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Development of Multi-Stage for Feedwater Heaters in Simplified Nuclear Power Plant∗

Tadashi NARABAYASHI∗∗,∗∗∗, Shuichi OHMORI∗∗∗∗, Michitsugu MORI∗∗∗∗, Yutaka ASANUMA∗∗ and Chikako IWAKI∗∗

A steam injector (SI) is a simple, compact and passive pump and also acts as a high- performance direct-contact compact heater to heat up feedwater by using extracted steam from the turbine. To develop high performance compact feedwater heater, it is necessary to quantify the characteristics between physical properties of the flow field. Its performance depends on the phenomena of steam condensation onto the water jet surface and heat transfer in the water jet due to turbulence on to the phase-interface. The analysis was conducted by using CFD code embedded separate two-phase flow models that were confirmed by the experimental data. As the four-stage SI is compact heater, the system is expected to bring about great simplification and materials-saving effects, and high reliability of its operation. Therefore, it is confirmed that the simplification of the power plant by replacing all low- pressure feedwater heaters with the four-stage SI system, having steam extraction pressures equal to those for the existing ABWR system.

Key Words: Jet, Multi-Phase Flow, Nozzle, Pressure Distribution, Turbulent Mixing, Nu- clear Reactor, Power Plant, CFD Code, Separate Two-Phase Model, BWR, Steam Injector, Feedwater Heater

large numbers of replacements involved. At some nuclear 1. Introduction power plants, degraded feedwater heaters have been re- Nuclear power plants have a number of advantages placed, resulting in power losses of several months. Anal- such as they do not produce carbon dioxide, and fuel ysis of this cost classifies into (a) the complicatedness of loaded in a reactor core has a stockpiling effect to be ad- the turbine condensation and feedwater heating systems vantageous in terms of Japan’s energy security. On the in the balance of plant (BOP), and (b) the volume and ma- other side, however, the cost of constructing new nuclear terials used in such systems. Such being the case, based power plants should be decreased to keep ascendancy of on the high-performance steam injector technology that power cost over advanced-combined-cycle thermal power has been developed to achieve high performance and ex- plants. In case of a fourth-generation nuclear reactor, ca- tend an application range(1) – (7). By substituting the steam pability of mitigating the severe accidents in a reactor de- for feedwater, thereby to substantially simplify sign. The high construction costs resulting from the com- system and components, achieve material reductions, en- plicatedness of plants and an enormous number of com- hancing the reliability and international price competitive ponents required, a long period of construction, enormous ness of Japanese nuclear power plants(11). numbers of systems and equipment to be inspected during A separate two-phase flow model was developed periodical inspections, and the increased manpower due to based on the fundamental test data using a single-stage vi- sualized steam injector that was made of heatproof acrylic ∗ Received 6th October, 2005 (No. 05-4205) ∗∗ resin. The obtained data set was the axial-velocity distri- TOSHIBA Corporation, 8 Shinsugita-cho, Isogo-ku, bution in the steam phase, and temperature/axial-velocity Yokohama 235–8523, Japan ∗∗∗ distribution in a water jet. Axial-velocity flow in the steam Present Address, Hokkaido University, Nishi 8, Kita 13, Kita-ku, Sapporo 060–8628, Japan. phase was measured by using the advanced measuring E-mail: [email protected] techniques of LDV method to measure supersonic veloc- ∗∗∗∗ R&D Center, Tokyo Electric Power Company, 4–1 ity. In order to enable to analyze steam injector perfor- Egasaki, Tsurumi-ku, Yokohama 230–8510, Japan mances, a separate-two-phase flow model was made as

