Energy From Thorium Discussion Forum

DOE Scales Back High-Temp Next-Gen Nuclear Amid Major Concerns
Energy Washington Week, Vol. 5, No. 37, 10 September 2008
The Energy Department -- responding to significant concerns -- has scaled back the extremely high temperatures at which it had proposed to develop the "next generation nuclear plant" (NGNP) but is moving forward in the expectation that the "new concept for nuclear utilization" still will produce a wide variety of energy-related benefits besides nuclear electricity, according to Shane Johnson, the DOE Principal Deputy Assistant Secretary and Chief Operating Officer for the Office of Nuclear Energy.
Even though the operating temperatures have been scaled back, Johnson asserts the new technology will still produce process heat that will allow petrochemical companies to reduce their natural gas use -- thereby making it available for home heating and other uses -- as well as the production of hydrogen that many envision as the cornerstone of clean transportation energy.
While potentially far-reaching for a number of energy benefits, the NGNP has also drawn significant controversy. The Union of Concerned Scientists (UCS), a major non-government organization in nuclear policy, believes the extremely high temperatures envisioned for the NGNP raise technical hurdles that warrant a different schedule for developing the technology than the 2021 deadline set forth in the Energy Policy Act of 2005. Sufficient time will be needed to develop and test ultra-high temperature materials, to develop and validate models for analyzing reactor performance, and to develop and qualify the fuel, a UCS source says.
In an interview with EnergyWashington Week, Johnson says that DOE shares the concerns raised by USC and others about the earlier proposal to run the NGNP -- a "very-high-temperature gas-cooled reactor" (VHTR) -- at temperatures up to 950 or 1,000 degrees Centigrade. Seeing the higher temperatures as "too big a stretch" because the department "has little experience outside the labs with such temperatures," DOE has scaled back to 850 degrees C, which is "within the experience base" DOE has with high-temperature reactors, Johnson says. DOE will nevertheless continue to research higher temperature systems because they offer higher efficiency than conventional light water reactors now widely used.

With light water reactors, which have a 33-34 percent efficiency, only a third of the thermal energy becomes electricity. But with the 950-1,000 degree temperatures, a 45 percent efficiency can be achieved. In backing off to 850 degrees, DOE is settling with 40 percent efficiency. An Aug. 15 report to Congress delineating the joint DOE and Nuclear Regulatory Commission (NRC) plan for developing and licensing the NGNP describes the VHTR as "a new and unproven reactor design" that can provide high-temperature process heat up to 950 degrees.
The reactors are also smaller -- ranging from 10 to 300 MW -- instead of the current 1100 MW-1700 MW unit size, according to an industry source.
Johnson explains that the VHTR was selected after DOE in 2001 initiated "a technology road map for next generation reactors on an international basis." Some 100 scientists and engineers from 14 countries participated in proposing and examining a range of options. The VHTR (and a sodium fast reactor) was selected because of its range of benefits besides electricity.
The UCS source believes the NGNP was forced on DOE by Congress at the behest of Sen. Larry Craig (R-ID), who criticized the department's Global Nuclear Energy Partnership during hearings and pushed the NGNP, which is to be built in Idaho. The report to Congress "makes it abundantly clear that the congressionally mandated timetable for developing, licensing and constructing the NGNP by 2021 is completely unrealistic," the source says.
Johnson acknowledges Craig has been a strong advocate of the VHTR and wants to see the DOE Idaho National Lab play a significant role in developing the technology. In addition, DOE was provided more appropriations than it asked for to promote the VHTR. But Craig did not force the technology on DOE, Johnson says, noting that DOE was "headed down this path before [EPACT 2005]" required it.
Although DOE "has tinkered with gas-cooled reactors" since the 1970s, the UCS source says the VHTR requires higher temperatures than the department has experience with, because of the interest in producing hydrogen with the heat. "They don't have materials suitable for nuclear use," the source says, explaining that materials must have greater reliability when nuclear energy is involved than when materials are used in high-temperature industrial processes. With gas-cooled reactors, the hundreds of thousands of small pellets used in the fuel must be symmetrical, with "no variation in the micro-spheres," and the source adds that they are "sensitive to manufacture defects."
"There's a certain rejection rate in every man-made process," Johnson says, so with the millions of fuel "kernels" that will be used in the VHTR "you'll see some defects." In response to this concern, DOE is developing inspection tools to identify and reject out-of-spec kernels. During the NRC licensing review fuel performance will be a key issue so a lot of effort is being focused on the issue, and the scientific community will be involved in peer review to assure quality, Johnson says.
A senior director with the Nuclear Energy Institute (NEI), an industry organization, also stresses that with VHTR designs the fuel quality must be higher than in other types of reactors "so there will be more emphasis on quality" because there are more manufactured kernels, raising the possibility for defects. Companies are planning to irradiate defective kernels in test facilities to assess what happens.
The NEI source says one or two companies are "pushing hard" to move the technology along and are "on the verge of full-scale testing" of materials under high temperatures, and developing the fuel. While 850 degrees is the more realistic temperature for now, companies are targeting 950 degrees "to eventually get there," the source says.
On the issue of highly reinforced cement and steel containment used for current nuclear facilities -- something the UCS source says must be a requirement -- Johnson says DOE has made no decision. Such containment is justified for the many light water reactors that subject water to 2,200 pounds per square inch (psi) pressure to keep it from boiling; containment structures are designed to be protective in the event that a cooling pipe rupture occurs, creating a "high energy" event as the water is released and flashes to steam. With VHTR, which is cooled by helium gas, the pressure is 800 psi. That lower pressure may mean less containment structure is needed, Johnson says, adding that the issue is being analyzed because heavy-duty containment would add significantly to the cost of VHTR and affect the technology's long-term economic viability.
DOE is developing a request for proposals to be published by the end of 2008 that will ask companies to estimate the cost of developing VHTR prototype facilities.

