Process for decontaminating a nuclear reactor coolant system

• US 5,305,360 A
• Filed: 02/16/1993
• Issued: 04/19/1994
• Est. Priority Date: 02/16/1993
• Status: Expired due to Fees

• Current Assignee: Westinghouse Electric Corporation (Paramount Global (f/k/a ViacomCBS Inc.))
• Original Assignee: Westinghouse Electric Corporation (Paramount Global (f/k/a ViacomCBS Inc.))
• Inventors: Remark, John F., Bengel, Thomas G.
• Primary Examiner(s): Walsh, Donald P.
• Assistant Examiner(s): VOSS, FREDERICK
• Application Number:
  US08/018,138
• Time in Patent Office: 427 Days
• Field of Search: 376/308, 376/309, 376/310
• US Class Current: 376/309
• 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 19/307 specially adapted for liquids decontamination of liquids G21F9/04
• CPC Class Codes: G21D 1/003 Nuclear facilities decommissioning arrangements decontamination arrangements, treating radioactively contaminated material G21F9/00
• CPC Class Codes: Y02E 30/30 Nuclear fission reactors

Abstract

High velocity reactor coolant water in a boiling water reactor or a pressurized water reactor transports radioactive ions and particles from a nuclear reactor vessel to the balance of the reactor coolant system where they deposit on chromium (III) oxide-containing surfaces. These radioactive deposits are removed in a dilute chemical decontamination process wherein permanganate ion-containing reactor coolant water is circulated throughout a reactor coolant system to oxidize chromium (III) oxide surfaces of the system to chromium (IV) oxide. Formic acid is added to the permanganate ion-containing reactor coolant water and then the formic acid-containing water is circulated throughout the reactor coolant system to reduce unreacted permanganate ions in the reactor coolant water to manganous ions.

Claims

1. A process for decontaminating a reactor coolant system wherein radioactive ions and particles are transported by flowing coolant water from a nuclear reactor vessel to the balance of the system where they deposit on chromium (III) oxide-containing surfaces, comprising the steps of:

circulating permanganate ion-containing reactor coolant water throughout a reactor coolant system to oxidize chromium (III) oxide surfaces of the system to chromium (IV) oxide, the reactor coolant water containing from about 20 to about 2000 ppm permanganate ion; and

then

adding formic acid to the permanganate ion-containing reactor coolant water to reduce the permanganate ions in the reactor coolant water to manganous ions.

2. The process of claim 1, wherein the formic acid is added to reactor coolant water having a temperature of from about 90°

C. to about 116°

C.

3. The process of claim 2, wherein the formic acid concentration of the reactor coolant water is from about 750 ppm to about 1500 ppm when the reactor coolant water is from about 90°

C. to about 116°

C.

4. The process of claim 1, wherein the reactor coolant system is maintained at a pressure of at least about 400 psig and carbon dioxide generated by the oxidation of formic acid is substantially maintained in solution.

5. The process of claim 1, wherein the coolant water contains from about 25 ppm to about 2,500 ppm boron.

6. The process of claim 1, including an additional step of valving the formate-containing reactor coolant water to ion exchange resins after the formate concentration of the reactor coolant water has stabilized at 10 ppm or more.

7. The process of claim 1, including an additional step of circulating the formate-containing reactor coolant water through ion exchange resin beds until the conductivity of the reactor coolant water is less than about 50 microhms/cm.

8. The process of claim 7, wherein the reactor coolant water is circulated through the ion exchange resin beds until the conductivity of the reactor coolant water is less than 10 microhms/cm.