Nuclear Energy for New Europe 2009

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No: 704

Conference: Nuclear Energy for New Europe 2009

Title: SCW NPPs: Layouts and Thermodynamic Cycles Options

Theme: Emerging Reactor Designs

Author(s): Maria Naidin, Igor Pioro, R. Duffey, Udo Zirn, Sarah Mokry

Contact : Igor Pioro

E-mail: Igor.Pioro@uoit.ca

Address: Faculty of Energy Systems and Nuclear Science University of Ontario Institute of Technology
Oshawa ON L1K 2S8

Country: Canada

Currently, there are a number of Generation IV SuperCritical Water-cooled nuclear Reactor (SCWR) concepts under development worldwide. The main objectives for developing and utilizing SCWRs are: 1) Increase gross thermal efficiency of current Nuclear Power Plants (NPPs) from 30 – 35% to approximately 45 – 50%, and 2) Decrease capital and operational costs and, in doing so, decrease electrical-energy costs.
SCW NPPs will have much higher operating parameters compared to current NPPs (i.e., steam pressures of about 25 MPa and steam outlet temperatures up to 625°C). Additionally, SCWRs will have a simplified flow circuit in which steam generators, steam dryers, steam separators, etc. will be eliminated. Furthermore, SCWRs operating at higher temperatures can facilitate an economical co-generation of hydrogen through thermo-chemical cycles (particularly, the copper-chlorine cycle) or direct high-temperature electrolysis.
To decrease significantly the development costs of a SCW NPP, to increase its reliability, and to achieve similar high thermal efficiencies as the advanced fossil steam cycles, it should be determined whether SCW NPPs can be designed with a steam-cycle arrangement that closely matches that of mature SuperCritical (SC) fossil-fired thermal power plants (including their SC-turbine technology). The state-of-the-art SC-steam cycles at fossil-fired power plants are designed with a single-steam reheat and regenerative feedwater heating. Due to that, they can reach thermal steam-cycle efficiencies up to 54% (i.e., net plant efficiencies of up to 43% on a Higher Heating Value (HHV) basis).
This paper presents and discusses several SCW NPPs layouts and, corresponding to that, thermodynamic-cycle options developed by AECL (Atomic Energy of Canada Limited), Hitachi Power Systems America and UOIT (University of Ontario Institute of Technology). An analysis of main parameters and thermal efficiency performance of SCW NPP concepts based on a no-reheat and single-reheat regenerative cycles are discussed.
The no-reheat configuration has a more simplified design: the Intermediate-Pressure (IP) turbine section is eliminated and the exhaust from the High-Pressure (HP) turbine is directly routed to the inlet of the Low-Pressure (LP) turbines. The cycle consists of a condenser, nine feedwater heaters, a topping de-superheater, associated pumps, and the nuclear source of energy, i.e., the SCWR. In general, the major technical challenge associated with a SC no-reheat turbine is the high moisture content in the LP turbine exhaust. A thermal-performance simulation reveals that the steam quality at the exhaust from the LP turbine is approximately 81%. However, the moisture can be reduced by implementation of contoured channels in the inner casing for draining water and moisture removal stages. The overall thermal efficiency of the cycle was determined to be not more than 50% (assumptions are made to account for turbine and pump efficiency losses).
The single-reheat cycles are comprised of: a SCWR, a SC turbine (consisting of one High-Pressure (HP) cylinder, one Intermediate-Pressure (IP) cylinder and two Low-Pressure (LP) cylinders), one deaerator, several feedwater heaters, and pumps. Since the single-reheat option includes a “nuclear” steam-reheat stage, the SCWR is based on a pressure-tube design. A thermal-performance simulation reveals that the overall thermal efficiency is approximately above 50%.
Previous studies have shown that direct cycles, with no-reheat and single-reheat configurations are the best choice for the SCWR concept. However, the single-reheat cycle requires a nuclear steam-reheat, thus increasing the complexity of the reactor core design.

