Induced nuclear reactions: processes – systems – and elements – Reactor protection or damage prevention – With pressurizer means
Reexamination Certificate
1999-06-21
2001-02-27
Jordan, Charles T. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Reactor protection or damage prevention
With pressurizer means
C376S283000, C165S302000
Reexamination Certificate
active
06195406
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a pressurizer with a casing, in which at least one spray line ends.
Such pressurizer are customary in a nuclear power plant with a pressurized water reactor. There, they are connected to a branch of a primary circuit which leads from a reactor. In the pressurizer, there is a spray system which is fed with water from a primary-circuit line that leads from a steam generator to the reactor. The water which is introduced through the spray system is therefore relatively cold as compared to the water which is situated inside the pressurizer. The spray system is generally closed off through the use of spray valves. The spray valves are only opened when an excessively high pressure is generated in the pressurizer, and the pressure in the pressurizer is lowered by praying-in relatively cold water. However, a valve cone of one of the spray valves may also have a small hole, so that some water is sprayed into the pressurizer continuously, even when the spray valve is closed.
Heretofore, it has been customary to guide the spray lines into the interior of the pressurizer through a so-called spray lid, which is screwed onto a central flange on an upper dome of the pressurizer. To that end, the spray lines initially run upward from the primary circuit and then, after they have passed through a bend above the pressurizer, they run downward into the pressurizer.
Heretofore, a so-called spray shroud has been necessary to ensure that the relatively cold water which is sprayed-in does not strike the hot wall of the pressurizer, which would lead to undesirable transient temperatures that would cause material fatigue. That spray shroud is a sheet-metal cylinder which is open at the top and bottom and is disposed concentrically inside the pressurizer. The water which is sprayed-in then strikes the inner wall surface of the sheet-metal cylinder, without coming into contact with the pressure-supporting casing wall.
Spray lines are made from austenitic steel. Due to their small diameter, it is not possible for weld seams to be ground internally. Consequently, it is not possible to completely rule out fracture of a spray line. If a spray line breaks, expensive measures are needed to ensure that line parts which are thrust outward or an emerging jet of steam do not cause secondary damage in the power plant.
Since the spray lines are guided downward into the pressurizer, at least the downwardly directed part of the spray lines empties when the spray valves are closed. Then, saturated steam from the pressurizer can penetrate into the spray lines and condense therein. The condensate then flows back into the pressurizer and makes room for fresh saturated steam. Therefore, according to the principle of conventional steam heating, at least the downwardly directed section of a spray line is continuously heated. Then, due to the temperature differences, feeding relatively cold water in when necessary may lead to material fatigue of the spray lines. If the spray valves are disposed above the pressurizer, the saturated steam also reaches the spray valves, where it can cause damage in the same way. Since the saturated steam inside the pressurizer is radioactive, there is also a risk of the spray lines as well as the spray valves being exposed to radiation.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a pressurizer with a spray device, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type, in which power-plant devices that are relevant to safety cannot be damaged by a fracturing spray line (causing line parts to strike outward or a jet of steam) and furthermore in which temperature fluctuation or radiation exposure does not impair the stability of any part of a spray line or of any spray valve.
With the foregoing and other objects in view there is provided, in accordance with the invention, a pressurizer, comprising a casing having a wall and a lower region; a volume-compensation line leading from a hot system and ending in the casing; and a spray line only intended for cooling, the spray line leading from a cooler system, guided through the wall in the lower region, extended upward inside the casing and ending in the casing at a geodetically highest point of the spray line.
In particular, this provides the advantage of exposing the spray line to only a minimal differential pressure with respect to its surroundings. Consequently, fracture of a spray line inside the pressurizer should not be expected. Even if a fracture were to occur, the minimal differential pressure means that there should be no expectation of any damaging movements of parts of the spray line which are to be attributed to a recoil. Simply because the spray line runs almost entirely inside the pressurizer, the risk of secondary damage caused by fracture of the line outside the pressurizer is minimized.
The fact that the spray line ends at its geodetically highest point means that when the spray line is closed, it is no longer possible for any water to flow out of the spray line into the pressurizer. The spray line remains full of water until it is opened into the pressurizer. In particular, a spray valve disposed outside the pressurizer is also always full of water. It is therefore impossible for any saturated steam to penetrate into the spray line and to the spray valve, a phenomenon which would lead to temperature fluctuations. This provides the advantage of considerably reducing loads exerted on the spray system by temperature fluctuations as well as by exposure to radiation.
Placing the spray line inside the pressurizer also provides the advantage of requiring only a few weld seams, at which it is not entirely possible to rule out a fracture of the line, on the relatively short portion of the spray line which still has to be situated outside the pressurizer. Inside the pressurizer, the spray line advantageously only has to have a relatively small wall thickness, since the differential pressure between the inside of the spray line and its surroundings is low.
In accordance with another feature of the invention, the spray line has one or more spray nozzles in the region of its highest point. This provides good distribution of water which is fed into the pressurizer.
In accordance with a further feature of the invention, a portion of the spray line which is provided with one or more spray nozzles is, for example, directed upward at an angle. In this way, the spray line remains full of water all the way to the spray nozzles when the spray valve is closed. However, it is ensured that the water is well distributed during spraying.
In accordance with an added feature of the invention, the spray line is, for example, guided through the wall of a lower cylindrical part of the casing of the pressurizer at an oblique angle with respect to the wall.
In accordance with an additional feature of the invention, the spray line is guided through the wall of a lower cylindrical part of the casing at right angles to the wall.
In accordance with yet another feature of the invention, the spray line is guided through the wall of a dome-like part of the casing, which part closes off the casing at the bottom, at right angles to the wall. This latter embodiment provides the particular advantage that the largest possible section of the spray line runs inside the pressurizer, where the pressure line only has to withstand a slight pressure difference between the inside and the outside. Consequently, a small wall thickness of the line is sufficient over the longest possible distance of the spray line. The spray line is therefore particularly economical to produce.
In accordance with a concomitant feature of the invention, the spray line is guided through the wall of the casing, where it forms a fixed point. This fixed point acts for the outer and inner parts of the line, resulting in the advantage that movements of one of the two parts of the spray line cannot be transmitted to the other part.
Since the spray
Conrads Hermann-Josef
Fäser Karl
Laurer Erwin
Model Jurgen
Greenberg Laurence A.
Jordan Charles T.
Lerner Herbert L.
Mun Kyoyetack K.
Siemens Aktiengesellschaft
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