Device for Passive Protection of a Nuclear Reactor

Abstract

The invention relates to nuclear reactor protection systems and can be used when building nuclear reactors, in particular, the fast neutron reactors. The Technical result of the invention consists in the expansion of 5 functional capabilities of the negative reactivity passive insertion device by securing its reliable actuation in various emergency conditions. The device has two vessels located in a common enclosure one under another with a ring-shape hollow space between the vessels and the enclosure to let the heat carrier flow. Fuel elements are located in the ring-shape hollow space, as well as the tooling for the heat carrier flow formation to cool the fuel elements and heat the upper vessel. The upper vessel is located above the reactor core and is divided with an internal partition wall to the central cylindrical and ring-shape hollow spaces. The partition wall has low thermal conductivity in the transverse direction. In the central hollow space of the upper vessel the cadmium isotope is mainly located, while in its ring-shape spacemercury. Lower vessel is mainly located in the active core of the reactor and filled with inert gas. The vessels and are connected with a pipe with a partition, made in the form of buckling rapture disc.

Claims

1. The device for the nuclear reactor passive protection is made in the form of two vessels located in the common enclosure one under another with a ring-shape hollow space to allow the heat carrier flow, the upper vessel is located higher than the reactor core and is partially filled with molten metal with large neutron-absorption cross-section, as well with molten metal with high vapour pressure within the range of the probable heat carrier temperatures; the lower vessel is mainly located in the reactor core and is filled with an inert gas; the vessels are interconnected with a partitioned pipe 10 made in the form of a buckling rapture disc, at that the fuel assemblies, as well as the means for the heat carrier flow forming to cool down the fuel assemblies and heat the upper vessel are located in the ring-shape hollow space.

2. The device according to claim 1, distinguished by the fact, that the mercury isotope.sup.199Hg is used as a molten metal with large neutron-absorption cross-section and a molten metal with high vapour pressure in the range of the possible heat carrier temperatures.

3. The device according to claim 1, distinguished by the fact, that In mercury alloys with cadmium isotopes .sup.ulCd and/or .sup.113Cd is used as a molten metal with large neutron-absorption cross-section and a molten metal with high vapour pressure in the range of the possible heat carrier temperatures.

4. The device according to claim 1, distinguished by the fact, that mercury can be used as molten metal with high vapour pressure in the range of the probable heat carrier temperatures, and the cadmium isotopes mCd and/or .sup.113Cd can be used as the molten metal with large neutron absorption cross-section.

5. The device according to claim 1, is distinguished by the fact, that an internal partition wall is located in the upper vessel to form the interconnected central cylindrical and ring-shape hollow spaces in the upper part, at that the partition wall has low heat conductivity in the transverse direction.

6. The device according to claim 5, distinguished by the fact that the wall 30 of the internal partition is made with two layers with a gas heat-insulating gap between the layers.

7. The device according to claim 5 distinguished by the fact, that in its central hollow space a molten metal with high neutron-absorption cross-section is located, and in the ring-shape upper vessel is mainly located a molten metal with high vapour pressures in the range of the probable heat carrier temperatures.

8. The device according to claim 1, distinguished by the fact, that the tooling of the heat carrier flow formation for the fuel assembly cooling is made as a lower pipe shell located between the lower vessel and the fuel elements, and with a transverse partition wall of the ring-shape hollow space in the upper part.

9. The device according to claim 1, distinguished by the fact, that the tooling of the heat carrier flow formation for the upper vessel heating is made as a lower pipe shell located between the upper vessel and the enclosure, and with a transverse partition wall of the ring-shape hollow space in the peripheral part.

10. The device according to claim 8, distinguished by the fact, that the hollow space between the lower vessel and the lower pipe shell, and the hollow space between the enclosure and the upper pipe shell are interconnected with each other via at least one pipe channel.

11. The device according to claim 1, distinguished by the fact, that in the cross-section the shape and the size of the enclosure mainly match the shape and the size of the reactor fuel assembly.

12. The device according to claim 11, distinguished by the fact that in the transverse cross-section the enclosure is made as a hexagon.

13. The device according to claim 8, distinguished by the fact, that in the cross-section the shape of the pipe shell for forming the heat carrier flow for the fuel element cooling mainly matches the shape of the device enclosure.

