09/09/2013 - 22:49

Fixing Fukushima’s water problem

Lake H. Barrett

Lake H. Barrett

Lake H. Barrett is a retired nuclear engineer and was the director of the Nuclear Regulatory Commission’s Three Mile Island Cleanup Site Office from 1980 to 1984.

All energy sources have benefits, costs, and risks. Nuclear reactors, among the largest power plants on Earth, do not produce greenhouse gas emissions, and nuclear energy has an overall low public-risk curve. That curve, however, is shaped by low-probability but theoretically higher-consequence accidents. Such a risk profile is frankly scary to the general public, because it is human nature to focus more on the ”what if” than to understand the “what is probable.” 

The major risk posed by a nuclear power plant stems from the decay of radioisotope fission products that produce heat, even after a reactor’s energy-producing fission process has stopped. Older reactors, like those at Three Mile Island and the Fukushima Daiichi Nuclear Power Station, require electrically controlled pumps to add water to remove this decay heat. Since the beginning of the nuclear energy era, extra precautions have been taken to assure that decay heat removal would occur, regardless of circumstances, but experience with the Three Mile Island and Fukushima Daiichi accidents clearly indicated that those precautions were not sufficient. 

Implementing corrective actions after Three Mile Island cost several billion dollars, but these improvements made US nuclear power plants safer and more productive. Multibillion-dollar post-Fukushima safety improvements are now also taking place worldwide. But even if reactor accidents have low radiological health risks, as was the case at Three Mile Island and has so far been true of Fukushima, they create severe social impacts and large cleanup costs.

Clearly, one significant aspect of recovery and cleanup from nuclear core-melt accidents involves managing the radioactive water that such accidents create. Water management was a challenge at Three Mile Island, and it is now a much larger challenge for Fukushima, because the accident at Fukushima is much more severe, and it has caused a wider spread of radioactivity. Some 90 million gallons of radioactive water are now stored on the Fukushima site, and that amount is growing.

Much of the water contamination at Fukushima is technically at a very low level and presents little risk to the public or the environment; however, any leakage or loss of control of radioactivity, regardless of the level, can be significant from a public-confidence perspective. So it is vitally important that Japan have a comprehensive accident cleanup plan in place that is not only technically protective of human health and the environment, but is also understood to be protective by the public.

The operator of Fukushima Daiichi, the Tokyo Electric Power Company (Tepco), has worked hard and has indeed contained most of the significant contamination carried by water used to cool the plant’s damaged reactor cores. Still, a series of events—including significant leakage from tanks built to hold radioactive water—has eroded public confidence. To address the water challenges, an improved water management plan should be created to deal with all levels of contamination, from slightly contaminated groundwater to highly radioactive cooling water flowing out of the damaged cores. This plan needs to build on the many good Tepco efforts of the past two years, but it should also incorporate new technologies that improve water cleanup performance and increase processing capacities. Importantly, this plan needs to include a new level of transparency for and outreach to the Japanese public, so citizens can understand and have confidence in the ultimate solution to the Fukushima water problem, which will almost certainly require the release of water—treated so it conforms to Japanese and international radioactivity standards—into the sea. 

The primary Fukushima water problem. On March 11, 2011, one of the largest earthquakes ever recorded hit the Japanese Tohoku Pacific Ocean coast. The destruction was immense, especially along the coast, where a tsunami struck with a height of approximately 15 meters (45 feet). Virtually all man-made facilities along the coast were severely damaged, and 20,000 people were killed (although none by radiation).  

Within seconds of the earthquake shock, all reactors that were operating along the coast automatically shut down, safely and as designed. Approximately 45 minutes after the main earthquake shock, however, a tsunami overwhelmed reactor units 1, 2, and 3 at the Fukushima Daiichi Nuclear Power Station. At these three units, all six emergency diesel generators, most switching equipment to control emergency power distribution, and many of the emergency battery power systems were flooded with seawater and destroyed. Plant operators worked heroically to add cooling water to keep the reactor core decay heat in check but were unable to do so quickly enough. This inadequate cooling led to severe reactor core overheating, breakdown of the tubes that encase the highly radioactive fuel pellets, and the generation of hydrogen gas that eventually resulted in explosions in three buildings and the release of massive amounts of radioactivity into the plant.  

