Since the earthquake and tsunami in Japan, the world’s attention has been fixed upon the Fukushima Daiichi Nuclear Power Plant. The six reactor plant suffered major damage that disabled the primary cooling systems on units one, two, three and four.
Yet there is another Fukushima nuclear plant, which was struck by exactly the same forces but has gone largely unnoticed, primarily because there have been so few problems. Fukushima Daiichi translates directly as “Fukushima Number 1,” and was built starting in 1967. In 1976 it was decided to construct a second nuclear power plant, Fukushima Daini, directly translated as “Fukushima Number 2.” The first units came online at Fukushima Daini in 1982, with a total of four reactors being built, the last coming online in 1986.
Both nuclear plants are located directly on the coast. Fukushima Daini is about seven miles south of Fukushima Daiichi. Both plants also have very similar breakwater designs.
Fukushima Daini is also where a worker took these amazing pictures of the tsunami surge flooding the area around the reactor containment buildings. The water actually came in even higher than these pictures show, but the worker didn’t stick around to take any more photos.
Fukushima Daini is also where the first death at a nuclear plant as a result of the tsunami was reported. A worker was trapped in the control booth of a crane at the plant’s exhaust stack by the inundation of water. Rescuers reached the worker several minutes later but found he was already dead.
The quake also triggered a shutdown of all four of the reactors at Fukushima Daini, which had been operating at full power at the time. Significant damage was sustained to numerous plant systems, both nuclear and non-nuclear. The fourteen meter high tsunami that struck the plant was more than twice the height the plant was designed to survive. Fires were reported in at least one turbine room. At least some of the on sight backup power systems were also destroyed.
Three of the four reactors at Fukushima Daini sustained significant damage to their primary cooling systems. Flooding of pump rooms rendered the essential service water systems inoperative for units one, two and four. Backup cooling systems continued to function. Even without the ability to dissipate heat into the environment, the internal cooling mechanism of the reactors assured that enough heat was dissipated into the wetwell of the reactor, providing more than a day of decay heat dissipation.
On March 12, officials began preparations for releasing pressure from the reactors at Fukushima Daini, but this was determined to be unnecessary before any pressure was released. Emergency cooling systems continued to function properly and within two days of the tsunami, the primary cooling systems of all reactors were once again functional. On March 30, secondary systems were once again required when a fault occurred in equipment that supplies power to pumps at one of the reactors. Full functionality was quickly restored.
Since then, Fukushima Daini has remained in a state of cold shutdown. As time as passed, the cooling of the cores has become less critical, and all cooling capacity has remained functional. There were no explosions or other major accidents. There have been no releases of pressure or radioactive material from the plant and spent fuel storage remains stable. At this time the plant is considered safe and secure.
Why Daini survived the quake and tsunami so much better than Daiichi:
There’s really only one glaring difference between Fukushima Daiichi and Fukushima Daini: the vintage of the nuclear technology of the plants. While Fukushima Daiichi was built with reactor designs from the late 1960′s and early 1970′s, Fukushima Daini was built with technology of the early to mid 1980′s.
A comparison of the reactors at Fukushima Daiichi and Daini:
Both plants use boiling water reactor designs developed by General Electric, although in the case of Fukushima Daini, the vendors were Hitachi and Toshiba, who had licensed the designs of General electric. These are similar to reactors operated in the United States and elsewhere.
The BWR-3 and BWR-4 reactors are very similar in design. The primary difference is that the BWR-4 is larger. Otherwise, most of the basic systems and design features are the same. They use a similar containment structure and general layout to the BWR-1 and BWR-2. The containment system is the Mark 1 containment design, first used at the Oyster Creek Nuclear Generating Station in 1969 for a GE BWR-2 reactor. These reactors would be considered early Generation II nuclear power reactors.
The BWR-5 represents a considerably greater change in design and technology from the BWR-4 than the BWR-4 did from the BWR-3 or than the BWR-3 did from the BWR-2. The BWR-5 introduced newly designed core spray and auxiliary cooling systems. The BWR-5 also introduced the Mark-2 containment design, a complete redesign of the reactor structure. The Mark-2 design integrates more of the cooling and support equipment into the central containment area of the reactor building. It also includes a number of new safety systems. The explosions that occurred at Fukushima Daiichi were the result of hydrogen buildup from a reaction between the zirconium alloy fuel cladding and the water in the reactor vessels. The Mark-2 containment system includes a system that can purge the reactor coolant with nitrogen gas to avoid such dangers. Further refinements were made to the Mark-2 Advanced containment design.
The BWR-5 represents what would technically be considered a late Generation-II nuclear reactor, although many of the design features continued to be used in the BWR-6 and later the ABWR and ESBWR, which GE Continues to market, members of the Generation_III and Generation-III+ reactor classes.
The conclusion that one can draw from the events at the two Fukushima plants is relatively straight forward: While the older BWR-3 and BWR-4 designs are sufficiently safe in most situations, their designs are nowhere near as robust and reliable as newer reactor designs. Of course, despite holding up so well against forces far beyond what designers had planned, the BWR-5 is, by today’s standards, old technology. Newer reactors are much safer still and have even more reliable passive-based safety features.
This is all the more reason why we should be building more nuclear plants. As newer reactors are built we will be able to eventually shut down the older reactors, thus improving economics and safety even further. The events in Japan do not diminish the picture of safety we have when it comes to new reactors. Rather than assuming that reactors will fail in the manner that they did at Fukushima Daiichi, we should consider how well they held up at Fukushima Daini. This is far more representative of new reactor designs, although those are even safer and more reliable still.
This entry was posted on Wednesday, May 25th, 2011 at 5:43 pm and is filed under Bad Science, Good Science, Nuclear, Politics. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
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