Passive cooling circuit with natural inert gas circulation and built-in start-up device

Abstract

The passive cooling circuit with natural inert gas control and built-in start-up device is designed in such a way that the start-up device is built into the gas system (1) of the HTHL, consisting of the storage tank (5) of the driving gas accumulated at pressure p c, which is connected through the pressure reducing valve (10) with the driving nozzle of the jet compressor (4) with pressure p f. The suction chamber of the jet compressor (4) with pressure p e is connected by the suction pipe (6) with the ejection nozzle (7) in the cold leg (12). The outlet of the diffuser of the jet compressor (4) with pressure p i is connected by the ejection pipe (8) with the injection nozzle (9) in the hot leg (11), wherein for the pressures of the gases the following is valid.

Description

[0001] Passive cooling circuit with natural inert gas circulation and built-in start-up device

[0002] Technical field

[0003] The invention relates to the passive cooling circuit with natural circulation of inert gas and the built-in start-up device. The invention falls within the field of mechanical engineering, energy resources and devices.

[0004] Background

[0005] Due to the change in requirements for the reconfiguration of the use of energy sources, a significant part of effort and resources invested in nuclear research and development is now also focused on improving the safety of reactor operation. Interest in this area has also been stimulated by incidents in the recent past, most famous of which is the Fukushima accident in 2011.

[0006] Research in the field of safety of the nuclear systems and facilities is moving in several directions. One of them is to ensure that residual heat is removed from the reactor if, after an accident, there is the complete loss of power and forced circulation water cooling is interrupted. Several options have been proposed to solve this problem. As one perspective way, the high temperature helium loop with natural circulation, so-called HTHL (High Temperature Helium Loop ), is shown to be one of the ways to remove the residual heat.

[0007] This method is also applicable to reactors of 4th generation with expected higher nuclear fuel efficiency, with lower nuclear waste production. This self-extracting passive residual heat removal system is designed in such a way that, at one point, a thermal flux QAis fed to the gas in the cooling system through the first heat exchanger. The input energy corresponding to the thermal flux is reflected by the increase in the values of the gas state variables TA, PA, r at the location of this cross-section of the first heat exchanger. Through the second heat exchanger at the second location of the cooling system, the heat flux QBis removed from the gas. The dissipated energy corresponding to the thermal flux is demonstrated by the decrease in the values of the gas state variables ZB, / ?B, / 'B at the cross-section of the second heat exchanger.

[0008] As the result of the thermodynamic imbalance between the first and second cross-sections of the cooling system, gas flow occurs between the above mentioned cross-sections, with heat transfer occurring between the inlet and the outlet of the passive cooling system of the circuit with natural circulation of the inert gas.

[0009] The safety function performed by the residual heat removal system is the removal of the heat produced from the fission reaction in progress and other residual heat from the reactor, generated after the reactor has been shut down and the fission reaction has stopped, without the need of electricity supply from the grid or batteries, characterized by the residual heat removal rate being set so that neither the design limits for the fuel nor the design limit pressure of the primary coolant are exceeded.

[0010] It is understood that some time is needed to establish the natural inert gas circulation function. This time depends on the magnitude of the thermal fluxes QA, QB, the thermodynamic properties of the gas in the cooling circuit and the geometrical dimensions, in particular the height of the cooling circuit. The length of the time interval that is strictly needed in order the HTHL to start fulfilling the heat transfer function has been verified experimentally. Nevertheless, the experimental results show that reaching steady state QA, = QBrequires a time tR = 15 500 s (4.3 hours).

[0011] Currently, electrically driven turbo-compressors using battery storages as the backup power source are used to start the circulation circuit. In terms of operating costs, these are expensive and less reliable in terms of operating time.

[0012] Therefore, efforts were made to design the start-up device of the passive cooling circuit with natural circulation of inert gas, which would reduce the start-up time of the emergency cooling.

