Proceedings of ICAPP ’04 Pittsburgh, PA USA, June 13-17, 2004 Paper 4195

Turbine Technologies for High Performance Light Water Reactors

D. Bittermann1, J. Starflinger2, T. Schulenberg2 1

Framatome ANP GmbH, Erlangen, Germany P.O. Box 3220 91050 Erlangen, Germany Tel: +49 9131 1895 263; Fax: +49 9131 1194 236; [email protected] 2

Forschungszentrum Karlsruhe, P.O. Box 3640, 76021 Karlsruhe, Germany

Abstract – Available turbine technologies for a High Performance Light Water Reactor (HPLWR) have been analysed. For the envisaged steam pressures and temperatures of 25MPa and 500°C, no further challenges in turbine technologies have to be expected. The results from a steam cycle analysis indicate a net plant efficiency of 43.9% for the current HPLWR design. HPLWR [12]. In addition turbine technology- and steam cycle analyses have been performed in the 5th Framework Programme which will be discussed as follows.

I. INTRODUCTION Since 1990, the University of Tokyo has studied the application of supercritical life steam conditions to light water reactor concepts with the aim to achieve a comparable cost and efficiency improvement also for nuclear power. With a target of 25MPa and 508°C for life steam pressure and temperature, an efficiency of 44.1% was predicted [1]. A preliminary cost study by the Japanese industry confirmed the potential economic benefit of the supercritical once-through concept [2]. As part of the 5th Framework Programme of the European Commission, European partners supported by the University of Tokyo have studied from 2000 to 2002 the feasibility of super-critical reactor systems, called High Performance Light Water Reactors (HPLWR), to determine whether light water reactors operating under supercritical steam conditions could be feasible considering European Utility Requirements (EUR) and Generation IV goals [3], to estimate their economic potential, and to study their safety features compared with existing LWRs. Results showed the High Performance Light Water Reactor as a promising concept [4]. Getting more than 30% additional electric power per thermal power input, a relatively small containment volume, and a direct, once-through cycle without the need for steam generators and steam separators should result in significant savings in power generating cost. Results from the 5th Framework Programme comprise a description of plant characteristics [5], HPLWR core design studies [6-9], selection of materials [10], analyses of the safety system [11] and an economic prospect of the

II. TURBINE TECHNOLOGIES Life steam temperatures up to 580°C and pressures up to 30MPa have been used in several applications for fossil fuelled power plants so that turbines can be regarded already to have a proven and reliable design. Recent power plants which just started operation are reaching even 600°C. Current R&D programs for a next generation of steam turbines are aiming at 700°C life steam temperatures. Looking at the envisaged steam pressures and temperatures of 25MPa and around 500°C for supercritical water reactor concepts like the HPLWR, no further challenges in turbine technologies have to be expected. Materials and blading design technologies can be taken from coal-fired power plants which are well established. As a consequence, the individual turbine design, adjusted for the mass flow to be selected, can easily be completed in parallel to the reactor design. Therefore, the following study is trying to use this available turbine technology as far as possible for nuclear applications. II.A. Steam turbine design features Siemens AG has developed steam turbine design series for use in power generating facilities which results in products of a high technical standard [13]. Figure 1 presents the reheat steam turbine series for fossil-fired

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Proceedings of ICAPP ’04 Pittsburgh, PA USA, June 13-17, 2004 Paper 4195

power plants. One major objective in steam turbine design is its highly efficient energy conversion. For large units, separate turbine casings are provided for the individual expansion sections, i.e. high-pressure (HP), intermediatepressure (IP) and low-pressure (LP) turbine sections. The individual turbine sections can be combined according to the given thermodynamic design conditions and design mass flow. This design series covers the entire spectrum of steam conditions up to ultra supercritical steam conditions. The structural dimensions of the HP and IP turbine sections are fixed, only the blading are adapted to the given application (steam conditions and rating). The LP sections are standardized turbines, i.e. the dimensions and blades are specific to each model.

