PGNAA system for non-invasively inspecting RPV weld metal in situ, to determine the presence and amount of trace embrittlement-enhancing element

• US 5,781,602 A
• Filed: 05/17/1996
• Issued: 07/14/1998
• Est. Priority Date: 05/17/1996
• Status: Expired due to Term

• Current Assignee: Westinghouse Electric Company LLC (Brookfield Asset Management Incorporated)
• Original Assignee: Westinghouse Electric Company LLC (Brookfield Asset Management Incorporated)
• Inventors: Anderson, Stanwood L., Congedo, Thomas V., Dulloo, Abdul R., Ruddy, Francis H., Fero, Arnold H.
• Primary Examiner(s): Wasil, Daniel D.
• Application Number:
  US08/649,370
• Time in Patent Office: 788 Days
• Field of Search: 376/157, 376/159, 376/160, 376/161, 376/162, 376/245, 376/249
• US Class Current: 376/159
• CPC Class Codes: B23K 31/12 relating to investigating the properties, e.g. the weldability, of materials
• CPC Class Codes: G01N 23/222 using neutron activation analysis [NAA]
• CPC Class Codes: G21C 17/003 Remote inspection of vessels, e.g. pressure vessels
• CPC Class Codes: Y02E 30/30 Nuclear fission reactors

Abstract

Prompt Gamma Neuteon Activation Analysis (PGNAA) is employed to determined in situ the content of nickel, copper, or other embrittlement-enhancing elements within the weld metal joints of nuclear reactor pressure vessels.

Claims

1. A method for analyzing a weld of a reactor pressure vessel (RPV), comprising the steps of:

(a) irradiating said weld with a neutron burst from a neutron source, said burst characterized by an intensity and pulse width and duty cycle, and thereby effecting an emission of fast and thermal neutron-induced gamma radiation from said weld;

(b) acquiring gamma radiation data indicative of the number or intensity of gamma rays and energies of said gamma rays during a predetermined time interval, said acquiring step including a separate identification of fast neutron-induced and thermal neutron-induced gamma rays, and wherein said gamma radiation is collected over only a fraction of said duty cycle; and

(c) analyzing said gamma data to detect the presence and determine the amount of a prescribed constituent element in said weld.

2. A method for analyzing a weld of a reactor pressure vessel as recited in claim 1, wherein step (b) comprises acquiring groups of gamma radiation data during a plurality of time intervals, each group being indicative of the number or intensity of gamma rays and energies of said gamma rays during a corresponding time interval.

3. A method for analyzing a weld of a reactor pressure vessel as recited in claim 1, wherein step (c) comprises determining the amount of said prescribed constituent element to an accuracy of about 0.1% by weight of the irradiated portion of the weld.

4. A method for analyzing a weld of a reactor pressure vessel as recited in claim 1, wherein said RPV comprises a metal cladding covering the irradiated surface.

5. A method for analyzing a weld of a reactor pressure vessel as recited in claim 4, wherein said metal cladding comprises cobalt.

6. A method for analyzing a weld of a reactor pressure vessel as recited in claim 1, wherein the method is performed in an environment containing a gamma radiation field of about 100 R/hr.

7. A method for analyzing a weld of a reactor pressure vessel as recited in claim 6, wherein step (a) is carried out with a neutron source submerged in water.

8. A method for analyzing a weld of a reactor pressure vessel as recited in claim 1, wherein an element selected from the group consisting of copper, nickel and phosphorous is measured.

9. A method for analyzing a weld of a reactor pressure vessel as recited in claim 1, wherein the RPV is an off-line, previously irradiated, water-containing RPV having an internal metal cladding covering the weld, characterized by the steps of:

(1) opening the off-line RPV; and

then

(2) introducing a neutron source into water in the off-line RPV before irradiating the vessel with the neutron source.

10. A method for analyzing a weld of a reactor pressure vessel as recited in claim 9, wherein the cladding contains at least about 8% by weight nickel.

11. A method for analyzing a weld of a reactor pressure vessel as recited in claim 10, wherein the weld contains less than 1% by weight nickel and the amount of nickel is to be determined.

12. A method for analyzing a metal body having a surface, comprising the steps of:

(a) irradiating said surface with a neutron burst from a neutron source, said burst characterized by a duty cycle, and thereby effecting an emission of gamma radiation from said surface;

(b) acquiring gamma radiation data indicative of the number or intensity of gamma rays and energies of said gamma rays during a predetermined time interval, said acquiring step including a separate identification of fast neutron-induced and thermal neutron-induced gamma rays, and wherein said gamma radiation is collected over only a fraction of said duty cycle; and

(c) analyzing said gamma data to detect the presence and determine the amount of prescribed constituents of said metal body.

13. A method as recited in claim 12, wherein step (b) comprises acquiring groups of gamma radiation data during a plurality of time intervals, each group being indicative of the number or intensity of gamma rays and energies of said gamma rays during a corresponding time interval.

14. A method as recited in claim 12, wherein step (c) comprises determining the amount of said constituents to an accuracy of about 0.1% by weight of the irradiated portion of the metal body.

15. A method as recited in claim 12, wherein said metal body comprises a metal cladding covering the irradiated surface.

16. A method as recited in claim 15, wherein said metal cladding comprises cobalt.

17. A method as recited in claim 12, wherein the environment surrounding the neutron source contains a gamma radiation field of at about 100 R/hr.

18. A method as recited in claim 12, wherein said neutron source is submerged in water while it is irradiating the metal body.

19. A method as recited in claim 12, wherein an element selected from the group consisting of copper, nickel and phosphorous is measured.

20. A method as recited in claim 12, wherein the metal body is formed of sections welded together and constituents of the weld are determined.

21. A method as recited in claim 20, wherein the metal body is a reactor pressure vessel (RPV).

22. A method as recited in claim 21, wherein the RPV is an off-line, previously irradiated, water-containing RPV having an internal, cobalt-containing, metal cladding covering the weld, characterized by the steps of:

(1) opening the off-line RPV; and

then

(2) introducing a neutron source into water in the off-line RPV before irradiating the vessel with the neutron source.

23. A method as recited in claim 22, wherein the constituents of a weld between adjacent sections of the RPV under the cladding are determined.

24. A method as recited in claim 23, wherein a constituent selected from the group consisting of copper, nickel and phosphorous is determined.

25. A method as recited in claim 24, wherein the cladding contains at least about 8% by weight nickel.

26. A method as recited in claim 25, wherein the weld contains less than 1% by weight nickel and the amount of nickel is to be determined.