Although unacceptable amounts of radioactivity were released to the air and seawater, the vast majority of the most abundant and long-lasting radionuclides—cesium and strontium—were retained in the core debris and cooling water injected into the destroyed cores to stabilize the situation. This injected cooling water became highly radioactive as it contacted the destroyed core, mixed with residual tsunami seawater, further flooded building basements, and leaked into onsite facilities.

Tepco and the Japanese government have done a good job of containing most of the highly contaminated water, which poses the highest risk to the public. They are, however, having great difficulty in managing the overall contaminated-water situation, especially from a public-confidence perspective. The engineering challenge—control of a complex, ad hoc system of more than 1,000 temporary radioactive water tanks and tens of miles of pipes and hoses throughout the severely damaged plant—is truly a herculean task. Explaining what is going on and what has to be done to an emotional, traumatized, and mistrusting public is an even larger challenge.

Approximately 340,000 tons (90 million gallons) of radioactive water is now stored in large tanks at the site. A variety of water-processing systems have been built fairly rapidly under very difficult circumstances. To minimize the increases in water inventory growth, all cooling water now being injected into the damaged reactor cores is recycled.  It is initially pumped from the building basements and processed through new systems that remove most of the gamma emitting cesium 137 and cesium 134, oils, and salt contaminates, so that the water can be pumped back into the three reactor cores to keep them cool. Because the cores are mostly melted debris, the injected water picks up more radionuclides and flows back into the basements. The water-processing systems now in use are not capable of removing strontium 90, which is only a beta emitter and not a major radiological hazard to trained workers who wear protective clothing. But strontium 90 is an environmental concern and will need to be removed from water before it can be returned to the environment.

The reactor and turbine buildings are not watertight up to the surface; the basements are below the present groundwater elevation, and relatively clean groundwater seeps into the buildings. Tepco is maintaining the water levels in the basements slightly below the groundwater elevation to prevent the leakage of highly contaminated water from the basements into the general environment. But this in-leakage—estimated to be approximately 400 tons (105,000 gallons) per day—mixes with the water already in the basements, also becoming highly contaminated. So each day, despite Tepco’s water-recycling efforts, the volume of contaminated water at the plant increases; this is why 340,000 tons of water are currently stored on site.

This building-basement water is the highest-risk water associated with the Fukushima situation. That water is being handled reasonably well at present, but because of the constant in-leakage of groundwater, some ultimate disposition will eventually be necessary. To further clean this huge and increasing volume of medium-level radioactive water, the Tepco team has built a major new water processing system called the Advanced Liquid Waste Processing System. Built by Toshiba, this state-of-the-art system is based on technology from a major US waste management company, EnergySolutions.

Although this system is in a testing phase, with startup design and operational issues being resolved, it aims to remove more than 99.999 percent of radioactive contamination for most radioisotopes. The radioactivity levels in the effluent of the Advanced Liquid Waste Processing System are expected to be very low and to meet international and Japanese discharge standards for the important isotopes of cesium and strontium. This means that, from a radiological risk point of view, the risk from water treated by this system and released to the sea will be extremely low—a small fraction of the natural variations in the environment’s background radiation. In fact, I am writing this article while sitting on an airplane, and I am receiving more ionizing radiation from cosmic rays at this higher altitude than I would receive from drinking effluent water from the Advanced Liquid Waste Processing System. 

The other water problems. Although contaminated water in the basements and tanks of Fukushima Daiichi are major risks, other water on the nuclear plant’s site is also of concern. In the first weeks of the accident, when workers were injecting the first cooling water into reactor cores, there were uncontrolled releases of highly contaminated water onto basement floors. This water flowed into underground tunnels that connect buildings at the plant, and into seawater intake structures. These many tunnels contain hundreds, if not thousands, of pipes and cables. Most of these were non-safety grade tunnels that were cracked by the earthquake. In March and April 2011, therefore, fairly large volumes of highly contaminated water likely flowed into the ground near the sea and, at some points, directly into the sea. 

