Measuring and testing – Vibration – By mechanical waves
Patent
1996-02-28
1997-07-29
Williams, Hezron E.
Measuring and testing
Vibration
By mechanical waves
376249, 73624, G01N 2910, G01N 2924
Patent
active
056523874
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a device for non-destructive ultrasonic testing of a surface accessible through a narrow annular passage. The invention may be applied in particular to the non-destructive testing of the inner surface of a tubular adaptor passing through the vessel head of a pressurized water nuclear reactor, without removing the thermal sleeve of the adaptor.
Pressurized water nuclear reactors generally include a vessel containing the core of the reactor which is immersed in the pressurized water for cooling the reactor.
The generally cylindrical vessel includes a hemispherical head which may be attached to its upper part. The head is pierced with openings, at each of which a tubular penetration part is fastened by welding, constituting an adaptor allowing passage and displacement control of a follower of a rod cluster for controlling the reactivity of the core or a through-passage for a means for measurement inside the core, such as a thermocouple column.
The mechanisms for controlling displacement of the core reactivity control rod clusters are fixed on the end parts of the adaptors.
A heat sleeve is fixed inside each of the tubular penetrations of the vessel head, in a coaxial arrangement with respect to the tubular penetration part and with some radial clearance, which thermal sleeve includes a diametrally widened part located at the upper part of the bore of the tubular penetration part and is mounted freely in rotation inside the penetration.
The nuclear reactor reactivity control rod followers and thermocouple columns pass through the vessel head inside thermal sleeves which are themselves arranged coaxially inside control rod adaptors or more generally inside tubular head penetration parts.
So as to increase the reliability and safety of operation of nuclear reactors and in order to extend their lifetime, operators have to carry out increasingly numerous tests on the various elements constituting the nuclear reactor.
In particular, it may be necessary to test the condition of the vessel head penetration parts in order to ensure integrity of these parts after a certain length of operation of the reactor, in particular in the zone in which these tubular parts are welded on the vessel head.
These tests, which make it possible to detect and repair faults on the cylindrical inner surface of the tubular penetration part, must be carried out through the inside of the bore of the tubular part and may consequently require removal of the thermal sleeve in order to access the inner surface of the bore of the penetration.
The tests and repairs are carried out during a shutdown of the nuclear reactor, the vessel head being removed and placed on a maintenance stand.
Removing the thermal sleeve requires complex operations insofar as the widening of the thermal sleeve resting on a bearing surface arranged at the upper part of the adaptor prevents removal of the sleeve by pulling downwards on its lower part which is accessible below the head.
Furthermore, neither is it possible to remove the sleeve by pulling upwards insofar as the rod cluster control mechanisms which are fixed by screwing and welding on the upper parts of the adaptors prevent passage of the thermal sleeve.
It is therefore desirable to limit the complex thermal sleeve removal operations to adaptors which actually exhibit defects requiring repair.
In Patent Applications FR-A-92.15788 and 92-15789 filed by the company FRAMATOME, a device is described for testing the internal surface of an adaptor, comprising a blade, deformable in flexion, carrying a testing probe at one of its ends and means for moving the testing probe fixed to the end of the blade inside the narrow annular space between the thermal liner and the inner surface of an adaptor. The blade is preferably made in the form of a laminated strip which absorbs vibrations, and the testing probe by an eddy-current sensor.
It is also envisaged, by way of a variant, to use an ultrasonic sensor for detecting the possible presence of cracks and for measuring their depth inside the adaptor.
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patent: 4472346 (1984-09-01), Takeda et al.
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patent: 5156803 (1992-10-01), Engding et al.
patent: 5327079 (1994-07-01), Haller et al.
patent: 5436944 (1995-07-01), Magnin et al.
Deltour Damien
Dumont Pascal
Framatome
Miller Rose M.
Williams Hezron E.
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