of a water-cooled nuclear reactor, said method comprising:

adding zinc oxide to water entering said water-bearing vessel continuously during operation of said water-cooled nuclear reactor, wherein the amount of zinc oxide is selected to achieve a concentration in the range from about 25 to 150 ppb.

2. A method in accordance with claim 1 in which the amount of zinc oxide added is selected to achieve a concentration of about 25 to about 100 ppb zinc oxide in said water-bearing vessel, whereby the inhibition of IGSCC is optimized.

3. A method in accordance with claim 1 in which said zinc oxide is added in the form of a member selected from the group consisting of a water-based slurry, a water-based paste and a water-based solution.

4. A method in accordance with claim 1 comprising adding said zinc oxide to a conduit selected from the group consisting of a recirculation water line and a feedwater line discharging into said water-bearing vessel.

5. A method in accordance with claim 4 comprising adding said zinc oxide to a recirculation loop branching off of said conduit.

6. A method in accordance with claim 4 in which flow through said conduit is maintained by a pump in said conduit, and said method comprises adding said zinc oxide to a recirculation loop drawing water from the discharge side of said pump and returning said water to the feed side of said pump.

7. A method for inhibiting intergranular stress corrosion cracking and the deposition of radioactive cobalt in a water-bearing vessel of a water-cooled nuclear reactor, said method comprising:

adding a paste comprised of zinc oxide and water to water entering said water-bearing vessel continuously during operation of said water-cooled nuclear reactor, wherein sufficient paste is added to achieve a concentration of about 25 to 150 ppb zinc oxide in said water-bearing vessel.

8. A method in accordance with claim 7 in which the amount of zinc oxide in said paste is from about 25% to about 95% by weight.

9. A method in accordance with claim 7 in which the amount of zinc oxide in said paste is from about 40% to about 80% by weight.

10. A method in accordance with claim 7 comprising adding said paste to a conduit supplying water to said water-bearing vessel at a flow rate maintained by a pump in said conduit, by mixing said paste with water passing through a recirculation loop drawing water from the discharge side of said pump and returning said water to the feed side of said pump.

11. A method in accordance with claim 10 in which said mixing of said paste with said water passing through said recirculation loop is achieved by continuously injecting said paste into said recirculation loop at an injection point therein from a motor-driven hydraulic cylinder, and passing said paste through a static mixer in said recirculation loop downstream of said injection point.

12. A method for inhibiting intergranular stress corrosion cracking and the deposition of radioactive cobalt in a water-bearing vessel of a water-cooled nuclear reactor, said method comprising:

(a) drawing water from a conduit supplying water to said water-bearing vessel and passing said drawn water through a recirculation loop discharging back into said conduit continuously during the operation of said water-cooled nuclear reactor; and

(b) continuously during said operation injecting into said recirculation loop a paste comprised of zinc oxide at about 40% to about 80% by weight in water at an injection point at a rate selected to achieve a zinc oxide concentration of about 25 to about 150 ppb in said conduit.

13. A method for inhibiting intergranular stress corrosion cracking and the deposition of radioactive cobalt in a water-bearing vessel of a water-cooled nuclear reactor, said method comprising:

adding an aqueous solution of zinc oxide to water entering said water-bearing vessel, continuously during operation of said water-cooled nuclear reactor, wherein a sufficient amount of the solution is added to achieve a concentration of about 25 to 150 ppb zinc oxide in said water-bearing vessel.

14. A method in accordance with claim 13 in which said aqueous solution is formed by passing a stream of water drawn from said water entering said water-bearing vessel through a receptacle containing said zinc oxide retained therein.

15. A method in accordance with claim 14 in which said solid zinc oxide is a bed of zinc oxide particles.

16. A method in accordance with claim 15 in which said zinc oxide particles are sintered into zinc oxide pellets.

17. A method in accordance with claim 13 in which said aqueous solution is formed in a recirculation loop branching off of a conduit supplying said water to said water-bearing vessel, said recirculation loop containing a bed of sintered zinc oxide pellets, and said aqueous solution is formed by passing a stream of water drawn from said conduit through said recirculation loop.

18. A method in accordance with claim 17 in which the flow rate through said conduit is controlled by a pump, and said recirculation loop is positioned to draw water from a point at the discharge side of said pump and to discharge water at the feed side of said pump.

19. A method for inhibiting intergranular stress corrosion cracking and the deposition of radioactive cobalt in a water-bearing vessel of a water-cooled nuclear reactor, said method comprising:

adding a slurry of zinc oxide in water to water entering said water-bearing vessel, continuously during operation of said water-cooled nuclear reactor, wherein sufficient slurry is added to achieve a concentration of about 25 to 150 ppb zinc oxide in said water-bearing vessel.

20. A method in accordance with claim 19 in which the zinc oxide content of said slurry is from about 0.1% to about 20% by weight.

21. A method in accordance with claim 19 in which the zinc oxide content of said slurry is from about 1% to about 5% by weight.

22. A method in accordance with claim 19 in which said zinc oxide in said slurry is fumed zinc oxide.

23. A method in accordance with claim 19 in which the rate of addition of said slurry to said water is selected to produce a zinc oxide content in the water of said water-bearing vessel of about 25 to about 100 ppb.