FIGURE 1: Module architecture of reheat steam turbines for fossil-fired power plants. An optimal grading of the individual modules guarantees the application for the wide range of output and steam parameters. The advantage of this concept lies in the large feedback of experience concerning the service reliability of these components, ultimately leading to a high degree of turbine availability. The series-based design concept has been highly successful; a wide range of positive experience with a high number of applications has been gained in operating these turbines. II.B. Materials for advanced steam conditions (up to 600°C) The materials used for the highly stressed turbine components play a key role when high steam conditions are applied. It is of primary importance when

manufacturing the associated castings and forgings that the properties of these components are matching to the specified operating requirements in order to retain the desired operational reliability and safety over the entire service life. The properties of steels used for large castings and forgings subjected to high steam temperatures have been improved considerably in recent years through research conducted in Germany and around the world. These efforts have included: • Optimisation of alloying elements and prevention of detrimental impurities • Improvement of homogeneity and reduction of segregation through improved steel making techniques (vacuum treatment and de-oxidation) • Improvement of forging, heat-treatment and welding techniques. These efforts have also made it possible for uniform material properties to be achieved in large forgings (monoblock rotors) and castings (casings and valve bodies) made from high-alloy steels. The most important property of high-temperature steels is a high creep strength which is dependent on temperature and duration of loading. Creep strength is mainly influenced by the chemical composition of a material and its heat treatment, i.e. the microstructure. In order to ensure that components function properly under all operating conditions, other material properties must also be considered: • Brittle fracture behaviour at low service temperatures • Long-term creep and fracture behaviour under cyclic loading conditions • Low-cycle fatigue strength. In addition to the above properties, other important requirements also play a role, such as corrosion and wear behaviour as well as manufacturing aspects: weldability, workability and examine-ability. Research conducted to date has centred on the objective to raise the main and reheat steam temperatures to approximately 600°C. Results of these research efforts have demonstrated that these steam temperatures can be implemented using improved, high-temperature ferritic steels. The following materials are thus employed for temperatures of up to 600°C: • Improved, 9 to 12% chromium steels for use in forgings and castings in place of the forging steel X21CrMoV121 and the casting material GX22CrMoV121 widely used in Germany in the past. The 9 to 12% chromium steels have a higher creep strength and fracture toughness than previously used steels, achieved through the addition of niobium, nitrogen and tungsten as alloying elements as well as through optimisation of the alloying elements and

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Proceedings of ICAPP ’04 Pittsburgh, PA USA, June 13-17, 2004 Paper 4195

chemical composition. The creep strength of this steel is expected to lie at about 100MPa based on operation at 600°C for 100000 hours. With regard to the properties specified above, experience gained with full-size rotor forgings and castings is available. Consistent testing of these steels in recent years has confirmed the improvement in material properties. Steels are therefore available for highly-stressed turbine components exposed to service temperatures of up to 600°C. In addition, these steels are also suitable for use under conventional, subcritical steam conditions to increase the time for component service. II.C. Increasing main and reheat steam temperatures up to 700°C As early as the 1950s and early 60s, operators of power generating facilities in Germany -predominantly in the chemical industry- employed small steam turbines (up to 150MW) which operated under ultra supercritical steam conditions (temperatures of between 600 and 650°C and main steam pressures of 18 to 30MPa). Their hightemperature components were already being made from austenitic steels and from conventional ferritic 12% chromium steel. A wide range of positive experience has been gained with these steels. However, it was not possible to expand applications of ultra supercritical parameters for steam turbines with higher output at that time due to the excessive cost of austenitic materials. In the future, steam turbines utilizing advanced steam conditions will, for economic reasons, be principally applied for high ratings of up to 1000MW using the same design features of the existing steam turbines. Current research goals are to improve the material properties of the newly developed 9 to 12% chromium steels for use in forgings and castings up to 625°C, which seems to be possible with a higher amount of the alloying element boron. It is expected to improve this type of steel for future application up to 650°C. In parallel it is expected to improve the austenitic steel and the above mentioned materials and also the techniques for manufacturing large components (rotors, casings and valve bodies) from these materials for applications in the 650°C temperature range and higher. Future steel mono-bloc rotors from others than 9 to 12% chromium steels for high temperature IP turbines in large turbine generators cannot be manufactured using current production techniques if the proven mono-bloc rotors of the size required here are to be manufactured. The material service limits defined by the steam temperature can be extended to a certain extent by intensive steam cooling of the rotor. Cooling of the rotor allows the high degree of creep strength at low

