Helping Small Reactors Survive the Licensing Process
Imagine fission in a bottle. That’s what Ed Wallace of NuScale Power described at the ELECTRIC POWER session on nuclear power Wednesday morning. What NuScale is cooking up is a small (45 MWe), modular, and scalable light-water reactor, contained inside what is essentially a large vacuum bottle resting with several other NuScale reactors in a 4 million gallon pool of water.

"The thermos bottle concept is completely novel," Wallace told the session. Wallace, who is in charge of getting the NuScale machine licensed, described the concepts underlying the licensing of new, unique reactor technologies, the challenges these new technologies present, and the need to get designers, developers, and regulators (the U.S. Nuclear Regulatory Commission staff) speaking the same language and understanding the technology.

Probabilistic risk assessment (PRA), Wallace said, is a key to answering the complex and intertwined licensing issues. The PRA, he said, offers a way to focus analysis, make sure the right questions are asked and answered—illuminating the "unknown unknowns"—and give muscle to the familiar concept of defense-in-depth. "The real value of PRA is in the journey," he said.

Pushing Coal Plants into Retirement
There’s been plenty of nervous buzz lately about the likely impact of recent and proposed environmental regulatory measures on U.S. coal-fired power plants. The capacity projected to be put out to pasture early ranges from about 10 GW to over 70 GW. In a Wednesday morning session on "Aging Infrastructure," Ken Davis (photo), principal consultant at Sargent & Lundy (S&L), said his company puts the estimate of coal retirements in the next five to seven years at close to 44 GW.

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New regulations aren’t the only factor pushing coal to retire. The combination of large shale gas deposits and potentially higher prices for coal (resulting from new regulations on the mining industry) is another. In many cases, Davis noted, it would be cheaper to retire a coal plant and build a new gas plant than to retrofit the existing unit with the necessary technologies to comply with new regulations. The plants most likely to face retirement in the face of these pressures are smaller, lower-capacity units—about 910 units, according to S&L’s calculations.

(For more on the issue of coal plant retirements, see the May feature stories in POWER, available from the home page through the end of this month and in the archives thereafter.)

Designing Water Systems for Thirsty Thermal Solar Plants
The operation and design of thermal solar power plants differs substantially from that of fossil fuel plants. The sun rather than markets determines the maximum possible plant dispatch, explained Daniel Sampson, senior technical consultant for WorleyParsons, at the solar power session on Wednesday morning.

"Ideal plant locations seldom include abundant or readily available water," he said. "Design of the power island is completely different from that of fossil plants, yet designers of thermal solar plant water systems often use the same principles and approaches common in their fossil plant cousins. This renewable technology requires fresh thinking in terms of water systems design."

Unlike fossil plants, solar plant operators can predict plant starts and stops to the minute. Water requirements, especially for the steam cycle, can be predicted with much more certainty than the water requirements of variable-dispatch fossil plants. Predictability may improve, but unique challenges exist:

  • Solar mirrors must be cleaned, so demineralized water usage increases.
  • Permits often require zero- or partial-zero-liquid discharge, but this complicated equipment requires a substantial commitment in capital and manpower.
  • Plant water supplies may be of poor quality, limited availability, difficult accessibility, and high cost.

Water systems design is always a balancing act, and that’s especially true of thermal solar plants. Operating cost and operator involvement are usually lower with simple designs. That’s true of pretreatment, demineralization, and wastewater treatment systems.

Thermal solar water system design requires a new path to achieving the traditional water balance, especially for the smaller flows that might once have been insignificant. In many cases, the tools don’t change, but they’re used differently and for different purposes.

Developers Making Progress with CCS Technologies
Speakers from three companies spearheading carbon capture and storage (CCS) technology development in Wednesday’s oxy-combustion session lauded the relatively new process—which essentially involves firing fossil-fueled power plants with an oxygen-enriched gas mix instead of air—as a cost-competitive near-term solution for carbon dioxide capture. Alstom’s Armand Levasseur said that while his company was making headway with projects testing postcombustion technologies, it was also on track to commercialize oxy-combustion by 2016. Results from Alstom-led oxy-combustion tests at Vattenfall’s 30-MWt pilot plant at Schwarze Pumpe in Germany and another 15-MW pilot in Windsor, Conn., looked promising, showing carbon capture rates of more than 90% with near-zero emissions, he said.

Oxy-combustion was the most attractive option for the DOE’s FutureGen 2.0, because it has the "highest efficiency and lowest levelized cost" of electricity compared with integrated gasification combined cycle and new postcombustion technologies, Babcock & Wilcox’s Dennis McDonald added. B&W’s efforts to repower a 200-MW Ameren coal unit in Meredosia, Ill., and conduct a large-scale test of the company’s oxy-combustion technology with carbon storage would likely be ready to test by 2015, he said.

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