Active Pit Tank Strainer of a Nuclear Power Plant

Abstract

An active strainer contains a housing with a cover, a base and side surfaces made in the form of filtering elements, pipes with channels fixed at one end at the central vertical axis of the strainer and configured to supply purified fluid from the central part of the strainer to the filtering elements from the other end of the pipe through channels, wherein the strainer housing is made of two parts, an upper and a lower one, each part is equipped with at least one filtering element, the turbine is installed between the upper and lower part and configured to rotate during the fluid flow passage through it, the turbine shaft is connected with the pipes, which are capable of sampling the purified fluid from the strainer housing during rotation of the turbine.

Claims

1. An active pit tank strainer of a nuclear power plant comprising a housing with a cover, a base and side surfaces made in the form of filtering elements, pipes with channels fixed at one end at the central vertical axis of the strainer and configured to supply purified fluid from the central part of the strainer to the filtering elements from the other end of the pipe through channels, wherein the strainer housing is made of two parts, an upper and a lower one, each part is equipped with at least one filtering element, the turbine is installed between the upper and lower part and configured to rotate during the fluid flow passage through it, the turbine shaft is connected with the pipes, which are capable of sampling the purified fluid from the strainer housing during rotation of the turbine.

2. The active strainer according to claim 1, wherein the side surfaces are cylindrical.

3. The active strainer according to claim 1 wherein the ends of the pipes supplying the purified fluid to the filtering elements are equipped with nozzles configured to supply the purified fluid in a wide range of angles.

4. The active strainer according to claim 1 wherein the filtering elements are made in the shape of a frame and a sector slotted grid located in it, composed of horizontal and vertical wires of a triangular section.

5. The active strainer according to claim 1, wherein the pipes are provided with holes for fluid intake during rotation of the turbine.

6. The active strainer according to claim 1, wherein the base is made in the shape of a flange with the possibility of attachment to the base of the pit tank.

Description

BRIEF DESCRIPTION OF FIGURES

[0025] FIG. 1 shows a side overall view of the active strainer of the pit tank of NPP and in sections A-A, B-B, D-D, and in the detail fragment C.

[0026] FIG. 2 shows a overall view of the filtering element and its parts.

[0027] FIG. 3 shows the arrangement of an active strainer cleaner pipe.

[0028] FIG. 4 schematically shows the interaction of the jets from the nozzle of the cleaner and the surface of the filtering element.

[0029] FIG. 5 shows the active strainer of the pit tank of NPP under normal operation, i.e. in the absence of impurities in the fluid.

[0030] FIG. 6 shows the active strainer of the pit tank of NPP when a debris layer is formed on the lower filtering elements in emergency mode, which causes fluid to flow through the upper filtering element.

[0031] FIG. 7 shows the active strainer of the pit tank of NPP in the cleaning mode from impurities and debris.

[0032] The active strainer of the NPP pit tank according to preferable embodiment includes a housing with a cover 15, a lower flange 1 and vertical supports 2 to which a lower filtering element 3 and an upper filtering element 14 are attached, located respectively in the lower and upper parts of the housing. Flange 1 is designed to install and connect the active strainer to the base of the pit tank. Vertical support 2 are connected to flange 1. The lower filtering elements 3 and the upper filtering elements 14 are installed between supports 2, made in the shape of a sector slotted grid connected to the frame 16 of the filtering element and composed of horizontal wires 17 and vertical wires 18 made of triangular wire elements. The cylindrical surface of the active strainer is formed of four sectors of the filtering elements 3, 14.

[0033] The turbine chamber 4 is installed between the upper and lower parts of the active strainer so that the entire flow of fluid entering the upper part of the active strainer passes through it. The turbine chamber 4 consists of a chamber casing, shaft struts 5, shaft 6, bearing 7, turbine sleeve 8 and turbine blades 9. In the turbine chamber 4, the translational fluid flow is converted into the rotational movement of the sleeve 8 and the turbine blades 9.

[0034] The shaft of the lower cleaner 10 and the shaft of the upper cleaner 11 are connected to the turbine sleeve 8. Pipes of cleaners 12 are attached to the shafts of the cleaners. Pipes 12 of the cleaner is made in the shape of a profile pipe. A nozzle 13 is installed at the end of the pipe, remote from the central axis of the active strainer, which ensures the distribution of the output jets within the service area of the cleaner. On the opposite side of the cleaner pipe, an opening 19 made in the shape of a through cut-out for fluid intake, when the cleaner rotates in direction 21 (FIG. 3) providing the fluid flow 20 into the pipe of the cleaner 12 and then to the holes 22 of the nozzle 13, which can be configured to spray the purified fluid in a wide range of angles in the direction of the filtering elements 3, 14 and in the general direction opposite to the flow of the filtered fluid 23 (FIG. 4).

