JP2014010105A - Liquid metal-cooled nuclear reactor, and operation control method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To relax temperature gradient at a stratification interface in the upper plenum of a liquid metal-cooled nuclear reactor.SOLUTION: A liquid metal-cooled nuclear reactor includes: a core 2; a nuclear reactor vessel 1 for holding the core 2 and a nuclear reactor coolant therein; a shield plug 10 for sealing an upper part of the nuclear reactor vessel 1; a core upper mechanism 9 suspended from the shield plug 10 and provided above the core 9; a main circulation electromagnetic pump 7 provided in the nuclear reactor vessel 1, for circulating the nuclear reactor coolant; an intermediate heat exchanger 6 for removing heat from the nuclear reactor coolant; and a temperature stratification relaxation device for relaxing temperature stratification of the nuclear reactor coolant in the nuclear reactor vessel 1 after the nuclear reactor shutdown. The temperature stratification relaxation device may be configured as a cooling device 20 including: cooling parts 21 arranged below a liquid level 100a of the nuclear reactor coolant and above the core 2, for cooling the nuclear reactor coolant; heat releasing parts 22 provided outside the nuclear reactor vessel 1, for releasing heat entering from the cooling parts 21; and a cooling pipe 23 for connecting each cooling part 21 and heat releasing part 22.

Description

  Embodiments described herein relate generally to a liquid metal cooled nuclear reactor and an operation control method thereof.

  The reflector-controlled reactor is a commercial reactor that burns fuel by moving the reflector at a minute speed. By adopting a reflector that moves at a minute speed in a metal fuel core that is easy to ensure passive safety. , Ensuring high safety (such as negative or zero void reactivity core) and long core life.

  Generally, in a reflector-controlled nuclear reactor, core power control is performed using the streaming effect of neutrons by moving a reflector provided on the outer periphery of the core up and down. The inside of the reactor vessel of the reflector control reactor is divided by a cylindrical partition wall.

  In general, in the upper plenum region provided above the core, when the core scram with the main circulation pump trip is in a state where the flow rate of sodium, which is the coolant, is reduced, It is expected that a thermal stratification phenomenon will occur between the upper high temperature region.

  When the thermal stratification phenomenon occurs, a steep temperature gradient and accompanying thermal stress are generated in the upper plenum, resulting in problems such as thermal deformation. This becomes a factor of lowering structural soundness not only in the reflector controlled reactor but also in the liquid metal cooled nuclear reactor.

  For example, during natural circulation, there is heat transfer from the core side in the reflector region between the core barrel and the bulkhead. Further, when the reflector absorbs neutrons by neutron irradiation, the reflector generates heat. The closer to the core, the greater the neutron irradiation, and the greater the heat generated.

  Furthermore, when an auxiliary cooling system for removing the heat of the coolant in the reactor vessel is provided separately from the reactor main cooling system, the flow path on the side close to the outer wall of the reactor vessel is cooled. Accordingly, since the temperature inside the reflector is high and the temperature outside is low, an upward flow due to a temperature increase develops in the radial direction inside the reactor vessel, and a downward flow can be generated outside.

  In addition, convection occurs in this reflector region because the low-temperature coolant flows from the lower part. Due to this convection, a temperature distribution in the radial direction is generated, and there is a risk that a thermal stress is generated and problems such as thermal deformation occur. This also causes a decrease in the structural integrity of the reflector controlled reactor. In order to avoid this, a technique has been disclosed in which a small hole is provided in the reflector support plate to control the heat flow of the reflector (Patent Document 1).

  However, no technical proposal has been made on a technique for mitigating the temperature stratification of the upper plenum during a pump trip.

JP 2012-042368 A

  After the core scram, since the heat received by the coolant from the core is greatly reduced, it flows into the upper plenum at a low temperature and temperature stratification occurs. The steep temperature gradient at the stratification interface due to this temperature stratification causes problems such as thermal deformation due to thermal stress.

  Therefore, an embodiment of the present invention aims to alleviate the temperature gradient at the stratification interface generated in the upper plenum of the liquid metal cooled nuclear reactor.