14. The device according to claim 9, distinguished by the fact, that in the cross-section the shape of the pipe shell for the upper vessel heating mainly matches the shape of the upper vessel.

15. The device according to claim 1 is distinguished by the fact that pipe elements with neutron moderator, e.g., beryllium oxide, are located between the lower vessel and the heat carrier flow forming device, to cool down the fuel elements.

Description

DESCRIPTION OF DRAWINGS

[0023] The device is illustrated with drawings in FIG. 2, FIG. 1 and FIG. 3, where some variants of its implementation are provided.

[0024] FIG. 1 shows a longitudinal section of the device in the central plane.

[0025] FIG. 2 shows a cross section of the device at the top of the tank.

[0026] FIG. 3 shows the cross-section of the device at the area of the lower vessel.

DESCRIPTION OF THE INVENTION REALIZATION VARIANTS

[0027] The fast neutron reactor protective device is made as an upper vessel (1) and lower vessel (2), located inside a common enclosure one over another.

[0028] Ring-shape hollow spaces (4) and (5) are located between the vessels (1) and (2) and the enclosure (3). The upper vessel (1) is located above the reactor core (7) and is partially filled with the molten metal (8), with large neutron absorption cross-section, as well as metal melt 5 (9) with high vapour pressure in the range of the probable heat carrier temperature range. In particular variants of the device design one substance, e.g., the mercury isotope 199 Hg or the mercury alloy with the cadmium isotopes luCd and/or 113 Cd can be used as molten metals (8) and (9). In accordance with the device design shown in FIG. 1, FIG. 2 and FIG. 3 mercury is used as the molten metal (9), and the cadmium isotopes ulCd and/or 113 Cd can be used as molten metals (8).

[0029] Lower vessel (2) is mainly located in the reactor core (7) reactor and filled with inert gas (10). The vessels (1) and (2) are connected with a pipe (11) with a partition, made in the form of buckling rapture disc (12).

[0030] In the design, shown in FIG. 1, FIG. 2 and FIG. 3 the molten metal (9)mercury and the molten metals (8)cadmium are located in different volumes of the upper vessel (1), and in its upper part they have a common gas vapour cushion (16). The volume of the hollow space(15) for mercury is significantly less than the volume of the hollow space (14) for cadmium. The internal partition (13) is located to form the central cylindrical (14) and the ring-shape (15) hollow spaces are located in the upper vessel (1). The partition wall (13) has low thermal conductivity in transverse direction, e.g., a two-layer wall with gas heat gap (16) between the layers. With such design of the upper vessel (1), in its central hollow space (14) a molten metal with high neutron-absorption cross-section (8) is mainly located, and in the ring-shape upper vessel (15) the molten metal with high vapour pressures in the range of the probable heat carrier temperatures (9) is mainly located. Such device design allows decreasing of the device actuation time at the emergency heat carrier temperature rise. This is reached due to the fact that in such design the mercury heating up to the extreme temperature and the corresponding growth of its vapour pressure required to break its membrane in such design are reached without heating the whole bulk of the metal absorber (8).

[0031] In a ring-shape hollow space (5) fuel elements (17) are located, as well as the tool for the flow forming (6) to cool the fuel elements (17), made as a lower pipe shell (18), with a transverse partition wall in its upper part (19), that divides the central part of the ring-shape hollow space (5). In the transverse cross-section the shape of pipe shell (18) mainly matches the shape of the enclosure (3) of the device, e.g, is designed as a hexagon. This design of the pipe shell (18) forms a narrow ring-shape flow of heat carrier (6) to cool the fuel elements (17). This allows forming the fuel element (17) cooling mode and the heat carrier temperature change (6) in the device in accordance with the fuel element cooling mode and the heat carrier temperature change in a regular fuel assembly.

[0032] In a ring-shape hollow space (4) there is a tooling for the heat carrier flow formation (6) for the upper vessel heating, made in the form of the upper pipe shell (20), located between the upper vessel (1) and the enclosure (3) and with a transverse partition wall (21) in its lower part, which overlies the peripheral part of the ring-shape hollow space (4).

