JPH07294686A - Steam condenser for nuclear-reactor protective system with spontaneous circulation - Google Patents

Abstract

PURPOSE: To improve safety and reliability of a plant by connecting a by-pass transporting vapor of a reactor pressure vessel(RPV) and a discharge line opening by a start of a protection system with a heat exchanger, and thus controlling a pressure in RPV constantly in a safe manner. CONSTITUTION: The heat exchanger 10 immersed in a cooling pool 30 is connected with RPV by an outlet port (a discharge line) S having a control valve V1 and a by-pass D, normally open, connected with a main vapor supply line A. In the case of a normal operation, the valve is closed till the heat exchanger 10 is filled up with a condensate at a temperature substantially same as a water temperature of the pool 30 and thereby the vapor does not flow into the heat exchanger 10. In the case of an emergency condition, when an excessive pressure is detected or predicted, the valve V1 is opened and the condensate in the heat exchanger 10 flows into RPV through the outlet S till a free surface of a liquid in RPV and a hydrostatic head H of a free surface of a liquid in the exchanger 10 come to be in a prescribed equilibrium and a flow of the vapor into the exchanger 10 from the by-pass D is accelerated. Thereby, An excessive pressure in a nuclear reactor is effectively controlled and decreased.

Description

Detailed Description of the Invention

[0001]

The subject of the invention is an innovative steam condenser with natural circulation for a reactor protection system.

[0002]

BACKGROUND OF THE INVENTION The present invention will be described in the context of a boiling water nuclear reactor (BWR), but apparently produces high pressure steam in a closed circuit requiring protection to ensure rapid dissipation of the contained heat. , It can be used in any power plant that uses it.

In a boiling water reactor, the pressurized water contained in the reactor pressure vessel (ie, RPV) is
Used as a reaction moderator or as a medium for heat exchange and conversion of reaction heat into other forms of energy.

The water contained in the RPV is guided to the boiling point,
The resulting steam goes by pipe from the high pressure RPV to a steam turbine that is coupled to a generator. The low pressure steam output from the turbine is condensed in a suitable condenser and the condensed water is pumped back into the RPV.

Most of the plants that are under pressure can withstand significant internal pressures, and the first container (P
It is housed in a very sturdy structure known as C). The first container is also intended to house at least some of the protective equipment and systems. In a conventional BWR plant, the excess pressure created by the temporary interruption of the main steam line causes the steam produced in the reactor vessel into a pool located in a first container under a certain hydrostatic head. Limited by the automatic opening of the releasing overflow safety valve.

This has the following drawbacks:

1. Pressure oscillations and cycling phenomena with the potential for one or more overflow safety valves to jam, ie sudden pressure drops that induce their repeated pulsed intervention.

2. It is necessary to have a plant with a fluid (water) replenishment system housed in the main reactor vessel by a pump that draws from a suitable reservoir to compensate for the amount released.

3. Circulation and cooling systems other than pool water need to transfer heat of condensation from the main container that is transferred by steam to the pool water.

[0010]

These problems are overcome by the protection system having a natural circulation steam condenser of the present invention.

[0011]

According to the invention, a steam condenser, called an isolation condenser, is connected to the steam zone of the reactor pressure vessel by a permanently open connection and condensate to the reactor pressure vessel. It is connected by a natural circulation circuit with passive actuation based solely on the automatic opening of a reduntant valve located in the return line.

The pressure of this first system under transient conditions is
It can be limited to values below the point at which the safety valve opens, limiting their intervention for exceptional situations and waste of coolant from the first circuit.

The isolation condenser must operate under the same pressure conditions as the reactor and at the same time be supplied with a suitable hydraulic head to ensure natural circulation, the isolation condenser being higher in the cooling pool, outside the main container. Must be placed at height.

It therefore has to meet a number of particularly stringent requirements, such as: -minimum pressure barrier outside the first container-minimum possibility of breakage-limitation of the effect of any breakage- -Resistance to sudden temperature changes, -Adaptation to considerable thermal expansion, and at the same time plant resistant to seismic stress.

All these special requirements are aimed at almost one purpose: maximum safety and reliability of the plant.

