Since the March 10 earthquake and tsunami in Japan, workers have struggled to cool damaged reactors and contain radiation at the Fukushima Dai-ichi nuclear power plant. Rizwan Uddin is a professor of nuclear, plasma, and radiological engineering at Illinois. In an interview with News Bureau physical sciences editor Liz Ahlberg, he discusses the ongoing struggles at the damaged plant and how it could affect safety procedures in the U.S. and elsewhere.
Why has it been so difficult to stabilize the damaged reactors? And how could the radiation levels fluctuate so much from day to day, or even hour to hour?
The bottom line is that this reactor design requires a power supply - for several days even after the reactor has been shut down - to pump water through the core and to keep the reactor cooled. Hence, the essential challenge has been to get the power lines to the site and to fix the circuitry at the plant. This has been complicated by the extensive damage caused by the tsunami as well as by fluctuating radiation levels.
It looks like there are two sources of spikes in the radiation level. Every time hydrogen is released to reduce the pressure in the pressure vessel, the radiation level goes up. It is mostly volatile radioactive material, which gets dispersed, thus reducing the level. Another potential source of radiation is the spent fuel pool. If rods in a pool are exposed to air, they also could be a radiation source.
Prone to earthquakes, Japan is known for its expertise in construction that can withstand natural disasters. How then could this have happened?
To the extent that we know, the disaster in Japan resulted largely from the tsunami that followed the earthquake and not from the earthquake itself. It appears that the crisis at the nuclear power plant is largely a result of the water wave that was higher than the protective wall. The water damaged the backup diesel generator fuel supply and the electrical circuitry, leading to the ongoing crises.
How does radioactivity spread from the plant to water and food sources? And what kind of risk does such contamination pose?
Gases produced inside the core because of elevated temperatures are vented out. Volatile radioactive material leaves the facility, becomes airborne and travels. Rain and snow may bring some of this substance back to the ground. If some fraction of the seawater that is being used to cool the facility is flowing back into the sea, it may be carrying some radioactive material with it. The danger posed by radiation depends upon its level. Unless there is a major breach of some containment facility, the radiation under the most likely scenario is expected to be contained to the immediate area - a few miles in radius - surrounding the plant.
Once the reactors are stabilized, what's next for the plant? What happens to the radioactive material?
The answer will depend upon several factors, including the level of damage, radiation level, and the treatment costs. The radiation levels outside the reactor in the case of Three Mile Island were quite normal. After waiting for several years, it was possible to enter the facility, and carry out cleaning work using robots. On the other hand, the owners of Fukushima may determine that it is safer to entomb the reactors as happened at Chernobyl.
Germany shut down seven reactors for three months of inspection. And the European Union is going to be inspecting all 143 reactors in Europe. Should the U.S. be considering similar precautions?
Most countries are having a review of their nuclear facilities and of procedures in place in case of emergency. In Europe we expect to see a wide range of responses - those from the likes of France on one end to Germany on the other. While I do not see any systematic design flaws to warrant shutting the reactors down, it would be foolish of us not to take this opportunity to review our safety procedures in the United States. These procedures are routinely revised. For example, a natural circulation cooling system that does not rely on electricity may be easily installed for the spent fuel pools.
The Nuclear Regulatory Commission has announced a "quick look" 90-day review of the country's nuclear power plants to determine if immediate changes in emergency preparedness are needed in the wake of Japan's ongoing nuclear crisis. This will be followed by a second, long-term safety review after U.S. officials know the outcome at the Fukushima Dai-ichi plant.
Are there nuclear power plants in the U.S. with the same design as the Fukushima plant? How has reactor technology improved and been made safer since the Fukushima plant was built?
There are some Mark-I models in the United States with the same primary containment design as the Mark-I at Fukushima Dai-ichi. However, there may be some differences because of different regulatory requirements. For example, since 9/11, additional power backup systems have been required at U.S. power plants. They must demonstrate that the core can be cooled for an extended period of time in case the primary backup diesel generator fails. This has resulted in some U.S. power plants installing a second diesel generator a distance away from the primary facility to reduce the chances of both backup systems failing as a result of a single event. Some newer plant designs do not rely on electric power to keep the core cooled in case of an accident. They rely on natural circulation to continuously circulate water through the core, without needing any human intervention in an emergency.
What are the lessons to be learned from what's happening in Japan?
There are several lessons that we can already learn from what we know; and I hope there will be several more that we will be able to learn after we have a better understanding of what actually did take place at Fukushima. There is no doubt that in post-Fukushima world, new reactor designs with certain features will be preferred. The immediate lesson that can be learned is to re-double the efforts to ensure that electricity can be supplied to these power plants in the case of emergency.