  In order to achieve the above object, a liquid metal cooled nuclear reactor according to an embodiment of the present invention includes a core, a reactor vessel containing a reactor coolant that cools the core and the reactor core, and A shielding plug that seals the upper part; a core upper mechanism that is suspended from and supported by the shielding plug and provided above the core; and a main circulation pump that is provided in the reactor vessel and circulates the reactor coolant. An intermediate heat exchanger provided in the reactor vessel for removing heat from the reactor coolant to the outside of the reactor vessel, and a reactor coolant in the reactor vessel after the reactor is shut down And a temperature stratification mitigation device for mitigating temperature stratification.

  In addition, an embodiment of the present invention includes a reactor core, a reactor vessel containing a reactor coolant that cools the reactor core and the reactor core, a shielding plug that seals an upper portion of the reactor vessel, and a suspension depending on the shielding plug. An upper core mechanism that is supported and provided above the core to support the control rod drive mechanism, a main circulation pump that is provided in the reactor vessel and circulates the reactor coolant, and the reactor vessel An intermediate heat exchanger that is provided inside and removes heat of the reactor coolant outside the reactor vessel, and a liquid metal cooled nuclear reactor operation control method, A reverse flow step of causing the reactor coolant to flow backward by reversing the driving direction by the main circulation pump and moving the low-temperature reactor coolant at the intermediate heat exchanger outlet to the vicinity of the intermediate heat exchanger inlet When, After the serial reflux step, the driving of the reverse stop, and having a forward flow step of returning the reactor coolant back to the forward direction in the forward flow, a.

  According to the embodiment of the present invention, the temperature gradient of the stratification interface generated in the upper plenum of the liquid metal cooled nuclear reactor can be relaxed.

It is an elevation sectional view showing the composition in the reactor vessel of the reflector control reactor according to the first embodiment of the present invention. FIG. 2 is a horizontal cross-sectional view taken along the line II-II in FIG. 1, showing a configuration inside the reactor vessel of the reflector controlled nuclear reactor according to the first embodiment of the present invention. It is an elevation sectional view showing composition in a reactor vessel of a reflector control nuclear reactor concerning a 2nd embodiment of the present invention. FIG. 4 is a horizontal cross-sectional view taken along the line IV-IV in FIG. 3, showing a configuration inside a reactor vessel of a reflector controlled nuclear reactor according to a second embodiment of the present invention. It is an elevation sectional view showing composition in a reactor vessel of a reflector control nuclear reactor concerning a 3rd embodiment of the present invention. FIG. 6 is a horizontal cross-sectional view taken along the line VI-VI in FIG. 5 illustrating the configuration inside the reactor vessel of the reflector-controlled nuclear reactor according to the third embodiment of the present invention. It is an elevation sectional view showing composition in a reactor vessel of a reflector control nuclear reactor concerning a 4th embodiment of the present invention, and movement of a coolant. It is a flowchart which shows the operation control method of the reflector control nuclear reactor which concerns on the 4th Embodiment of this invention.

  Hereinafter, a liquid metal cooled nuclear reactor and an operation control method thereof according to an embodiment of the present invention will be described with reference to the drawings. Here, the same or similar parts are denoted by common reference numerals, and redundant description is omitted.

[First Embodiment]
FIG. 1 is an elevational cross-sectional view showing a configuration in a reactor vessel of a reflector controlled nuclear reactor according to a first embodiment of the present invention.

  A reactor core 2 is provided in a reactor vessel 1 containing a reactor coolant, and a radially outer side of the reactor core 2 is surrounded by a cylindrical core barrel 4. A cylindrical partition wall 5 is provided on the outer side of the core barrel 4, and a shield 8 is provided on the outer side thereof.

  In the annular space between the core barrel 4 and the partition wall 5, a reflector 3 that is driven up and down is provided, and the reactivity of the core 2 is controlled by the vertical position of the reflector 3.