The isolation condenser or heat exchanger of the present invention comprises:
These results are achieved by a combination of several measures which are briefly listed below and which are functionally interdependent over a wide range: -a double wall of the main supply line of the capacitor outside the PC-a small cross section Capacitor structure with several identical modules supplied by the line of: -a single forged, unwelded body for distributing steam to the modules-minimizes the effect of any downstream damage A flow limiter integral with the distributor body for the purpose of: -a single forged steam and condensate manifold of the module; Capacitor structure with identical vertical modules supported by suspension with lateral restraining means to allow expansion and ensure resistance to seismic stress.

The features and advantages of the present invention will become more apparent from the following description of the preferred embodiments and from the accompanying drawings.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENT With particular reference to FIG. 1, a boiling water nuclear plant surrounded by a first container 60 is schematically shown. In addition to radioactive materials and components to control the reaction, the reactor pressure vessel RPV contains water used as a moderator and as a vehicle for transferring the heat generated. In the upper part of the vessel RPV, the water is brought into high-pressure steam, which is then carried by the supply line A to a turbine T which drives a generator G. The expanded steam output from turbine T is cooled in condenser C and the condensed liquid is recharged by pump P into vessel RPV.

Under normal operating conditions, the flow of vapor output by the vessel RPV is
Is equal in weight to the flow of water. In the event of a breakage or intervention that impedes the flow of steam from A to the turbine T, the pressure in the container RPV rises, leading to the intervention of the safety valve V, which opens at some hydrostatic head from A The steam is discharged to the pool P1. This is the container RPV
Includes the need for immediate replenishment of water to and distribution of heat dissipated into pool P1.

According to the invention, the valve V and the pool P1
Instead of, or preferably in addition to, the bypass D is connected to the vapor supply line A, or directly to the container RPV, extending through the shield of the first container and immersed in the pool 30. Carry steam to 10. This pool 30 is arranged outside the first container at a height higher than the container RPV and is therefore preferably arranged above the first container to minimize the length of the pipe which becomes a large volume at high pressure. .

The condenser 10 has a condensate outlet S which is connected to the container RPV by a control valve V1. On the other hand, the bypass D for sending steam to the condenser 10 is permanently open.

According to the invention, the capacitor 10 thus connected to the container RPV and to which it is thus spatially arranged, constitutes a very effective protection system,
Its operation is clear.

In the rest or "standby" state, valve V1 is closed and the vapor flowing from D to condenser 10 condenses until the condenser is completely filled with liquid at a temperature approximately equal to the temperature of the water in pool 30. .

In an emergency situation and when overpressure is detected or expected, the valve V1 is opened and the hydrostatic head H existing between the free surface in the reactor and the free surface in the condenser 10 is closed. As a result, the liquid contained in 10 flows back into the container RPV.

The output of the condensate from 10 opens up space for the incoming steam from D, which is rapidly cooled and condensed, and provides effective control and reduction of excess pressure in the reactor. , Discontinue any fluid dissipation or need for additional replenishment.

The design of the condenser-heat-exchange device 10 is described in further detail below with reference to FIGS.

In FIG. 2, the heat exchanging device, indicated by dashed line 10, is formed by a wall 40 and is submerged in a pool 30 which is placed on a slab 50 which bounds the first container 60. It is constituted by the same module 20 (shown by a broken line).

With continued reference to FIGS. 3-6, each heat exchange module is comprised of an upper manifold 100, an array of vertical pipes 110, and a lower manifold 120. Each manifold 100 is closed at the ends by two covers 200 and two lines 13 extending from an "X" type distributor 140 connected to a main steam line 150.
Supplied by 0. This constitutes a vertical axis of symmetry about which the modules are systematically arranged.

The main steam line 150 is in direct communication with the RPV steam zone and forms a slab forming the main container 60.
Its part, which is outside of 50, has a second wall 160.

The exhaust line 170 of each lower manifold 120 extends through the slab 50 and in the region just above the core the RPV.
They will be joined together on the main line 171 which will be reconnected to. Distributor
140 has a steam inlet that draws vertically along the axis of symmetry and a plurality of outlets that are oriented radially with respect to the axis of symmetry. Each of these has a flow restrictor 180 shaped like a Venturi tube. Manifolds 100 and 120 are a single structure with no welds (except those required by condensate pipes) and flanges for cover 200
190 and both inlet 210 and outlet 220. Figure 7
The upper support 230 is capable of sliding in a direction perpendicular to the axis of the manifold 100, and
It consists of a block 231 with a very precise limit to 232.

