Riffing on the great American philosopher Lawrence “Yogi” Berra, it’s déjà vu all over again, but backwards.
Holtec International, perhaps the most ambitious nuclear-oriented company ever, says it can use its aspirational small nuclear reactor, SMR-160, to repurpose coal-fired power plants. The Holtec SMR design is for a 160-MW pressurized light-water reactor, still in the design approval process in the US.
There is a fundamental disconnect between nuclear plants and coal-fired plants, although both are steam-electric generators. It turns out that nukes produce a much lower-grade steam than coal-fired units. The Holtec SMR would produce steam at 450⁰F and 700 pounds per square inch, while coal plants produce steam at 1000⁰F and 3500 psi.
In a news release Jan. 10, Holtec said, “The technical breakthrough that we announce today seeks to minimize the impact of this looming wholesale loss of existing coal plants by preserving most of their physical assets and replacing their boilers with Holtec’s SMR-160 nuclear steam supply system. The concept underpinning this approach is the use of multi-stage compressors which are capable of uprating SMR-160’s relatively low enthalpy steam (700 psi @ 595 Deg F) to the elevated pressure and superheat needed to run the turbogenerator of a fossil power plant.”
Holtec says it has filed a “provisional patent application” for its compression enthalpy enhancer, without providing any details. Presumably, the technology will employ the standard Gay-Lussac’s pressure temperature law: “The pressure (P) of a fixed mass of gas held at a constant volume is directionally proportional to its Kelvin temperature (T). Therefore, as the pressure of a particular system goes up, the temperature of that system also goes up, and vice versa.” The amount of power needed for compression and its source is unstated.
The company adds, “The ability for SMR-160 to deliver steam at any desired pressure also opens new vistas to use clean energy, such as for high-pressure steam as feed stock for industrial applications or providing low pressure steam for district heating to cities and municipalities wishing to eliminate their current use of methane and CO2-producing fossil fuels, whether to meet clean energy goals or to protect against a forced scarcity of fossil fuels due to geo-political tensions.”
There appear to be no previous cases of coal-to-nuclear conversions, although there are two known examples going to other way, one in 1991 and the other in 1968. The best-known conversion was the Zimmer plant in Moscow, Ohio. Announced in 1969 by three Buckeye State investor-owned utilities, managed by Cincinnati Gas & Electric (which was eventually absorbed into Duke Energy), the plant was to consist of two 840-MW GE boiling water reactors, at an estimated cost of $420 million. The plant was named for William Zimmer, who was CG&E’s CEO at the time of the announcement.
Construction at Zimmer didn’t begin until 1972 and, in 1974, the utility upgraded the second unit to 1170 MW. The utility chose Kaiser Engineering, which had never built a nuclear plant, as the constructor and CG&E did its own contracting for equipment, procurement, and quality assurance. Th project was in serious troubled by 1978. In 1981, the Nuclear Regulatory Commission fined the project $200,000. A year later, NRC ordered construction to stop and the FBI launched an investigation into falsified documents and intimidation of inspectors. The three owners mothballed the project in 1983, after assuring regulators and investors for years that the plant was 97% complete, despite the NRC’s refusal to accept its claims. At its work suspension, the nuclear project had sunk costs of $1.6 billion. CG&E’s share of $716 million was 90% of the company’s net worth. The owners then hired Bechtel to estimate https://en.wikipedia.org/wiki/William_H._Zimmer_Power_Stationagwhat it would cost to resurrect the project and win NRC approval. Bechtel’s estimate was $1.5 billion.
The three utilities decided in 1984 to convert the plant to coal and reconstruction began in 1987. There were advantages to that action: a large site with lots of infrastructure in place, including various useful buildings, switchgear, and the like. But there was a major problem: The plant’s steam turbine generator was designed to handle the low-quality nuclear steam. The project required a new and expensive steam turbine generator.
The unique nuke-to-coal conversion went into service in 1991, at a final cost of $3.1 billion. They plant operated well, passed through several owners, and was closed last year, after failing to qualify for payments in the PJM Interconnection’s May 2021 capacity auctions. The announcement came from its owner, Vistra.
The other, earlier nuclear-to-coal conversion is obscure. In the early days of nuclear power, the old Atomic Energy Commission held three rounds of public-private support for early atomic power plants between 1955 and 1964, called the Power Reactor Demonstration Program, jointly funded by the AEC and private developers. Among the third round of projects was the Pathfinder reactor in Sioux Falls, S.D., sponsored by Northern States Power, featuring a boiling water reactor with a steam superheater, to be designed and built by Allis-Chalmers Manufacturing, best known for making high-quality farm tractors.
Pathfinder got an AEC construction permit in 1960. Construction ended in 1966. The only time the plant was brought up to full power, in 1967, it ran for only 30 minutes, when the reactor operators quickly shut it down as an imminent safety risk. It was eventually converted to run on fossil fuels, including coal, oil, and natural gas, where it ran as a peaking unit until 2000. In 1990, the reactor vessel was removed and transported to a low-level nuclear waste dump in Washington state.
In 1987, when researching the Zimmer conversion story, I contacted my former Pittsburgh neighbor Warren Witzig, a nuclear pioneer, who was then dean of the prestigious Penn State nuclear engineering program. I asked him if he knew of any other cases of a nuclear plant being converted to coal. He pondered for a bit and then came up with Pathfinder.
–Kennedy Maize
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