Series B, Vol. 49, No. 2, 2006 JSME International Journal 369 user subroutines in some CFD codes, such as PHONICS that heats up feedwater by using extracted steam from the and Star-CD. The validity of the model was confirmed turbine. For this purpose, we have been developing the by analyzing the fundamental test results. The analysis multi-stage steam injector system as shown in Fig. 2, com- results showed in good agreement with the set of test re- posed of the first-stage, second-stage, third-stage steam in- sults(6). jectors, and jet as the final-stage. In this paper, we focused on the merits of simplifying As it is compact equipment, steam injector is ex- the feedwater system by using a four-stage steam injector, pected to bring about great simplification and materials- and also focused on improving the performances of the saving effects, while its simple structure ensures high reli- steam injector especially in the 1st-stage, to enhance the ability of its operation, thereby greatly contributing to the plant thermal efficiency. simplification of the power plant. The high-performance steam injector system with multi-stage parallel opera- 2. Nomenclature and Abbreviations tion, having been developed(8) – (11). The high-performance A : area of bubble surface [m2] steam injector, because of its wider operating and appli- T : water temperature cation ranges from higher through lower steam pressures, m : mass flow rate [kg/s] compared with conventional steam injectors, which attains h : enthalpy [kJ/kg] higher discharge pressure than the supply steam pressure. Cpl : specific heat Figure 3 shows BOP system of an ABWR. The low- Subscripts pressure feedwater heating system has a total of 12 (four- “mix” represents mixing flow stage × three-series) low-pressure feedwater heaters. The l : liquid phase size of a low-pressure heater is about 2 m in diameter g : vapor phase and 13 m long. The feedwater heating system of ABWR, Abbreviations shown in Fig. 4 (a), can be simplified by the six parallel ABWR : Advanced boiling water reactor four-stage SI systems as shown in Fig. 4 (b). BOP : Balance of plant (Turbine and feedwater system) As the low-pressure feedwater heaters of ABWR, CFD : Computer fluid dynamics which are placed inside the huge condenser as necked LDV : Laser Doppler velocimeter heaters as shown in Fig. 5. For the case, by using the four- SI : Steam injector stage steam injectors, as shown in Fig. 6, the large necked 3. Development for Simplified Feedwater System heaters will be removed and the turbine building height can be reduced by ∼3.5 m. 3. 1 Simplified feedwater system 3. 2 Scaled model test for simplified feedwater sys- Steam injector is a passive jet pump that has no mov- tem (1) – (7) able part and drives water jet by supersonic steam jet . In this study, we aimed at using reduced-scale test- When water is injected from the water jet nozzle at the ax- based analytical improvement development. The perfor- ial center in the case of Fig. 1 and steam is supplied to the mance test was carried out with 1/7-scaled tests to confirm annular steam nozzle composed of the outside of the water the numerical simulation. The multi-stage steam injector jet nozzle and the mixing nozzle inlet, the steam becomes test facility is shown in Fig. 7. Then, 1/5-scaled steam a supersonic flow in the mixing nozzle and accelerates the injector test model was made geometric-analogy to 1/7- water jet, producing a high-speed water flow at the throat. scaled SI model, and also conducted the performance test. The steam condensation is completed and the flow Table 1 shows the test results summary for both a 1/7- changes into a single-phase water flow in a diffuser, with scaled and a 1/5-scaled test models with the full-scale tar- its pressure rising to a high level in accordance with get value of the actual steam injectors. Since the ratios Bernoulli’s principle. of the inner diameter and length are ∼21/2,theflowrate In addition to its function as a pump, steam injector of the 1/5 scaled SI is twice of that for the 1/7-scaled test works as a through direct contact between model. The 1/5-scaled SI test model was made analogy to steam and water. This provides steam injector with ca- pability to serve also as a direct-contact feedwater heater

Fig. 1 Principle of a steam injector Fig. 2 Four-stage steam injector system

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Fig. 3 BOP system heat balance of the current ABWR

(a) Low-pressure heater system of the current ABWR

Fig. 5 Low-pressure necked feedwater

(b) Steam injector heater system models. The authors developed the separate-two-phase Fig. 4 Feedwater heater system flow model and wrote a user subroutines compiled with some CFD codes, such as PHONICS and Star-CD. The 1/7-scaled SI model. The test results of the outlet temper- validity of the model was confirmed by analyzing the fun- atures and pressures at each stage by the 1/5-scaled model damental test results. The analysis results showed in good were almost similar to those of the 1/7-scaled model. agreement with the set of test results, and also showed lit- tle effect on scaling of a steam injector(6). 4. Improvement of SI with CDF analysis In this study, analyses of the multi-stage steam in- 4. 1 CFD analysis model jector for feedwater heater were conducted, by using the In relation to a steam injector improvement, super- separate-two-phase flow model in the Star-CD codes. This sonic steam condensation onto a water jet was developed, paper describes the analyses results to improve the steam without relying on full-scale demonstration of operational injector improvement. equipment, with the results of experiments using scaled The performance improvement of steam injectors will

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Fig. 6 Simplified steam injector feedwater heaters in a turbine condenser