[0013] Summary of the invention

[0014] The invention relates to the passive cooling circuit with natural circulation of inert gas and the built-in start-up device. The basis of the passive cooling circuit with natural inert gas circulation is the high temperature helium loop, HTHL, wherein the HTHL gas system is formed in the gas flow direction by the hot leg between the heat exchanger with thermal flux QAand the heat exchanger with thermal flux QB, and the cold leg between the heat exchanger with thermal flux QBand the heat exchanger with thermal flux QA.

[0015] Essence of the invention is that the start-up device for initiating natural circulation is built into the HTHL gas system with natural circulation, intended to reduce the start-up time of the functionality of the HTHL system. In order to initiate flow in the passive natural circulation inert gas system, the inert gas must be supplied with the additional energy required to overcome the hydraulic losses.

[0016] The start-up device is made of the tank of driving gas accumulated at pressurec, the pressure level of the compressed gas for industrial use is 20 MPa. The compressed gas is connected through the pressure reducing valve to the drive nozzle of the jet compressor at pressure pt. The source for increasing the energy is the jet compressor, which is driven by the compressed gas from the storage tank accumulated at pressure pc. The driving gas storage tank is the pressure vessel in which there is very little degradation of stored energy over time - the pressure drop pcis very small - it is proportional only to the leakage of compressed gas from the industrial pressure drop litre / year. When the start-up device is activated, the compressed gas flows through the pressure reducing valve on the jet compressor, whereas the pressure of the driving medium stream has the value pt. For the values of the pressure at the outlet of the pressure vessel and the pressure at the inlet of the jet compressor drive nozzle, it is valid: pc» pt. The increase of gas energy in the natural circulation system is expressed by the compression ratio pj pi.

[0017] The inlet of the suction chamber of the jet compressor with pressure is connected with the ejection nozzle in the cold leg of the system by the suction pipe. The profile of the nozzle is hydraulically designed so that the kinetic energy of the gas flowing in the cold leg of the system is minimised when the gas is ejected from the pipe. Since this volume has the lowest pressure, the gas in that cross-section is ejected (sucked) out of the system.

[0018] The outlet of the diffuser of the jet compressor with pressure p is connected with the injection nozzle in the hot leg by injection pipe, Since the pressure is highest in this volume of the compressor, the injection (injection) of gas occurs in the given cross-section into the system. The nozzle profile is hydraulically designed so that when gas is injected into the pipe, there is the maximum increase in the kinetic energy of the gas flowing in the hot leg of the system. Since the pressure is highest in this volume, gas injection (makeup) occurs in the given cross section of the system. Thus, the following is valid for the gas pressures:

[0019] Pc » Pf > Pi > Pe

[0020] The function of the passive cooling circuit with natural inert gas circulation and built-in start-up device can be explained as follows. In applications where the HTHL will be used as the emergency cooling system, the start-up time of the cooling system needs to be shortened. Shortening the HTHL run time can be achieved by adding the device for initiating of effect of the natural circulation of the system SISTE (system for initiating the self-tightening effect). The natural circulation system for residual heat removal is the passive system with the activation of the natural circulation function initiated by the kinetic energy of the gas flowing from the compressed gas source. The compressed gas source is the energy source that is capable of driving the pneumatic systems even without electrical power supply. The SISTE pneumatic start-up device initiates the flow in the system even without the fulfilment of the condition of natural circulation. This multiplies the effect that, due to the thermodynamic imbalance between the A and B cross-sections of the system, the gas flow between the mentioned cross-sections occurs in the indicated direction, with heat transfer between the inlet and the outlet of the system, in the manner of natural circulation initiated by the SISTE device. When the steady state is reached, the SISTE start-up device is automatically disconnected from the HTHL.

[0021] The advantages of the passive cooling circuit with natural inert gas circulation and built- in start-up device according to the invention are evident from the effects by which it demonstrates itself externally. The developed HTHL technology was primarily developed for emergency cooling of reactors of the 4th generation, with assumed higher efficiency of nuclear fuel utilization, with lower nuclear waste production. The full functionality is verified on the prototype plant built and operated by the applicant within the ALLEGRO research centre, up to power of 250 kW. By integrating the SISTE start-up device, the solution is also applicable as the emergency cooling for other technological equipment in the process, if a complete power failure occurs after an accident and the forced circulation water cooling is interrupted. The SISTE startup initiation device is verified at level of the laboratory prototype.

