#
Structural and Parametric Optimization of S–CO_{2} Nuclear Power Plants

^{1}

^{2}

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## Abstract

**:**

_{2}nuclear power plants was carried out to ensure the maximum efficiency of electricity production. Based on the results of mathematical modeling, it was found that the transition to a carbon dioxide working fluid for the nuclear power plant with the BREST–OD–300 reactor leads to an increase of efficiency from 39.8 to 43.1%. Nuclear power plant transition from the Rankine water cycle to the carbon dioxide Brayton cycle with recompression is reasonable at a working fluid temperature above 455 °C due to the carbon dioxide cycle′s more effective regeneration system.

## 1. Introduction

#### 1.1. Promising Way to Increase Efficiency and Decrease the Capital Cost of Nuclear Power Plants

_{2}) working fluid. It allows for use of the Brayton cycle with low auxiliary power consumption, moderate initial temperature, and compact dimensions of the main energy equipment [1,2,3]. This direction has been actively developed since the middle of the past century [4,5,6,7]. This area of development arises scientists′ interests around the world largely because of carbon dioxide′s competitive advantages compared to other working fluids.

_{2}density is quite high at the near–critical parameters) [8,9], reducing the compressor work and the temperature of heat removed from the cycle without the working fluid condensing. Besides, carbon dioxide is less aggressive than water and shows its corrosion activity only in the presence of moisture content in the working fluid or with a water film on a metal surface. The carbon dioxide and water working fluid prices are compatible.

_{2}turbine mass and dimensions being smaller than those of the steam or gas turbines. The airfoil grid friction losses in an S–CO

_{2}turbine will be smaller than those in a steam or gas turbine because of carbon dioxide′s smaller viscosity [10].

#### 1.2. A State-of-the-Art Review of the S–CO_{2} Brayton Cycles

_{2}power facilities resulted in the development of the five cycles presented in Figure 2.

_{2}cycle is a closed Brayton cycle with the heat utilization of the exhaust gases (Figure 2a). The recirculating carbon dioxide enters the compressor (C), then the compressed fluid enters the regenerator (RH). The pre-heated flow enters the reactor (R) where its temperature increases. Then, the supercritical fluid is sent to the turbine (T) that drives the electricity generator (G). After the expansion, the turbine exhaust gas enters the regenerator, where it transfers heat to the compressed working fluid. Before it enters the compressor, the cooled CO

_{2}flow is sent to the cold source, or pre-cooler (PC), where the working fluid is additionally cooled.

_{2}Brayton cycle′s efficiency show that its increase by 2 MPa in the range of 13.8–27.6 MPa causes an efficiency increase of 0.71% [11], and a 150 °C initial temperature increase leads to a thermal efficiency increase of 5.5%.

_{2}Brayton cycle efficiency. This cycle differs from the previous one (Figure 2a) by the second working fluid supply to the reactor. Pressurized carbon dioxide flow is sent by the compressor to the regenerator, where it is heated by the low-pressure turbine (LPT) outlet flow. Then, the flow is sent to the reactor for its temperature increase up to the cycle initial temperature. After that, the flow is sent to the high-pressure turbine (HPT) flow path, where it expands to half of the initial pressure. Then, the flow re-enters the reactor for reheat. Afterward, the CO

_{2}flow expands in the LPT and enters the regenerator, where it transmits heat to the compressor outlet flow. From the regenerator outlet, the hot flow is sent to the cooler, and then it re-enters the compressor.

_{2}Brayton cycle efficiency increase by 0.20 to 0.26% at the heater pressure losses below 125 kPa.

