Analyses of the Associated Technical and Economic Risks of the Simple and Intercooled Brayton Helium Recuperated Gas Turbine Cycles for Generation IV Nuclear Power Plants

of The Simple Cycle Recuperated (SCR) and Intercooled Cycle Recuperated (ICR) are highly efficient Brayton helium gas turbine cycles, designed for the Gas-cooled Fast Reactor (GFR) and Very-HighTemperature Reactor (VHTR) Generation IV (Gen IV) Nuclear Power Plants (NPPs). This paper documents risk analyses which considers technical and economic aspects of the NPP. The sensitivity analyses are presented that interrogate the plant design, performance and operational schedule and range from component efficiencies, system pressure losses, operating at varied power output due to short term loadfollowing or long term reduced power operations to prioritise other sources such as renewables. The sensitivities of the economic and construction schedule are also considered in terms of the discount rates, capital and operational costs and increased costs in Decontamination and Decommissioning (D&D) activity due to changes in the discount rates. This was made possible by using a tool designed for this study to demonstrate the effect on the ‘non-contingency’ baseline Levelised Unit Electricity Cost (LUEC) of both cycles. The SCR with a cycle efficiency of 50%, has a cheaper baseline LUEC of $58.41/MWh in comparison to the ICR (53% cycle efficiency), which has a LUEC of $58.70/MWh. However, the cost of the technical and economic risks is cheaper for the ICR resulting in a final LUEC of $70.45/MWh (ICR) in comparison to the SCR ($71.62/MWh) for the year 2020 prices. A cc ep te d M a u sc ri p t N o t C o p ye d it ed

operations and end of life. Thus, the objective of this paper is to conduct technical and economic risk analyses associated with plant design, performance operation and capital finance and to assess the effect on the 'non-contingency' baseline LUEC. The analyses is performed using a tool specifically design for this study to analyse the Simple Cycle Recuperated (SCR) and Intercooled Cycle Recuperated (ICR) in a closed Brayton direct configuration using helium as the working fluid.

Generation IV (Gen IV) Systems
The Gas-Cooled Fast Reactor System (GFR) and Very-High-Temperature Reactor System (VHTR) are the focus of this paper. The GFR makes use of helium as the coolant with a high temperature combined with a fast spectrum nuclear core. The Core Outlet Temperature (COT) is between 850-950°C and is configured using an efficient direct thermodynamic Brayton gas turbine cycle. Single phase cooling is provided by the helium coolant due to its chemical inertness, stability and neutronic transparency. The VHTR as a thermal reactor also has high temperature capability, which is also cooled using helium in its gaseous phase. The core can be a prismatic block or a pebble bed. Moderation is provided by graphite in the solid state. The core delivers a COT of 750-1000°C meaning significant increases in cycle efficiency are expected without altering the gas properties of helium. Graphite also possesses the necessary mechanical properties for moderation. The list of on-going and planned demonstration projects are described and discussed in [1].

The Simple Cycle Recuperated (SCR) and Intercooled Cycle Recuperated (ICR) Helium Brayton Cycles
The SCR includes the compressor and turbine components which form the plant turbomachinery. The Compressor Work (CW) is less than the work requirement generated by the Turbine Work (TW). This means that the Useful Work (UW), which is the remaining work after the compressor load requirements have been met, is used to drive the generator load. Limitations to 8 this process are brought on by component inefficiencies during the compression and expansion phases. The component inefficiencies means that the compression and expansion phases are not isentropic [2]. Consequentially, the heating and cooling stages of the cycle when heat exchangers are not taken into account, are not isobaric. This effect means that the cycle experiences losses that translate into additional work input which is required for the helium to be compressed to some pressure due to the increase in temperature. This high temperature translates into higher than preferred exit temperature at the compressor. Due to the fact that the heat added into the cycle is not isobaric, the total gas exit pressure is reduced accordingly [2]. This means that the total power extracted from the cycle is less than ideal due to the reduced gas exit pressure combined with reduced component efficiencies. The turbine exhaust heat is hotter than expected, which in turn influences the inlet compression temperature as it becomes hotter than necessary.
A typical NPP would include a precooler and a recuperator in addition to the turbomachinery. The addition of a precooler reduces the turbine exhaust gas temperature using a cooling medium such as seawater. The cooled helium at the compressor entry is necessary at the cycle inlet because it reduces the CW but in turn, the compressor exit temperature rises but not enough for the cycle. This leads to increases in the reactor input thermal power beyond the reactor design intent. Due to the thermal power being fixed for a given COT, the precooler alone will not provide the necessary Specific Work (SW) and cycle efficiency and reduces the plant economics. The recuperator is introduced to improve the economics of the cycle. This is achieved by exchanging the heat from the turbine exhaust gas to the helium upstream at the inlet of the reactor. This raises the temperature of the helium thereby reducing the amount of thermal heat input and reactor power to have a positive effect on cycle efficiency.
The SCR and ICR comprise all of the components as stated above. However, the ICR has an intercooler and an additional compressor which are both downstream of the first compressor. The ICR improves the SW and UW by reducing the compressor work in comparison to the SCR. The helium downstream of the first compressor is reduced to a lower temperature as it passes through the intercooler, before entering the second compressor upstream, with some negligible reductions in pressure observed.
The thermodynamics which results from changing to helium in a nuclear gas turbine have been extensively covered in [3]. The study is also documented in [7] and [8] and focuses on off-design, control and transient operational modes of a helium gas turbine, which is also applicable to the plant operations for this study. With present day technologies, the potential for reliable helium gas turbines has never been greater. Improvements such as magnetic bearings and high performance 9 adjustable seals to reduce leakage and helium ingress in the bearing assemblies, supported by precision manufacturing and computational power help make this a possibility.