Table 1 Test results of pressures and temperatures

Fig. 8 3D-CAD of multi-stage steam injector’s analysis model from 1st to 3rd stage

produce the enhancement of the plant thermal efficiency, on which the performance of the 1st-stage SI, especially, has remarkable impact, since it is worked with the lowest- pressure extracted steam of 0.05 MPa from the turbine. Figure 8 illustrates the 3D-CAD modeling of the multi- stage steam injector from the first through third stages with the large-diameter bell mouth and mixing nozzle. The steam-liquid interface is shown by blue-water jet. Fig- ure 9 shows analysis modeling of extended large inlet bell- mouth with the mesh for numerical simulation and the boundary conditions for analyses. The pressures of the extracted steam as the input set were 0.05 MPa, 0.11 MPa, 0.21 MPa from the first stage to the third stage, respec- tively. The inlet pressure and temperature of the feedwater flow as the boundary conditions were set to 1.60 MPa and 42◦C. 4. 2 Analysis results (a) 1st-stage steam injector The analyses were parametrically carried out, varying the inner diameter of the inlet bell mouth, and the diameter and the length of the mixing nozzle through the first stage steam injector. The series of the parametric survey was performed to seek for the better configuration of the first- stage SI to increase the outlet temperature. When the bell mouth was applied for the mixing noz- zle adopted in the last design to enlarge the steam nozzle inlet, the outlet temperature of the first-stage SI decreased to 51.7◦C, the fact of which showed that the configuration of the mixing nozzle with the bell mouth including the ff (b) 1st and 2nd-stage steam injector shape of a curve surface a ected the SI performance. The temperature distribution from the 1st-stage to the Fig. 7 Multi-stage steam injector test facility 3rd-stage SI predicted by analysis is shown in Figs. 10 and

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Fig. 9 Analysis model of normal and extended large inlet-bell mouth

(a) Pressure distribution (b) Temperature distribution Fig. 10 Temperature distribution from the 1st to the 3rd-stage SI

11. The temperature of the steam flow can be found to be Table 2 Analysis results of 4-stage steam injector feedwater heater lower than expected in the down stream of the 1st-stage SI, which may cause the performance degradation of the 1st-stage SI and, therefore, the temperature increase at the outlet of the 1st-stage SI could not be attained. The outlet mixed temperature of the 1st stage SI can be determined by:

Tmix = (mlhl +mghg)/[(ml +mg)Cpl](1) where m is mass flow rate (kg/s), h is enthalpy (kJ/kg); and Cpl is specific heat, as shown in the nomenclature. We conducted over 10 cases to improve the perfor- mance of the 4-stage steam injector feed-water heaters, that was described in section 3.2. As shown in Fig. 10 (a), especially the 1st-stage. Among ten cases, typical three pressure in each stage is almost the same as the supplyed cases were shown in Table 2. The analysis results for the steam from the turbine extracted steam port, except in a three cases are described in following order: (a) Original mixing nozzle in the 1st-stage. The analysis results of the case of test nozzle, (b) Extended large inlet-bell mouth water temperature in Fig. 10 (b) were 67◦C. The 1st-stage case, and (c) Improved thick mixing nozzle case. outlet water temperature calculated Eq. (1) by using the 4. 2. 1 Original case The original case of the calculated steam flow rate in the 1st-stage mixing nozzle analysis result is shown in Figs. 10 and 11. The 1st-stage was also 67◦C. The value was less than that of the current mixing nozzle used in the test was the same dimensions ABWR’s feedwater heater. As shown in Fig. 10 (b), the

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(a) Axial velocity contour

(b) Pressure contour

(c) Temperature contour Fig. 11 Temperature, pressure and axial velocity contour from the 1st to the 3rd-stage SI: Case (a)

(a) Axial-velocity distribution (b) Temperature distribution Fig. 12 Temperature distribution from the 1st to the 3rd-stage SI: Case (b) analysis results of steam temperature distribution curve in ity peak in Fig. 11. the 1st-stage had a valley in the mixing nozzle from 80◦C 4. 2. 2 Extended large inlet-bell mouth In order to 70◦C at the bottom. The reason why the steam temper- to improve the heater efficiency of the 1st stage SI, the ex- ature decreased to 70◦C was to the steam velocity in the tended large inlet-bell mouth at the inlet of the 1st-stage mixing nozzle was too high to decrease static pressure, mixing nozzle, which had a longer water jet, was ana- according to the polytropic expansion line(4) and steam lyzed. As shown in Fig. 12 (a), there were also still the temperature was also decreased according the saturation steam axial-velocty peak, the 1st-stage exit temperature temperature of the steam pressure decrease, making some increase was only 2◦C, from 67◦Cto69◦C. The predicted moisture in the two-phase flow area, as shown axial veloc- exit temperatures and pressures at each stage for the full

