Review of the Deployment of and Research into Generation III & IV Nuclear Fission Reactors for Power Generation

Nuclear fission is one of the more popular and efficient sources of energy that has been used in the last few decades. In the setting of the ongoing worldwide debate of the energy problem, this paper will review the different types and generations of nuclear reactors, and do comparisons with other notable energy sources (biofuel and fusion). The current generations III, III+, IV of reactor (mostly pressurized water reactors), their thermal efficiency, technical (structure and configuration), lifetime, energy output and how the systems contrast are discussed. The paper was written by gathering information from UTS library online database, as well as online articles related to fission power, all sources dating from 2000s onwards. Nuclear fission power is a very dense energy source as it provides PAM Review Energy Science and Technology 68412 www.uts.edu.au


Introduction
Nuclear Fission for commercial power generation has been in operation since 1957 5 .Over this time many different reactor designs have been researched and implemented.Today most commercial nuclear power plants are Light Water Reactors of the Boiling Water Reactor or Pressurized Water Reactor Design.Other common reactor types currently used are Heavy Water Reactors and Gas Cooled Reactors.
Many of the reactors that are currently in operation were commissioned decades ago and are reaching the end of their operating lives.The need for new reactors as well as safety concerns over older designs brought on by the 2011 Fukushima Daiichi Nuclear Disaster has fostered renewed research and development into new reactor designs.This research has not just been into upgrading and improving existing designs of Light Water Reactors it is also looking at some technologies that have lain relatively dormant since mid-last century as well as completely new reactor designs.This report will look at the current state of research into and implementation of Generation III+ nuclear fission reactors as well as the emerging research being done into Generation IV reactor technologies.It will review existing research literature dealing with these reactor designs and their thermodynamic properties, and evaluate whether the thermal efficiency delivered or promised is competitive with existing designs of nuclear fission reactors as well as other systems of electricity generation.

Methods
A wide net was cast to obtain information into both the background and fundamental principles of nuclear fission for power generation.This information was checked against multiple sources to ensure that it was accurate.
When selecting papers and articles providing information about current research into, and development of modern fission reactors a more selective approach was used.Articles had to be discussing a current or planned generation III, III+, or IV reactor design, unless the source was being used to obtain a comparative statistic for an older generation reactor.Articles dealing with the thermodynamic properties of reactor designs were used, whereas articles that only dealt with other properties (i.e.safety or cost) were generally not used, unless these properties stemmed from thermodynamic properties.

Results and Discussion
Thermal Efficiency is an important property of any commercial power production system.It is defined as the ratio of the work we get out of the system and the energy we put into the system.

𝜂 ≡ 𝑊 𝑜𝑜𝑜 𝑄 𝑖𝑖
There are two main ways of increasing the thermal efficiency of fission reactors that are being focused on in the development of modern reactors.One is increasing the percentage of fissile fuel that is burnt by reactor before being removed and the other is decreasing the energy lost in steam generators when heat is transferred from the primary coolant loop to the secondary.

Percentage of Fuel Burnt
All generations of Light Water Reactors that use Solid Fuels have the problem that the solid fuel assemblies are, over time, damaged by the heat and radiation products produced by the nuclear reaction.Radioactive impurities that hinder the ongoing reaction build up inside the fuel rods.These solid fuel assemblies have to be regularly rotated within the core, and are eventually taken out of the core when only 3-5% of the available energy has been burnt (Hargraves, et al).This early removal of the fuel rods also means that dangerously radioactive trans-uranic elements are present in the spent fuel.These problems are not present in liquid fueled reactors such as liquid Fluorine Thorium reactors, as the fissile fuel in a solution of molten salt is not easily damaged by heat and radiation.This means the fuel can stay in the reactor much longer allowing almost all of the fissile fuel (including the trans-uranic byproducts) to be burnt.As the fuel is a liquid solution it remains homogenous throughout the core, it can be easily pumped through a processing loop in order to remove impurities without having to shut down the reactor.

Generations of fission reactor
Among many ways to classify nuclear reactors, classification by generations is one of the most common and will be used in this paper in order to analyze different types of reactors.Table 2 below summaries the features of generations of reactors for the last over half decade.Table 2. Generations of nuclear power (Generation IV International Forum)

Generation III reactors
Generation III reactors, developed in the nineties, are replacing generation II reactors, which were built in the seventies and eighties (generation I reactors were early prototypes, built in the 50's and 60's).They have better economics, use natural resources more efficiently, produce less radioactive waste, have increased resistance to proliferation and have greater passive safety features, compared to previous generation reactors (Marques J.G.).Also generation III reactors' standardized designs mean licensing and inspection process is easier and more reliable (NRC's Section 3, Nuclear Reactors 2011-2012 Information Digest, pp 35-38).This section will discuss two leading generation III systems of reactors, their properties and features.