Method of Modelling of Nuclear Power Plants -Technical Performance Model
When focusing on the technical model, this part of the tool was created using FORTRAN.

Compressor
Prerequisite parameters for performance design considerations of both compressors include the compressor pressure ratio (PR), compressor inlet conditions (temperature, pressure and mass flow), component efficiency and the working fluid gas properties ( and ). The compressor outlet pressure (Pa) is: The isentropic efficiency of the compressor is and is also indicative of the specific work input or total temperature increase. Thus, the temperature (°C) at the exit can be derived from the inlet temperature, PR, isentropic efficiency and ratio of specific heats:

A c c e p t e d M a n u s c r i p t N o t C o p y e d i t e d
The mass flow (kg/s) at inlet is equal to the mass flow at outlet as there are no compositional changes: The CW (W) is the product of the mass flow, specific heat at constant pressure and the temperature delta: Bypass splitters are incorporated within the performance simulation tool, to allow for compressed coolant to be bled from the compressor(s) for Reactor Pressure Vessel (RPV) cooling and turbine cooling. The method of estimating the required turbine cooling is detailed in [6].

Turbine
Prerequisite parameters of the turbine include the turbine inlet conditions (temperature, pressure and mass flow), the pressure at outlet, component efficiency and the working fluid gas properties ( and ).
The temperature (°C) at the outlet is derived from the following expression: As with the compressor, eqs (3) and (4) also apply to the turbine for mass flow (kg/s) conditions and TW (W) but:

A c c e p t e d M a n u s c r i p t N o t C o p y e d i t e d
A mixer is incorporated within the performance simulation tool to allow for the coolant to mix with the hot gas to simulate turbine cooling.

Precooler and Intercooler (ICR Only)
Prerequisite parameters for the precooler and intercooler takes into account that the precooler is upstream of the compressors and the intercooler (ICR only) is downstream of the first compressor and upstream of the second compressor. As a result, the compressor inlet temperature and pressure are of importance including the pressure losses. The conditions for the precooler are as follows: With regard to the intercooler, eqs (8), (9) and (10) apply but are differentiated within the code to ensure exclusivity to the respective components. The for ICR, the addition of a second compressor for the intercooled cycle means that the PR for both compressors is determined as:

Modular Helium Reactor
As a heat source with inevitable pressure losses, the prerequisite are the thermal heat input from burning the fuel and the known reactor design pressure losses.
The heat source does not introduce any compositional changes thus mass flow (kg/s) is:

A c c e p t e d M a n u s c r i p t N o t C o p y e d i t e d
Pressure (Pa) taking into account losses (%): and the thermal heat input (Wt) is: whereby A mixer is incorporated within the code to allow for the coolant to be mixed with the heated fluid upstream of the reactor, in order to simulate reactor vessel cooling.