No:	704
Conference:	Nuclear Energy for New Europe 2009
Title:	SCW NPPs: Layouts and Thermodynamic Cycles Options
Theme:	Emerging Reactor Designs
Author(s):	Maria Naidin, Igor Pioro, R. Duffey, Udo Zirn, Sarah Mokry
Contact :	Igor Pioro
E-mail:	Igor.Pioro@uoit.ca
Address:	Faculty of Energy Systems and Nuclear Science University of Ontario Institute of Technology Oshawa ON L1K 2S8
Country:	Canada

Currently, there are a number of Generation IV SuperCritical Water-cooled nuclear Reactor (SCWR) concepts under development worldwide. The main objectives for developing and utilizing SCWRs are: 1) Increase gross thermal efficiency of current Nuclear Power Plants (NPPs) from 30 – 35% to approximately 45 – 50%, and 2) Decrease capital and operational costs and, in doing so, decrease electrical-energy costs. SCW NPPs will have much higher operating parameters compared to current NPPs (i.e., steam pressures of about 25 MPa and steam outlet temperatures up to 625°C). Additionally, SCWRs will have a simplified flow circuit in which steam generators, steam dryers, steam separators, etc. will be eliminated. Furthermore, SCWRs operating at higher temperatures can facilitate an economical co-generation of hydrogen through thermo-chemical cycles (particularly, the copper-chlorine cycle) or direct high-temperature electrolysis. To decrease significantly the development costs of a SCW NPP, to increase its reliability, and to achieve similar high thermal efficiencies as the advanced fossil steam cycles, it should be determined whether SCW NPPs can be designed with a steam-cycle arrangement that closely matches that of mature SuperCritical (SC) fossil-fired thermal power plants (including their SC-turbine technology). The state-of-the-art SC-steam cycles at fossil-fired power plants are designed with a single-steam reheat and regenerative feedwater heating. Due to that, they can reach thermal steam-cycle efficiencies up to 54% (i.e., net plant efficiencies of up to 43% on a Higher Heating Value (HHV) basis). This paper presents and discusses several SCW NPPs layouts and, corresponding to that, thermodynamic-cycle options developed by AECL (Atomic Energy of Canada Limited), Hitachi Power Systems America and UOIT (University of Ontario Institute of Technology). An analysis of main parameters and thermal efficiency performance of SCW NPP concepts based on a no-reheat and single-reheat regenerative cycles are discussed. The no-reheat configuration has a more simplified design: the Intermediate-Pressure (IP) turbine section is eliminated and the exhaust from the High-Pressure (HP) turbine is directly routed to the inlet of the Low-Pressure (LP) turbines. The cycle consists of a condenser, nine feedwater heaters, a topping de-superheater, associated pumps, and the nuclear source of energy, i.e., the SCWR. In general, the major technical challenge associated with a SC no-reheat turbine is the high moisture content in the LP turbine exhaust. A thermal-performance simulation reveals that the steam quality at the exhaust from the LP turbine is approximately 81%. However, the moisture can be reduced by implementation of contoured channels in the inner casing for draining water and moisture removal stages. The overall thermal efficiency of the cycle was determined to be not more than 50% (assumptions are made to account for turbine and pump efficiency losses). The single-reheat cycles are comprised of: a SCWR, a SC turbine (consisting of one High-Pressure (HP) cylinder, one Intermediate-Pressure (IP) cylinder and two Low-Pressure (LP) cylinders), one deaerator, several feedwater heaters, and pumps. Since the single-reheat option includes a “nuclear” steam-reheat stage, the SCWR is based on a pressure-tube design. A thermal-performance simulation reveals that the overall thermal efficiency is approximately above 50%. Previous studies have shown that direct cycles, with no-reheat and single-reheat configurations are the best choice for the SCWR concept. However, the single-reheat cycle requires a nuclear steam-reheat, thus increasing the complexity of the reactor core design.