ACPR1000 Reactors
Advanced CPR -ACPR1000 reactor is the improved version of generation II+ reactor CPR -1000 to generation III.They are both pressurized water reactors (PWR) that originate from China and use design based on the 900 MWe-class French M310 three-loop technology (Nuclear Power in China).Figure 1 below shows the design of a PWR.The ACPR1000 has 14inch fuel reactor core, digitalized instrument control system, three safety systems, large and double layer containment, in-built refueling water tank, safety shutdown earthquake (Dynabond).All in all the reactor meets all the technical and economical measures required by generation III standards, China's latest safety regulation, American standard URD as well as European standard EUR (Dynabond).The construction cost of ACPR1000 reactor power plant is expected to be $2500/kw (Nuclear Power in China).
ACPR1000+ is the improved version of ACPR1000 that takes into account Fukushima nuclear disaster and fulfil post-Fukushima as well as international safety requirements (China General Nuclear Power Group).Some of the main technical features of the reactor include (China General Nuclear Power Group).ACPR1000+ is predicted to be exported from 2014 (Nuclear Power in China): -Reactor: 157 fuel assemblies, in-core instrumentation is inserted from the top, metal reflector that extends the RPV design lifetime to 60 years.
-Nuclear Steam Supply System: large capacity pressure relief valve implemented to quick relief coolant in sever conditions, LBB technology is adopted to simplify design.
-Double Containments: outer containment can withstand large impact, the double containment reduces radioactive release during accident compared to CPR1000.Advanced Boiling Water Reactor (ABWR) is the first generation III boiling water reactor to enter the market in 1996 (Marques, J.G.).Older boiling water reactor designs have their external pumps replaced by ABWR's internal recirculation pumps inside of the reactor pressure vessel (Marques, J.G.).The system, with power output is around 3926 Mega Watt Thermal, also include control rod drives that can be controlled by a screw mechanism, microprocessor-based digital control and logic systems, as well as digital safety systems.Other features compared to older generations of boiling water reactors are protection against over pressurizing the containment, passive core debris flooding capability, independent water makeup system, three emergency diesels and combustion turbine as alternative power source.Seven ABWR units are in operation or under construction in Taiwan and Japan, with two more planned to start operation in 2016-2017 in the US (Marques, J.G.). Figure 2 below shows the design of a boiling water reactor.

The reactor technical features (General Electric Company):
-Output power 1350 to 1460 MW net -Emission: Nearly zero C02 greenhouse gas emissions -Lifetime: 60 years -Core Damage Frequency: 1E-7 -Availability and Capacitor Factor: >90% Overall, the reactor provides an economical, dependable energy solution.It is a great power source when environmental and safety concerns are a high priority.

Generation III+ reactors
Generation III+ reactors designs are evolutionary development of generation III reactors, providing improvements in safety.The development started in the 1990s by building on the experience of light water reactor fleets of the time (amacad.org).The most significant improvement over previous designs is believed to be the inclusion of passive safety features (amacad.org).Generation III+ reactors are expected to get higher fuel burn up than their predecessors (hence reducing fuel consumption and waste consumption.More than two dozen generation III+ reactors are planned for the US (amacad.org).This section will continue with two examples of generation III+ reactor.Table 4 shows a comparison for several generation III and III+ reactors.

Advanced CANDU Reactor (ACR-1000)
The Advanced CANDU Reactor (ACR) is a generation III+ heavy water reactor that has a 1200 MWe output.The reactor uses light water reactor coolant and higher burn up lowenriched-uranium fuel, while keeping operating CANDU 6 plant design's heavy water moderator and on-load refueling (candu.com).The Preliminary Safety Analysis Report demonstrates that ACR-1000 is safe, in compliance with international regulatory requirements and expectations.
To attain better operational savings than previous CANDUs, the ACR uses slightly enriched uranium fuel (0.9% 235 U) instead of natural uranium (Marques J.G.).The coolant of ACR is light water, while heavy water is used as moderator (Marques J.G.).The expected lifetime is 60 years and the planned lifetime capacitor factor is greater than 90%.The first ACR-1000 is planned to be operational by 2016 (Marques J.G.).

Technical features other than included above (iaea.org):
-Reactor thermal output: 3200 MW thermal -Power plant efficiency, net: 36.5% -Two fueling machines -Safety measures including two shutdown systems, emergency core cooling, emergency heat removal system, and containment system.-Steam flow rate at nominal conditions: 1728 kg/s

Table 4. Comparisons between generation III and III+ reactors:
Overall compared to previous generation reactors, ACR has improved burn up, better safety margins, increased turbine cycle efficiency (thanks to higher pressure and temp in coolant and steam supply systems), improved performance thanks to new information systems.

