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The Most Economical Generation IV Reactor System: Nuclear Technology Expert's Opinion

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Mark Gino Aliperio's picture
Student Graduate KEPCO International Nuclear Graduate School

Nuclear Power Plant Engineer. In my study at KEPCO International Nuclear Graduate School in which I specialized in Project Management in Nuclear Power Plant (NPP) Construction, my team and I...

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by Mark Gino Aliperio

Generation IV nuclear power plants are deemed to be an important source of baseload power for long-term goals. Currently, there are several designs but few will be deployed in the near future due to strategic, economic, and even political reasons. Such factors pose a challenge in selecting an ideal Generation IV technology to commit time and financial resources to. This study presents a systems approach to decision making for an appropriate Generation IV nuclear power plant program. A methodology commonly used in Systems Engineering projects, the Analytic Hierarchy Process, was applied to evaluate the survey results from expert opinions. As input to the decision analysis methodology, a set of selection criteria was developed and evaluated by nuclear power technology experts. Safety and Reliability emerges as the most important goal area, followed by Waste Management and Economics in terms of priority. This article presents which of the six (6) Generation IV reactors is the most competitive in the goal area of Economics.

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A Review on the six (6) Generation IV Nuclear Systems

  1. Very-High-Temperature Reactor (VHTR)
  • VHTR is a thermal reactor cooled by helium gas and moderated by graphite (solid, can be recycled). The core outlet temperature (COT) of over 900°C and aiming for 1000°C enables the production of hydrogen for other co-generative industrial applications. VHTR is a small modular reactor (SMR) that has potential for high burn-up, complete passive safety, low operation and maintenance (O&M) cost, and modular construction that could partially compensate the loss of economies of scale. Although its basic technology has been established in former high-temperature gas reactors with hundreds of operation hours, the main research needs for VHTR are fuel, materials, and hydrogen production.

2. Molten Salt Reactor (MSR)

  • MSR is the only Gen IV reactor that utilizes liquid fuel (uranium is dissolved in the fluoride salt coolant) which circulates through the graphite core channels (also acts as moderator). This novel feature provides the foundation for an enhanced safety profile based on low pressure operation, eliminating the need for solid fuel fabrication and handling criticalities. Compared with solid-fueled reactors, MSR systems offer far more complete and efficient fuel consumption having lower fissile inventories and large negative reactivity feedback. Such characteristics may enable MSRs to have competitive economics, but needs more research and development (R&D) works in fuel treatment, materials, and reliability.

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3. Super-Critical-Water Cooled Reactor (SCWCR)

  • SCWCR, considered to an evolution of actual boiling water reactor (BWR), is a high-temperature and very high-pressure water-cooled reactor which operated above the thermodynamic critical point of water, giving a higher net electrical efficiency (10% higher than BWR). The super-critical water directly drives the turbine without the need for any secondary steam system (e.g. steam generator, dryer, recirculating system, etc.), thus improving economics because of plant simplification resulting in potential cost reductions of 30% compared with present pressurized-water reactors (PWR). With operational experience and passive safety features similar to those of BWRs, R&D is still needed on materials and thermal-hydraulics.

4. Gas-Cooled Fast Reactor (GFR)

  • Like other helium-cooled reactors, GFR will be a high-temperature and a fast-spectrum reactor that employs similar technology with VHTR, which is suitable for electricity generation and thermochemical hydrogen production for industrial applications. With a high COT of 850°C, it enables an elevated efficiency for helium Brayton cycle. GFR is the only Gen IV design with no operating antecedent and experience, Moreover, the main R&D needs for this reactor system are fuels, thermal-hydraulics, and material as core internals are exposed to high temperatures and elevated irradiation.