[0035] Thus, the design of the active strainer provides for self-cleaning of the surfaces with a reverse flow of purified fluid leaving the nozzles 13. At the same time, a fluid flow through an active strainer is used as an energy source to create a reverse flow, which increases the safety of NPP operation in emergency conditions, since it does not require the use of external energy sources, for example, pumps, whose operation in emergency conditions is not guaranteed. In addition, the power consumption from the fluid flow for the operation of the turbine and the cleaning of the filtering elements 3, 14 occurs only when the lower filtering elements 3 are clogged, which reduces the total energy loss of the fluid flow through the active strainer and thereby increases the safety of NPP in emergency conditions.

[0036] In a preferred embodiment, the active strainer can be installed at the bottom of the pit tank and tight attached by a flange 1 to the base mounted above a vertical water intake channel that drains the fluid from the pit tank into the reactor core, so that debris and impurities are discarded from active strainer during its cleaning, settled on the bottom of the pit tank and subsequently did not settle on the filtering elements 3, 14, nor in the cooling system of the reactor core.

DETAILED DESCRIPTION OF INVENTION

[0037] During normal operation of NPP, no coolant leaks occur in it, therefore, there is no fluid flow through the active strainer.

[0038] In the event of an accident that caused the loss of liquid coolant in the core of NPP, this coolant begins to accumulate in the pit tank and upon reaching the level of the lower filtering elements 3 of the active strainer, flows through them in the water intake system and, subsequently, with the help of pumps, returns to the core. At the same time, the lower filtering elements 3 are not initially clogged with extraneous impurities and debris; therefore, almost the entire fluid flow passes through the lower filtering elements 3, bypassing the turbine blades 9, as a result of which there is no flow through the turbine (FIG. 5). In this case, the cleaners do not rotate and the surface of the filtering elements (3, 14) is not cleaned, which eliminates the energy consumption from the fluid flow for rotation of the turbine 9.

[0039] Subsequently, upon a fluid with extraneous impurities and debris inflow, the lower filtering elements 3 become clogged with a debris layer, as shown in FIG. 6, from bottom to top. This process is determined by the distribution of fluid flow over the surface of the filtering elements 3, in which approximately 80% of the total volume of fluid flows through the lower 20% of the area of the lower filtering elements 3. This process continues until the surface of the lower filtering elements 3 is completely covered with a debris layer.

[0040] During this process, the pressure losses on the lower filtering elements 3 remain almost constant and are determined by the losses on the strainer surfaces of the lower filtering elements 3. The resulting debris layer has a small thickness and a loose structure.

[0041] When the lower filtering elements 3 are completely covered with a debris layer, the main fluid flow begins to flow through the upper filtering elements 14 and, accordingly, through the turbine chamber 4. The turbine begins to rotate and rotates the pipe 12 of the cleaners, which leads to the flow of fluid into the hole for the fluid intake 19 (FIG. 3). Further, the incoming fluid accelerates under the action of centrifugal force and with excessive pressure is thrown into the nozzle orifice 13. The distance from the nozzle 13 to the surface of the filtering element 3, 14 can be chosen so that the jets from the nozzle 13 clean the entire space between adjacent cleaners (FIG. 4).

[0042] Thus, a local flow is created, directed outward of the active strainer through its filtering elements 3, 14. The debris layer is destroyed, and its particles are thrown to the bottom of the pit tank. The cleaning of the filtering elements 3, 14 when fluid enters through the upper filtering elements 14 is shown in FIG. 7.

[0043] During the time the debris is on the filtering elements 3, 14, its components coagulate, so debris particles destroyed by jets have a significant size and high density. This leads to their settlement at a higher speed, and the fragments of destruction either reach the filtering surfaces 3, 14, but much lower, or they settle to the bottom of the pit tank.

[0044] After cleaning the lower filtering elements 3, the fluid enters the lower part of the active strainer, as a result of which the turbine speed drops.

[0045] Further, the filtering-cleaning cycle is periodically repeated. The location of the turbine between the upper and lower parts of the active strainer allows for cleaning periodically after clogging of the lower filtering device 3. As a result, losses for the rotation of the turbine are reduced in a situation where the cleaning of the filtering devices 3, 14 is not required, in addition, the load on the bearings of the shaft 6 is reduced, which allows to extend its service life. As mentioned above, both of these factors directly affect the safety of NPP in emergency mode.

[0046] In a preferred embodiment, a graphite plain bearing can be used as a shaft support 6. Graphite bearings have the following advantages: they work in a liquid medium; have a low coefficient of friction; resistant to aggressive environments; used at temperatures up to 500° C. Moreover, since the design of the active strainer provides for the rotation of the shaft 6 only in the presence of debris in the solution, i.e. only at the accident. Thus, the service life of the bearing is limited to a period of maximum 30 days.

[0047] A full scan of the filtering surfaces with nozzles 13 is carried out per one revolution of the cleaner shaft 10, 11. At the same time, less than 0.5% of the total area of the filtering elements 3, 14 is simultaneously cleaned.

INDUSTRIAL APPLICABILITY

[0048] The active pit tank strainer of a nuclear power plant allows to increase its safety under emergency conditions and can be applied for various types of nuclear power plants.