Induced nuclear reactions: processes – systems – and elements – Seal arrangements – For nozzle
Patent
1996-09-30
1998-10-27
Behrend, Harvey E.
Induced nuclear reactions: processes, systems, and elements
Seal arrangements
For nozzle
376245, G21C 1300
Patent
active
058287116
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a sealing device for an instrumentation column, and in particular for a thermocouple column penetrating the head of a pressurized-water nuclear reactor vessel.
BACKGROUND OF THE INVENTION
In pressurized-water nuclear reactors, the vessel containing the core of the reactor includes a head of substantially hemispherical shape having openings in which there are fixed adapters allowing the passage of the control rods of the reactor and instrumentation columns such as thermocouple columns of cylindrical shape. In each of the thermocouple columns there is arranged a set of thermocouples making it possible to measure the temperature of the coolant fluid at the outlet of a set of fuel assemblies of the core of the reactor.
Each one of the adapters includes a part projecting under the head providing guidance for the thermocouple column and a part projecting above the head including means for connecting a tubular bearing assembly of the thermocouple column, which assembly can be fixed in the extension of the adapter.
Inside the bearing assembly fixed to the adapter are arranged sealed bearing means intended to interact with a surface of the thermocouple column in order to provide the sealed passage of the thermocouple column through the bore in the bearing assembly extending the adapter in the axial direction.
The thermocouple column which passes through the bore in the bearing assembly and the bore in the adapter which are situated in the axial extension of one another includes an end which projects relative to the bearing assembly which is in engagement with a lifting device which works by pulling, allowing the thermocouple column to be moved in the axial direction. The bearing surface of the thermocouple column and the sealed bearing means of the bearing assembly can thus be brought into contact, with a certain pressure.
The sealed bearing means of the thermocouple column inside the bearing assembly generally consist of a bearing surface of frustoconical shape machined into the internal bore of the bearing assembly and the shape of which complements the shape of the bearing surface of the thermocouple column, and of a gasket which is compressed between the bearing surfaces of the thermocouple column and of the bearing assembly when clamping is performed by pulling on the upper end of the thermocouple column.
A drawback of such a sealing device is that it requires a certain amount of axial movement of the thermocouple column between its lowered unclamped position and its raised, leaktight clamped position, this distance of axial movement being defined rather vaguely by the position of the bearing surface inside the bearing assembly relative to the position of the bearing surface of the thermocouple column in the unclamped position.
After the nuclear reactor has been in use for a certain length of time, or after a certain number of operations of opening the vessel by removing the head, some thermocouple columns may become slightly deformed, so that they are no longer perfectly straight.
In this case, it may be difficult or even impossible to move the thermocouple column axially inside the adapter and the bearing assembly over sufficient distance to provide clamping of the sealing gasket.
It then becomes necessary to exchange the entire thermocouple column, which leads to substantial additional costs in the operation of the nuclear reactor.
To date, no device was known for sealing an instrumentation column such as a thermocouple column penetrating the head of the vessel of a nuclear reactor which allows sealed clamping of the column even in cases where the latter has suffered deformation which prevents sufficient axial movement inside the adapter to allow the sealing gaskets to be compressed.
FR-A-2,642,217 describes a sealing device for an instrumentation column penetrating the vessel head of a nuclear reactor in which the bearing assembly consists of two successive lengths which are assembled in such a way that the instrumentation column can be extracted quickly
REFERENCES:
patent: 5084228 (1992-01-01), Lhwillier
patent: 5323428 (1994-06-01), Porter et al.
patent: 5513227 (1996-04-01), Margotta et al.
Atea, Societe Atlantique de Techniques Avancees
Behrend Harvey E.
Framatome
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