Patent Number: 054147433
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is seen a residual-heat removal system which belongs, for example, to a pressurized-water nuclear reactor with a four-loop primary circuit configuration. In this case a reactor R is assigned to four primary-circuit loops (primary loops), which are denoted by reference symbols L1 to L4. The loops are represented fully only in the case of the primary loop L1, but in each case they have a steam generator D1 and a main coolant pump P1. Of course, the invention can also be applied in the case of three-loop or two-loop installations. All of the primary loops L1 to L4 are identically constructed. In the case of the primary loop L1 which is represented in greater detail, a hot leg r1 leads from the reactor R to a primary chamber 1 of the steam generator D1. The steam generator D1 has a tube bundle which is denoted by reference symbol W1 and a secondary chamber which is denoted by reference symbol 2. Re-cooled primary medium is fed back from the primary chamber 1 through a cold leg r2 and the main coolant pump P1 into the nuclear reactor R through a non-illustrated inlet nozzle of the latter. Primary medium 1.1 circulates through a tube bundle W1 and fills the latter (which is diagrammatically indicated by horizontal dashes at a diagonal line symbolizing the tube bundle W1). The pressure on the primary side is, for example, 155 bar and on the secondary side is, for example, 64 bar. A level of a secondary medium 2.1 in the secondary chamber 2 is denoted by reference symbol 2.0. Above the level 2.0 there is a steam space 2.2, in which non-illustrated steam moisture separators or steam driers are disposed. The live steam generated passes through a steam dome 3 into a live-steam line d1 and from there through a non-illustrated live-steam valve to a non-illustrated steam turbine and further components and pipelines of a secondary-side thermal cycle of the nuclear power plant. The steam generator D1 (and accordingly also the non-illustrated steam generators of the other loops L2 to L4) is connected to its operational live-steam line d1 and a feed-water line d5, through the circuit line d1 (up to a branching point 4), through a circuit line d2 (these two line parts d1, d2 form the hot leg) and through line parts d3, d4 of the circuit lines forming the cold leg. The steam generator D1 is also connected to one side of a safety condenser SK1, which has a tube bundle W2 that is diagrammatically indicated by a diagonal line (in just the same way as in the case of the steam generator D1). The circuit lines d1 to d4, which connect the secondary sides of the steam generator D1 and of the safety condenser SK1 to each other, are referred to below as SACO circuit lines, and the safety condenser itself is referred to as SACO (which is an abbreviation for safety condenser). Through the use of the feed-water line d5, the feed-water is delivered from a main feed pump P2 through a non-return valve A2 into the secondary chamber 2. The SACO SK1 is set up on its other (tertiary) side for cooling the secondary medium circulating in the SACO circuit d1-d4 (this secondary circuit is denoted as a whole by reference symbol N1) by supplying a cooling medium (demineralized water), which is still to be explained in further detail below. According to the invention, the lines d3-d4 of the cold leg of the SACO circuit N1 or the SACO circuit lines d1-d4 leading from the SACO SK1 to a feed-water connection 5 of the lower-situated steam generator D1, are led by its line part d3 to a supply connection S of a swirl chamber valve WV. The swirl chamber valve WV has a control connection C which is connected by a pressure-side feed-water line part d51 to a downgradient of the main feed-water pump P2 and is connected through the line part d51 to the feed-water line d5 at a connection point 6. An outlet E of the swirl chamber valve WV opens out through the line part d4 into the secondary chamber 2 in the region of the connection point 5, i.e. into its inflow space filled by the feed-water 2.1. The difference in level between the SACO SK1 and the steam generator D1, i.e. in particular the difference in level between a level 7.0 and the level 2.0 of the feed-water 2.1 in the secondary chamber 2, is dimensioned in such a way that a natural circulation through the SACO circuit N1 or its corresponding circuit lines d1-d4 can be accomplished during residual-heat removal operation. This difference in level is diagrammatically indicated by dashed level lines and an arrow 8 representing the distance between the levels. In order to provide for the natural circulation, a level distance 8 on the order of magnitude of about 2 m is sufficient. FIGS. 3 and 4 show that the swirl chamber valve WV, which may also be referred to as a vortex chamber valve, includes a flat hollow-cylindrical housing 9 with three openings c1, s1 and e1 and with a tangential connection nozzle 10, a radial connection nozzle 11 and an axial connection nozzle 12 respectively connected thereto. The tangential control connection C, the radial supply connection S and the axial outlet E are respectively formed by the openings with nozzles c1/10, s1/11 and e1/12. A supply stream Qs fed through the radial opening s1 is not disturbed when there is no control stream Qc or only a small control stream Qc and leaves a swirl chamber 13 through the axially disposed outlet E or the outlet nozzle 12 as an outlet stream Qe, which is indicated by an arrow f1 in FIG. 3. With the aid of a tangential control stream Qc conducted through the