GUIDING DEVICE OF A SYSTEM FOR CONFINING AND COOLING MELT FROM THE CORE OF A NUCLEAR REACTOR

Abstract

The invention is applicable to the corium localizing and cooling systems of a nuclear reactor designed for localization of severe beyond design-basis accidents, in particular, to the devices for directing corium of a nuclear reactor to the corium trap.

The technical result of the claimed invention is to increase the efficiency of localization and cooling of the nuclear reactor core melt.

The goal of the invention is to eliminate the guide assembly failure due to the concentration of impact load in the conical part of the guide assembly and, therefore, the instantaneous penetration of the core, fragments of the reactor vessel internals and the reactor vessel head into the core catcher.

In accordance with the invention, the guide assembly of the corium localizing and cooling system installed under the reactor pressure vessel and resting on the cantilever truss apart from the load-bearing frame contains the thermal elements that in the aggregate allows providing guaranteed entry of core, debris of the internals and the head of the reactor pressure vessel into the corium trap by excluding melt-through of the walls of conical and cylindrical parts and by redistributing the corium jet streams.

Claims

1. A guide assembly (1) of a corium localizing and cooling system of a nuclear reactor, installed under the reactor pressure vessel and resting on the cantilever truss, containing the cylindrical part (2) and conical part (3) with aperture (4) executed in it, bearing ribs (5), located radially relative to the aperture (4) and separating walls of the cylindrical (2) and conical (3) parts for the sectors (7), characterized in that it additionally contains the load-bearing frame, consisting of the external upper thrust ring (8), external lower thrust ring (9), internal central thrust ring (10), external upper thrust shell (11), middle thrust shell (12), separated into sectors by bearing ribs (5) and having aperture (14) in the upper part, external lower thrust shell (15), base (16), bearing stiffeners (17), upper tilted plate (18), connecting the conical head (19), bearing ribs (5) and middle thrust shell (12), lower tilted plate (20), connecting conical head (19), bearing ribs (5), middle thrust shell (12) and external upper thrust shell (11), thermal plate metal shields (23), installed on bearing stiffeners (17) and installed with gap (22) along the internal surface of middle thrust shell (12), and along the upper tilted plate (18), dismountable thermal plate metal shield (13), installed on bearing stiffeners (17) and covering the aperture (4), cooling channel (21), outgoing from the header (6) and passing between the upper and lower tilted plates (18 and 20), and between the middle and external upper thrust shells (12 and 11), connected through the aperture (14) with gap (22) forming a space between the thermal plate metal shield (23) and middle thrust shell (12), as well as between the thermal plate metal shield (23) and upper tilted plate (18), in addition, the space (24) limited by the base (16), conical head (19), lower tilted plate (20), part of the upper thrust shell (11), external lower thrust ring (9), external lower thrust shell (15), as well as the space (25) between the external lower thrust shell (11) and middle thrust shell (12), and the space (26) between the upper and lower tilted plates (18 and 20) is filled with concrete or ceramic material (27), leak-tight head (28), connected with the external lower thrust shell (15) and bearing ribs (17).

Description

BRIEF DESCRIPTION OF DRAWINGS

[0032] The guide assembly of the corium localizing and cooling system of the nuclear reactor executed in accordance with the claimed invention is shown in FIG. 1.

[0033] The sectional view of the guide assembly of the corium localizing and cooling system of the nuclear reactor, executed in accordance with the claimed invention is shown in FIG. 2.

[0034] The guide assembly fragment of the corium localizing and cooling system of the nuclear reactor, executed in accordance with the claimed invention is shown in FIG. 3.

EMBODIMENTS OF THE INVENTION

[0035] As shown in FIG. 1, the guide assembly (1) of the corium localizing and cooling system of the nuclear reactor installed below the reactor pressure vessel and resting upon the cantilever truss contains the cylindrical part (2) and conical part (3). An aperture (4) is made in the base of the conical part (3). Bearing ribs (5) pass along the conical and cylindrical parts (2 and 3) located radially with respect to the aperture (4). The bearing ribs (5) divide the walls of the cylindrical (2) and conical (3) parts into sectors (7). The guide assembly (1) contains the load-bearing frame, which consists of the following basic (load bearing) elements: external upper load-bearing ring (8), external lower load-bearing ring (9), internal central load-bearing ring (10), external upper load-bearing shell (11), middle load-bearing shell (12). Middle load-bearing shell (11) is divided into sectors by the bearing ribs (5) similar to the wall of the cylindrical part (2). The bearing frame is also composed of the external lower load bearing shell (15), base (16), knife edges (17), upper tilted plate (18). The upper tilted plate (18) connects the conical head (19), bearing ribs (5) and middle load-bearing shell (12). The lower tilted plate (20) connects the conical head (19), bearing ribs (5), middle load-bearing shell (12) and external upper load-bearing shell (11).