_{2}Brayton cycle is the introduction of intermediate cooling that reduces the compressor energy consumption (Figure 2c). In contrast to the regeneration cycle (Figure 2a), this cycle uses low- pressure compressor (LPC) and high-pressure compressor (HPC) as well as an intermediate cooler (IC). After the low-pressure compressor, the working fluid passes the cooler, where it cools and enters the high-pressure compressor, where it reaches the cycle initial parameters. The maximal increase of this cycle′s thermodynamic efficiency is reached when the second compressor pressure ratio is 1.5–1.9 times higher than the first compressor one. In this case, the S–CO

_{2}Brayton cycle efficiency increases by 0.8%.

_{2}Brayton cycle efficiency improvement is the use of partial cooling (Figure 2d) [6]. This cycle differs from the cycle with regeneration by the application of a high-temperature regenerator (HTR) and low-temperature regenerator (LTR), condenser (CR), pump (P), and recompressing compressor (RC). The flow pressurized in the compressor is split into two parts: the first is sent to the RC and the second is cooled in the condenser and also compressed by the pump. The second flow of compressed CO

_{2}is heated in the LTR by the exhaust gas heat and then mixes with the first CO

_{2}flow in the HTR. After that, the flow is supplied to the reactor, where it is heated up to the cycle′s initial temperature. The reactor exhaust supercritical CO

_{2}enters the turbine that drives the power generator. Then, the expanded gas is directed to the sequentially connected HTR and LTR for heat utilization. Afterwards, the flow is cooled in the pre-cooler before it enters the compressor. This solution improves the regeneration system efficiency by means of the heat exchangers′ operation at different pressures. The S–CO

_{2}Brayton cycle has 44.8% efficiency at a 550 °C cycle initial temperature and 25 MPa initial pressure.

_{2}Brayton cycle with recompression, which is a simplified modification of the partial cooling cycle presented in Figure 2d. This cycle differs from the partial cooling cycle by the absence of a pump and condenser. The carbon dioxide flow is split into two parts upstream of the pre-cooler. The first part is cooled and supplied to the main compressor, where it reaches the initial parameters. The second part is directly supplied to the recompressing compressor, where it is also compressed up to the initial cycle pressure. After the main compressor, the compressed CO

_{2}flow enters the LTR, where it is heated by the outlet carbon dioxide flow up to the temperature equal to the second CO

_{2}flow temperature after the RC. Then, the two flows merge and enter the HTR, where they are also heated up to the reactor inlet temperature by heat utilization of the exhaust gases. Then, the reactor heats the working fluid up to the cycle′s initial temperature. Then, the flow enters the turbine that drives the power generator. After the flow expands in the turbine, the hot exhaust gases are cooled in the sequentially connected HTR and LTR and then split into two flows again.

_{2}Brayton cycle with regeneration. In other words, the split of compressed flow and introduction of the LTR and HTR provides deeper utilization of the exhaust gases heat and smaller heat losses in the cooler. The result of this technical solution is that the S–CO

_{2}Brayton cycle efficiency increases up to 46%.

#### 1.3. Summary of the Thermodynamic Investigation Results for the S–CO_{2} Brayton Cycles

_{2}recompression Brayton cycle efficiency [11] shows that a 100 °C increase in the turbine inlet temperature in the 500–1000 °C range increases the efficiency by a 2.0% average, but according to the results in [6], this increase is 3.3%. On the other side, study [7] shows that a 100 °C increase of the turbine inlet temperature in the 550–850 °C range increases the mean cycle efficiency by 4%, and according to [13], in the 550–700 °C range, the same temperature increase leads to the 5% increase in efficiency.

_{2}recompression Brayton cycle. The results show a remarkable evaluation difference and determine the relevance of the comparison of carbon dioxide cycles under comparable conditions.

_{2}power cycles, a preliminary optimization of key parameters was carried out using the Aspen Plus software package. Table 3 summarizes the main thermodynamic performance of the five cycles described above. The supercritical CO

_{2}Brayton cycle with recompression has a maximal net efficiency of 47.28% at the initial temperature and pressure of 550 °C and 35 MPa. The high working fluid temperature at the heat supply source inlet of the S–CO

_{2}recompression Brayton cycle defines its prospects for the NPP reactor heat utilization.