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5. Sodium-Cooled Fast Reactor (SFR)

  • SFR is a fast reactor that uses liquid sodium as coolant allowing high power density with low coolant volume operated at low pressure. Having a high specific heat, sodium is a good coolant and is less corrosive than lead, but it chemically reacts with water and air, so a sealed coolant system is required. SFR builds on 390 reactor-years of operational experience and remains the forefront as the main technology of interest in GIF. Three variants are proposed: a 50-150 MWe modular-type; a 300-1500 MWe intermediate-to-large size pool-type; and a 600-1500 MWe large size loop-type reactor. While SFR is the most researched type of fast reactor, R&D is focused on safety in loss-of-coolant scenarios, fuels and its handling, and advanced recycle options.

6. Lead-Cooled Fast Reactor (LFR)

  • LFR is a flexible fast neutron reactor that can be fueled by depleted uranium or thorium matrices. It is cooled by liquid lead or lead-bismuth eutectic (LBE) which has a high boiling point, does not react to water and air, and has an excellent neutron and thermos-fluid-dynamic properties. Compared to LBE, pure lead is more abundant, less expensive, and less corrosive at high temperature. A wide range of unit size envisaged from a battery type producing 20-180 MWe, to modular-types producing 300-400 MWe, and to large size plants of 1400 MWe. COT of 550°C is achievable but 800°C is aimed to enable hydrogen production. The main research needs for LFR are fuels and advanced materials.

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Economics Goal Area

The goal area of economics focuses on the economic competitiveness with efficiency and reactor size are great factors in implementing Gen IV programs. Fuel abundance and availability is included as a criteria (not part of GIF’s metric), and should have a reasonably high weight factor for the reason that Gen IV was initiated in the first place due to a projected shortage of uranium in the upcoming decades. Although one of GIF’s motivations is the co-generation of hydrogen in Gen IV reactors, that criteria is ignored due the reasons that it needs further study on the development of heat exchangers, coolant gas ducts and valves necessary to isolate the nuclear island from the production facilities. It would require additional structures and manpower which are not beneficial in an economic and radiation-exposure safety points-of-view. Moreover, many industries are not prepared to use hydrogen yet. The original GIF criteria of overnight construction cost is also not reflected in this developed metric as this risk to capital is out-of-scope and not attributed to the technological nature of Gen IV reactors but dependent on the construction performance of an implementing country or company.

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The figure above shows the roll up of goals and criteria for this goal area. Under the goal of EC1 Efficiency there are two criteria to be considered, EC1-1 thermal efficiency and EC1-2 burnup. Under the goal of EC2 Size there is one criteria to be considered, EC2-1 unit size. Under the goal of EC3 Life Cycle Cost there are five criteria to be considered, EC3-1 fuel cost, EC3-2 fuel abundance and availability, EC3-3 construction cost, EC3-4 operation and maintenance costs, and EC3-5 modular construction.

Technology Experts' Opinion

To quantify the metric of the selection process, opinions of nuclear power technology experts were obtained through a survey. The goals were compared in pairs. Each pairing was evaluated by the respondents based on importance in a 1 to 5 scale, where 1 implies equal importance for both, otherwise, one is more important than the other. goals. The figure below shows the sample survey form as well as the affiliations of experts who participated and demonstrates a wide range of companies and institutions involved in the different sectors of nuclear power technology such as research, academics, plant design and engineering, operation, utility, maintenance, and fuel design and fabrication.

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Analytical Hierarchy Process and Decision Analysis

To determine the importance factor to be used in decision-making process, the answers from the survey for each pairing are analyzed. The values of judgement of 1 to 5 scale of the survey is transmuted to a 1 to 9 scale for decision analysis. The interpretation of such values for a pair a comparing criteria j and k, are described in the figure below. The Analytical Hierarchy Process (AHP) is employed in this project for decision analysis and is implemented through Super Decisions, a decision support software.

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Evaluation of Economics Goal Area

For Economics goal area, Life Cycle Cost is found to be the most important goal. It includes the criteria of fuel cost, fuel abundance and availability, construction cost, operation and maintenance (O&M), and modular construction. In addition, Life Cycle Cost goal area also contains size and efficiency goals.

