RU2606381C1 - Nuclear reactor heavy accident differential localisation system with breaking reactor floor and large surface area trap - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: invention relates to nuclear reactor severe accident localisation means. Nuclear reactor foundation bed (6) structure strength, mounted on nuclear reactor foundation bearing grate (7), does not exceed strength of nuclear reactor upper and lateral structures. With accident pressure nuclear reactor foundation bed (6) is broken into small parts by instantaneous breakthrough of small window openings with side of up to 20 cm over entire reactor foundation inner area. Reactor foundation bed (6) is simultaneously pushed out through bearing grate (8) along reactor foundation (7) entire internal perimeter. Through reactor foundation bearing grid accident melt is dropped into trap (2) receiving device. Melt intakes (4) are uniformly distribute accident melt along horizontal shafts (3). Horizontal shafts (3) are sector-wise arranged in vertical direction around trap (2) receiving device, along entire perimeter in range NPP unit main building (5), tiered, on required depth, in sufficient amount, providing accident melt guaranteed natural cooling and long-term storage, retardation of its heating, minimization of hydrogen formation, preventing formation of repeated criticality.

EFFECT: technical result is reduction of probability of destruction of outer nuclear reactor sealed loop (1) in case of accident pressure exceeding, nuclear explosion inside reactor.

1 cl, 2 dwg

Description

Melt trap (Melt localization device) is an optional part of a pressurized shell of a nuclear reactor, a design used to localize the melt of the core of a nuclear reactor in severe accidents with melting of the reactor core and fusion of the reactor vessel. It is one of the systems of passive nuclear safety. It provides isolation of the foundation from the melt, subcriticality of the melt and cooling of the melt.

Melt traps designed in Russia are used at the Tianwan NPP (operated since 2007, VVER-1000 reactors), Kudankulam NPPs and are part of the VVER-1200 projects (Novovoronezh NPP-2, Leningrad NPP-2 [2], Baltic NPP [3] ]), VVER-TOI.

In Russian pressurized shells, a melt trap is constructed directly below the reactor (at the bottom of the reactor shaft) and is a cone-shaped metal structure with a total weight of about 750 tons. The trap is filled with a special, so-called sacrificial material (filler), consisting mainly of iron and aluminum oxides. The filler dissolves in the fuel melt to reduce its volumetric energy release and increase the heat transfer surface, and water through special pipelines in the trap body fills this mass.

In European EPR reactors, the trap is an inclined surface mounted below the reactor. On it, the melt, the burnt body, is sent to a pool of water and a cooled metal bottom of a special design.

The main disadvantages of the above traps are the high cost of the project and sacrificial materials, low natural heat transfer, the need for continuous active cooling with melt water.

The main reason leading to the melt of nuclear fuel in the reactor is the insufficient flow of the cooler or its absence in the primary circuit of the NPP unit.

The cause of insufficient cooler in the primary circuit of the reactor may be a technical malfunction or violation of the operating rules.

At maximum workloads, a short-term emergency interruption in the supply of the cooler to the working zone can cause gas-vapor emission with subsequent destruction of the reactor.

The melt of nuclear fuel inside a nuclear reactor, with the release of a huge amount of energy in excess of the permissible operating pressure limits, leads to mechanical destruction of the sealed circuit of the reactor.

The existing systems for localizing the melt in the core of a nuclear reactor provide for their use in the case of penetration of the base of the reactor vessel. However, the penetration of the nuclear reactor vessel is preceded by a sharp increase in pressure inside the reactor, leading to the destruction of the reactor vessel and the release of most of the nuclear fuel into the environment.

The primary objective of the "Differential System for Localizing the Accident of an Atomic Reactor" is to prevent the destruction of the external sealed circuit of the nuclear reactor (1) (Fig. 1, 2) as a result of emergency overpressure, a nuclear explosion inside the reactor. In the future, to localize the nuclear fuel melt and stabilize the decay process in the zones of natural cooling.