Recuperator
The calculation method for the rate of heat transfer is based on the Number of Transfer Units (NTU) method, which has been documented by [7] and applied for complex cross flow heat exchangers by [8]. The algorithm in the code ensures satisfactory results and numerical stability.
Prerequisite parameters include the recuperator effectiveness, hot and cold inlet conditions (pressure and temperature) and the delta pressures due to losses at high and low pressure sides.
The effectiveness of the recuperator is given as: The maximum amount of heat flux (W/m 2 ) of the recuperator !! !"# must consider the hot and the cold inlet conditions. It must also consider the minimum specific heat because it is the aspect of the fluid with the lowest heat capacity to experience the maximum change in temperature. This is expressed as:

A c c e p t e d M a n u s c r i p t N o t C o p y e d i t e d
and the real heat flux (W/m 2 ) is: With helium as the working fluid, is considered to be constant, thus !! !"# = !! !"#$ = !! !!" in the energy balance equation. The temperatures at the hot and cold ends can be obtained when considering eq (18) (either hot or cold sides) and considering an arbitrary effectiveness. The temperature for the cold end (°C) is then expressed as: With !! !"# = !! !"#$ = !! !!" , the energy balance is: thus, the hot outlet (°C) is:

A c c e p t e d M a n u s c r i p t N o t C o p y e d i t e d
Due to no compositional changes, mass flow rate (kg/s) conditions are:

Cooling Calculations
The prerequisites for calculating the cooling flow, which is required to operate the turbine at the extreme temperatures are the turbine metal temperature (simply known as blade metal temperature), compressor exit coolant temperature, COT/TET (simply known as gas) and cooling effectiveness. The cooling flow is a percentage of the mass flow and is taken from the compressor exit. The cooling effectiveness (<1) is expressed as:

Cycle Calculations
The UW, SW and thermal efficiency output values are of interests after executing each set of station parametric calculations. The UW (We) that is the work available for driving the load is: whereby is the is the compressor(s') work requirement to be delivered by the turbine. The specific work (SW) or capacity of the plant (J/kg K) is: and the thermal efficiency (%) of the cycle is:

Long Term Off-Design Point Calculations
Long term operation indicates the need to operate at optimum reduced power settings due to prioritisation of other generating sources such as renewables over the NPP. When calculating the ODP performance for long term operation the maps become part of the process. Furthermore, they are scaled for capacity purposes to suit the particular plant cycle configuration, thereby avoiding the use of multiple maps. For constant speed steady state ODP performance, the temperature inlet conditions into the compressor is expressed as a referred parameter for standard ISA conditions of temperature for the purpose of determining the reference speed curve. This is corrected into a dimensionless parameter for the purpose of adapting the map for helium and is expressed as: Equation 30 defines the speed as the handle and determines the corresponding polynomial speed curve for the inlet temperature. Once the inlet conditions are defined, the model proceeds to calculate each component station condition.

A c c e p t e d M a n u s c r i p t N o t C o p y e d i t e d
With consideration of a given matching tolerance, the NDMF compatibility is expressed as: whereby Eq. (32) is for the SCR (see Figure 1) and also applicable to the ICR. For the ICR, the sequence in Eq. (32) begins from station 2a (see Figure 2). The complete process of matching and calculating the ODP performance for long term operation is detailed in [9].

Short Term Off-Design Point Calculations
With regard to load-following operations for short term Off-Design (OD) operation, the capabilities for steady state and transient inventory pressure control relies on the model to debit and credit the flow at the subject stations. For transient conditions, the calculations are repeated to represent incremental changes of the mass flow rate (kg/s) to simulate the control method. The process including the control strategies applicable are described in [10], with load following demonstrated in [11].

Method of Modelling of Nuclear Power Plants -Economic Model
A top down approach was adopted to estimate the component costs. The component costs are primarily based on [12] which provides the costing for the helium GT-MHR plant. Other cost methods were derived to estimate the turbomachinery and the heat exchangers using non-dimensional functions that account for mass flows, temperatures and pressures. Scaling factors were also appropriately applied where necessary using the power output. However, the derived costs using the non- Costs (TCC) and the Interest During Construction (IDC) in accordance with [13], [14]. The economic model was used to match the economic assessments of the GTHTR300 NPP detailed in [15], [16] with satisfactory results.

Interest During Construction (IDC)
The IDC (constant dollars) which is applied to the capital loan for the period the plant is being built is determined as follows: whereby is the period number, is the number of periods (quarters or years of construction), ! is cash flow for year or quarter and reflects the 'beginning of the borrowing' period, is the real discount rate expressed annually or quarterly as appropriate and !" is the quarterly or yearly commercial operation.

