Induced nuclear reactions: processes – systems – and elements – Testing – sensing – measuring – or detecting a fission reactor... – Optics
Patent
1997-08-27
1998-11-10
Jordan, Charles
Induced nuclear reactions: processes, systems, and elements
Testing, sensing, measuring, or detecting a fission reactor...
Optics
376245, 376249, 376252, G21C 1700
Patent
active
058355472
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to inspecting the rods of clusters suitable for insertion in the core of a nuclear reactor, and it relates more particularly to a method and to apparatus for eddy current and ultrasound inspection, enabling the wear of the rods to be determined.
A major application of the invention lies in inspecting rods constituted by cladding containing an absorbent material and belonging to the reactivity-adjusting clusters insertable into the fuel assemblies of reactors that are cooled and moderated by light water. In such reactors, adjustment clusters are used, each constituted by a bundle of absorbent rods, e.g. twenty-four such rods, carried by the arms of an upper handling part known as a "spider".
Periodically, it is necessary to verify the state of the rods to discover faults therein in order to detect sufficiently early any risk of the cladding becoming pierced or of the rod jamming because of swelling.
A method of inspecting rods has already been proposed (FR-A-2 585 869) in which the rods and an examination assembly are moved longitudinally relative to one another. In a first step, the cluster is lowered through an inspection assembly and a plurality of rods are inspected simultaneously by eddy currents. During a second step, doubtful rods are verified one by one by ultrasound probing, over the axial lengths thereof found to be doubtful and over various different profiles. Only one ultrasound sensor is provided. It can be rotated about a rod while the rod is simultaneously being displaced longitudinally.
That method has advantages over the previously known solutions. It makes it possible to perform ultrasound probing only on rods that have already been recognized as being doubtful during eddy current inspection, which can be performed with means that are much more simple. However, it does not provide full information concerning the type of defect to which the cladding of the rods has been subjected at all longitudinal levels thereof. Unfortunately, the number of defects can vary very considerably from one cluster to another. In the case of control clusters used in present-day pressurized water nuclear reactors, wear at different levels can be in the form of a bullet shape, a balloon, a flat, etc. It is also possible for the cladding to swell.
SUMMARY OF THE INVENTION
The invention seeks to provide a method and apparatus making it possible to obtain full information, and to do so without having any significant influence on the duration of inspection.
To this end, the invention provides a method of inspecting the rods of a cluster insertable in the core of a reactor, in which the rods and an inspection assembly that provides a measurement signal are displaced longitudinally relative to each other, the method being characterized in that:
a) the cluster, comprising n rods is displaced through an inspection assembly whereby eddy current inspections are performed on n/m rods simultaneously, where m is an integer submultiple of n, and simultaneously the echoes obtained by electronically scanned ultrasound probing over the entire periphery of n/m rods simultaneously are recorded at successive longitudinal levels;
b) operation a) is performed m times, after rotating the cluster on each occasion through an angle of 360.degree./m; and
c) the recordings of the ultrasound echo results are analyzed at least over those axial lengths of the rods found to be doubtful by the eddy current inspection.
Eddy current analysis serves to provide an overall measure of the degree of external wear of the rods. Ultrasound operation serves in addition to locate the places where matter is missing or swollen. Detailed analysis, which constitutes a complex operation, need be performed only on small zones and can be performed in differed time. It therefore does not lead to the inspection apparatus being tied up for a greater length of time.
In an advantageous implementation, the elevation of the rod while the cluster is moving is measured, and electronically scanned ultrasound expl
REFERENCES:
patent: 4741878 (1988-05-01), Gebelin et al.
patent: 5145637 (1992-09-01), Richardson et al.
Patent Abstracts of Japan, vol. 002, No. 044 (M-013), 24 Mar. 1978, and JP 53 000394 A (Toshiba Corp), 5 Jan. 1978, voir abrege.
Bour Denis
Pigelet Jerome
Compagnie Generale des Matieres Nucleaires
Framatome
Jordan Charles
Lattig M. J.
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