_{2}operating NPPs, many questions are not yet answered. Specifically, the studies do not consider the nuclear reactor influence upon the outer CO

_{2}circuit [15,16]. Therefore, this work is devoted to the optimization of thermal flow parameters in NPPs, including actual operation conditions and limits for three nuclear reactors including VVER-1000, BN-800, and BREST-OD-300.

## 2. Research Object

#### 2.1. Existing Nuclear Reactors and Operation Regimes′ Limitations

_{2}O, which produces power. The turbine inlet is supplied with 1633 kg/s of primary steam at a 274 °C temperature and 5.9 MPa pressure. The feed water temperature at the steam generator inlet is about 220 °C. This unit efficiency is about 31.7%. In changing the steam circuit to the carbon dioxide one, the possibility must be retained for the first circuit′s water cooling from 322 down to 289 °C.

_{2}O, which produces the work. The turbine inlet conditions are 875 kg/s primary steam mass flow, 485 °C temperature, and 14.2 MPa pressure. The feed water temperature at the steam generator inlet is about 210 °C.

_{2}cycles might be more efficient than the traditional Rankine cycle.

_{2}does not actively react with sodium with the production of a lot of vapor and heat, in this case the second circuit is still needed. As mentioned before, the Na-Na heat exchangers are located inside the reactor vessel, so this technical solution retains the reactor structure; only the steam equipment and the steam generator shall be changed. The retained second circuit sodium temperature at the Na-Na heat exchanger inlet and outlet will provide the reactor stability.

#### 2.2. Schemes and Parameters for the Promising S–CO_{2} Nuclear Power Plants

_{2}pressurized in the compressors. The gas cooled in the regenerators is split into two flows, the main and recompression. The recompression gas is 29% of the total mass flow. It is sent to the recompressing compressor. The main flow is sent to the cooler, where its temperature drops down to 32 °C, which improves the main compressor efficiency. In the cooler, the cooling agent is water at 1.3 bar and 15 °C supplied by the circulation pump. After the main flow is compressed up to the 20 MPa supercritical pressure, it is heated in the low-temperature regenerator. The remaining flow part passes by the cooler and enters the recompressing compressor where its pressure grows up to 20 MPa. The recompressing compressor outlet flow merges with the main flow heated in the low-temperature regenerator. Then, it is heated in the high-temperature regenerator and sent to the heat exchanger that transfers heat to the carbon dioxide cycle. Thus, the cycle is closed.

_{1}shows the heat supply from the reactor to the outer circuit. In this case, the difference with the VVER reactor scheme is the higher initial temperature, 505 °C for the BN-800 and 535 °C for the BREST-OD-300 reactors, and absence of main circulation pump (MCP) because of natural circulation.

## 3. Methods

- ${h}_{outlet.\mathrm{C}}$, ${h}_{inlet.\mathrm{C}}$—working fluid enthalpy at the compressor outlet and inlet, kJ/kg;
- ${h}_{outlet.is.\mathrm{C}}$—working fluid enthalpy at the compressor outlet at isentropic expansion, kJ/kg;
- ${\mathsf{\eta}}_{\mathrm{C}}$—compressor isentropic efficiency.

- ${N}_{\mathrm{CO}2-\mathrm{T}}$—turbine internal power, MW;
- ${N}_{MC}$—main compressor internal power, MW;
- ${N}_{RC}$—recompressing compressor internal power, MW;
- ${N}_{CP}$—circulation pump internal power MW;
- ${N}_{MCP}$—reactor main circulation pump internal power (to be involved in forced circulation), MW;
- ${Q}_{t}$—reactor thermal power, MW;
- ${\mathsf{\eta}}_{mech}$—mechanical efficiency, %;
- ${\mathsf{\eta}}_{eg}$—power generator efficiency, %;
- ${\mathsf{\eta}}_{em}$—electric motor efficiency, %;
- ${\mathsf{\eta}}_{tr}$—heat transportation efficiency, %;
- ${\mathsf{\eta}}_{hx}$—heat exchanger inter-channel efficiency, %;
- ${{\mathsf{\eta}}_{hx}}^{\prime}$—heat exchanger inter-channel efficiency (applied for the heat carrier two circuit reactor), %;
- ${\mathsf{\eta}}_{r}$—nuclear reactor efficiency, %.

