Patrick McDaniel

Nuclear Systems for a Low Carbon Electrical Grid

The intermittency of renewable power generation systems on the low carbon electric grid can be alleviated by using nuclear systems as quasi-storage systems. Nuclear Air-Brayton Combined Cycle systems can produce and store hydrogen when electric generation is abundant and then burn the hydrogen by Co-Firing when generation is limited. The rated output of a nuclear plant can be augmented by several hundred per cent by Co-Firing. The incremental hydrogen to electricity efficiency can far exceed that of hydrogen in a stand-alone gas turbine.Copyright

Modeling the Nuclear Air-Brayton Recuperated Cycle

The Nuclear Air-Brayton Recuperated Cycle (NARC) has some unique advantages. Its biggest advantage is that the simple recuperated cycle is not tied to a water source. The NARC power plant is not tied to a seacoast or river valley. Currently the largest power station in the United States, Palo Verde is restrained from expanding, not for any safety reason, but for lack of additional freshwater to dump its waste heat. In the recuperated cycle, a heat exchanger is placed in the exhaust from the last turbine, and instead of transferring heat to water as a working fluid, it transfers its heat to the air exiting the compressor to preheat it before it enters the first sodium-, or molten salt-, to-air heat exchanger. It is possible to split the compressor and add an intercooler to improve the efficiency of the recuperated cycle. This allows more heat to be extracted from the exhaust stream with the recuperator. However, only if the intercooler uses water to cool the air from the first compressor is the efficiency of the cycle improved. The amount of water required is significantly less than in a traditional waste heat removal system. Both of these systems will be analyzed as well as adding a recuperator to the NACC system after the Heat Recovery Steam Generator. As in the previous chapter, a near-term option based on a 510 °C turbine inlet temperature will be considered, as well as an advanced system with a 660 °C turbine inlet temperature.

Modeling the Nuclear Air-Brayton Combined Cycle

Given that the combined cycle (CC) code does a good job of modeling current-generation gas turbine combined cycle (GTCC) plants, it is useful to extrapolate its capabilities to Nuclear Air-Brayton Combined Cycle (NACC) power plants and Nuclear Air-Brayton Recuperated Cycle (NARC) power plants. The combined cycle plants will be dealt with in this chapter and the recuperated plants in the next chapter. In the Nuclear Air-Brayton power plants, the combustion chamber of the gas turbine system is replaced by the nuclear reactor and a heat exchanger. The nuclear reactor will heat a working fluid, and that working fluid will in turn pass through a heat exchanger to heat the air for the turbine. Because the heat transfers process for a nuclear system is in the opposite direction (solid to gas) from that in the gas turbine (gas to solid), the peak temperatures achievable in a Nuclear Air Brayton system will never be as high as those in a gas turbine system. However, the nuclear system can reheat the air multiple times and expand it across multiple turbines to increase the available power.

Vapor Power Cycles

Vapor (or Rankine) power cycles are by far the most common basis for the generation of electricity in large fixed plant operations. They were one of the first developed for steam engines and have been adapted to many applications. They have also been modified in a number of ways to improve their thermal efficiency and better utilize combustible fuels.

Gas Kinetic Theory of Entropy

This chapter will attempt to provide a physical understanding of the concept of entropy based on the kinetic theory of gases. Entropy in classical thermodynamics is a mathematical concept that is derived from a closed cycle on a reversible Carnot heat engine. For many students it lacks physical meaning. Most students have a physical understanding of variables like volume, temperature, and pressure. Internal energy and enthalpy are easy to understand, if not intuitive. However, entropy is a bit more difficult. The discussion that follows is an attempt to provide physical insight into the concept of entropy at the introductory level. Prof. Leonard K. Nash, Dover Edition, 2006, bases this discussion on the excellent text, Elements of Statistical Thermodynamics [1–4].

Work and Heat

This chapter deals with two quantities that affect the thermal energy stored in a system. Work and heat represent the transfer of energy to or from a system, but they are not in any way stored in the system. They represent energy in transition and must carefully be defined to quantify their effect on the thermal energy stored in a system. Once they are quantified, they can be related to the conservation of energy principle known as the first law of thermodynamics.

Second Law of Thermodynamics

The second law stipulates that the total entropy of a system plus its environment cannot decrease; it can remain constant for a reversible process but must always increase for an irreversible process.

Safety, Waste Disposal, Containment, and Accidents

The public acceptance of nuclear energy is still greatly dependent on the risk of radiological consequences in case of severe accidents. Such consequences were recently emphasized with the Fukushima Daiichi accident in 2011. The nation’s nuclear power plants are among the safest and most secure industrial facilities in the United States. Multiple layers of physical security, together with high levels of operational performance, protect plant workers, the public, and the environment.

First Law of Thermodynamics

The first law of thermodynamics states that the total energy of a system remains constant, even if it is converted from one form to another.

Circulating Water Systems

Nuclear power plants are usually built next to lakes, rivers, and oceans. Not for the scenic views that such locales provide, but because water can absorb the waste heat produced by the plants. Nuclear power plants consume vast amounts of water during normal operation to absorb the waste heat left over after making electricity and to cool the equipment and buildings used in generating that electricity. In event of an accident, nuclear power plants need water to remove the decay heat produced by the reactor core and to cool the equipment and buildings used to provide the core’s heat removal. This chapter describes the reliance of nuclear power plants on nearby bodies of water during normal operation and under accident conditions.