The proposed accident localization system provides for:

- absorption of the initial shock wave from a nuclear explosion or gas-vapor emergency release;

- reception, distribution and storage with natural cooling of emergency alloys of nuclear fuel.

In the proposed differential system for localizing a severe accident of an atomic reactor, a nuclear melt trap consists of a receiving device (2) and horizontal shafts (3).

Structurally, the receiving device of the trap (2) is located within the subreactor space. The composition of the receiving device of the trap includes melt intakes (4) with inclined guides.

Horizontal shafts (3) are located around the perimeter, within the main building of the NPP unit (5), in tiers, to the required depth.

The uniform differentiation of the emergency melt along the horizontal shafts (3) is achieved due to the design feature of the reactor base sheet (6) (Fig. 2) of the support base of the reactor base (8) (Fig. 2) and the location of the melt intakes (4) (Fig. 1 ) traps.

Structurally, the trap should provide instantaneous shock wave discharge to a critical level of conservation of the upper and side structures of the nuclear reactor and the distribution of the emergency melt in the mines (3) (Fig. 1) with natural cooling without burning concrete structures.

The absorption of a shock wave or gas-vapor emergency release is achieved by the design feature of the base of a nuclear reactor (7) (Fig. 1). The structural strength of the base web (6) of the nuclear reactor should not exceed the strength of the upper and side structures of the nuclear reactor. The destruction of the canvas of the base (6) of a nuclear reactor under emergency loads should be planned, that is, provided for by design surveys. Active emergency destruction of the lower part of the reactor should look like a simultaneous rupture into small parts of the entire structure of the base fabric of the reactor according to the example of broken tempered glass. Or in the form of the possibility of instant breakthrough of small window openings with a side of up to 20 cm over the entire floor area of the reactor.

The possibility of initial destruction (rupture) of the base web of a nuclear reactor (6) until the criticality of the destruction of the side and upper parts of the reactor is achieved by the unique design of the base of the reactor (7).

The canvas of the base of the reactor (6) is laid on a strong supporting grid of the base of the reactor (8) (Fig. 2) with a cage up to 20 cm, a wall thickness of not more than 3-5 cm, a height that can withstand critical pressure loads inside the reactor. The strong support grid of the base of the reactor is made of high-strength and heat-resistant material, is part of the design of a nuclear reactor, with its external side rests and integrates seamlessly with the walls of the trap. The design of a solid support grid of the base of the reactor must withstand supercritical shock and temperature loads until the emergency melt is completely drained. In this case, the bed of the reactor base upon reaching the beyond, emergency loads should be destroyed (squeezed out) within the cell of the supporting grid of the base of the reactor. To achieve a rectangular gap, in the form of window openings, the base fabric of the reactor is pre-formatted with risks of weakening strength. The base web of the nuclear reactor is destroyed only along the inner perimeter of the reactor, while the reactor vessel is monolithically supported by the supporting walls of the trap. Structurally, the invention requires extensive research and design work to change the base of a nuclear reactor.

The proposed design of the web and the supporting lattice of the base of a nuclear reactor that collapses to the point of destruction of the walls and loading plate (upper part) of the reactor allows the task of quenching the shock wave, reducing pressure, simultaneously removing the nuclear melt from the reactor, and preventing the release of radionuclides into the environment, and evenly drain the nuclear melt around the entire perimeter of the receiver of the trap (2).

The strong concrete walls of the trap receiver (2) for receiving the melt of nuclear fuel are the basis and foundation for a nuclear reactor (1). Structurally, the trap has a main vertical shaft and lateral horizontal branches (horizontal shafts) (3) arranged sector-by-sector along the perimeter around the receiver of the trap.

This design option traps involves the placement of the receiving device (2) emergency melt within the sub-reactor space, with horizontal lateral branches, shafts (3), within the main body of the NPP unit (5) (Fig. 1).