  Above the shield 8, a main circulation electromagnetic pump 7 for circulating the reactor coolant in the reactor vessel 1 is provided, and further above that, an intermediate heat exchange for removing heat from the reactor coolant A vessel 6 is provided.

  A shielding plug 10 is provided on the upper portion of the reactor vessel 1 to seal the opening at the upper portion of the reactor vessel 1. The reactor coolant (for example, metallic sodium) in the reactor vessel 1 forms a liquid surface 100a, and the upper space of the liquid surface 100a is filled with an inert gas such as argon gas.

  A core upper mechanism 9 is provided through the center of the shielding plug 10. The upper core mechanism 9 is supported by being suspended from the shielding plug 10 and extends to the position immediately above the outlet of the core 2. The core upper mechanism 9 houses a control rod drive mechanism 9a that drives a safety rod inserted in the center of the core. The core upper mechanism 9 may store core outlet instrumentation such as core outlet temperature and flow velocity.

  A cooling device 20 is attached to the shielding plug 10 as a temperature stratification mitigation device for the reactor coolant in the reactor vessel 1 after the reactor shutdown. The cooling device 20 includes a cooling unit 21, a heat radiating unit 22, and a cooling pipe 23. A cooling medium is sealed in the high temperature side of the cooling unit 21, the cooling pipe 23, and the heat radiation unit 22. The cooling medium may be, for example, a gas or a liquid refrigerant.

  The cooling unit 21 is provided below the liquid level 100a of the reactor coolant and above the level at which the stratification interface 100b is considered to be formed, and the reactor coolant around the cooling unit 21 is disposed. Cooling. The heat radiating unit 22 is a heat exchanger and is provided outside the reactor vessel 1 and the shielding plug 10, for example, on the shielding plug 10. The reactor cooling is transferred from the cooling unit 21 via the cooling pipe 23. The heat from the material is released by transferring it to the secondary heat transfer medium.

  In addition, since the heat dissipation amount may be a level necessary for canceling the temperature stratification, the heat dissipation part 22 may be discharged to a heat pipe or an atmosphere, for example.

  FIG. 2 is a horizontal cross-sectional view showing the configuration inside the reactor vessel of the reflector controlled nuclear reactor according to the first embodiment of the present invention. The cooling unit 21 is provided in the vicinity of the core upper mechanism 9 and the reactor vessel 1 in the radial direction in order to avoid temperature stratification around the core upper mechanism 9 and the reactor vessel 1. Further, in order to avoid the occurrence of temperature imbalance in the circumferential direction of the core upper mechanism 9 and the reactor vessel 1, the cooling unit 21 is disposed so as to be symmetrical in the circumferential direction.

  In the present embodiment configured as described above, during normal operation, the reactor coolant is driven by the main circulation electromagnetic pump 7 and circulates in the reactor vessel 1.

  That is, the reactor coolant is discharged downward by the main circulation electromagnetic pump 7, flows into the area of the shield 8, flows downward around each shield 8, and enters the lower plenum 11 at the lower part of the reactor vessel 1. Inflow.

  The flow is changed upward in the lower plenum 11 and flows into the core 2. A part of the gas flows into the region where the reflector 3 is provided, that is, the annular flow path between the core barrel 4 and the partition wall 5 in parallel with the flow into the core 2.

  After flowing out from the core 2 in a high temperature state, it rises around the core upper mechanism 9 and enters the upper plenum 12 above the core 2. The upper plenum 12 gets over the upper end of the partition wall 5. After exiting the partition wall 5, the reactor coolant turns downward and flows into the intermediate heat exchanger 6, and after being cooled by the intermediate heat exchanger 6, the main circulation electromagnetic pump again. Enter 7.

  When the nuclear reactor is stopped, the main circulation electromagnetic pump 7 stops normal operation. If the main circulation electromagnetic pump 7 is healthy, the operation proceeds to the low flow rate mode. In this state where the circulation flow rate in the reactor vessel 1 is low, the flow of the reactor coolant in the reactor vessel 1 does not sufficiently reach the vicinity of the liquid level 100a of the reactor coolant. If this situation progresses, the stratification gradually proceeds due to the thermal stratification phenomenon, and the stratification interface 100b is formed.

