The station
How it works
Fission makes heat. Heat makes steam. Steam turns a turbine, the turbine turns a generator, and the generator feeds the loop. Three separate loops of water, none of which ever mixes with another, and nothing burned.
One drawing
A pressurized-water unit, left to right
- Reactor water, hot, under pressure
- Reactor water, cooled, pumped back
- Steam, the second water
- Feedwater, the steam condensed
- Seawater, the third water, in
- Seawater out, a few degrees warmer
Both units at Sixes River are built this way, each with three steam generators and three pumps; the drawing shows one of the three loops.
Six steps
From the fuel to your kitchen
Fission
The fuel is uranium oxide in ceramic pellets, stacked inside thin metal tubes bundled into assemblies. When a uranium nucleus absorbs a neutron it splits, releasing heat and more neutrons, which split more nuclei. Control rods and the water itself keep the chain reaction steady.
Hot water, no boiling
Water flows through the reactor and comes out at about 600 degrees. It does not boil, because the pressurizer keeps the whole loop at about 2,200 pounds per square inch. This is the first water, and it stays inside the containment.
Steam generators
The hot water passes through thousands of tubes in the steam generators and gives its heat to a second, separate body of water on the outside of the tubes, which boils. The two waters never touch. The cooled reactor water is pumped back to the reactor.
Turbine and generator
The steam leaves the containment and drives a turbine at 1,800 revolutions a minute. The turbine turns a generator, and the generator makes the electricity: more than a thousand megawatts from each unit.
Condenser
Below the turbine, seawater flowing through the condenser's tubes turns the spent steam back into water, which is pumped back to the steam generators as feedwater. The seawater, the third water, goes back to the Pacific a few degrees warmer. It never meets the other two.
The loop
A transformer steps the generator's output up to 230 kV for the switchyard, and the lines carry it round the South Coast Loop to the substations in Langlois, Port Orford, Bandon and Gold Beach and north to the state's interconnection at Coos Bay.
No smoke, no carbon
What comes out, and what does not
Nothing is burned at Sixes River, so there is no smoke, no ash and no carbon dioxide from making the power. There are no cooling towers, so there is no plume. What leaves the site is seawater a few degrees warmer than it arrived, measured at the diffuser and at the edge of the mixing zone against the state's limits, and the plant's building air, which passes through filters and monitors before it leaves the stack. The stack monitors read a small fraction of the limit the federal regulators set, every day of the year, and the readings are reported.
The used fuel stays here, first in the pools and then in the dry casks on the pad, as the station page describes. Everything the plant has ever used is on this site and accounted for.
Questions people ask
On the tour, and in the visitor center
Does the water that touches the fuel go into the sea?
No. The reactor water is a closed loop inside the containment and never leaves it. The steam is a second closed loop. The seawater is a third loop that only ever touches the outside of the condenser's tubes. The three are kept apart by metal walls that are tested for leaks continuously, and a leak between any two would be found in minutes and the unit shut down.
Why does the water not boil at 600 degrees?
Because it is kept under pressure. At about 2,200 pounds per square inch, water stays liquid far above its ordinary boiling point. That is what pressurized-water means, and it is why the fuel stays covered and cooled.
What does a megawatt power?
Roughly 800 homes on this coast. Each unit makes more than a thousand megawatts; together about 2,270, enough for about 1.8 million homes, which is far more than the South Coast uses. The rest goes north on the loop to the state's interconnection at Coos Bay.
Could the reactor explode like a bomb?
No. The physics does not allow it. Weapons need uranium that is almost pure in the fissile kind; reactor fuel is about five percent, and the chain reaction in it is slow and self-limiting. A reactor can be damaged by losing its cooling, which is what every safety system here is for, but it cannot detonate.
How often do you refuel?
Every 18 months on each unit, in a month-long outage in spring or autumn. About a third of the fuel is replaced each time. See refueling.
Why seawater and not cooling towers?
Because the Pacific is at the foot of the bluff and it is cold. Once-through seawater cooling is more efficient than towers and leaves no plume; what it asks in return is care for the sea, which is the environment program.
See the real thing.
The visitor center's model control room runs a scripted shift with a real operator beside it on open days, and the fuel assembly mock-up is full size.