opening c1 as is seen in FIG. 4, a swirl flow is generated in the swirl chamber 13, as arrows f2 symbolize. The centrifugal force has the effect of building up a counter pressure in the swirl chamber 13, whereby the inflow of the supply flow Qs comes to a standstill. In this case, a control pressure Pc must be slightly higher (by about 5 to 10%) than the supply pressure Ps. In this state, all that flows is the control stream Qc, which makes up about 5 to 10% of the required supply stream Qs through the swirl chamber 13. A higher control stream Qc would also not have any adverse effects. Following the functional explanation of the swirl chamber valve WV with reference to FIGS. 3 and 4, it can now be recognized from FIG. 1 that when the main feed-water pump P2 is switched off, the swirl chamber valve WV is set in motion due to the reduced control pressure Pc, or the control stream Qc, at the control connection C of the secondary-side SACO circuit N1 through the then released flow section between the supply connection S and the outlet E. On the tertiary side, a water reservoir B with a water pool 14 having a water level which is denoted by reference symbol 14.0, is disposed at a geodetically higher level than the SACO SK1 and is connected to a tertiary-side intake 15 of the SACO SK1 through a parallel connection of a minimum flow bypass line b1 with a shut-off valve A0 as well as a line branch b11 with a control valve A1, that is connected in parallel with the minimum flow bypass line b1. A level of a water pool 16.1 in a tertiary chamber 16 establishing itself during residual-heat removal operation is denoted by reference symbol 16.0. A discharge line for evaporating tertiary medium, which is connected to the tertiary chamber 16, is denoted by reference symbol b2. The evaporated tertiary medium can be blown out over the roof, with it being possible for there to be provided a non-illustrated steam moisture separator having condensate which may enter the water reservoir B through a non-illustrated return feed line. During operation of the nuclear reactor installation as intended, the secondary circuit of the SACO SK1, which is synonymous with the SACO circuit N1, and also the tertiary side of the SACO SK1, are to be in readiness, so that they are filled with condensate and demineralized water, respectively. In order to avoid energy losses by the discharge of vapor over the roof, a low circulation in the secondary circuit of the SACO SK1 is also to be avoided, which happens by blocking the swirl chamber valve WV by means of the tangential control stream Qc through the control connection C. The required control stream Qc is produced in power operation or in start-up and shut-down operation of the installation by the main feed-water pump P2 or the non-illustrated start-up and shut-down pumps. As soon as the control stream Qc approaches zero due to failure or deliberate switching off of the pump concerned, the natural circulation in the SACO circuit N1, i.e. the cooling of the steam produced in the steam generator on account of the decay heat in the SACO SK1 and the return of the condensate through the elements d3-WV-d4-5 into the secondary chamber 2 of the steam generator, begins to start up automatically. In order to maintain continuous operation, all that is necessary is to ensure the non-illustrated secondary circuit shut-off (for example live-steam shut-off valve in the live-steam line d1 in the closed position). In order to control the heat removal in dependence on the amount of residual heat produced, there is provided the control valve A1, which is in the open position during normal operation and is controlled according to the requirements of the system. The falling filling level in the water reservoir B has the effect of assisting control. The volume of this reservoir B must be constructed to be great enough to allow a residual-heat removal operation of preferably at least 24 hours to be maintained. In the case of the second illustrative embodiment according to FIG. 2, a tube bundle W2 of a SACO SK2 is integrated in the water pool 14 of the water reservoir B, so that a combined SACO/water reservoir SK2/B is formed. The water level 14.1 of the water pool 14 is geodetically higher than the tube bundle W2 of the SACO Sk2. The outlet E of the swirl chamber valve WV opens out into the feed-water inflow space, or the secondary chamber 2, of the steam generator D1, through a control valve A3 that is open during normal operation of the steam generator, with it being possible in principle for the control valve also to be connected between the SACO SK2 and the swirl chamber valve WV. In the case of this circuit, control takes place in the condensate return by condensate retention in the tube bundle W2 of the safety condenser SK2. Otherwise, the function of the circuit according to FIG. 2 is analogous to that according to FIG. 1: the flow path S-E of the swirl chamber valve WV is blocked by a control stream Qc at the control connection C as long as the main feed-water pump P2 is in operation. If the secondary-side heat removal is blocked off through the live-steam line d1 to a downstream steam turbine by means of closing the live-steam valve and if the pump P2 is switched off, the natural circulation in the secondary-side SACO circuit N1, and consequently the residual-heat removal operation, commences so that the primary medium flowing through the heat-exchanging tubes W1 can give off its heat to the secondary medium 2.1, with the secondary medium in the SACO SK2, in the form of steam, cooling again and condensing.