- -
- Turbine inlet pressure p
_{0}, MPa; - -
- Turbine exhaust pressure p
_{ex}, MPa; - -
- Recompression ratio x, %.

_{0}values were varied with 2 MPa step. The investigated variable ranges for the reactors VVER-1000, BN-800, and BREST-OD-300 were 12–32, 12–40, and 19–31 MPa, respectively. The next stage was a variation of the turbine outlet pressure p

_{c}with 0.5 MPa step for reactors VVER-1000, BN-800, and BREST-OD-300 in ranges 7.4–12, 7.4–13, and 7.5–10.5 MPa, respectively. At the optimal pressure values, the recompression rate x was varied with the 5% step for reactors VVER-1000, BN-800, and BREST-OD-300 in ranges 10–50%, 10–50%, and 20–50%, respectively.

## 4. Results

#### 4.1. Thermodynamic Optimization of the Turbine Inlet and Outlet Pressure for the S–CO_{2} NPPs

_{0}optimization presented in Figure 4a show that the carbon dioxide NPP net efficiency increase follows the inlet pressure raise in the following pressure ranges:

- -
- From 12 MPa (22.51%) to 22 MPa (27.68%)—for reactor VVER-1000;
- -
- From 12 MPa (29.53%) to 28 MPa (39.61%)—for reactor BN-800;
- -
- From 19 MPa (40.97%) to 25 MPa (41.78%)—for reactor BREST-OD-300.

**Figure 4.**Influence of pressures upon the S–CO

_{2}NPP thermal efficiency: (

**a**) inlet pressure; (

**b**) outlet pressure. Dependencies are given for different reactor types: 1—VVER-1000; 2—BN-800; 3—BREST-OD-300.

- -
- From 22 MPa (27.68%) to 32 MPa (25.92%)—for reactor VVER-1000;
- -
- From 28 MPa (39.61%) to 40 MPa (39.22%)—for reactor BN-800;
- -
- From 25 MPa (41.78%) to 31 MPa (41.47%)—for reactor BREST-OD-300.

- -
- 22 MPa—for reactor VVER-1000;
- -
- 28 MPa—for reactor BN-800;
- -
- 25 MPa—for reactor BREST-OD-300.

_{c}‘s influence upon the carbon dioxide NPP thermal efficiency are carried out at fixed optimal initial pressures. Results in Figure 4b demonstrate equal values of the optimal exhaust pressure 9 MPa for the reviewed facilities. Maximal net efficiency values are 29.12, 40.44, and 42.98% for the recompression cycles with reactors VVER-1000, BN-800, and BREST-OD-300, respectively.

^{3}/kg) at a small reduction of final pressure from 7.6 to 7.4 MPa and at 32 °C (Figure 5). At the same time, the compression work in the main compressor grows by 33%, and the compressor outlet temperature grows up to 31.5 °C (Table 6). In these conditions, the thermal efficiency is an order below the studied trend at the turbine outlet pressure of 7.4 MPa.

#### 4.2. Thermodynamic Optimization of the Recompression Ratio in the S–CO_{2} NPP

- -
- From 10% (26.71%) to 35% (29.39%)—for reactor VVER-1000;
- -
- From 10% (36.80%) to 31% (40.48%)—for reactor BN-800;
- -
- From 20% (40.76%) to 32% (43.08%)—for reactor BREST-OD-300.