Total Capital Investment Cost (TCIC)
The TCIC ($) is determined as: whereby BCC is the Baseline Construction Cost derived from estimating the direct and indirect costs using either a top down or bottom up approach, TOCC is the Total Overnight Construction Cost, which includes the cost of the fuel, contingencies e.t.c. and CFC is the Capitalised Financial Cost.

Specific Overnight Cost (SOC)
The SOC ($/kWe) is the cost derived after the TCIC cost is calculated. This is expressed as: whereby the !"!# is the power output at the generator (We).

Levelised Capital Cost (LCC)
As part of the assumptions of equal energy generation as advised by the GIF Economic Modelling Working Group (EMWG) [13], the LCC ($/kWh) is: whereby the is the Fixed Charge Rate and !"!#_!""#!$ is the annual electricity production for a single plant (kWh/year).
The FCR is typically used to account for various entities such as the interim replacements, return on capital, income and property tax and depreciation. For Gen IV NPP projects, the cost estimation tax and depreciation are ignored. This is due to the process being generalised and is not inclusive of tax [13]. For this reason, it is calculated as a capital recovery factor or the principal loan repayment over a time period: whereby represents the real discount rate of 5% or 10%, and !"#$ represents the operational life of the plant. The TCIC plus the cost of the construction loan is converted into a mortgage-type loan, which recuperates the capital investment (principal loan including the interest) over the life of the plant [13].

Levelised Operation and Maintenance (O&M) Cost
The levelised O&M cost ($/kWh) is the overall total annual costs divided by the annual electricity produced. The main assumption here is that the constant dollar costing will be the same for the entire plant life.

Levelised Fuel Cycle Cost
The Levelised Fuel Cycle Cost (LFCC) is expressed as: whereby ! is the reference commissioning date, is the operational life of the plant, ! is the maximum value of lag time (in the back-end), ! is the maximum value of lead time (in the front end) and r is the discount rate. A simplified method of estimating the fuel costs prior to levelising the annual costs is detailed in [13].

Levelised Decontamination and Decommissioning (D&D) Costs
The D&D funds accumulate over the operational life of the plant into the sink fund as expressed below: whereby is the annual constant dollar payment to the D&D sinking fund, is the decommissioning costs, !"#$ , !"#$ is the sinking fund factor at a rate of r for a time period in years of t, which is expressed as: Thus, the D&D can be levelised and expressed as:

Levelised Unit Electricity Cost (LUEC)
The LUEC is calculated after deriving the aforementioned components of the economic model. This is expressed as:

Method of Modelling of Nuclear Power Plants -Risk Model
The risk assessment capabilities within the model focuses on four areas as described in [17]: 1. Risks associated with design impact studies / improvements.

2.
Risks associated with 'lower than design intended' cycle performance.

3.
Risks associated with plant operation.

4.
Risks associated with financing the capital and D&D.
For this study, areas 2-4 are being considered. These are described in the proceeding sub-sections:

Cycle performance
The technical analyses of factors affecting performance are detailed in [2]. The analysis concluded that component efficiencies and pressure losses consequentially affect plant power output. The technical model is used to calculate the conditions; the outputs are subsequently used to assess the effect on the LUEC.

Plant Operation
The risks associated with operating the plant take into account operating in Off-Design (OD) mode, whereby the plant inlet conditions are altered, or part power operation is demanded. The technical analyses are detailed in [9]- [11] for long term OD operation and part power load control and following methods. Plan conditions are altered by changes in inlet temperature or COT. The conditions are calculated in the technical model and the outputs are used to assess the effect on the LUEC.

Financial Risks
These financial risks are concerned with unfavourable discount rates, variation in capital and operational costs and increased D&D due to changes in discount rates. These are considered important because they aid sound financial judgement of the financial risks and their impact impact on the final LUEC. These are calculated using the economic model.
Where changes to plant performance, operation or the financing costs conditions affect the costs, these sensitivities are assessed and combined. The combined summation (average) of the worst-case specific LUEC for each risk in terms of sensitivities and adverse effect on the plant, is added to the 'non-contingency' LUEC of the plant to deduce the final LUEC.