Those poor guys, dreaming of efficiencies of 45% if they can get to 1000 C and now having to settle for 40% at 850C with gas cooled reactors. Wake up guys, molten salt reactors (LFTRs) can get you 45% and even better with only a 700 C peak temperature with proven materials (Hastelloy N). Switching to carbon based materials and the 850 to 1000 degree range can easily get things above 50%, maybe even 60%.

Gas cooled reactors fall short on efficiency for a couple reasons based on the poor coolant qualities of gases. First, the peak might be 1000 C, but there is such a low heat capacity in a gas that the minimum or entry temp needs to be hundreds of degrees lower. Molten salt reactors can give up their heat all very near the peak temperature. Add to that the usual need to transfer heat to a secondary gas and again the poor qualities of gas mean that the temp drop between primary and secondary gas loops is large and further lowers the efficiency.

I am confused by this statement. Since the molten salt cannot be used directly by the turboelectric generator, a secondary cooling loop is a requirement in the LFTR. No coolant is perfect; every secondary coolant has a downside. For example, sodium and/or potassium will explode in the air or water; CO2 becomes radioactive. Isn’t lower efficiency a tradeoff that is worth making for safety sake?

I am confused by this statement. Since the molten salt cannot be used directly by the turboelectric generator, a secondary cooling loop is a requirement in the LFTR. No coolant is perfect; every secondary coolant has a downside. For example, sodium and/or potassium will explode in the air or water; CO2 becomes radioactive. Isn’t lower efficiency a tradeoff that is worth making for safety sake?

Yes a LFTR also needs to transfer heat to a secondary loop but the temperature drop across these liquid-liquid heat exchangers is typically much lower then when you have a gas-gas heat exchanger. The bottom line is simply that LFTRs can have efficiencies matching gas cooled reactors running hundreds of degrees hotter.

The project faces technical and finding hurdles and is already running behind schedule. "The Department of Energy asked us to complete the plant by 2016, but we are revising the date to 2021," said Sten A. Caspersson Jr. of Westinghouse in an interview with Design News following a presentation at the annual Congress of the American Society of Mechanical Engineers in Boston, MA. Caspersson is project manager of next-generation, high-temperature reactors at Westinghouse, a Pennsylvania company owned primarily by Toshiba.

Licensing. Will federal authorities look favorably on the technology? President-Elect Barack Obama says he will support nuclear power if safety issues are adequately addressed. Caspersson told Design News: "Light water reactors are very safe. These (next generation nuclear plants) are even safer." For example, he said it would be almost impossible to extract fissionable materials from spent fuel balls. In addition, the spent balls could be safely stored in a remote location, such as the Yucca Mountain site in Nevada proposed for nuclear waste.

Also, the story for nuclear-generated hydrogen ain't so good anymore, since the electric cars of the future will function quite well on the electrical distribution grid we have right now, thank you very much.

Boy, there's a way to guarantee that we won't see a closed-fuel cycle...ever!

The story for nuclear generated hydrogen is as good as ever unless all anyone thinks of is passenger cars going on 30 mile trips. We need nuclear hydrogen for ammonia based fertilizer, and synfuel production for all the fuel requirements in the world that cant be met by electric vehicals... which honestly are most of them.

And the LFTR is the best candidate for producing nuclear hydrogen IMHO.

What exactly is wrong with onsite dry cask storage anyways?

I honestly do not understand. Fuel qualification started two+ years ago, with good results so far. The HTGR (=PBR) existed in Germany, exists in China, is being prototyped in South Africa, is committed to production in China. So why wait to 2016+5 years?

I have been a promoter of the PBR (http://pebblebedreactor.blogspot.com). My concerns are (a) the available uranium fuel supply if deployed rapidly, and (2) the waste, and (3) the escalating cost. [Frankly, I believe the waste is already prepackaged for immediate burial.]

Yes, but when you can produce electricity at 50% efficiency, you can produce hydrogen ANYWHERE electrolytically, rather than at a high-temp reactor thermochemically and then face the nightmare of hydrogen distribution.