[0036] Apart from the load-bearing elements, the following thermal elements are used as part of the guide assembly (1): thermal plate metal shields (23), dismountable thermal plate metal shield (13). The thermal plate metal shields (23) are installed on the knife edges (17), and with gap (22) along the internal surface of the middle load bearing shell (12) and along the upper tilted plate (18). The dismountable thermal plate metal shield (13) is installed on the knife edges (17) and closes the aperture (4).

[0037] The cooling channel (21) passes between the upper and lower tilted plates (18 and 20) and between the middle and external upper load-bearing shells (12 and 11).

[0038] The cooling channel (21) exits from the header (6) and connects through the aperture (14) with gap (22) forming the space between the thermal plate metal shield (23) and middle load bearing shell (12), as well as between the thermal plate metal shield (23) and upper tilted plate (18).

[0039] The space (24) limited by the base (16), conical head (19), lower inclined plate (20), part of the upper external load-bearing shell (11), external lower bearing ring (9), external lower load-bearing shell (15) and space (25) between the external upper load-bearing shell (11) and middle load-bearing shell (12), as well as the space (26) between the upper and lower tilted plates (18 and 20) is filled with concrete or ceramic material (27).

[0040] A leak-tight head (28) is welded below to the external lower load-bearing shell (15) and knife edges (17).

[0041] The claimed guide assembly functions as follows.

[0042] As shown in FIGS. 1-3, the guide assembly (1) installed on the cantilever truss below the reactor pressure vessel head, in accordance with the gist of the claimed invention, performs the thermal barrier functions between the reactor pressure vessel and the reactor cavity equipment in its lower part, and between the reactor pressure vessel head and corium trap located below the guide assembly (1). The availability of thermal barrier during normal operation allows provide thermal insulation of the reactor pressure vessel head, and during severe accident at the time of reactor pressure vessel damage by corium provide conditions for diagnosis of the start of melt entry into the trap.

[0043] Heat insulation consisting of plate metal thermal shields (23), executed in the form of packets assembled from dimple and non-dimple thin stainless steel sheets is installed on the guide plate for providing thermal insulation of the reactor pressure vessel head during normal operation. Such packets are installed on the walls (6) of the cylindrical and conical parts (2 and 3), and on the inner surface of the middle load-bearing shell (12) and upper tilted plate (18) using the fasteners providing thermal displacements of heat insulating packets and guide plate frame with respect to each other during normal operation, operational occurrence and design-basis accident.

[0044] The dismountable thermal plate metal shield (13) is installed directly below the reactor pressure vessel head pole that provides if required access to the external surface of the reactor pressure vessel. An hatch with displacing inset is executed for access to the dismountable thermal plate metal shied (13) in the lower part of the guide assembly (1) on the service platform side. Such a design allows exclude water accumulation in the hatch during operational occurrence, during design-basis and beyond design-basis accidents.