**Figure 6.**Net efficiency vs. recompression ratio x for different reactor types. 1—VVER-1000; 2—BN-800; 3—BREST-OD-300.

- -
- From 35% (29.39%) to 50% (26.10%)—for reactor VVER-1000;
- -
- From 31% (40.48%) to 50% (36.46%)—for reactor BN-800;
- -
- From 32% (43.08%) to 50% (40.42%)—for reactor BREST-OD-300.

## 5. Discussion

_{2}compressor power, the cooler flow pump circulation power, the main circulation pump in the VVER-1000, and BN-800 reactors that provide the heat carrier circulation in the reactor circuits, and the compressors drive power. In the NPP with water working fluid, auxiliary consumption consists of the condensate circulation, feeding and booster pumps power, and the same main circulation pumps as in the recompression cycle of the VVER-1000 and BN-800 reactors.

**Figure 7.**Technical performance comparison of recompression cycle and steam turbine unit for NPP with the different reactor types: (

**a**) gross power; (

**b**) net power; (

**c**) working fluid compression power consumption; (

**d**) circulation pumps′ power consumption; (

**e**) total auxiliary power consumption; (

**f**) cooler heat losses.

_{2}flow produces power in the whole turbine flowpath. Therefore, the carbon dioxide turbine power production is approximately 1.5 times larger (Figure 7a). On the other side, the main carbon dioxide power consumption is the CO

_{2}recompression compressor drive power (Figure 7c), which is about 18% of the reactor thermal power.

_{0}above 455 °C, it is reasonable to apply the carbon dioxide working fluid due to the higher thermal efficiency. At the initial temperature of 525 °C, the carbon dioxide NPP net efficiency is more than 2% higher than the steam turbine one.

_{2}NPP net efficiency compared to the steam turbine NPP at the initial temperature above 455 °C may be explained as follows. In the carbon dioxide power cycle, the initial temperature increase is followed by the significant increase of hot source gas inlet temperature (Table 7). (The flow temperature at the inlet of the heat exchanger transfers heat from the NPP internal circuit to the external one.) This increase is due to the carbon dioxide facility′s effective regeneration system that increases the mean integral temperature of the heat supply into the cycle, and the related cycle thermal efficiency. In turn, the initial temperature increase for the traditional steam turbine NPP equipped with BN-800 and BREST-OD-300 reactors is not followed by the feedwater temperature increase because it is limited by the upper bleeding pressure, which is relatively low in the subcritical steam turbine cycles.

## 6. Conclusions

- (1)
- The published literature review shows that the most prospective S–CO2 power cycle is the Brayton cycle with recompression. The facilities operating this cycle have a remarkable degree of flue gas heat utilization and low cold source losses. This is due to the split of compressed flow into two parts and by the introduction of low-temperature and high-temperature regenerative heat exchangers. This cycle′s thermal efficiency may be above 40%, which determines its relevance for application for the NPP equipped with the existing reactors including VVER-1000, BN-800, and BREST-OD-300.
- (2)
- The computer simulation models of the S–CO2 NPP with VVER-1000, BN-800, and BREST-OD-300 were developed to evaluate the key thermodynamic parameters across the thermal flow scheme and thermal efficiency. These are used for the thermodynamic optimization.
- (3)
- The 1 MPa turbine inlet pressure increase causes the following carbon dioxide NPP net efficiency increase:
- -
- 0.52% in facilities with VVER-1000 reactor in the initial pressure range 12–22 MPa;
- -
- 0.63% in facilities with BN-800 reactor in the initial pressure range 12–28 MPa;
- -
- 0.14% in facilities with BREST-OD-300 reactor in the initial pressure range 19–25 MPa.