temperatures to be utilized. This obviates the need to use a higher grade material. However, the service limits for rotor cooling are affected greatly by the steam temperature of the operating steam and cooling steam and by the cooling steam flow rate and the geometry of the turbine rotor. In addition, rotor cooling has an inherent impact on turbine efficiency. Further investigations of the application of advanced steam temperatures in the range of 700°C revealed that high nickel alloyed materials (super alloys) are necessary to expand the use of steam turbines to this temperature level. A number of materials which have a proven service record in superheated steam turbine and gas turbine blading applications are available for temperatures above 560°C. These materials are austenitic steel and hightemperature alloys, such as Nimonic 80. In addition to their high creep strength, these materials also meet corrosion-resistance criteria and can be processed using current manufacturing technology. A wealth of empirical knowledge is available on these materials. The steels used for large steam turbine components operating under the conditions applied up until now as well as those planned for the future are compiled in the following Table 1. II.D. Design of steam turbines employing high steam conditions Figure 2 shows a longitudinal section through a power plant steam turbine employing a single reheat cycle and high steam conditions. Steam turbines designed for high steam conditions and high output range have the following significant features: separate HP, IP and LP cylinders for various expansion sections.

FIGURE 2: Steam turbine for power plants with single reheat The use of separate turbine cylinders for the various steam expansion sections provides optimum space for highly effective energy conversion. The steam admission arrangements of the separate turbine casings allow various main and reheat steam temperatures under all load conditions, thereby preventing thermal stressing in the steam admission area due to temperature differentials.

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Proceedings of ICAPP ’04 Pittsburgh, PA USA, June 13-17, 2004 Paper 4195

TABLE 1: Steels for power station components exposed to high temperatures

Component

max. 565°C

Superheater Reheater tubes

1-2% CrMo steels 9% Cr steels

Main steam pipes, headers, valve bodies

2% CrMo steels

High temperature rotors

1-2% CrMo steels

High Temperature Turbine inner casing HP/IP Turbine outer casing HP/IP

1-2% CrMo steels

Temperature Range max. 600°C 625 – 650 °C (625°C) Highly corrosionAustenitic steels resistant austenitic 9% Cr steels steels Austenitc steels 9% Cr steels (9-12% Cr steels) Austenitc steels 9-12% Cr steels 9-12% Cr steels 9-12% Cr steels 1-2% CrMo steels High Purity 3.5% NiCrMoV steels

LP rotors II.E. Blading

Reaction blading with integral shrouds is used for the pressure range down to approximately 0.2MPa. Blades are installed with pre-stressing of the root platforms and shrouds against each other to ensure good damping. The last-stage blades are free-standing without shrouds or lacing wires. Reaction blades with an optimum pressure ratio yield high turbine efficiency. Extensive research and development work in the field of fluid dynamics has been performed to reduce flow losses in the blading. The following blading designs have been applied: In turbine stages with relatively short blades, the percentage of peripheral and secondary losses in overall stage losses is very high. Here, it is intended to use three dimensional directionally solidified blades (3DS-blades, see Figure 3).

FIGURE 3: Three dimensional directionally solidified blade (3DS-blade)

Austenitc steels 9-12% Cr steels

max. 720°C Superalloys Superalloys Superalloys Superalloys Austenitc steels 9-12% Cr steels Super clean 3.5% NiCrMoV steels