[0045] The space between the load-bearing elements (5, 8, 11, 9, 15, 16, 19, 18, 12) of the guide assembly is filled with heat-resistant concrete for providing thermal insulation of structural concrete and cantilever truss during beyond design-basis accident. The load-bearing elements (5, 8, 11, 9, 15, 10) and concrete and ceramic material (27) form according to their function the guide assembly in the form of a funnel, providing coverage of the lower part of the reactor pressure vessel above the connection plane of the head with the cylindrical part (2). In the process of corium exit, the guide assembly (1) can be subjected both to a relatively slow loading under plastic deformations of the reactor pressure vessel, and to impact loading when the head of the reactor pressure vessel is torn off due to the residual pressure. These loads are taken up by the guide assembly, formed by the load-bearing elements (5, 8, 11, 9, 15, 10) and concrete and ceramic material (27). Such a design shall provide: [0046] free-flow drainage to the corium filler after damage or melt-through of reactor pressure vessel; [0047] retention of large-sized debris of internals and head of the reactor pressure vessel against fall into the corium trap; [0048] protection of corium trap casing against damages on fall of large fragments; [0049] protection of the cantilever truss and its communications against damage on corium movement. [0050] excluding direct contact of corium with the reactor cavity equipment and construction concrete; [0051] exclusion of direct radiant impact on the part of the corium on reactor cavity equipment and reactor pressure vessel fittings. The layers of sacrificial material (concrete or ceramic) are located under the tilted surfaces of the guide assembly—under the upper and lower tilted plates (18 and 20). directly below the upper tilted plate (18) is the sacrificial layer prepared for example based on aluminium and ferrous oxides, and under the lower tilted plate (20) is the thermally durable heat-proof layer, made for example based on aluminium oxide.

[0052] The sacrificial material located under the upper tilted plate (18), by melting in the corium ensures increase of the cross-section in the guide assembly (1) sectors, if the increase of the effective cross-section provided by the flattening and melting of the thin elements of the plate metal shied (23) was not sufficient for example on outflow of the melt from the reactor pressure vessel with large flow exceeding the cross-section throughput capacity of the guide assembly (1) or on outflow of corium with core debris covering the cross-section and preventing free outflow of corium. The dissolving of the sacrificial material allows to not allow overheat and damage of bearing ribs (5). The complete blocking of the cross-section is possible on damage of the bearing ribs (5), and sectoral damage of the guide assembly (1) as a consequence of this.

[0053] The thermal-resistant heat-proof layer located below the lower tilted plate (20) provides strength and stability of the structure on reduction of the thickness of sacrificial material located between the upper and lower tilted plates (18 and 20). Thermal resistant concrete protects the underlying equipment against the corium impact, by not allowing the corium to sectoral through melt-through or damage the guide assembly.

[0054] The guide assembly (1) on reactor pressure vessel damage takes on itself the dynamic loads occurring: [0055] on lateral outflow of corium under the action of residual pressure in the reactor pressure vessel; [0056] on increase of the lateral cavity cross-section in the reactor pressure vessel and change of its profile in the process of corium outflow; [0057] on detachment of reactor pressure vessel head parts following plastic deformation under the action of thermal and mechanical loads and residual pressure; [0058] on detachment of the reactor pressure vessel head parts following impulse pressure rise inside the pressure vessel (on flooding the corium with water) and their shock diffusion about the guide vanes; [0059] during external effects and auto shocks in the process of beyond design-basis accident propagation.

[0060] Before the start of corium inflow the filler present in the trap casing is tightly closed by the head (28) of the guide assembly (1) that provides: [0061] water drainage from the head surface (28) and as a consequence of this no steam explosions at the time of corium inflow to the accumulator. [0062] retention of integrity of the accumulator and structural materials in the process of the total period of normal operation, and on abnormal operation and during design-basis accident.

[0063] The following is performed for providing unconstrained inflow of corium: [0064] leak-tight head (28) is executed in the form of an easily damageable membrane; [0065] thermal plate metal shields (13 and 23) are executed with easily damageable high-temperature corium so as to not prevent its displacement. On melting of the thermal insulation the cross-section for the tricking of corium along the surface of the guide assembly increases several times. Various degree of increase of the cross-section is provided for the vertical and tilted thermal plate metal shields (23) that is related to different geometry of the channels formed by the vertical bearing fins; [0066] An aperture (4) is made in the central part of the guide assembly for corium passage, sizes thereof is limited by the scatter of solid and liquid fragments of the core in the process of its outflow from the reactor pressure vessel.

[0067] Thus, the thermal plate metal shields (23) and sacrificial material installed below the upper and lower tilted plates (18 and 20), used as guide assembly (1) of the core localizing and cooling system of the nuclear reactor perform anti-impact, channel forming and protection functions.

[0068] The plate metallic heat shields (23) provide initial damping of the impact load on the part of the separated sectors of the damaged head considering the acceleration created by residual pressure inside the reactor pressure vessel. Moreover, the crushed plate metal heat shields (23) provide the initial protection of the guide assembly (1) and against impact action of the corium jet at small residual pressure in the reactor pressure vessel.