In turn, the 1 MPa turbine inlet pressure increase causes the following carbon dioxide NPP net efficiency reduction:- -
- 0.18% in facilities with VVER-1000 reactor in the initial pressure range 22–32 MPa;
- -
- 0.03% in facilities with BN-800 reactor in the initial pressure range 28–40 MPa;
- -
- 0.05% in facilities with BREST-OD-300 reactor in the initial pressure range 25–31 MPa.

- (4)
- The 0.1 MPa turbine outlet pressure reduction is causing the following mean carbon dioxide NPP net efficiency reduction:
- -
- 0.1% in facilities with VVER-1000 reactor in the range 9–12 MPa and BREST-OD-300 reactor in the range 9–13 MPa;
- -
- 0.08% in facilities with BN-800 reactor in the range 9–10.5 MPa.

In turn, every 0.1 MPa turbine outlet pressure reduction in the range below 9 MPa is followed by a 0.1% net efficiency reduction. - (5)
- The mean thermal efficiency increase at a 1% recompression ratio increase is:
- -
- 0.1% in facilities with VVER-100 reactor at the recompression ratio range 10–35%;
- -
- 0.18% in facilities with BN-800 at the recompression ratio range 10–31%;
- -
- 0.19% in facilities with BREST-OD-300 at the recompression ratio range 20–32%.

In turn, the mean thermal efficiency reduction at a 1% recompression ratio increase is:- -
- 0.2% in facilities with VVER-1000 reactor at the recompression ratio range 35–50%;
- -
- 0.21% in facilities with BN-800 reactor at the recompression ratio range 31–50%;
- -
- 0.15% in facilities with BREST-OD-300 reactor at the recompression ratio range 32–50%.

- (6)
- The results of comparison of the NPP power production performance working with water and carbon dioxide working fluids show that the change of steam to carbon dioxide is reasonable at the initial working fluid temperature above 455 °C. This maximal thermal efficiency increase is due to the more effective regeneration system operation.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

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**Figure 1.**Thermophysical performance of the promising heat carriers: (

**a**) heat carrier critical temperature; (

**b**) heat carrier critical pressure.

**Figure 2.**Supercritical CO

_{2}Brayton cycles: (

**a**) S–CO

_{2}Brayton cycle with regeneration; (

**b**) S–CO

_{2}Brayton cycle with reheating; (

**c**) S–CO

_{2}Brayton cycle with intermediate cooling; (

**d**) S–CO

_{2}Brayton cycle with partial cooling.; (

**e**) S–CO

_{2}Brayton cycle with recompression.

**Figure 3.**Schemes of the S–CO

_{2}nuclear power plants: (

**a**) VVER-1000 NPP reactor; (

**b**) BN-800/ BREST-OD-300 NPP reactor.

**Figure 8.**Influence of the working fluid type and initial temperature upon the NPP net efficiency. 1—S–CO

_{2}NPP; 2—steam turbine NPP.

**Table 1.**Thermophysical properties of different working fluids at typical parameters for steam, gas, and carbon dioxide turbine facilities.

Facility Type | Turbine Inlet/Outlet Temperature and Pressure | Turbine Inlet/Outlet Working Fluid Density, kg/m^{3} | Turbine Inlet/Outlet Working Fluid Kinematic Viscosity, 10^{7} m^{2}/s |
---|---|---|---|

Steam turbine power plant (H_{2}O) | 540 °C, 23.5 MPa/29 °C, 4 kPa | 74.6/0.004 | 4.3/26.5 |

Combined cycle power plant (air) | 1100 °C, 1.3 MPa/515 °C, 0.1 MPa | 3.3/0.44 | 162.4/840.4 |

S–CO_{2} power plant (CO_{2}) | 540 °C, 25 MPa/407 °C, 8 MPa | 155.8/70.8 | 2.4/4.5 |

Parameters | Parameter Range | Influence upon Efficiency | Reference |
---|---|---|---|

Compressor outlet pressure, p_{max}, MPa | 15–30 | 1 MPa increase ⇒ 0.2–0.8% efficiency increase | [7] |