Three-dimensional flow programs taking friction into account enable exact computation of the flow field and peripheral and secondary flow effect with reduced secondary losses. A salient feature of this type of blade is its inclination in the root and shroud areas. This improves flow conditions in the peripheral zones. Cylindrical blades with integral shroud and a constant profile over the blade length are used for expansion sections with relatively low secondary losses, i.e. in the centre sections of HP and IP turbines. By applying modern computational methods and performing accompanying tests, it has been possible to increase the efficiency of the blade profile used to date for the proven cylindrical blades. In the rear section of HP and IP turbines and in the front section of LP turbines, the blades are relatively long and twisted tapered blades with integral shroud are used (Figure 4a). By using different blade profiles whose cross section is reduced over the length of the blade, the profile losses of long blades are considerably reduced by comparison with those of a cylindrical blade. The thermodynamic design of the LP blading optimises the flow distribution over the length of the blade in which regions subject to steam friction or secondary flows have a low mass flow density. As a result of this, the last-stage stationary blades are of twisted design, and curved in the circumferential direction. This curvature induces an additional radial force and thus counteracts any possible flow separation in the root area (Figure 4b). Blade section with transonic discharge velocities in the range up to Mach 1.3 are designed with suction sides that are as straight as possible in order to eliminate over-expansion, and sections with higher Mach numbers are provided with backward-curved suction-face profiles. The above measures lead to blades with lower profile losses. The velocity distribution at the hub and tip profiles of a larger last-stage blading with locally supersonic flow conditions with convergent/divergent stationary and moving blade

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Proceedings of ICAPP ’04 Pittsburgh, PA USA, June 13-17, 2004 Paper 4195

channels at the blade hub and blade tip section. Special attention is also being given to LP turbine design of the steam path with regard to reducing the amount of water film in the respective areas and to control droplet erosion on last-stage blades by various measures. The last-stage blading is made from steel by which an axial exhaust area up to 12.5m² is provided. A last-stage blade with an axial exhaust area of 16 m² made of titanium alloy will be available in the future.

Table II: Summary of efficiencies used in the IPSE Pro simulation Isentropic efficiency - all turbines - all pumps Mechanical efficiency Electrical efficiency

0.90 0.80 0.98 0.98

The resulting characteristic parameters, defining the steam cycle of a 1000MWel class HPLWR, are given in the following Table III. Table III: Summary of characteristic parameters of the HPLWR steam cycle

a)

b)

FIGURE 4: a) Twisted blades with integral shrouds; b) Last-stage stationary and moving blades. II. STEAM CYCLE As a first approach to apply supercritical steam conditions to nuclear applications, Oka and Koshizuka [1] proposed a life steam temperature of 508°C at 25MPa pressure at core outlet to provide the input to a high pressure steam turbine. Part of the steam was separated at core outlet to allow a reheat of the steam behind the IP turbine (at 1.2MPa) up to 485°C by means of two heat exchangers (see Figure 5). Upstream of these heat exchanges a droplet separator was foreseen, because the expansion in the IP turbine caused condensation at its exit. The plant net efficiency was predicted to be 44.1%. A supercritical steam cycle has now been proposed to avoid such condensation and the droplet separator associated with it. Using the commercial program IPSE Pro [14], steam cycle analyses have been performed for the same life steam conditions like in the previous proposal. Instead of the 1500MWel class of a Supercritical Water Reactor (SCRW) [1], the steam cycle analysis focuses on the current HPLWR layout of 1000MWel [5]. The main assumptions for efficiencies of plant components are summarized in Table II.

Thermal Power Input Gross Power Output Net Power Output Life Steam - Mass Flow Rate - Temperature - Pressure Reheat - Temperature (exit HP) - Temperature (entrance IP) - Pressure Condenser - Pressure No. of Pre-heathers

2187.7 MWth 1000.0 MWel 960.6 MWel 1113 kg/s 508°C 25MPa 245°C 485°C 3.7MPa 0.005MPa 8

Different from the first approach, the reheat pressure has been increased to 3.7MPa. Hence, the steam will not expand into the two-phase region in the HP turbine, but will only reach saturation (or slightly superheated) conditions. Such steam cycle is much closer to those of coal fired power plants, in which condensation in the HP and IP steam turbines is avoided as well. Re-arrangements of pressure levels, temperatures and pass-out mass flow rates were adjusted accordingly. The following Figure 6 depicts the flow chart of HPLWR steam cycle with the core on the left hand side, the turbines at the top of the drawing, the condenser on the right hand side and in total eight pre-heaters at the bottom. Additional information about the steam mass flow rate, the actual pressure, temperature and enthalpy is given for each flow path depicted. The steam cycle of a HPLWR can be described as follows: Superheated steam leaves the HPLWR core with a temperature of 508°C and a pressure of 25MPa. Approximately 920 kg/s life steam (82.7 w% of the total mass flow rate) is delivered to the HP turbine.