JSME International Journal Series B, Vol. 49, No. 2, 2006 374 scale steam injector by analysis also showed the almost steam temperature in the 1st-stage mixing nozzle were in- similar results against those of 1/7-scaled and 1/5-scaled creased. Thus, the 1st-stage outlet temperature were in- test models, which exhibited the applicability of the scale creased from 69◦Cto75◦C as shown in Fig. 15 (a) and (b), law on analogy in the design of the enlarged multi-stage and the steam flow rate was also increased to heat up water steam injector. jet in the 1st-stage higher than about 8◦C compared with 4. 2. 3 Improved mixing nozzle of the 1st-stage the original case. It was almost compatible steam pressure As shown in Fig. 12, the axial velocity in the mixing noz- and exit water temperature at each stage. The 4th-stage of zle was too high to decrease the steam temperature in the jet deareator exit temperature is saturation temperature of mixing nozzle of the 1st-stage, an improved mixing noz- extracted steam of 0.4 MPa. Therefore, exit temperature zle was analyzed as Case (c). Inner diameter of the mix- of 4th-stage steam injector is higher than that of ABWR’s ing nozzle was enlarged from 31 to 36.5 mm as shown low-pressure heater. Thus, it will be possible to increase in Fig. 13. The comparison of the analyses results of the plant thermal-efficiency by using the steam injector case (b) and case (c) are shown in Fig. 14. By using the feedwater heater system. improved thick-diameter mixing nozzle, the steam axial- 5. Effects of Material-Saving Using Steam Injector velocity peak was decreased to about 260 m/s, and the In order to demonstrate the merits of applying the multistage steam injector for the feedwater heating sys- tem, the comparison was made estimating the volume and weight reduction between ABWR and the simplified feed- water system as shown in bird’s eye view layout design in Fig. 16. As the diligent tally up working results as shown in (a) Extended large bell-mouth Fig. 17, the weight and volume of the feedwater heating system of the simplified plant can be reduced by around one-third, compared with those of ABWR. The high construction costs resulting from the complicatedness of plants and an enormous number of components will be reduced, and a long period of construction and outage days for inspection and replace the heaters will also (b) Improved thick-diameter mixing nozzle shortened. The four-stage steam injector is simple devices Fig. 13 Improvement of the 1st-stage mixing nozzle: Case (c)

(a) Axial-velocity distribution

(b) Pressure contour

(c) Temperature contour Fig. 14 Comparison of the improved effects on steam injectors from the 1st to the 3rd-stage SI: Case (c)

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(a) Axial-velocity distribution (b) Temperature distribution Fig. 15 Temperature distribution from the 1st to the 3rd-stage SI: Case (c)

(a) Current ABWR’s turbine building layout (b) Simplified steam injector feedwater heaters Fig. 16 Bird’s eye view of a turbine-building layout

6. Conclusions Using high-performance SI system technologies that can be as a direct-contact heater for a wide operating range, we have carried out a study on a simplified nuclear power plant design for feedwater heater systems. In order to develop high performance compact feedwater heater, it is necessary to improve the performances of exit tempera- Fig. 17 Comparison of volume and weight for the feedwater ture. Its performance depends on the axial-steam velocity system between ABWR and simplified plant condensed onto the water jet surface and heat transfer in the water jet due to turbulence in the water jet. The analy- and easy maintenance only changing nozzles in steam sis was conducted by using Star-CD code embedded user injector casings. subroutine of separate two-phase flow models. In this point of view, the proposed system can con- It was confirmed by the CFD analysis, the improve- tribute greatly to enhance reliability; in addition to eco- ment of the outlet water temperature increase to obtain the nomic efficiency and marketability both in domestic and high-performance direct-contact heaters that were almost overseas markets by simplified feedwater heater system. compatible steam pressure and exit water temperature at

