Induced nuclear reactions: processes – systems – and elements – Reactor protection or damage prevention – Shield or barrier between radiation or heat source and...
Reexamination Certificate
2001-05-14
2004-01-13
Keith, Jack (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Reactor protection or damage prevention
Shield or barrier between radiation or heat source and...
C396S352000, C396S377000, C396S389000, C396S399000, C396S246000
Reexamination Certificate
active
06678345
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a reactor pressure vessel with an upper support plate, which occupies its cross section above upper connecting branches and divides an upper dome chamber from a lower chamber. The support plate has openings to accommodate control rods and at least one equalization opening (dome bypass).
The invention also relates to a process for temperature equalization between an upper dome chamber above and a lower chamber below a support plate in a reactor pressure vessel of a reactor plant. The support plate occupying the cross section of the reactor pressure vessel above the upper connecting branches, and a medium flowing through an equalization opening in the lattice plate.
In a nuclear power station with a pressurized water reactor an upper support plate, which occupies the cross section of the reactor pressure vessel, is generally disposed in the reactor pressure vessel above the upper connecting branches of the primary circulation. The plate divides the reactor pressure vessel into a larger lower chamber and a smaller upper dome chamber facing the pressure vessel dome and serves to hold control rods in position.
At least two different configuration variants exist. The first variant is used mainly in Germany. It provides for the upper support plate to be configured as a lattice plate. In such a lattice plate the openings for the control rods are each significantly larger than the cross section of a control rod. This therefore leaves a relatively large free cross section surrounding the control rod in each opening. Through this free cross section an exchange of medium (coolant exchange) is possible between the upper dome chamber and the lower chamber in the reactor pressure vessel. An additional opening (dome bypass) nevertheless exists in the edge area of the upper lattice plate. This configuration is referred to as a “hot dome”.
The second configuration variant for a reactor pressure vessel, which is used mainly in France and the USA, provides for openings in the support plate to accommodate control rods, in which the cross section of an opening largely corresponds to the control rod cross section. Very little space, if any, therefore remains for an exchange of medium (coolant exchange) between the two chambers adjoining the support plate. This variant is referred to as “cold dome” and requires a relatively large equalization opening (dome bypass) in the edge area of the support plate in order to ensure a sufficient exchange of coolant at all times.
During continuous power output operation of a nuclear power station a small dome bypass with a small cross section is sufficient. The small bypass must merely be capable of ensuring that a homogeneous boron concentration is maintained throughout the reactor pressure vessel. Too large a dome bypass is undesirable in power output operation, since this would result in the coolant circulation in the reactor pressure vessel being led not only through the reactor core but also through the upper dome chamber, which would lead to a reduction of the reactor outlet temperature of the coolant and to an increase in the necessary capacity of the coolant pump in the primary circulation and hence to a power output loss of the power station.
A reactor pressure vessel of the “cold dome” variant largely keeps the hot coolant away from the dome chamber, since the control rods are fitted as tightly as possible into openings provided for them in the support plate. The above-mentioned power output loss occurs, however, if a relatively large dome bypass is provided.
The variant of the reactor pressure vessel referred to as “hot dome” has large openings in the lattice plate, large parts of which remain free even with the control rods are inserted. Because the coolant circulation in the reactor pressure vessel is also always led through the upper dome chamber, in power output operation the temperature of the coolant in the dome chamber is consequently largely identical to the temperature below the support plate.
Another situation results when shutting a nuclear power station down for an inspection or for changing fuel elements. In both variants of the reactor pressure vessel, the coolant present in the reactor pressure vessel must then be cooled from approximately 300° C. to approximately 50° C. The cooling time for the content of the dome chamber and the reactor dome itself is determined by the size of the dome bypass.
In the “cold dome” variant a relatively large dome bypass would be needed in order to obtain a sufficiently short cooling time. As stated, however, such a dome bypass would cause a high power station output loss.
Although a coolant exchange through the lattice plate is in principle possible in the case of the “hot dome” variant, when running the plant down, that is to say when cooling by way of the coolant circulation, the hot coolant of lower relative density above the connecting branches remains in the upper dome chamber, while the temperature in the lower part of the reactor pressure vessel continually falls.
The temperature difference between the lower part of the reactor pressure vessel and its dome that occurs when shutting the nuclear power station down results in different thermal expansions of the two parts. This may lead to the dome bolts being somewhat skewed in their threads so that they cannot be immediately screwed out. An additional cooling time is therefore necessary, so that the reactor dome can also assume the temperature of the rest of the reactor pressure vessel.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a reactor pressure vessel and a process for temperature equalization in the reactor pressure vessel that overcome the above-mentioned disadvantages of the prior art devices and methods of this general type, in which a minimum possible loss is to be sustained in power output operation, and in which temperature differences between the lower part of the reactor pressure vessel and the upper reactor dome do not occur or are rapidly equalized when running down the nuclear power station.
With the foregoing and other objects in view there is provided, in accordance with the invention, a reactor pressure vessel. The reactor pressure vessel contains a reactor pressure body having a chamber formed therein and a cross-section, and upper connecting branches connected to the reactor pressure body. An upper support plate is disposed in the reactor pressure body above the upper connecting branches and expanding over the cross-section of the reactor pressure body. The upper support plate divides the chamber of the reactor pressure body into an upper dome chamber and a lower chamber. The upper support plate has openings formed therein for accommodating control rods and at least one equalization opening formed therein, the equalization opening has a cross section being variable as an inverse function of a temperature in the lower chamber.
Another object of the invention is to specify a suitable process for temperature equalization between the upper dome chamber and the lower chamber in the reactor pressure vessel, situated above and below the support plate respectively.
According to the invention the first aforementioned object is achieved in that the cross section of the equalization opening (dome bypass) is variable as an inverse function of the temperature in the lower chamber.
This affords the advantage that in power output operation of the nuclear power station with a small cross section of the equalization opening (dome bypass) only a little medium (coolant) passes into the dome chamber, whereas when running or shutting the nuclear power station down with a large cross section of the equalization opening (of the dome bypass) a rapid exchange of medium and hence temperature exchange occurs between the upper dome chamber and the lower chamber of the reactor pressure vessel.
Power losses otherwise attributable to a large dome bypass are advantageously minimized. It is consequently possible to manage with a correspondingly small
Hartmann Heinz-Werner
Model Jürgen
Framatome ANP GmbH
Keith Jack
LandOfFree
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