Turbine inlet temperature, t_{0}, °C | 550–850 | 100 °C increase ⇒ 4% efficiency increase | [7] |

Turbine inlet temperature, t_{0}, °C | 500–1000 | 100 °C increase ⇒ 3.33% efficiency increase | [6] |

Turbine inlet temperature, t_{0}, °C | 500–1000 | 100 °C increase ⇒ 2% efficiency increase | [11] |

Turbine inlet temperature, t_{0}, °C | 550–700 | 100 °C increase ⇒ 5% efficiency increase | [13] |

Turbine inlet temperature, t_{0}, °C | 32–50 | 10 °C increase ⇒ 2,7% efficiency reduction | [7] |

Turbine inlet pressure, p_{0}, MPa | 10–25 | 1 MPa increase ⇒ 0.2–0.4% efficiency increase | [14] |

Turbine efficiency, η, % | 85–95 | 5% increase ⇒ 2% efficiency increase | [13] |

Compressor efficiency, η, % | 85–90 | 5% increase ⇒ 1% efficiency increase | [13] |

Regenerators minimal temperature difference, Δ, °C | 5–10 | 5 °C increase ⇒ 1% efficiency reduction | [13] |

With Regeneration | With Reheat | With Inter-Cooling | With Partial Cooling | With Recompression | |
---|---|---|---|---|---|

Cycle initial temperature t_{0}, °C | 550 | 550 | 550 | 550 | 550 |

Cycle initial pressure, p_{0}, MPa | 35 | 35 | 45 | 25 | 35 |

Cycle final pressure, p_{c} MPa | 7.5 | 7.5 | 7.5 | 5 | 7.7 |

Reheat pressure, p_{rh}, MPa | – | 10 | – | – | – |

Heat supply to the cycle in reactor, Q_{0}, MW | 33.03 | 33.91 | 39.12 | 28.85 | 26.43 |

Heat loss from the cycle in coolers, Q_{c}, MW | 19.09 | 19.09 | 22.17 | 15.84 | 13.88 |

Turbine power N_{t}, MW | 19.66 | 20.54 | 22.46 | 20.28 | 18.96 |

Compressor power, N_{c}, MW | 5.73 | 5.73 | 6.05 | 7.35 | 6.46 |

High-temperature and low-temperature heat exchanger thermal power, Q_{reg}, MW | 30.80 | 44.92 | 32.60 | 18.61/9.73 | 13.00/20.22 |

Working fluid temperature at the source of heat inlet, t_{react.in}, °C | 295 | 427/398 | 280 | 320 | 344 |

Cycle net efficiency, η, % | 42.2 | 43.70 | 41.96 | 44.80 | 47.28 |

Reactor Type | |||
---|---|---|---|

VVER-1000 | BN-800 | BREST-OD-300 | |

Reactor thermal power, MWt | 3000 | 2100 | 700 |

First cicuit heat carrier mass flow, kg/s | 17,778 (H_{2}O) | 8550 (Na) | 41,600 (Pb) |

First cicuit heat carrier pressure, MPa | 15.7 | 0.16 | 0.155 |

First cicuit inlet temperature, °C | 289 | 354 | 420 |

First cicuit outlet temperature, °C | 322 | 547 | 535 |

Second circuit heat carrier mass flow, kg/s | 1633 (H_{2}O) | 8418 (Na) | 420 (H_{2}O) |

