Method and apparatus for detecting malassembled nuclear fuel rods

• US 3,901,090 A
• Filed: 02/15/1972
• Issued: 08/26/1975
• Est. Priority Date: 02/15/1972
• Status: Expired due to Term

• Current Assignee: US Tool & Die Incorporated
• Original Assignee: John G. Akey, William J. Wachter
• Inventors: Wachter, William J., Akey, John G.
• Primary Examiner(s): Myracle, Jerry W.
• Assistant Examiner(s): Beauchamp, John P.
• Application Number:
  US05/226,483
• Time in Patent Office: 1,288 Days
• Field of Search: 73/67,67.1,67.2,71.6 176/19R
• US Class Current: 73/572
• CPC Class Codes: G01H 13/00 Measuring resonant frequency
• CPC Class Codes: G21C 17/06 Devices or arrangements for monitoring or testing fuel or fuel elements outside the reactor core, e.g. for burn-up, for contamination G21C17/08, G21C17/10 take precedence; detecting leaking fuel elements during reactor operation G21C17/04
• CPC Class Codes: Y02E 30/30 Nuclear fission reactors

Abstract

A fuel bundle having fuel rods supported by a plurality of grids with supporting fingers arranged at two axes of support is vibrated over a predetermined frequency range with in-phase and out-of-phase shakers while establishing signal representations of various rod resonant frequencies and magnitudes at particular frequency modes as well as bundle fundamental frequencies and harmonics thereof. A comparison of the rod resonant frequency responses along one of the axes as, for example, the X axis, provides a method of determining that a loose rod exists along a particular grid line. The characteristic detected, according to the invention, is the relatively low amplitude of the rod resonance response at that line of grid detection as compared to the response, along the same axis, of the responses detected along the same parallel axis of the two adjacent grids. The particular defective support location within the grid may then be determined by performing a similar test along the other axis, such as the Y axis, so that the intersection of the two points of abnormal vibration response will locate the defective point. In addition to providing an accurate and precise method of determining a loose rod, the invention also permits development of a total bundle '"'"''"'"''"'"''"'"'signature'"'"''"'"''"'"''"'"' characteristic which may be compared to the known '"'"''"'"''"'"''"'"'signature'"'"''"'"''"'"''"'"' of a good bundle to determine the adequacy of the total assembly. In the specific method of testing and defect location, provision is made to provide for seismic response testing along with those tests designed to locate a loose rod, or an abnormal bundle characteristic. In addition, provision is also made to detect the occurrence of '"'"''"'"''"'"''"'"'extra'"'"''"'"''"'"''"'"' frequencies as an added insurance that no defect or loose particles or pieces will go undetected and, further, to detect the occurrence of an impact (pinging) which may occur from a loose rod.

Claims

1. The method of detecting loose, malpositioned or broken fuel rods or loose particles in a nuclear fuel assembly comprising the steps:

vibrating the assembly in phase with a constant input over a frequency range in the order of 1 to 120 Hz to cover the lowest bundle frequency of the assembly to the highest first mode frequency of a single rod correctly supported;

detecting the amplitude and phase response along an axis of each of the grids of the assembly;

performing a total frequency spectrum analysis of the signal response at each grid axis;

comparing the amplitude and phase responses of adjacent grid vibrations along an axis to detect unusual differences characteristic of a loose rod;

detecting in said total frequency spectrum analysis the presence of frequencies other than the excitation frequencies including frequencies characteristic of '"'"''"'"''"'"''"'"'impacts'"'"''"'"''"'"''"'"' or '"'"''"'"''"'"''"'"'pinging'"'"''"'"''"'"''"'"' due to rods impacting against fingers or of loose particles; and

repeating all of the above steps with the excitation being applied out of phase.

2. The method of claim 1 wherein the steps are first performed throughout a frequency range of 1 to 120 Hz in coarse steps to first determine whether any '"'"''"'"''"'"''"'"'extra'"'"''"'"''"'"''"'"' frequencies are present or unusual amplitude variations among the vibration sensed along different grid axes and then is repeated in fine steps to precisely determine which grid plane contains a malassembled fuel rod or loose particle.

3. The method of claim 2 wherein all of the steps are performed with respect to X- and Y-axes of the nuclear assembly to provide a representation of the grid coordinates where a defective assembly is present.

4. A method of detecting malassembled or defective nuclear fuel rod assemblies comprising the steps of applying vibrations to an assembly to be tested at two spaced locations, said vibrations being in phase and having constant input and the same frequency, varying said frequency over a range extending at least from the lowest resonant frequency of the complete assembly to the highest resonant frequency of a single fuel rod correctly supported, detecting vibrations in said assembly at predetermined positions between said spaced locations, and analyzing the frequency responses at each of said positions by comparison with the frequency responses at adjacent positions and with known frequency responses of good assemblies.

5. The method of claim 4 in which vibrations are detected on two mutually perpendicular axes in each of said positions.

6. The method of claim 4 including the further steps of applying vibrations 180* out of phase at said spaced lOcations, and repeating the previously defined procedure.

7. The method of claim 4 wherein a sensing detector is placed in contact with each rod in the nuclear fuel assembly, thus obtaining a representative frequency response from each rod, and electrically analyzing the representative frequency response from each of said rods.

8. A system for detecting malassembled or defective nuclear fuel rod assemblies consisting of a bundle of fuel rods supported in a series of spaced, parallel grids, said system comprising vibrator means for applying exciting vibrations to a fuel rod assembly at spaced locations adjacent opposite ends of the assembly, means for detecting vibrations in the assembly on the plane of each of said grids, means for controlling said vibrator means to apply vibrations in predetermined phase relation and at the same frequency in said spaced locations, means for varying said frequency over a predetermined range, means responsive to said vibration detecting means for determining the frequency response of the assembly at each of said planes throughout said range of frequencies, and means for analyzing the frequency responses at each plane by comparison with the frequency responses at adjacent planes and with known frequency responses of good assemblies.

9. The system of claim 8 in which the means for analyzing frequency responses includes means for detecting the amplitude of vibration in said planes.

10. The system of claim 8 in which the vibration detecting means includes transducers applied to each of said grids on mutually perpendicular axes.