As the world watches the Japanese nuclear disaster unfold from afar, many residents who live in the shadow of the Comanche Peak Nuclear Power Plant’s twin towers in Glen Rose wonder what the situation over there could mean for the plant’s future here.
Rafael Flores, senior vice president and chief nuclear officer of Luminant’s Comanche Peak plant, said that “it’s too early to tell” what impact the crisis there could have on the industry — and certainly much depends on the outcome in Japan, where workers still are struggling to restore full power to the crippled Fukushima Daiichi Power Station north of Tokyo.
Luminant and Mitsubishi Heavy Industries are partnering to pursue a license and financing to build two more reactors at Comanche Peak. The combined operating and constructing license have been moving through the U.S. Nuclear Regulatory Commission’s process.
Many lessons will be learned from the Japanese disaster and taken into account, Flores said in a telephone interview with the Reporter.
The Japanese plant design was based on a “worst-case scenario.” But who could have predicted a major earthquake and a tsunami of such force smashing into a nuclear plant?
“Things can happen beyond the design of the plant,” he noted. “Water also plays a major role in how a reactor will be able to respond.”
Flores pointed out several key differences between the design of the Japanese reactors and safety systems and those used at Comanche Peak.
The Japanese reactors used boiling water to generate steam, while the Comanche Peak reactors use pressurized water.
“The design is totally different,” Flores said.
In a boiling water reactor, nuclear fission in the reactor core brings water to the boiling point, producing steam. The steam bubbles rise to a turbine and feed a geneator that produces electricity. Then the water is cooled in a condenser, returned to liquid form and returned to the reactor core.
The design was developed by General Electric and U.S. research laboratories in the 1950s and marketed as cheaper and easier to build. Reactors based on that design, the Mark 1, use a smaller and less expensive containment structure than the dome design.
With pressurized water reactors, water is pumped under high pressure to the reactor core. There is it heated by the energy from nuclear fission and flows to a steam generator that makes steam that goes to turbines that spin an electric generator. The water does not boil within the reactor.
“That water has no radiation in it and is not radioactive, where the boiling water is radioactive throughout the cycle,” Flores noted.
About two-thirds of the nuclear power plants in the United States use pressurized-water reactor designs, while the remaining third use boiling-water reactors.
“Both designs are very robust and very safe,” Flores said.
The containment structures also are very different in design. The Japanese reactors are rectangular-shaped, while Comanche Peak uses the dome-shaped design.
The New York Times reported that as early as the 1970s a safety official with the Atomic Energy Commission — the predecessor agency to today’s Nuclear Regulatory Commission — recommend that the GE Mark 1 system be discontinued because it presented “unacceptable safety risks.” A former chairman of the NRC considered banning such a system, but the technology had become so accepted and widely used that he feared taking such an action “could well be the end of nuclear power,” according to the Times report.
The earthquake that rocked Japan measured 9 on the Richter scale and was “beyond the deisgn” parameters the Fukushima Daiichi plant was built to withstand, Flores said.
Even so, “the reactors responded appropriately. They all shut down and everything was functioning according to the design,” Flores said.
Then the tsunami struck, creating a “double whammy” situation that was well beyond the scope of anything planned for.
Of course, a tsunami seems like an extremely unlikely occurrence in Glen Rose. But the Comanche Peak plant was designed to be protected from earthquakes, flooding, loss of off-site power and tornadoes, Flores said.
U.S. nuclear power plants also subscribe to what the NRC calls “defense in depth,” meaning plants are built on redundancy.
For example, in the event of a loss of power, Comanche Peak has diesel generators to provide power to all necessary equipment. But there are some key differences between the plant here and the Japanese power plant, Flores noted.
It had diesel fuel tanks, but they were located above ground level. When the tsunami struck, it washed them away.
“Our diesel fuel oil tanks are located underground so they are protected,” Flores said.
Comanche Peak’s control center has sensitive seismic sensors to detect movement underground. If the monitoring system detects any activity, the reactors automatically shut down.
During last year’s natural gas pipeline explosion east of Glen Rose, the sensors did not detect any ground movement. But plant managers kept an eye on the situation.
“What we would typically do (in the case of a major event) is go out and do plant tours to make sure nothing is out of the ordinary even though nothing has been detected,” Flores said.
Since the Three Mile Island nuclear accident in 1979, the U.S. nuclear industry has adopted “Severe Accident Mitigation Guidelines” that prescribe actions to take to protect the reactor core, which is the top priority, Flores said.
Nuclear energy opponents last week seized on the events in Japan at a hearing for a new nuclear plant in South Texas. They said the industry remains a “high risk” business. Texans for a Sound Energy Policy pointed out that Victoria County is located on a “growth fault” in which the earth’s plates can shift slowly and create cracks.
Attorneys for Exelon, the energy company that may build the plant, countered that the fault doesn’t pose a seismic threat unlike the sudden geologic plate movement in Japan.