JSME International Journal Series B, Vol. 49, No. 2, 2006 376 each stage. The 4th-stage of jet deaerator exit temperature Steam Injector to Next-Generation BWR, Proc. of Int. is saturation temperature of extracted steam of 0.4 MPa. Conf. on Nucl. Eng., (ICONE-3), Kyoto, Japan, (1994), Therefore, it was concluded that the four-stage steam in- pp.877–883. jector is suitable for compact feedwater heater and it will ( 4 ) Narabayashi, T., Nei, H., Ozaki, O., Shioiri, A. and Mizumachi, W., Study on High-Performance Steam In- be possible to increase the plant thermal-efficiency. jector (1st Report, Development of Analytical Model The comparison exhibited the volume and weight re- for Characteristic Evaluation), Trans. Jpn. Soc. Mech. duction between ABWR and the simplified plant by apply- Eng., (in Japanese), Vol.62, No.597, B (1996), pp.155– ing the multistage parallel steam injector for the feedwater 162. heating system, the weight and volume of the feedwater ( 5 ) Iwaki, C., Narabayashi, T., Mori, M. and Ohmori, S., heating system of the simplified plant can be reduced by Study on High-Performance Steam Injector (2nd Re- around one-third, compared with those of ABWR. In ad- port, Measurement of Jet Structure), Trans. Jpn. Soc. dition, plant maintenance and operations will be stream- Mech. Eng., (in Japanese), Vol.69, No.684, B (2003), pp.1814–1821. lined, and the competitiveness of nuclear power will be ( 6 ) Narabayashi, T., Mizumachi, W. and Mori, M., Study enhanced through improvements in techniques for nuclear on Two-Phase Flow Dynamics in Steam Injectors, Nu- power plant simplification and materials saving. clear Engineering and Design, Vol.175 (1997), pp.147– Acknowledgment 156. ( 7 ) Narabayashi, T., Mori, M., Nakamaru, M. and Ohmori, The research project was carried out by Tokyo Elec- S., Study on Two-Phase Flow Dynamics in Steam In- tric Power Company, Toshiba Corporation, and six Uni- jectors, II. High-Pressure Tests Using Scale-Models, versities in Japan, funded from the Institute of Applied En- Nuclear Engineering and Design, (2000), pp.261–271. ( 8 ) Ohmori, S., Mori, M., Narabayashi, T., Nakamaru, M., ergy (IAE) of Japan as the national public research-funded Asanuma, Y., Yasuoka, M. and Kato, T., Development program. Authors express our gratitude to all the members of Steam Injector Feedwater Heater System, Proc. of of the project, and Mr. Naofumi Shibata of Toshiba Infor- Int. Conf. on Nucl. Eng., ICONE-7371, Tokyo, Japan, mation Systems Corporation for CFD analysis expert. (1999). ( 9 ) Ohmori, S., Mori, M., Narabayashi, T., Nakamaru, M., References Asanuma, Y. and Yasuoka, M., Development of Steam ( 1 ) Narabayashi, T., Ishiyama, T., Miyano, H., Nei, H. and Injector Feedwater Heater System, Proc. of Int. Conf. Shioiri, A., Feasibility and Application on Steam In- on Nucl. Eng., ICONE-8582, Baltimore, USA, (2000). jector for Next-Generation Reactor, Proc. of Int. Conf. (10) Mori, M., Ohmori, S. and Narabayashi, T., Develop- on Nucl. Eng. a-4, (ICONE-1), Tokyo, Japan, (1991), ment of Simplified Steam Injector Feedwater System— pp.23–28. Large Scale Model Tests and Design Improvement by ( 2 ) Narabayashi, T., Iwaki, C. and Nei, H., Thermal- CFD, Proc. of Int. Conf. on Nucl. Eng., ICONE11- hydraulics Study on Steam Injector for Next- 36488, Tokyo, Japan, (2003). Generation Reactor, Proc. Int. Conf. on New Trends (11) Mori, M., Narabayashi, T. and Ohmori, S., Research in Nucl. Systems Thermohydraulics, Pisa, Italy, Vol.1 and Development Program of Innovative Simplified (1994), pp.653–661. and Severe-Accident-Free BWR by High-Performance ( 3 ) Narabayashi, T., Iwaki, C., Kudo, Y., Mizumachi, Steam Injector System, Proc. of ICAPP ’03, Cordoba, W., Shioiri, A., Tanaka, T., Mori, M., Horie, A. Spain, Paper 3294, (2003). and Machida, Y., Analytical Study on Large Scale

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