Reactors, EPR, KERENA, ATMEA1

Areva models are much larger reactors telegraphjournal.com –Tamsin McMahon,  July 27th, 2010“….All three are light-water reactors, which is significant since all of Canada’s nuclear plants, including Point Lepreau, use heavy water.

Heavy water is refined from natural water. It has two atoms of deuterium, an isotope of hydrogen, making it denser. It allows a reactor to use natural uranium rather than more expensive enriched uranium.

Light-water reactors use regular water, which is cheaper than heavy water, but require enriched uranium.

However, heavy-water reactors are facing extinction, said Toronto-based energy consultant Tom Adams.

“The disadvantages of heavy-water reactors strongly outweigh the advances,” he said. “I think the days are numbered for heavy-water reactors.”

Canada is the only country to pioneer a major reactor design – its CANDU model – based on heavy water. India is developing its fleet of heavy-water reactors derived from CANDU.

Much of the rest of the world has gone with light-water reactors, which were designed in the United States to propel naval submarines and later adapted for power generators. Canada has shut down its heavy-water refining plants and has been left with large stockpiles of heavy water it can’t export as more countries move toward building light-water reactors…….

Heavy-water plants use much more pipe, driving up costs, Adams said. “There’s no more expensive pipe in the world than a pipe inside a nuclear power plant,” he said. “All that stuff has to get inspected and verified and has to be built to super-standards and all this huge, huge overhead.”

Areva has an advanced design with its third-generation-plus reactors, Adams said. The designation refers to advancements in fuel technology and efficiency, greater safety features and lower maintenance and capital costs.

The company’s nuclear reactors are designed to withstand a commercial airplane crash and earthquakes. Their largest plant has a “spreading compartment” in case of a meltdown. If the core overheats and melts through the reactor wall, the molten radioactive liquid will spill into a separate room that is designed to cool the core and protect it from leaking into the environment…………

Of the three plants Areva is proposing to build in New Brunswick, one is a large, high-power reactor called European pressurized reactor, or EPR. It can generate 1,650 megawatts of electricity – about 2.5 times the capacity of Lepreau.

The two others, called KERENA and ATMEA1, are mid-sized reactors…….

In a statement, Areva said it planned to build a mid-sized reactor, such as KERENA or ATMEA1. Constructing a plant as large as Areva’s EPR would require rebuilding the province’s transmission grid, which had a capacity of about 4,000 megawatts in 2008, according to NB Power’s most recent annual report.

All of Areva’s reactors are designed to last 60 years, while Lepreau, opened in 1983, was designed to last about 25 years.

According to Areva, the reactors use less uranium to generate electricity, which lowers costs and reduces the amount of nuclear waste. The reactors are designed so that routine maintenance can be performed without shutting down the plant.

The EPR houses its reactor within two walls, both more than a metre thick. The reactor building also contains steam generators, a water pressurizer and cooling pumps.

The EPR reactor has four identical systems that are used to cool the core to prevent a meltdown. They are housed in separate buildings so that a flood or fire in one building won’t affect the other systems.

A separate facility houses the turbine, which transforms steam into electricity. It is connected to the electrical grid.

There are also two diesel generators that are housed in separate buildings. They are used to power safety systems in case of a power outage……

Of the two mid-sized reactors, ATMEA1 is a pressurized water reactor, while KERENA is a boiling water reactor.

Pressurized water reactors are more common worldwide. They use a closed-loop system where the water that runs through the reactor is kept under pressure so it doesn’t boil, even as it is heated to extreme temperatures.

The thermal energy then heats water housed separately within a steam generator. That water boils and the steam turns a turbine, which powers a generator. The system is designed to separate the water that runs through the radioactive core from the steam that powers the turbine, reducing the risk that radioactive water could accidentally escape.

In boiling water generators, the same water that runs through the reactor is allowed to boil and turn to steam, which is then used to power the turbine.

Pressurized water reactors are more expensive to build, since they require costly steam generators. Boiling water reactors are more expensive to operate because they have to ensure radioactive water doesn’t contaminate other parts of the system.

telegraphjournal.com – Areva models are much larger reactors | Tamsin McMahon – Breaking News, New Brunswick, Canada