Few sources of energy are as controversial as nuclear energy. Building costs balloon out of control. Mishaps lead to shutdowns or melt downs. There is no good way to dispose of the waste. Just saying nuclear energy can send people into a panic. Enter NuScale Power. They have developed a small modular nuclear reactor that is safer to build and safer to run.
NuScale Power small modular nuclear reactors are Light Water Reactors (LWRs). The small modular nuclear reactors (SMNRs) use a modular design that combines the containment vessel and reactor system. Each module also has “its own designated turbine-generator set.” Unlike other LWRs, “in NuScale’s system the reactor pressure vessel contains both the nuclear fuel, or reactor, and the steam generators.”
The SNRs use six foot nuclear rods rather than the twelve foot rods used in larger systems. They will need to be refueled every 24 months and will work at 90 percent capacity 330 days out of the year.
The reactors use water as its coolant in a “natural circulation cooling system” which is a convection system that doesn’t require pumps or external power. This process is safer than other methods of cooling.
The NuScale design eliminates concerns about a Loss of Coolant Accident (LOCA) in other designs that could result from a break in the large pipes that connect the reactor to steam generators. In addition, there are no pumps on the reactor system that require an emergency electrical power supply for cooling if power is lost to the site.
The natural circulation cooling system draws off the heat of the nuclear fuel. The heated water rises in the cylinder and is “drawn down over the steam generator tubes where it passes its heat to a second enclosed system to produce the steam that makes electricity.” Once the heat is transferred the water is cooled and drops back down the outside of the cylinder to be sucked back. The process begins again. The water re-circulates through the system cooling the core while heating the steam generator. (See illustration at the end of the article.)
Like modular homes, the SMNR components are designed to be manufactured and fabricated in existing factories within the US and around the world. Manufacturing these systems would create and keep jobs here in the US. Once manufactured the NuScale containment and reactor vessel along with other modules are shipped by truck, train or ship to their permanent destinations.
Since the SMNRs are scalable, new 45 MW reactors can be added to a power plant to increase energy production. The total number of modules per plant is 24. Also, when one module goes down it doesn’t affect the others so maintenance can be rotated through out the modules without losing total output.
The scalable modular design also means shorter lead and construction times. Building costs are easier to control and expansion is quicker (relatively speaking) and easier than the current model.
Although these NuScale reactors are supposed to be safer than the large scale reactors being built today, there is always a chance that a disaster will happen. NuScale has several safety features built in.
They include a high-pressure containment vessel, two passive decay heat removal and containment heat removal systems, a shutdown accumulator, and in-vessel retention for severe accident mitigation.
Unfortunately, the spent fuel will be handled just as it is today.
The August 2009 edition of Scientific American, carried an article, “Is There a Place for Nuclear Waste?” that discussed current methods of disposing of nuclear waste and some proposed future methods. The current method is to remove the spent fuel (fuel is considered spent after three to six years in a nuclear reactor) and submerge it in a concrete and steel lined pool of water for about 10 years. After the initial submersion in water to cool off the spent fuel, the fuel is removed in steel casings that are placed in a concrete cask for storage on site.
Until the nuclear waste problem is adequately addressed, nuclear power plants will continue to pose a risk no matter how small. Cheap abundant electricity and new jobs are both desperately needed. The question is can we afford risk of more nuclear waste?
Illustrations from NuScale.
