To Cut Nuclear Costs, Cut Concrete

New Reactor Technologies Can Minimize its Use

By Matthew L. Wald

Nuclear construction is still too expensive. That central problem confronting the nuclear renaissance has come into sharp focus with recent announcements about projected costs for new plants.

Two recent developments involving concrete, though, might show the way to lower costs. But the industry needs to be more aggressive, and the Nuclear Regulatory Commission will need to re-think its rules to allow developers to skip the use of high-grade concrete in components that are needed for traditional, large light-water reactors, but are less important to some newer designs.

Using less expensive concrete is a pressing problem, because it is one of the most used materials in a nuclear plant. The recent financial data isn’t promising. Korea Hydro & Nuclear Power recently won a contract to build two 1,055 megawatt pressurized water reactors in the Czech Republic, for a little over $8,500 a kilowatt of capacity, or roughly $18 billion total. That’s expensive but seems like a bargain compared to Ontario Power Generation’s budget for four BWRX small modular reactors, at $12,500 per kilowatt. The SMR design was supposed to be less expensive to build than the big reactors. And those are the prices estimated before construction, not including any potential delays and cost overruns.

Finding ways to lower the cost of construction is the name of the game. Nuclear-grade concrete, being one of the most expensive inputs, is a prime target for innovation and improvement.

A 50 percent premium

Concrete is pricey. A 2022 analysis estimated the cost of nuclear concrete at $527 per cubic meter, compared to $352 per cubic meter for non-nuclear concrete, a premium of nearly 50 percent. The price of each has gone up since then, but the ratio may be constant. A 2007 report by the Economic Modeling Working Group, for example, found that nuclear concrete cost $421 a cubic meter, vs. $281 a cubic meter for non-nuclear concrete.

For concrete to be nuclear-grade the mixture of water and cement must be more precise so it will not crack as it sets. That means more care in mixing. Too much water in the mix will leave voids in the finished product. Nuclear-grade concrete also has a thick network of steel reinforcing bars, far denser that is used in bridges and other civil structures. That re-bar is tedious and expensive to install and inspect.

The Department of Energy’s Idaho National Laboratory reviewed nuclear construction costs in 2017, and found that as measured by weight, three-quarters of a large pressurized water reactor is concrete. The concrete pours for nuclear concrete take a lot of time, about twice as long for foundations, and 50 percent longer for superstructures, compared to ordinary concrete. Cutting the installation time in half would reduce the cost by 28 percent, the researchers found. Construction experience and engineering analysis suggests that this is possible with better project management and better construction equipment. Strict quality-control standards represent another 23 percent of the cost of the concrete.

But a simpler strategy than reducing the cost of nuclear-grade concrete is to just use less of it. Two nuclear plants now under construction are trying this route.

One is the GE-Hitachi BWRX small modular reactor, with a basemat and reactor building that will be built from modules made of steel and concrete.

Researchers recently tested steel and concrete composite blocks at Purdue University to simulate loading conditions that they would see in an earthquake, and found that their strength exceeded expectations. Two steel plates are connected with adjoining steel plates with holes to allow insertion of concrete. The modules can be factory-fabricated and assembled on site, and then filled, allowing for quicker construction. With the composite-blocks, the re-bar typical in nuclear-grade concrete is no longer needed. GE-Hitachi hopes to cut construction costs by 10 percent with the technique.

Minimizing the Critical Area

The Natrium project, in Kemmerer, Wyoming, is taking a different approach. It separates the reactor from the “energy island,” the part of the plant that produces electricity by using steam to spin a turbine and then a generator. In a conventional reactor, these components are adjacent, but Natrium, designed by TerraPower, uses the reactor to heat up a big external tank filled with molten salt. The salt’s main function is to be a battery, storing heat energy by varying its temperature. Operators can draw heat off the salt to boil water and make electricity, but at variable rates so they can time their production to match price changes on the grid.

A side benefit, though, is that the part of the plant that has to meet nuclear-grade standards is substantially smaller. Concrete for the area away from the reactor can be fabricated to normal industrial standards.

The NRC has recently endorsed the concept of a smaller “nuclear island,” separate from the “energy island” where electricity is made, although the Kemmerer plant does not yet have a construction permit for the nuclear portion.

In a letter sent to the company on May 7 of this year, the NRC gave TerraPower an exemption from its rules on the electricity-generating half of the plant. Normally the agency pays close attention to the turbine and generator because a problem there can trigger a reactor shut-down, but in the Natrium case, the reactor is designed to be immune to those upsets.

There are other opportunities to reduce the use of nuclear-grade concrete. One is by taking full advantage of “pebble” type fuel to redefine what constitutes a containment, and thus reduce the need for nuclear-grade concrete.

Today’s reactors are fueled by ceramic pellets wrapped in thin metal tubes. The entire reactor lives within the containment, which is a very strong building. If cooling stops and the pebbles overheat, they can leak radioactive materials into the cooling water and if that water boils it can raise the pressure in the primary cooling system, opening a valve and sending radioactive steam into the containment.

But the pebbles, more properly called Tristructural Isotropic, or TRISO, have particles of fuel wrapped in concentric layers of heat-resistant materials. Thus, the containment doesn’t have to be a concrete dome building surrounding the reactor; the containment can be the fuel itself. With this technology, there is one less significant reason to hermetically seal the building that houses the reactor.

For example, in Kairos Power’s SMR design the fuel floats in a salt mixture that can withstand tremendous heat without boiling away. If the fuel fails, the salt will absorb the radionuclides. This means the whole operation is low pressure, despite being very high temperature, making containment a lot less of an issue.

Even new pressurized water reactors could get by with less concrete in their containments. The requirement for nuclear grade concrete is to assure that a crack-free structure would not allow radioactive gases or particles to escape in an accident. In practice, reactor containments are lined with steel that can also do that job.

Flattening the Nuclear Construction Cost Curve

While the price of nuclear construction needs to come down, it does not have to reach the levels of solar or wind installations. A kilowatt of nuclear capacity, after all, is worth more than a kilowatt of renewable capacity.

The standard way to measure construction cost is the price per kilowatt of capacity. Buyers can afford to spend more on a nuclear plant per kilowatt of capacity than on a solar or wind plant, because the nuclear plant will run more than 90 percent of the hours in a year. But the capacity factors for solar and wind (the amount of energy they will produce in a year, compared to what would result from 24/7/365 operation) is far lower; 30 to 40 percent for a good wind site, and 25 percent or less for solar. And the reactor will be designed to run for 60 years or more, while wind machines in the United States are often retired after 10 years, and solar after 20 at most.

The price requirement for new nuclear construction depends on three other factors that are more difficult to nail down. One is the future cost of natural gas, which has become the dominant competitor in the United States. The fuel cost to run a gas-fired plant has varied by a factor of three in recent years. The future price will depend in part on how much natural gas the United States exports, and thus how much the world price tends to pull the domestic price upward.

A second factor is the value that a utility puts on a zero-carbon generator. That was a federal priority in the last administration but isn’t now. It is still a priority in many states.

And the third is the confidence that the buyer can put in the estimated price and schedule. No matter what the estimate for a new plant, a company shopping for new capacity won’t be confident until several units have been built.

Flattening the cost curve of nuclear construction will require even more innovations in design, materials, and management. Developments in nuclear concrete are just the beginning.