Referring to FIGS. 8 and 9, lower support system 250 has a vertical gap 260, but manifold 12
There is no gap in the direction at right angles to 0 and only in the outer part there is a gap 170 in the axial direction of the manifold 120.

The operation of the isolation capacitor is summarized below to better point out the advantages of the present invention and the various technical problems addressed and solved.

Isolation capacitor 10 during normal operation of the reactor.
RPV by main steam line 150, which is always open
Of the condensate drain line on the other hand
170 is closed from the inside of container 60.

Since it is submerged in the water of pool 30 at low temperature, the component gradually condenses the vapor coming from the RPV, filling the condensed fluid to the height of distributor 140 perfectly.

As a result, the main steam line 150, the distributor 14
0, and all parts of the supply line 130 are typically at the temperature of the pool water.

Therefore, the pressure (equal to that of the first circuit) between this situation and the cold depressurized device, even when this component is inactive, or "stand-by". There is stress in the element due to not only the difference, but also the difference in temperature.

In normal operation, heat-induced stresses are minimized by making the supply lines sufficiently flexible; however, this type of solution has various problems associated with the potential vibration of pipes. Have a problem.

In accordance with the present invention, maximum thermal expansion is absorbed by allowing the supply line 130 to expand perpendicular to the manifold 100 up to a specified displacement 232. The vibration of the heat exchange device normal to the manifold. The restraining means has a shape suitable for both limiting the movement of the sliding block support 231 on the one hand, and restraining the movement of the manifold on the other hand, and giving sufficient rigidity to the line.
Formed by a book supply pipe 130.

On the other hand, the main steam line 150 is protected by a double wall or jacket 160 which isolates it from direct contact with pool water, limiting heat dissipation to the pool and in the event of line 150 failure. In addition, a second partition is provided to protect the container from the outside.

Expansion of the main steam line 150 is allowed within the main container body.

Another important aspect of the present invention consists of a high degree of reliability and protection against any damage to the outside of the main container. In fact, as already explained, the main steam line 150 has a double wall 160 and is connected to a safe and secure single forged distributor 140. The four flow restrictors 180 housed in the distributor 140 upstream of the supply line to the manifold are at some part of the component against critical spill levels due to the limited cross sectional area of the restrictors. Limits the effects of any damage of However, it should be emphasized that the possibility of failure downstream of the restrictor is minimized by the use of forged weld-free manifolds.

A situation will now be considered in which the isolation condenser is required to operate as a result of the closing of a valve in the steam line leading to the turbine.

This component is operated by opening the normally closed valve of the discharge line to completely empty the condensate, and to the vapor zone of the RPV that feeds the machine, to which the condensed vapor returns. A closed circuit is created between the area and the area below it.

The most important aspects of this stage are as follows: 1-Extreme transients experienced by the component when the cold condensate is replaced by the hot saturated vapor in a very short time. -Thermal expansion of the various parts of the result; 3-Establishment of natural circulation between the RPV and the condenser, mainly based on the equilibrium between the pressure drop on the steam side and the hydrostatic head on the condenser side. According to the invention, the first aspect is explained by the use of a modular concept which allows the use of smaller, thinner components and therefore less sensitive to the effects of transient thermal conditions. To be done. In fact, this concept makes the module of the heat exchanger a symmetrical structure, simplifying the solution of another problem.

The problems associated with thermal expansion are solved by the suspension mounting of the upper manifold in combination with the support of the lower manifold 120 of the special type already described. In fact, this support 250 allows the downward extension of the heat exchange pipe 110 and additionally the axial extension of the lower manifold 120; vibration suppression is "stand-by" and in the actuated state. Both are obtained by proper selection of gaps 260 and 270 which keep the component in contact with the support.

For the third aspect, natural circulation is preferred, while protection against any damage achieves the objective of low total pressure drop in the natural circulation circuit due to the low pressure drop of the flow control body. It is maintained at the same time by the use of this flow control body in the shape of a Venturi tube to help.