Effect of Component Efficiencies (Cycle Performance Risk)
The results of the derived plant configurations with the highest efficiencies are listed in Table 2. Technically, The lower ranges of compressor and turbine efficiencies have a greater impact on both cycles. For the compressor, the lower component efficiency range reduces the plant cycle efficiency by 1.1% (SCR) and 0.9% (ICR) because more work is required by the compressors to raise the helium to the required pressure. However, the ICR is more sensitive to reduction in turbine efficiencies due to reduced power extraction from the hot gas pressure. This translates into a 1.4% drop in plant cycle

A c c e p t e d M a n u s c r i p t N o t C o p y e d i t e d
efficiency for the ICR and is more than the SCR (1.2%) for the 0.85<η<0.89 component efficiency range. The recuperator has the greatest effect on cycle efficiency for the SCR (1.6% drop) and ICR (1.8% drop) at the 0.85<ε<0.89 recuperator effectiveness range. This is because of the reduced quality of the heat exchange of the turbine exhaust gas back into the cycle to raise the temperature of the helium going into the reactor. The results for the ICR are comparable to the SCR. These results including the results for the SCR, are illustrated and discussed in detail in a previous study by the authors' in [2]. In terms of quantifying the risk, the analyses looked at a reduction of 5% in compressor efficiency, 10% in turbine efficiency and 11% in recuperator effectiveness for both cycles from their DP input values (Table 1). Based on the above reductions from the DP levels in Table 1, the average cost of all 3 components combined is $5.84/MWh for the SCR and $5.36/MWh for the ICR. The recuperator cost effect on the ICR is larger but the SCR has a bigger cost effect due to the turbine.   (see table 1) of the other components of interest. The results trend is similar for the SCR although the SCR does not have an intercooler. The risk analyses looked at pressure losses between the 0.5 -5% range for each component. Based on Figure 4, it can be observed that the effects of pressure losses on cycle efficiency have a negative correlation for every component being investigated. When the focus is on the cycles, the ICR is more sensitive to the recuperator High Pressure (HP) side, reactor and intercooler pressure losses. This is also the case for the SCR but without an intercooler. The effects of pressure losses on the cycle as described in figure 4 including the results for the SCR, are illustrated and discussed further in a previous study by the authors' in [2]. When analysing the risk of operating with pressure losses at the extreme values of 5% per component in comparison to the DP pressure losses (see Table 1

Effect of Long and Short Term Off-Design Operations (Plant Operation Risks)
As described, the circumstances associated with this risk include the effect of precooler outlet/compressor inlet temperature on meeting load demand, the variation of load demand to operate at part power for short term purposes and for long term, a reduction in power capacity due to long term seasonal temperature changes or to prioritise other sources such as renewables on the grid. One thing to note is the operational aspect is a risk that is managed after the plant has been built but it is important to consider it at an early stage. Figure 5 provides the times for short-term IPC operation due to changes in compressor inlet temperature (5°C changes). It demonstrates how quickly each cycle is able to modulate the power. The IPC is used to control the NPP to not exceed reactor thermal power for integrity purposes. Tables 3 and 4 show the effects of variation in compressor inlet temperature on the power output and quantifies the risk for the SCR and ICR respectively. Operating above the DP compressor inlet temperature means a greater compromise of the power output for the SCR in comparison to the ICR when maintaining reactor thermal power. However, when the average LUEC based on a compressor inlet temperature of 0°C to 50°C is analysed, there is a positive benefit for the LUEC, because at lower than DP compressor inlet temperatures, there is an increase in plant capacity. This benefit results in an average LUEC that is 35$ct less per MWh for both cycles. There are greater benefits for the LUEC if the NPP operates at even lower compressor inlet temperatures. The ICR at lower compressor inlet temperatures provides the bigger benefits for the LUEC. The potential gains from operating at lower compressor inlet temperatures are not considered in the final LUEC (post risk assessment). This is to ensure conservatism in the price. Tables 5 and 6 show the effect on the LUEC when the NPP is operated at part power using the IPC method. The power level is reduced by up to 50% of power output. An average LUEC increase of $18/MWh across the power range is observed, with the SCR having a negligibly larger increase. It is possible that the NPP will operate at a reduced power output for short periods using IPC and for long periods when the reactor power will be adjusted to meet prioritisation for renewables.
As such, the final LUEC (post risk assessment) takes into account OD operation based on a plant availability, which is a reduction of 20% per year. Other effects of compressor inlet temperature are covered in [18].