5

6

354 66

2919.8 319.36

110 69

464 66

1658.3 281.84

1266.4 281.84

2919.8 316.22

2919.8 319.36

238 69

110 66

2919.8 319.36

1093.5 251.3

1123.3 257.7

464 66

1658.3 281.84

2833.1 260.81

1816 250

464 66

135 41.01

2833.1 265.23

2919.8 319.36

1352 69

135 44.01

2919.8 319.36

1352 69

3195 502.1 4.289e+005

1590 69

1590 236

90 22

599 41.01

944.63 220.1

907.5 210.17

2717.4 217.24

2717.4 219.55

2833.1 265.23

90 23

1816 250

1217 44.01

2833.1 265.23

53.8 12

1127 23

689 22

1816 250

2610 187.96

2717.4 219.55

2717.4 219.55

1127 23

1217 44.01

2717.4 219.55

1217 23

1352 44.01

2833.1 265.23

6.817e+005

5.437e+005

1266.4 281.84

FIGURE 5: Steam cycle of a 1500MWel class SCWR [1].

1230.2 279.98

3195 507.96

1816 250

1816 250

3195 502.1

3195 502.1

1816 236

1816 236

354 66

799.07 188

764.42 177.34

2610 187.96

798.43 187.96

2610 184.07

93.42 12

128 69

979.8 12 2610 187.96

2610 187.96

1073 12

53.8 11

1073 12

1127 12

8.003e+005

147.2 11

93.42 11

2782.7 187.96

1085.8 250

836.2 11

654.22 151.54

676.19 160.1

2919.8 319.36

3022.3 288.76

3195 502.1

6.138e+004

1816 250

1460.4 184.07

798.43 184.07

128 69

979.8 12

226 236

1816 4.9

33.88 5.1

33.88 5.4

33.88 5.4

979.8 12

226 236

621.09 147.43

3215.5 372.9

3215.5 373.14

3215.5 373.14

3443.6 485

1368.7 306.94

870.1 5.1

1816 4.9

63 2.4

63 2.5

63 2.5

945.9 5.4

979.8 5.4

3215.5 373.14

547.75 130.3

512.18 121.94

3027.4 278.44

3027.4 278.58

3027.4 278.58

3215.5 373.14

1.019e+006

933.1 2.4

1816 4.9

45 0.5

45 0.58

45 0.58

882.9 2.5

945.9 2.5

1.194e+006

mass[kg/s] p[bar]

366.98 87.6

333.27 79.524

2746.1 132.55

2746.1 132.91

2746.1 132.91

3027.4 278.58

3027.4 278.58

h[kJ/kg] t[°C]