Horizontal shafts are structurally made in the form of standard concrete shafts with bases at the melt intakes (4), horizontally expanding in area, along the perimeter of the NPP unit (5).

The concrete structures of the mines are simultaneously the supporting foundation of the building and units of the NPP unit.

Structurally, the receiving device of the trap (2) and horizontal shafts (3) are a monolithic concrete block and are a solid supporting base for a nuclear reactor, the building of the NPP unit and its internal technological units.

The number of horizontal shafts is calculated based on the estimated amount of emergency melt that spreads uniformly over the horizontal area of the shafts, with the possibility of natural cooling, without supplying a cooler. The filling of the shafts depends on the height of the inlet opening above the floor of the shaft and should not exceed 5 cm. Thus, the natural filling of the horizontal shaft with the melt will amount to 100 or more square meters. m with a melt height of up to 5 cm. Knowing the volume of the expected emergency melt, we plan the number of horizontal shafts.

The structural feature of the horizontal mine (3) is its limited filling, that is, when the emergency melt is completely filled with a height of up to 5 cm, the melt naturally flows into the lower mines. The process of filling the mine is regulated by means of melt intakes (4) (Fig. 1), protruding into the receiving device of the trap (2). The inclination of the intake to the side of the shaft provides a natural flow of the melt into the shaft with further distribution over the expanding horizontal surface of the shaft.

The structural arrangement of emergency melt intakes (4) should ensure uniform distribution of the melt between all mines (3). The temperature resistance of the intakes depends on the estimated time of filling the mine with the melt. After filling the mine with the melt, the process of complete destruction of the intake is desirable, this will accelerate the distribution of the melt into the lower mines.

Guaranteed natural cooling of the melt, slowing down its heating, minimizing the formation of hydrogen and preventing the formation of repeated criticality is achieved by a large area and volume of horizontal shafts, the number of which can be increased in depth indefinitely.

After an accidental explosion and destruction of the base fabric of the reactor, it is necessary to provide for an instantaneous cessation of the supply of coolant to the reactor in order to prevent the re-formation of gas-vapor emission. The standard pressure reduction system inside the reactor is actively switched on and used to prevent the occurrence of explosive concentrations of hydrogen.

Without the supply of a cooler, a chain reaction will lead to a complete melt of nuclear fuel and its outflow into a trap with differentiable distribution of the melt along horizontal mines.

The proposed design of horizontal shafts allows you to create a large specific surface of the heat sink through concrete walls in the surrounding soil. The plugged technical openings provided in external walls of mines allow partial extraction of a melt for further processing.

The above-described accident localization system is capable of ensuring the localization of a nuclear accident of the Chernobyl or Japanese type in Fokusima.

An ALS with a differential system for localizing a severe accident of an atomic reactor with a collapsing canvas of the base of the reactor and a trap with a large area and volume for storing the emergency melt complies with the highest standard for countering the terrorist threat. Those. in case of deliberate actions of the NPP personnel or terrorists, which led to a critical melt of nuclear fuel in the reactor, the base sheet in the reactor is destroyed by explosive pressure, the melt is discharged into the receiver of the trap (2), it is evenly distributed across horizontal shafts (3), and the tight loop of the nuclear reactor is preserved. This design of the ALS will not allow terrorists to carry out external destruction of the reactor and contaminate the territory with radionuclides.

For the implementation of the invention will require a lot of research work on the design of the collapsing canvas of the base of the reactor, its reliability to withstand long to critical loads.

The trap and its components are structurally the foundation of the building and units of the NPP unit. They are made of high-strength concrete and slightly increase the cost of the project.

Claims (1)

Differential system for localization of a severe accident of a nuclear reactor, consisting of a programmed collapsing web on the support grid of the base of a nuclear reactor and a melt trap, consisting of a receiving device with inclined melt intakes and sectorial horizontal concrete shafts, made around the receiver to the required depth around the entire perimeter of the NPP unit with limited occupancy and the possibility of overflow, uniform distribution and free cooling of emergency distribution Av.

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