[0069] On strong dynamic response on the part of the separated sectors of the damaged head of the reactor pressure vessel, the concrete or ceramic materials (27) forming the protective layer around the critically important load-bearing elements (5, 11, 15, 9) of the guide assembly (10) takes the impact load, moreover the bearing fins (5) may be partially melted, especially this concerns the tilted part protected by layers of sacrificial material under the upper and lower tilted plates (18 and 20).

[0070] Together with the load-bearing elements (5, 8, 11, 9, 15, 18, 20, 12) of the guide assembly (1) the concrete or ceramic material (27) creates impenetrable barriers for the flying objects and corium jet.

[0071] Thus, the thermal plate metal shield (23) and concrete or ceramic material (27) forming the protective layers of load-bearing elements (5, 9, 11, 12, 15) of the guide assembly (1) ensure breaking and blocking of large fragments of reactor pressure vessel and its internals, at the same time providing sequential input of corium, fragments of internals and head of the nuclear reactor pressure vessel in the corium trap.

[0072] The removable thermal plate metal shields (23) provide increase of the cross- section for displacement of corium in each radial vertical and tilted sectors and in azimuth direction on horizontal flow of corium.

[0073] During severe thermo-mechanical impact on the part of corium outflowing from the reactor pressure vessel the cross-section increases in the guide assembly (1) for displacement of corium by thermo-chemical interaction of the concrete or ceramic material (27) with corium, besides the chemical activity and thermo-mechanical impact on the load-bearing frame of the guide assembly (1) are reduced that retention of its integrity.

[0074] Thus, the thermal plate metal shields (23) and concrete or ceramic material (27) forming the protective layers of the load-bearing elements (5, 9, 11, 12, 15) of the guide assembly (1) provides protection of the structural and serpentine concretes of the reactor cavity against interaction with corium.

[0075] The concrete or ceramic material (27) forming the protective layers around the critically important load-bearing elements (5,11, 15, 9) of the guide assembly (1) create thermal and chemical barriers preventing the surface and structural damage of the load-bearing elements (5, 8, 11, 9, 15, 18, 20, 12) of the guide assembly (1) on thermal and thermo-mechanical impacts on the part of corium jet, for which purpose the thermal resistance of concrete or ceramic material (27) is selected different in different directions of corium flow that provides earlier damage of the sacrificial material under the upper tilted plate (18) located close to the reactor pressure vessel than is achieved by quicker escape of corium and reduction of thermo-chemical and thermo-mechanical impacts on the critically important load-bearing elements (5, 6, 9, 7, 11, 14, 10) of the guide assembly (1).

[0076] Thus, the concrete or ceramic material (27) forming the protective layers of the load-bearing elements (5, 6, 9, 7, 11, 14, 10) of the guide assembly (1) provides their strength on lateral melt-through of the reactor pressure vessel and as a consequence protection of the structural and serpentine concretes of the reactor cavity against interaction with corium.

[0077] The use of guide assembly (1) having load-bearing frame equipped additionally with thermal elements allowed provide gradual input of corium (melt) after damage or melt-through of the reactor pressure vessel, retention of large-sized fragments of the internals, fuel assemblies and head of the reactor pressure vessel against fall into the corium trap, protection of the cantilever truss and its communications against damage on corium input from the reactor pressure vessel to the corium trap, without blocking of the central aperture made in the conical part, preservation of the concrete cavity and dry protection with serpentine concrete against direct contact with corium.

[0078] Sources of information:

[0079] 1. RF patent No. 2253914, IPC G21C 9/016, priority dated 18 Aug. 2003

[0080] 2. Corium localizing device, 7th International Research and Training Conference “Safety assurance of NPP with VVER”, OKB Gidropress, Podolsk, Russia, May 17-20, 2011.

[0081] 3. RF patent No. 2576516, IPC G21C 9/016, priority dated 16 Dec. 2014;

[0082] 4. RF patent No. 2576517, IPC G21C 9/016, priority dated 16 Dec. 2014;

[0083] 5. RF patent No. 2575878, IPC G21C 9/016, priority dated 16 Dec. 2014.