Effects of Financial Risks on the Capital
The risks associated with the capital, operational finance and end of life of the NPP is based on understanding the sensitivities of the individual costs. Table 7 provides a list of the cost areas that are used to assess the cycles. Figure 6 shows a graphical representation of how each cost affects the LUEC. The LUEC in this illustration applies to the SCR.  Reactor Performance Contingency +10% Figure 6 applies to the SCR but the results are also applicable to the ICR. The LUEC in the analyses shown in Figure 6 is for a plant capacity of 92%, with contingency on capital of 25%, contingency of 20% on availability to include OD operations and a reactor performance contingency of 20%. This brings the LUEC to $61.84/MWh (SCR) and $62.13/MWh (ICR).  Table 7 for Bar Chart Legend.
The results indicate that the discount rate, operational non-fuel recurring costs, fuel cycle and reactor performance have the biggest impact on the NPP LUEC. The discount rate assumes the minimum and maximum values that can be applied to an NPP project, whilst the reactor performance has a +10% tolerance due to the combined OD operations and uncertainty in reactor performance for the GFR and VHTR concept designs. However, the operational non-fuel annual costs and the fuel cycle costs are the most sensitive due to the fact that these costs are annually applied over the operational life of the NPP.
With regard to the discount rate and the Decontamination and Decommissioning (D&D) costs, it is worth pointing out that a +2% sensitivity on the D&D cost has a negligible effect on the LUEC. For the SCR, the cost variation of 2% is +$0.26ct/MWh, whereby a reduced D&D cost means a reduced overall LUEC. However, when the discount rate is altered by +2% on the D&D alone, the LUEC is +$1.66/MWh, whereby a reduced discount rate means an increased LUEC. This represents an increase of 640% on the LUEC due to altering the discount rate on the D&D and highlights a key problem in civil NPP projects. The significantly high start up and end costs are unlike other generating sources. The sensitivity of the D&D activity is as a result of the discount rate, which is used to determine the sink fund factor. Thus a lower discount rate that improves the overall LUEC will increase the amount that has to be paid at the end of life to complete the D&D activity. 1" 2" 3" 4" 5" 6" 7" 8" 9" 10" 11" 12" 13" 14" 15" 16" 17" 18"

Conclusion
In summary, the objective of this paper is to conduct technical and economic risk analyses associated with the plant design, performance operation and capital finance and to assess the effect on the 'non-contingency' baseline Levelised Unit Electricity Cost (LUEC). The analyses is performed using a tool specifically design for this study to analyse the Simple Cycle • With regard to the risk of operating with low component efficiencies, the average cost of all 3 components (compressor, turbine and recuperator) are $5.84/MWh for the SCR and $5.36/MWh for the ICR. The recuperator cost effect on the ICR is larger but the SCR has a bigger cost effect due to the turbine.
• When focusing on the risk of operating with very high pressure losses, the average cumulative cost of all the component pressure losses is $4.08/MWh for the SCR compared to $3.05/MWh for the ICR. The reason for the higher cost to the SCR is because the recuperator High Pressure (HP) side results in a greater drop in power output, which affects the LUEC. This is irrespective of the greater cumulative effect on the cycle efficiency of the ICR whereby a drop in the ICR cycle efficiency is greater by 1% in comparison to the SCR.
• There is no negative effect on the LUEC when operating the plants across an inlet temperature range of 0°C to 50°C. At extremely lower temperatures, the effect on the price is positive due to the extra power output generated. When reducing the power output due to grid prioritisation for renewables sources, the effect on the LUEC can add as much as $18/MWh (average) to the final cost of the plant, with this cost increasing if operated regularly at up to 50% reduced power. However, a 20% reduced availability is considered in the final LUEC.
• For the financial risks, the results indicate that the discount rate, operational non-fuel recurring costs, fuel cycle and reactor performance have the biggest impact on the NPP LUEC. For the the Decontamination and Decommissioning (D&D) costs, the sensitivity is as a result of the discount rate, which is used to determine the sink fund factor. Thus a • A key area that needs to be investigated is whether the most efficient plants are the most economical in terms of price.
This is important in order to ensure that the configurations are driven by economics to make the plants more competitive with other generating sources.
• Validation is recommended for the tools such as the one developed for this study. This will enable optimisation to improve the applicability and accuracy and will encourage its use thereby reducing costs associated with extensive test activities and inaccurate analyses and cost estimations.

Acknowledgements
The authors wish to thank the Gas Turbine Engineering Group at Cranfield University for providing the necessary support in progressing this research study and EGB Engineering LTD. UK for funding the overall research.

Conflicts of Interest
The authors declare no conflict of interest.