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Literature review suggest that in terms of economics compared to the conventional LWRs, VHTR, SCWR, and MSR has higher economics. This provides an early estimation on the economic competitiveness based on cost differences between the current and the next generation of reactors. Moreover, LFR has economics similar to LWR while SFR is lower than LWR. On the other hand, no relevant data was found for GFR.

In addition, Efficiency goal has a strong correlation with economics as for a given power output, the scale of components is directly influenced by the efficiency of a certain reactor type. Also, plant unit size affects construction cost and thus the over-all economics of the project. VHTR, GFR, and MSR are found to be the most competitive in terms of efficiency having a net electrical efficiency ranging from 44% to 50% while SFR has the least. These factors are also correlates with Operational Safety & Reliability (SR1) goal as higher core outlet temperature yields higher thermodynamic efficiency. Although SCWR has a net electrical efficiency of 44%, it has a potential of improved economics because of plant simplification, as supercritical water directly drives the turbines eliminating the need for any secondary steam system, resulting to an estimated potential cost reduction of 30% compared with present PWRs.

Regardless of being the least important goal having a corresponding score of 0.024 (EC2 Size), SCWR and SFR has the largest power output reaching 1500 MWe. However, small- and medium-sized plant designs could compensate the loss of economies with reduced construction due to size and scale of components. Furthermore, type of fuel as a criterion in Economics goal area, focuses on the abundance. GenIV system is developed initially as a shortage of Uranium is expected in the upcoming decades according to several energy foresight studies. Reactor types that are flexible in the choice of fuel such as VHTR, LFR, SFR, and GFR has more advantage as it can utilize non-uranium fuels. However, although GFR, SFR, and LFR, can be fueled with it, Plutonium is less abundant than Uranium. Thus, VHTR and LFR are the competitive reactors in this criteria as they can also be fueled with Thorium. IAEA Technical Document No. 1450 reported that Thorium is 3 or 4 times more abundant than Uranium. It is also widely distributed in nature as an easily exploitable resource in many countries so thorium fuels and fuel cycles are particularly relevant to countries having large thorium deposits but very limited uranium reserves to achieve long term nuclear power goals. In general, based on Economics Goal Area, VHTR should be pursued. The VHTR also has the highest net electrical efficiency and is flexible in choice of fuel. VHTR also has the potential for high burn-up (150-200 GWd/t), low O&M costs, and modular construction.

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Economics Goal Area, having the least relative score, focuses on the economic competitiveness of the Gen IV reactor systems. It appears that VHTR. SCWR, and MSR has better economics compared to today’s conventional LWR’s. In terms of efficiency, VHTR, GFR, and MSR are the most competitive having a net electrical efficiency ranging from 44% to 50%. Moreover, VHTR, LFR, SFR, and GFR are more advantageous as it is flexible in terms of fuel type as it can utilize non-uranium fuels. Based on this goal area, VHTR provides the highest competitiveness regardless of being as the only SMR in the Gen IV reactors.

In general, the results of this project are partially conclusive as it based on experts’ opinion as well as literature review. It is important to note that there are still a number of factors and criteria that may affect the entire selection and evaluation procedure. For example, political factors are not reflected in this project but it can significantly influence future judgement, and may overshadow other critical criteria. Nonetheless, the outcomes of this project can be used as reference for decision making. However, the level of priorities or importance is flexible depending on an implementing agency or a country’s specific need for future generation of nuclear systems.

This article is a part of a work published in the Journal of the Korea Management Engineers Society, Vol. 24, No. 2, 2019. This work was supported by the 2019 Research Fund of the KEPCO International Graduate School, Republic of Korea.

Mark Gino Aliperio's picture
Thank Mark Gino for the Post!
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Matt Chester's picture
Matt Chester on Feb 12, 2021

Really compelling-- thanks for sharing! When getting the opinions of the experts, was there anything that jumped out to you as surprising? 

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