978.1 0.5

1816 4.9

12 0.12

12 0.13

12 0.13

837.9 0.58

882.9 0.58

1.437e+006

226.43 54.1

198.62 47.356

2530.8 49.446

2530.8 51.062

2530.8 51.062

2746.1 132.91

2746.1 132.91

-1117

1816 4.9

825.9 0.12

825.9 0.0507

825.9 0.0507

825.9 0.13

837.9 0.13

1.614e+006

990.1 0.12

178.6 42.567

130.46 31.145

130.45 31.146

2413.7 33.146

2530.8 51.062

2530.8 51.062

Efficiency

217.65 49.446

1816 0.12

990.1 0.12

-9.536

825.9 0.0507

1.709e+006

178 42.523

217.65 49.446

2413.7 33.146

Proceedings of ICAPP ’04 Pittsburgh, PA USA, June 13-17, 2004 Paper 4195

7

1230.3 279.98

1113 250

338.5 66

67.44 66

1755.7 281.84

2919.8 316.22

2919.8 319.36

2919.8 319.36

145.9 69

67.44 69

2919.8 319.36

920.9 69

920.9 236

338.5 66

1113 250

338.5 66

2801.5 240.75

1085.8 250

1026.6 236.74

1755.7 281.84

45.98 33.92

2801.5 245.63

2919.8 319.36

775 69

45.98 36.92

2919.8 319.36

775 69

3195 502.1 2.484e+005

1466.1 281.84

729 36.92

1114.9 256

78.49 69

2801.5 245.63

2801.5 245.63

2801.5 245.63

729 36.92

775 36.92

3.383e+005

78.49 69

384.4 33.92

1113 250

2919.8 319.36

2995.8 308.49

3195 502.1

943.97 220

906.8 210.01

729 36.92

192.5 236

FIGURE 6: Steam cycle of a 1000MWel class HPLWR.

1466.1 281.84

3195 507.96

1113 250

271 66

3195 502.1

3195 502.1

1113 236

1113 236

271 66

49.05 22

49.05 23

729 36.92

192.5 236

3277.3 414.48

3277.3 415.16

3414.6 485

1609.2 347.03

433.5 22

1113 250

735.55 170.62

3109 327.67

768.13 181

38.84 11

3109 328.7

3277.3 415.16

3277.3 415.16

38.84 12

680 23

729 23

4.363e+005

1113 250

472.3 11

614.9 142.26

3109 328.7

3109 328.7

3.731e+004

641.1 12

680 12

5.485e+005

676.19 160.1

1113 4.9

2931 235.84

2931 236.39

2931 236.39

3109 328.7

582.06 138.34

20.85 5.1

20.85 5.4

20.85 5.4

641.1 12

38.63 2.4

38.63 2.5

493.2 5.1

1113 4.9

2931 236.39

547.75 130.3

482.95 115.05

2785 159.43

2785 159.78

2785 159.78

2931 236.39

38.63 2.5

620.3 5.4

641.1 5.4

6.603e+005

531.8 2.4

1113 4.9

27.59 0.5

27.59 0.58

366.98 87.6

318.99 76.118

2559.9 81.345

2559.9 85.087

2559.9 85.087

2785 159.78

2785 159.78

27.59 0.58

581.7 2.5

620.3 2.5

7.49e+005

mass[kg/s] h[kJ/kg] p[bar] t[°C]