[0033] In the cross-section the shape of the pipe shell (20) mainly matches the shape of the lateral space of the upper vessel (1). Such design of the pipe shell (20) forms a narrow ring-shape heat carrier flow (6) for heating the lateral surface of the upper vessel (1) and metal melt (9). At that, the location of the transverse partition walls (19) and (21) allows forming the heat carrier flow (6) in the device and directing it from the ring-shape hollow space (4), where fuel elements (17), are located to the hollow space (5) right to the lateral surface of the upper vessel (1) to heat the melt (9). Such device design allows forming the heat carrier circulation channel in the device where the its temperature change corresponds to the heat carrier temperature change in the regular fuel assembly, including at emergency situations. Such design of the device allows the reduction of the negative reactivity introduction (decreasing its response time) and increasing the reliability of its actuation at the heat carrier temperature rise in the reactor core higher than the pre-set limit value.

[0034] the hollow space (22) between the lower vessel (2) and the lower pipe shell (18), and the hollow space (23) between the enclosure (3) and upper pipe shell (20) are interconnected with each other via pipe channels (24) and form the second channel for liquid flow in the device, that serves to drain parts the flow of the heat carrier flowing through the ring-shape hollow space (22), without letting its mixing with a hotter heat carrier flow from the ring-shape hollow space (4) with fuel elements (17), to the hollow space (5) and washing the lateral surface of the upper vessel (1).

[0035] To simplify the deployment of the nuclear reactor core (7) the shape and the dimensions of the enclosure (3) of the device cross-section mainly correspond to the shape and size of reactor fuel assembly. E.g., when the fuel assemblies with hexagonal covers are used, the transverse cross-section of the enclosure is a Hexagon, and in the case of square-shaped FA without covers the enclosure (3) is made in the form of a square with relevant dimensions.

[0036] To improve the reactor shut-down efficiency at the device actuation and when the molten metal is fed (8), e.g., in the form of cadmium isotopes ulCd.sup.113 and/or Cd, in particular, there are pipe elements (25) located longitudinally between the lower vessel (2) and the lower pipe shell (18), with the neutron moderator, e.g., beryllium oxide. Introduction of moderator is intended to mitigate the range of neutrons in a zone of lower vessel (2) and improve the efficiency of the negative reactivity introduction into the reactor core (7).

[0037] The protection device of a fast neutron nuclear reactor is shown in Fig. FIG. 1, 2 and FIG. 3 operates as follows. In the normal reactor operation mode, the cylindrical hollow space (14) of the upper vessel (1) is filled with molten cadmium, the ring-shape hollow space (15) is filled with mercury, and the lower vessel (2) is filled with an inert gas. Mercury vapour pressure in the gas cushion (16) in the upper vessel (1) with the operating heat carrier temperatures (6) below the buckling rapture disc actuation pressure (12). In case of emergency operation modes caused by rapid growth of neutron flux or loss of heat carrier flow, the heat carrier (6) in a ring-shape hollow space (22) is heated above the maximum allowable temperature and goes to the ring-shape hollow space (23) to the lateral surface of the upper vessel (1).

[0038] Mercury in the ring-shape hollow space (15) gets heated up to the temperature when the pressure of its vapours in the upper part (16) of the vessel (1) is compared with the actuation pressure of the buckling rapture disc (12) that abruptly changes its shape and brakes at the contact with the needle (26). The molten cadmium (8) is discharged though the pipe (11) under the effect of gravity to the lower vessel (2), and the inert gas from the vessel (2) goes to the upper vessel (1). When the melt with large neutron absorption cross-section goes to the vessel (2) located in the reactor core (7), chain reaction stops, and the reactor switches to the subcritical condition and the reactor protection is realized.

[0039] The practical use of the device in the new-generation fast neutron reactors provides the following benefits: [0040] for all initial events in the reactor facility associated with rapid introduction of positive reactivity or loss of cooling (heat carrier flow rate) in the reactor core, the actuation of the reactor shut-down system that uses the proposed passive protection device, will result in the termination of the fission chain reaction in the reactor core when the heat carrier reaches the pre-set and experimentally verified temperature at the outlet from the reactor core; [0041] the device has high-degree reliability and readiness for actuation, as it has no external power sources and information signals for the actuation, has no actively or passively moving mechanical parts that can get stuck and result to the actuation failure; the power that causes the device actuation (heat carrier temperature growth) is released in the process to be stopped by the device; [0042] with such degree of reliability the device will get actuated in the cases when the source events are followed by multiple failures of other protective systems and devices.