  At this time, the cooling device 20 is activated to cool the surrounding reactor coolant provided with the cooling unit 21 in the vicinity of the reactor coolant liquid level 100a. The high-temperature reactor coolant above the stratification interface 100b by temperature stratification is cooled and the temperature decreases and flows downward. As a result, the stratification interface 100b due to the temperature stratification of the reactor coolant is disturbed. By this mixing, the steep temperature gradient formed at the stratification interface 100b is relaxed.

  As described above, according to this embodiment, the temperature gradient of the stratification interface 100b generated in the upper plenum 12 of the liquid metal cooled nuclear reactor can be relaxed.

[Second Embodiment]
FIG. 3 is an elevational cross-sectional view showing the configuration inside the reactor vessel of the reflector controlled nuclear reactor according to the second embodiment of the present invention. The temperature stratification mitigation device according to the present embodiment includes a mixing electromagnetic pump 31 provided on a side surface of the core upper mechanism 9. The broken line shows an example of the approximate height of the stratification interface 100b by temperature stratification. The mixing electromagnetic pump 31 is provided over and under the assumed stratification interface 100b.

  FIG. 4 is a horizontal cross-sectional view showing the configuration inside the reactor vessel of the reflector controlled nuclear reactor according to the second embodiment of the present invention. The mixing electromagnetic pump 31 is provided so as to wrap around a part of the periphery of the core upper mechanism 9. It is desirable to arrange them as symmetrically as possible in the circumferential direction so that a large temperature distribution does not occur in the circumferential direction of the core upper mechanism 9.

  In the present embodiment configured as described above, when the mixing electromagnetic pump 31 is driven so as to generate an upward flow in a low flow rate state after shutting down the reactor, the reactor cooling at a lower temperature below the stratification interface 100b is performed. Since the material rises and flows into a high temperature region above the stratification interface 100b, a circulating flow is generated up and down, and temperature stratification is alleviated.

  Further, when the mixing electromagnetic pump 31 is driven so as to generate a downward flow, the reactor coolant having a high temperature above the stratification interface 100b descends and flows into a low temperature region below the stratification interface 100b. The stratification interface 100b due to the temperature stratification of the reactor coolant is disturbed. By this mixing, the steep temperature gradient formed at the stratification interface 100b is relaxed.

  As described above, according to this embodiment, the temperature gradient of the stratification interface 100b generated in the upper plenum 12 of the liquid metal cooled nuclear reactor can be relaxed.

[Third Embodiment]
FIG. 5 is an elevational cross-sectional view showing the configuration inside the reactor vessel of the reflector controlled nuclear reactor according to the third embodiment of the present invention. The temperature stratification mitigation device according to the present embodiment includes an electromagnet 41 provided on a side surface of the core upper mechanism 9. The broken line shows an example of the approximate height of the stratification interface 100b by temperature stratification. The electromagnet 41 is provided below the assumed stratification interface 100b.

  FIG. 6 is a horizontal cross-sectional view showing the configuration inside the reactor vessel of the reflector-controlled nuclear reactor according to the third embodiment of the present invention. The electromagnet 41 is provided to wrap around a part of the periphery of the core upper mechanism 9. It is desirable to arrange them as symmetrically as possible in the circumferential direction so that a large temperature distribution does not occur in the circumferential direction of the core upper mechanism 9.

  In the present embodiment configured as described above, a magnetic field is generated around the electromagnet 41 when the electromagnet 41 is excited in a low flow rate state after stopping the reactor. Due to the magnetocaloric effect of this magnetic field, the temperature of the surrounding reactor coolant rises.

  The reactor coolant whose temperature has risen flows upward from below the stratification interface 100b due to buoyancy. After flowing upward, the temperature returns to the original state because it is released from the influence of the magnetic field. For this reason, a low-temperature reactor coolant exists in a high temperature region above the stratification interface 100b, and descends downward again. As a result, a circulating flow by natural convection is generated, and the stratified interface 100b fluctuates and mixes with temperature. By this mixing, the steep temperature gradient formed at the stratification interface 100b is relaxed.