[0022] The application of the SISTE start-up device will reduce the start-up time of the emergency cooling from the operation point of view. Considering the competing solutions currently available or under development, where the compressor is used to start up the circulating circuit, the solution provides substantially more reliable solution in terms of the dependency on the type of primary energy (electrical) used for circuit operation.

[0023] The solution is also maximally efficient in terms of long-term provision of the driving energy source: the SISTE uses the compressed gas pressure vessel as the energy source. The solutions currently in use, using the electric-driven turbo-compressor, use battery storages as the back-up energy source. These are incomparably more costly to operate and less reliable in terms of operating time.

[0024] Brief description of the drawings

[0025] The passive cooling circuit with natural inert gas circulation and built-in start-up device according to the invention will be further explained in the drawings, on which: Figure 1 illustrates the high temperature helium loop natural circulation (HTHL) system with the integrated device to initiate the natural inert gas circulation effect of the SISTE start-up device.

[0026] Figure 2 shows the design of the ejector nozzle installed in the cold leg of the HTHL.

[0027] Figure 3 shows the design of the injection nozzle installed in the HTHL hot leg.

[0028] Examples of embodiment

[0029] It is understood that the various embodiments of the invention are presented for purposes of illustration and not as limitations of solutions.

[0030] In this example of the specific embodiment, the passive cooling circuit with natural inert gas circulation and built-in start-up device according to the invention is described, used as the emergency cooling system with the reduced start-up time of the cooling system, as shown in Fig. 1.

[0031] The HTHL high-temperature helium loop gas system 1 with the HTHL natural circulation is formed in the gas flow direction by the hot leg 11 between the heat exchanger 2 with thermal flux QAand the heat exchanger 3 with thermal flux QB, and the cold leg 12 between the heat exchanger 3 with thermal flux QBand the heat exchanger 2 with thermal flux QA.

[0032] The start-up device is built into the HTHL gas system 1, comprising the storage tank 5 of driving gas accumulated at pressure pc(at industrial level 20 MPa), which is connected through the pressure reducing valve 10 with the driving nozzle of the jet compressor 4 with pressure pt. The suction chamber of the jet compressor 4 with pressure peis connected through the suction pipe 6 with the ejection nozzle 7 in the cold leg 12 as shown in Figure 2. The outlet of the diffuser chamber of the jet compressor 4 with pressure pi is connected by the ejection pipe 8 with the injection nozzle 9 in the hot leg 11 as shown in Fig. 3. In doing so, the following applies for the gas pressures:

[0033] Pc » Pf > Pi > Pe.

[0034] Industrial applicability

[0035] The passive cooling circuit with natural inert gas circulation and built-in start-up device according to the invention is applicable in power sources and installations, especially in the field of nuclear power.

Claims

CLAIMS1. A passive cooling circuit with natural inert gas circulation and built-in start-up device, containing high temperature helium loop (HTHL), wherein a gas system (1) of the HTHL is formed in a gas flow direction by a hot leg (11) between a heat exchanger (2) with thermal flux QAand a heat exchanger (3) with thermal flux QB, and a cold leg (12) between the heat exchanger (3) with thermal flux QBand the heat exchanger (2) with thermal flux QA, characterized in that the start-up device is built into the gas system (1) of the HTHL, comprising a storage tank (5) of driving gas accumulated at pressure pc, which is connected through a pressure reducing valve (10) with a driving nozzle of a jet compressor (4) with pressure pf, the suction chamber of the jet compressor (4) at pressure peis connected with a ejection nozzle (7) by a suction pipe (6) in a cold leg (12); the outlet of the diffuser of the jet compressor (4) at pressure pi is connected with a injection nozzle (9) by an ejection pipe (8) in a hot leg (11), where for the pressures of the gases the following is valid:Pc » Pf > Pi > Pe.

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