As the second-largest nuclear generator in North America, Entergy has a vetted interest in high-temperature gas reactor (HTGR) technology. The US utility firm has recently completed an economic analysis of the concept and its results have been so surprising that the company has since changed the direction of its plans.
Entergy's stake in nuclear reactors for power generation dates back to a strategic decision in 1997, which has since enabled the company to operate facilities that power more than ten million homes in the US states of Arkansas, Louisiana, Massachusetts, Michigan, Mississippi, Nebraska, New York and Vermont.
In the near term, the company is focusing on advanced light water reactors, and was instrumental in forming an industry alliance, NuStart Energy Development, to support its development. In the longer term, however, Entergy's attention will be on high-temperature gas reactors with much broader applications beyond electricity.
To support this move, Entergy has become part of an alliance of industry partners working with the US Department of Energy on HTGR, as part of the next-generation nuclear plant (NGNP) project. Members of the alliance include refiners and reactor manufacturers Westinghouse, Pebble Bed Modular Reactor (Pty), General Atomics and Areva.
Dan Keuter, Entergy Nuclear vice-president of planning and innovation, says he believes the alliance is growing evidence that HTGR technology on the reactor side is becoming fairly well known.
"If we were only interested in electricity, we wouldn't be pursuing HTGR," he says. "Hydrogen production is of interest, in particular, because hydrogen has lots of potential to be used in fuel cells that are the power supply in transportation and other applications."
There are three main processes under investigation for producing hydrogen (H2) using nuclear energy. These processes include thermochemical water-splitting processes: sulphur-iodine, hybrid sulphur and high-temperature electrolysis. All three processes need heat in excess of 750°C to be economical.
One of the main issues of concern for a facility that produces hydrogen, from a licensing and regulatory standpoint, is the proximity of such production to nuclear power plants and the risk of explosion.
"Entergy's Waterford 3 plant in south Louisiana is surrounded by petroleum plants," says Keuter. "The experience at Waterford 3 has successfully demonstrated that nuclear power plants co-located such industrial facilities can be safely operated."
The profitability of the H2 production depends on the demand price of the energy commodity used in production. Profits are maximised when supply costs are low and demand prices are high. Entergy participated in a study to compare estimated costs of production of electricity, H2 and process heat using an HTGR with natural gas.
This study, which was conducted by the Idaho National Laboratory, indicates that H2 production using an HTGR can become competitive with steam methane reforming (SMR), the primary or most prevalent process used for H2 production worldwide, when natural gas costs approach $8 per million Btu (MMBtu). The price of H2 produced by SMR is directly related to the price of natural gas, which over the recent years has been volatile and often exceeded $8/MMBtu.
The study compared the cost of high temperature steam production and the results were so significant, according to Keuter, that it has forced Entergy to shift its development emphasis.
"Originally, when we were looking at HTGRs we focused on electricity and hydrogen production," says Keuter. "After the analysis, we have seen that process heat is even more economical. Using an HTGR in the supply of process heat to industrial processes is similar to its application in hydrogen production and we hope to demonstrate this capability in the NGNP project. One of the things we are looking at with process heat is, depending on demand, switching from process heat production to electricity production and eventually, H2 production. I think what might happen is that we look to develop a reactor with an intermediate heat exchanger that has the ability to produce any of the three – process heat, H2, electricity – and leverage the three of them to economic advantage."
Therefore, an HTGR could heat steam and also produce electricity for high-temperature electrolysis.
For example, Entergy's NGNP partner Dow Chemical is talking about having four HTGR units in one of its plants, which primary usage would be to process heat, but as a backup, it also wants to ensure they produce electricity.
Dow has joined up with Entergy to encourage the Department of Energy and US Congress to continue to develop the very high temperature reactor design that is part of the Next Generation Nuclear Plant initiative. The NGNP programme is scheduled to build and licence a reactor design by 2021, according to the Energy Policy Act of 2005.
"The next step of the alliance is mainly to show industry interest in developing and deploying this technology," Keuter says. "Studies need to show that the technology will be commercially viable in a variety of industrial applications. To support a project as far as licensing, the NRC is hesitant to move unless there is a potential customer. Entergy has said it would consider being a surrogate owner/operator in an alliance project."
This article originally appeared on our sister publication Nuclear Engineering International