  As described above, according to this embodiment, the temperature gradient of the stratification interface 100b generated in the upper plenum 12 of the liquid metal cooled nuclear reactor can be relaxed.

[Fourth Embodiment]
FIG. 7 is an elevational sectional view showing the configuration of the reactor vessel and the movement of the coolant in the reflector controlled nuclear reactor according to the fourth embodiment of the present invention. The temperature stratification mitigation device according to the present embodiment includes a post-furnace control device 50 that controls the main circulation electromagnetic pump 7 after shutting down the nuclear reactor.

  After receiving a signal indicating that the reactor has been stopped, the control device 50 after the reactor shuts down drives the main circulation electromagnetic pump 7 in a direction opposite to the normal direction after an appropriate time delay in which the stratification interface 100b is assumed to occur. Command signal.

  The main circulation electromagnetic pump 7 drives the reactor coolant in the reactor vessel 1 in the reverse flow direction, so that the reactor in the vicinity of the outlet (lower side) of the intermediate heat exchanger 6 is cooled and has a low temperature. The coolant returns to the inlet side (upper side) of the intermediate heat exchanger 6.

  After an appropriate time interval in which the low-temperature reactor coolant on the outlet side (lower side) of the intermediate heat exchanger 6 is supposed to return to the inlet side (upper side) in this way, the control device 50 after the reactor shutdown is operated in the reverse direction. A command signal is issued to the main circulation electromagnetic pump 7 so as to stop and drive in the forward flow direction. If necessary, the same control is repeated thereafter.

  Next, the effect | action by control by such a control apparatus 50 after a furnace stop is demonstrated.

  By driving the reactor coolant in the reactor vessel 1 in the reverse flow direction, the low-temperature reactor coolant near the outlet (lower side) of the intermediate heat exchanger 6 returns to the inlet side of the intermediate heat exchanger 6. At this time, the low-temperature reactor coolant also flows into the annular gap formed by the intermediate heat exchanger 6 and the partition wall 5, and the temperature of the partition wall 5 decreases.

  In this state, when returning to the forward flow, since the partition wall 5 is at a low temperature, the high-temperature coolant above the stratification interface 100 b is cooled by the partition wall 5, and a downward flow is generated in the vicinity of the partition wall 5. In this way, natural convection occurs in the high-temperature reactor coolant from the stratification interface 100b to the upper end of the partition wall 5, and the rapid temperature distribution generated at the stratification interface 100b is relaxed.

  As described above, according to this embodiment, the temperature gradient of the stratification interface 100b generated in the upper plenum 12 of the liquid metal cooled nuclear reactor can be relaxed.

  In addition, although this embodiment showed the example by the control apparatus 50 after a furnace stop, it is not limited to the automatic control by a control apparatus, You may operate artificially.

  FIG. 8 is a flowchart showing an operation control method of the reflector controlled nuclear reactor according to the fourth embodiment of the present invention.

  At the time when the stratification interface 100b is considered to be formed after the reactor shutdown, the reactor coolant is caused to flow backward by reversing the driving direction of the main circulation electromagnetic pump 7 and the vicinity of the outlet of the intermediate heat exchanger 6 The low-temperature reactor coolant is moved to the vicinity of the inlet of the intermediate heat exchanger 6 (S01).

  After step S01, when it is considered that the low-temperature reactor coolant near the outlet of the intermediate heat exchanger 6 has moved to the vicinity of the inlet of the intermediate heat exchanger 6, the reverse flow is stopped and returned to the forward flow (S02).

  Also in this modification, the same operation and effect can be obtained.

[Other Embodiments]
As mentioned above, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. For example, although each embodiment has shown the example which applied this invention to the reflector control nuclear reactor, it is generally applicable to liquid cooling type reactors other than a reflector control nuclear reactor. Further, for example, the circulation in the reactor vessel is not limited to the electromagnetic pump, and may be a mechanical pump.