Second circuit heat carrier pressure, MPa | 5.9 | 1.96 | 17 |

Second circuit heat carrier inlet temperature, °C | 220 | 309 | 340 |

Second circuit heat carrier outlet temperature, °C | 274 | 505 | 505 |

Third circuit heat carrier mass flow, kg/s | – | 875 (H_{2}O) | – |

Third circuit heat carrier pressure, MPa | – | 14.2 | – |

Third circuit heat carrier inlet temperature, °C | – | 210 | – |

Third circuit heat carrier outlet temperature, °C | – | 485 | – |

First circuit main circulation pump power, MW | 5.3 | 5 | – |

Second circuit main circulation pump power, MW | – | 2.5 | – |

Reactor Type | |||
---|---|---|---|

VVER-1000 | BN-800 | BREST-OD-300 | |

Basepoint values of optimization variables | |||

Turbine inlet pressure, MPa | 20 | ||

Turbine outlet pressure, MPa | 7.6 | ||

Cycle recompression rate, % | 29 | ||

All heat flow versions fixed parameters | |||

Cooler minimal temperature difference, °C | 17 | ||

Working fluid temperature at the main compressor inlet, or the cycle minimal temperature, °C | 32 | ||

Cooler circulation water pressure, bar | 1.3 | ||

Cooler inlet cooling water temperature, °C | 15 | ||

Cooling water temperature at the cooler outlet, °C | 25 | ||

Heat exchangers temperature difference, °C | 5 | ||

Main compressor specific internal efficiency, % | 90 | ||

Recompressing compressor specific internal efficiency, % | 90 | ||

Turbine specific internal efficiency, % | 90 | ||

Pumps specific internal efficiency, % | 75 | ||

Power generator/motor efficiency, % | 99 | ||

Mechanical efficiency, % | 99 | ||

Heat exchanger from reactor efficiency, % | 98 | ||

Heat transportation efficiency, % | 99 |

**Table 6.**Initial pressure influence on the main thermodynamic parameters of working fluid in compressors.

Element | Process Station | Value | |||
---|---|---|---|---|---|

T, °C | p, MPa | S, KJ/(kg·°C) | υ, m^{3}/kg | ||

Main compressor, compression from 7.4 MPa | before compression | 32 | 7.4 | 1.5857 | 0.00317 |

after compression | 99.81 | 22 | 1.5956 | 0.00189 | |

Main compressor, compression from 7.6 MPa | before compression | 32 | 7.6 | 1.3759 | 0.00179 |

after compression | 68.32 | 22 | 1.3831 | 0.00142 | |

Recompressing compressor, compression from 7.4 MPa | before compression | 105 | 7.4 | 2.0463 | 0.008 |

after compression | 215.63 | 22 | 2.0633 | 0.00371 | |

Recompressing compressor, compression from 7.6 MPa | before compression | 73 | 7.6 | 1.916 | 0.00636 |

after compression | 172.95 | 22 | 1.931 | 0.00311 |

**Table 7.**Temperature comparison at the hot source inlet for the NPP with water and carbon dioxide working fluids.

Reactor | Working Fluid Temperature at the Hot Source Inlet, °C | |
---|---|---|

S–CO_{2} Power Cycle (CO_{2}) | Steam Turbine Power Cycle (Feed Water) | |

VVER-1000 | 198 | 220 |

BN-800 | 328 | 210 |

BREST-OD-300 | 367 | – |

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## Share and Cite

**MDPI and ACS Style**

Rogalev, N.; Rogalev, A.; Kindra, V.; Komarov, I.; Zlyvko, O.
Structural and Parametric Optimization of S–CO_{2} Nuclear Power Plants. *Entropy* **2021**, *23*, 1079.
https://doi.org/10.3390/e23081079

**AMA Style**

Rogalev N, Rogalev A, Kindra V, Komarov I, Zlyvko O.
Structural and Parametric Optimization of S–CO_{2} Nuclear Power Plants. *Entropy*. 2021; 23(8):1079.
https://doi.org/10.3390/e23081079

**Chicago/Turabian Style**

Rogalev, Nikolay, Andrey Rogalev, Vladimir Kindra, Ivan Komarov, and Olga Zlyvko.
2021. "Structural and Parametric Optimization of S–CO_{2} Nuclear Power Plants" *Entropy* 23, no. 8: 1079.
https://doi.org/10.3390/e23081079