AP1000 reactor
The AP1000 reactor is a generation III+ reactor developed by Westinghouse (USA).It is an advanced passive PWR that is a scaled up version of AP600, with expected output of 1000 MWe (Marques J.G.).The system's passive protection means that emergency diesel generators are not needed in case of electricity loss, making the reactor more environmentally friendly.The reactor safety is further enhanced by the fact that in the case of core melt, flooding by operator prevents core debris from spilling into containment (Marques J.G.).Thanks to the lower amount of pipes, valves and associated components, AP1000 is cheaper than other PWRs.Two AP1000 reactors started operation in China in 2011 (Marques J.G.).The AP1000 coolant system includes two heat transfer circuits, with each having a steam generator, two coolant pumps, one hot leg and tow cold legs for transferring coolant between reactor and steam generators (T.L.Schulz).Other than reactor coolant pump, all major components of AP1000 have been verified under similar flow, temperature and pressure conditions (T.L.Schulz).AP1000 technical features improved compared to AP600:  From figure 4, it can be seen that from the use of more advanced technology, AP1000 gained many simplifications, bringing in many benefits over other current PWRs, such as less redundancy, operational cost and improved safety system.Overall, AP1000 design is much simpler, mature, proven to have benefits in construction and operation.

Generation IV reactor
Generation IV reactors are systems expected to reach maturity 2030 (Frank Carre and Gian Luigi Fiorini), in other words they are in development and expected to be the future of nuclear energy.The designs take into consideration economic and safety progress, aim to support sustainable energy worldwide, and to open up the range of applications other than electricity production (Frank Carre and Gian Luigi Fiorini).
The general aims of generation IV reactors based on international agreement comprise of: -Sustainability -Economic viability -Safety and reliability -Resistance to proliferation risks and invulnerability from external attacks.
The range of applications can include hydrogen production, desalination of sea water, coal to diesel production, fertilizer production, and many more.The Generation IV International Forum (GIF) outlined six reactor concepts for future generation IV reactor development, shown in Table 4. Overall, there are many perceived changes between generation IV and previous generations in parameters such as coolant medium, temperature, and fuel used as well as applications.From these changes generation IV reactors are expected to operate better than previous generations in many factors.
Generation IV reactors are however, not without problems.Two most significant problems are the fuel composition' impact on safety of reactor and the required materials for reactors (Marques J.G.). Figure 3 demonstrates that materials used presently are not suitable for GIF reactors.With higher operating temperatures and higher radiation (as shown by table 3, 4,5 and 6), GIF reactors are more demanding on coolant.In order to overcome the displacement damage, materials such as water in supercritical state, liquid metals, molten salts, high pressure helium gas (Marques J.G.).These materials can cause high corrosion, hence materials technology (possibly even nanomaterial) should be applied in order to maintain protective surface layers.

Other power generating systems
In 2012, nuclear power provided only about 5.7% of world's energy and 13% of world's electricity in 2012 (International Energy Agency).In the grand scheme of things, it is important to compare and contrast with other power sources in the discussion of nuclear power, to really know how efficient and viable nuclear power really is.

Biofuels
Biofuels are energy derived from biomass, bio materials made of living and recently living organisms.Biofuels are classified as primary and secondary, primary biofuels being used for heating, cooking or infrequently electricity production.Primary biofuel is in fact inefficient and toxic to the environment (Biomass to biofuel).Secondary biofuels are produced from the processing of biomass that can be used for many applications.Secondary biofuel is further categorized into first, second and third generations (Biomass to biofuel).Table 7 indicates the varying efficiency through different biomass utilization ways.From the processing to the fuel used, biofuel attracts attention as a cleaner power sources.It provides a way to produce transportation fuel from renewable sources hence reducing net CO2, as CO2 from combustion of fuel is recaptured by the growth of feedstock (c2es.org).

Fusion power
Fusion power is generated from nuclear fusion processes, in which, two light atomic nuclei fuse to form a heavier nucleus, by the heating of nuclei plasma so they move at high speed and collide.The force which stick the two positive particles together is the Strong Force, which holds protons and neutrons together.From here the mass-energy equivalence equation comes in, dictating the energy released from the releasing of the smaller leftover particles (efda.org).
From the process of fusion it can be seen that it has many advantages: -No carbon emissions, as the only by products are small amount of helium.
-Large amount of fuels.Deuterium can be extracted from water and tritium from lithium (abundant in Earth's crust) -Energy efficiency: 10 million more efficient than fossil fuel (ccfe.ac.uk)Once the technology can commercialize fusion, its efficiency means lower costs.The problems with fusion includes (Magaud, P., G. Marbach, and I. Cook): -Materials for withstanding the high energy release of fusion products -The reaction chamber's walls and the blankets themselves will become radioactive due to the neutrons depositing energy -Methods needed to contain radioactive dust and radioactivity induced by neutrons

Table 7 .
Characteristics and Operating Parameters of the Eight Generation IV Reactor Systems under Development (amacad.org).

Figure 5 .
Figure 5. Operating temperatures and expected displacement damage (in displacement per atom, dpa) of Generation IV designs compared with previous generations.(Marques J.G.)

Table 3 .
Generation III reactors under construction or undergoing a licensing procedure.

table 4 ,
it can be highlighted: that most designs use closed fuel cycles; half of the designs are fast reactors, and four designs are high temperature type.The high temperature designs can be used to produce hydrogen, synthetic fuels, or have application in transport (Generation IV International Forum).More technical features of generation IV systems are provided by table 5.

Table 8 .
Biomass to fuel efficiency through different biomass utilization pathways (Wei-Dong Huang and Y-H Percival Zhang)