  Moreover, you may combine the characteristic of each embodiment. That is, the cooling unit 21 is provided in the reactor vessel 1, the mixing electromagnetic pump 31 is provided in the core upper mechanism 9, the electromagnet 41 is provided in the core upper mechanism 9, and the control device 50 after the reactor shutdown is provided. Are not contradictory to each other and may be combined.

  Furthermore, these embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention.

  These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 ... Reactor vessel 2 ... Core 3 ... Reflector 4 ... Core barrel 5 ... Bulkhead 6 ... Intermediate heat exchanger 7 ... Main circulation electromagnetic pump (main circulation pump )
8 ... Shielding body 9 ... Upper core mechanism 9a ... Control rod drive mechanism 10 ... Shielding plug 11 ... Lower plenum 12 ... Upper plenum 20 ... Cooling device 21 ... Cooling Part 22 ... Radiating part 23 ... Cooling pipe 31 ... Electromagnetic pump for mixing 41 ... Electromagnet 50 ... Controller after furnace stop 100a ... Liquid level 100b ... Stratification interface

Claims (6)

The reactor core,
A reactor vessel containing the reactor core and a reactor coolant that cools the reactor core;
A shielding plug for sealing the top of the reactor vessel;
A core upper mechanism that is suspended from and supported by the shielding plug and is provided above the core;
A main circulation pump provided in the reactor vessel for circulating the reactor coolant;
An intermediate heat exchanger provided in the reactor vessel for removing heat from the reactor coolant to the outside of the reactor vessel;
A thermal stratification mitigation device for mitigating thermal stratification of the reactor coolant in the reactor vessel after the reactor shutdown;
A liquid metal cooled nuclear reactor. The temperature stratification mitigation device is:
A cooling unit that cools the reactor coolant below the liquid level of the reactor coolant in the reactor vessel and above the core;
A heat dissipating part that is outside the reactor vessel and releases heat input from the cooling part;
A cooling pipe connecting the cooling part and the heat dissipation part;
The liquid metal cooled nuclear reactor according to claim 1, wherein The temperature stratification mitigation device is:
An electromagnetic pump disposed on a side of the core upper mechanism and below the liquid level of the reactor coolant and above the core to raise the surrounding reactor coolant;
The liquid metal cooled nuclear reactor according to claim 1 or 2, wherein The temperature stratification mitigation device is:
An electromagnet disposed on a side of the core upper mechanism and below the temperature stratification interface of the reactor coolant to raise the temperature of the surrounding reactor coolant by magnetocaloric effect;
The liquid metal cooled nuclear reactor according to any one of claims 1 to 3, wherein The temperature stratification mitigation device is:
After the reactor shutdown, it has a post-reactor control device that controls the main circulation pump so as to return to the forward flow after the reactor coolant is made to flow backward.
The liquid metal cooled nuclear reactor according to any one of claims 1 to 4, wherein the liquid metal cooled nuclear reactor is provided. The reactor core,
A reactor vessel containing the reactor core and a reactor coolant that cools the reactor core;
A shielding plug for sealing the top of the reactor vessel;
An upper core mechanism that is suspended from and supported by the shielding plug and is provided above the core to support the control rod drive mechanism;
A main circulation pump provided in the reactor vessel for circulating the reactor coolant;
An intermediate heat exchanger provided in the reactor vessel for removing heat of the reactor coolant to the outside of the reactor vessel;
An operation control method for a liquid metal cooled nuclear reactor comprising:
After the reactor is shut down, the reactor coolant is caused to flow backward by reversing the driving direction of the main circulation pump, and the low-temperature reactor coolant at the intermediate heat exchanger outlet is moved to the vicinity of the intermediate heat exchanger inlet A backflow step to move to,
After the reverse flow step, stop the reverse direction drive, return to the forward direction and return the reactor coolant to the normal flow step,
An operation control method for a liquid metal cooled nuclear reactor.

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