According to the invention, in its "stand-by" state, which exhibits a very good state during its operating life,
Both, and especially in operating conditions characterized by harsh thermal loads, the isolation capacitors are in the following situations: -obtaining operation with natural circulation, -minimizing stress, -safe in terms of vibration -Protects the system from any damage on the outside of the PC.

While the above description relates to the preferred embodiment of the present invention, it will be apparent that many modifications may be made to the structural and detailed aspects set forth without departing from the spirit of the invention. obtain.

In particular, the number of modules that make up the heat exchange device of the present invention can be varied from 2 to 4 with all other means conceivable to meet the various demands stated. .

[Brief description of drawings]

FIG. 1 is a functional diagram of a reactor having a protection system with a steam condenser with natural circulation of the present invention.

FIG. 2 is a vertical cross-sectional view of the heat exchange device of the present invention showing its location in the facility.

3 is a longitudinal cross-sectional view of the heat exchange device taken on the plane I-I of FIG.

4 is a view of the heat exchange device taken on plane II-II of FIG.

5 is a partial cross-sectional view taken along plane III-III of FIG. 4 of a distributor for a heat exchange device showing a flow limiter integral with the distributor.

FIG. 6 is a view of the upper manifold of the heat exchange device, one structure with integral flange and inlet, one of which is taken on plane IV- of FIG. 4;
Sectional view in the longitudinal direction taken at IV.

FIG. 7 is a view of the upper support system of the heat exchange device.

FIG. 8 is a diagram showing a lower support system of the heat exchange device.

9 is a cross-sectional view taken along plane VV of FIG. 8 showing the lower support system of the heat exchange device.

[Explanation of symbols]

10 ... condenser, 30 ... pool, 40,160 ... wall, 50 ... slab, 60 ... first container, 100,120 ... manifold, 110 ...
Pipe, 200… Cover, 130,150,170,171… Line, 1
40 ... Distributor, 180 ... Flow control body, 210 ... Inlet, 220 ...
Outlet, 230 ... Support, 231 ... Block, 232 ... Travel (displacement), 250 ... Support system, 260,270 ... Gap, A ... Supply line, D ... Bypass, G ... Generator, P ... Pump, S ...
Condensate outlet, T ... turbine, V ... valve.

Claims (9)

[Claims] 1. A heat exchange device submerged in a cooling pool for condensing steam at high pressure; a normally open line for carrying steam from a steam generator to said exchange device;
A nuclear reactor, a steam plant, and a so-called exchange device, comprising a controlled discharge line that is opened and normally closed by the intervention of a protection system, the exchange device comprising a plurality of exchange modules, and the like. A steam condenser with natural circulation for a system to protect natural objects. 2. Arranged symmetrically about a vertical axis,
A condenser is provided in the pool for condensing the vapor at high pressure, each of which comprises a plurality of identical exchange modules formed by an upper manifold, an array of vertical pipes, and a lower manifold. Reactors, steam plants that operate in natural circulation as a result of soaking,
And thermal capacitors for systems to protect such. 3. The capacitor of claim 2, wherein there are two modules. 4. The condenser according to claim 1, further comprising a main steam supply line constituted by a double-walled tube arranged on a symmetrical vertical axis. 5. A vapor inlet duct for distributing vapor received from a supply line to an upper manifold of each module for condensation, on-axis with respect to a symmetrical vertical axis, and said inlet duct. Capacitor according to any one of the preceding claims, also comprising a steam distributor having a plurality of radial distribution ducts with respect to, and constituted by a single forged part. 6. The thermal condenser of claim 5 wherein each radial duct of the distributor has a flow control device. 7. The capacitor of claim 6, wherein the flow control device is of the Venturi type. 8. The upper and lower manifolds of each module are comprised of a single forged tubular piece each having an end flange and at least one vapor inlet or one condensate outlet. The capacitor according to any one of claims 1 to 7. 9. At least one suspension bracket for each upper manifold having a predetermined radial clearance with respect to the axis of symmetry and a clearance for sliding vertically along the axis of symmetry, respectively. 9. A capacitor as claimed in any one of the preceding claims, comprising at least one pair of restraining means having a predetermined gap transverse to the axis of symmetry.