559.4 0.5

1113 4.9

7.36 0.12

7.36 0.13

7.36 0.13

554.1 0.58

581.7 0.58

8.774e+005

226.43 54.1

194.04 46.262

2365.2 49.446

2365.2 51.062

2365.2 51.062

2559.9 85.087

2559.9 85.087

-676.3

1113 4.9

546.7 0.12

546.7 0.0507

546.7 0.0507

546.7 0.13

554.1 0.13

9.831e+005

175.6 41.847

130.46 31.145

130.45 31.146

2256.3 33.146

2365.2 51.062

2365.2 51.062

Efficiency

960.6370

566.8 0.12

1113 0.12

566.8 0.12

-6.312

546.7 0.0507

1.041e+006

217.96 49.446

175 41.804

217.96 49.446

2256.3 33.146

Proceedings of ICAPP ’04 Pittsburgh, PA USA, June 13-17, 2004 Paper 4195

Proceedings of ICAPP ’04 Pittsburgh, PA USA, June 13-17, 2004 Paper 4195

Pass-out steam at 6.9MPa and the remaining 17.2 w% life steam are then used to reheat the steam downstream of the HP turbine (3.7MPa, 245°C) by means of two heat exchangers. With a temperature of 485°C steam is then expanded in an IP- and a LP turbine to a pressure level of 0.005MPa. The steam quality at the outlet of the LP turbine amounts to 0.87. In the condenser, the steam is sub-cooled to 31°C. Condensate pumps then increase the pressure back to 0.49MPa. Four LP surface pre-heaters, which are heated by pass-out steam from the LP turbine, increase the feed water temperature to 138°C. The main feed water pump, which consumes about 39MWel, levels the pressure to nominal conditions of 25MPa. Another four surface preheaters being fed by pass-out steam from the HP- and IP turbine as well as by waste steam from the superheating, rise the feed water temperature to 280°C (nominal entrance temperature of the HPLWR core). The cycle analysis indicates a net efficiency of 43.9%, a decrease by about 0.2% absolute compared with the previously proposed design of the SCWR by Oka and Koshizuka [1]. The steam cycle will continuously be updated and refined within the next phase of the HPLWR research project. III. START-UP SYSTEM As the coolant mass flux in the core decreases with decreasing load in the reactor core, the HPLWR needs to be equipped with a start-up system to avoid burn out of the core fuel pins. Like in fossil fired power plants the following two start-up alternatives exist: • •

start-up at fixed pressure which is mainly used for UP-type (Universal Pressure) boilers today, or start-up at sliding pressure mainly used for Benson type boilers for coal fired power plants.

Comparing both alternatives, the sliding-pressure mode would allow a pressurization of the reactor vessel in parallel to the temperature increase, and thus minimize pressure losses in the turbine valve. A higher thermal efficiency at part load and lower costs can be expected then. As a new challenge, however, the core would be operated as a boiling water reactor with low mass flux at part load, and dryout has to be considered for core design. Such a start-up system is sketched in Figure 2 in [15] as part of the Balance-of-Plant. During the start-up phase, a separator extracts the water from the two-phase mixture and recalculates it by means of the start-up pump into the main circuit. The remaining steam is driving the turbine under part load conditions. The detailed operation of the start-up system will also be investigated within the next HPLWR research project.

IV. CONCLUSIONS As part of the 5th Framework Programme of the European Commission, European partners supported by the University of Tokyo have studied from 2000 to 2002 the feasibility of super-critical reactor systems, called High Performance Light Water Reactors (HPLWR). Within this study, the turbine technologies have been reviewed and a steam cycle analysis has been performed. Life steam temperatures up to 580°C and pressures up to 30MPa have been used in several applications for fossil fuelled power plants so that turbines can be regarded already to have a proven and reliable design. Materials and blading design technologies are well established. As a consequence, the individual turbine design for HPLWR steam parameters of 508°C and 25MPa can easily be completed in parallel to the reactor design; no further challenges in turbine technologies have to be expected. Oka and Koshizuka proposed a steam cycle for the SCWR with a plant net efficiency of 44.1%. This high efficiency could be reached because part of the life steam was separated at core outlet to allow a superheat of the steam behind the IP turbine at 1.2MPa. As the expansion in the IP turbine caused condensation under these conditions, a droplet separator was foreseen in front of the reheat exchanger. The cycle analysis for the HPLWR indicates that this droplet separator (expensive equipment) can be avoided if the pressure at the IP turbine outlet will be increased from to 3.7MPa (being slightly overheated). After adjustments of pressure levels, temperatures and pass-out mass flow rates of the steam cycle a net efficiency of 43.9% can be achieved, a decrease by about 0.2% absolute, compared with the previously proposed design. ACKNOWLEDGMENTS This project has been supported by the European Commission, Fifth Framework Programme of the European Atomic Energy Community, under contract No. FIKI-CT-2000-00033. The information provided herein is the sole responsibility of the authors and does not reflect the Community’s opinion. The Community is not responsible for any use that might be made of data appearing in this publication. ACRONYMS EUR HP HPLWR IP

8

European Utility Requirements High Pressure High Performance Light Water Reactor Intermediate Pressure

Proceedings of ICAPP ’04 Pittsburgh, PA USA, June 13-17, 2004 Paper 4195

LP LWR SCWR

Low Pressure Light Water Reactor Supercritical Water Reactor

9.

O. ANTONI, P. DUMAZ, ”Preliminary Calculations of a Supercritical Light Water Reactor Concept Using the CATHARE Code”, 2003 International Congress on Advances in Nuclear Power Plants, ICAPP '03 Cordoba Spain, May 4-7, 2003.

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