When this situation was discovered, Tepco immediately did its best to seal the tunnels with grout, but considerable contamination likely remains in pockets underground, and some surface contamination has migrated downward, into groundwater near these tunnels near the sea. This contaminated groundwater moves, naturally, down-gradient and toward the sea. Although the amount of radioactivity in this groundwater is only a very small fraction of what was released in March and April 2011, this contamination has become an emotional issue, because the public believes it had been told the leakage was stopped. It is in fact true that the gross leakage of highly contaminated water from Fukushima buildings and pipes has been stopped. Still, approximately 400 tons (105,000 gallons) of groundwater per day is moving toward the sea from these areas, and it contains some contamination from these earlier leakage events. The amount of radioactivity in this water flow does not represent a high risk; the concentrations are generally fairly low. Small pockets of the earlier high-contamination water are likely still present; they may be slowly leaking into the ground water, and groundwater sampling has shown many ups and downs in radiation levels over time. On average, however, this low-level of contamination will likely be unmeasureable, once the water enters the sea. Tepco is trying to control this ground water flow by constructing a wall along the edge of the sea and by pumping groundwater into tanks. Regardless of the relatively low concentration of radioactive contaminants and Tepco’s efforts at containment, the water entering the sea in an uncontrolled manner is very upsetting to many people.

There is another pathway by which radioactive water is entering the ocean at Fukushima.

In the first days of the accident, when the cores were not cooled and radioactive cesium was being released into the air, much of the airborne contamination settled on the grounds of the plant. Although not a high radiological hazard to trained workers, who were the only people there, the cesium did not just stay put. Rain dissolved and carried some of the cesium from the ground surface into the normal subsurface water, which naturally flows down from the hill and plateau above the nuclear plant’s buildings toward the sea. Although the contamination levels are very low, generally within release standards, there is some radioactive cesium present in this groundwater, which causes public concern. Given that the hillside is large, it is estimated that about 1,000 tons (250,000 gallons) per day of water flows down toward the plant buildings and approximately 600 tons per day eventually enters the sea (400 tons through and near the damaged units 1, 2, and 3 tunnels). This massive amount of water is far beyond what can be actually contained, even if Tepco tried to do it. Regardless of the company’s intentions, most of this large flow of water is going to mostly end up in the sea.

Public confidence and a practical solution. Although Tepco has worked hard to address the water management situation with extensive tankage and new water processing systems, successfully containing almost all of the significant water-borne contamination, a series of events has completely eroded public confidence in the firm’s ability to handle the situation at Fukushima. The site needs help, and the Japanese government is now going to provide direct assistance to improve the situation. For example, the government has allocated approximately $350 million dollars to build a refrigerated ice wall around the building basements to reduce groundwater in-leakage. 

To address the water challenges at Fukushima Daiichi, an improved, holistic, integrated water-management plan should be created. It should be risk based and address all levels of contamination, from groundwater slightly contaminated by airborne fallout all the way to highly radioactive cooling water flowing out of the damaged cores. It needs to build on the many good Tepco efforts of the past two years, but to move forward by adding new technologies to improve water cleanup system performance in some areas and increase processing capacities in others. Higher-integrity storage systems, such as welded rather than bolted storage tanks, and equipment, including level indicators to monitor the tanks, need to be added. Management and operating processes need to be improved to provide increased coordination between organizations and more efficient water processing. 

Enormous amounts of scarce human and financial resources are being spent on the current ad hoc water-management program at Fukushima, to the possible detriment of other high-importance clean up projects. Although Japan is a rich country, it does not have infinite resources. Substantial managerial, technical, and financial resources are needed for the safe removal of spent nuclear fuel from the units 1, 2, 3, and 4 spent fuel pools, and to develop plans and new technologies for eventually digging out the melted cores from the three heavily damaged reactor buildings. Spending billions and billions of yen on building tanks to try to capture almost every drop of water on the site is unsustainable, wasteful, and counterproductive. Such a program cannot continue indefinitely.

The overall goals for an improved water-management regime should be better monitoring and control of a process that renders all waters to international and Japanese safety release standards within a reasonable period of time. Technical excellence and disciplined hard work, always Japanese strengths, need to be coupled with innovative solutions to develop this new, integrated management framework, which should incorporate external independent monitoring to confirm that all activities are performed in a manner that provides adequate public and environmental protections. I see no realistic alternative to a program that cleans up water with improved processing systems so it meets very protective Japanese release standards and then, after public discussion, conducts an independently confirmed, controlled release to the sea. 

An important part of this plan must be a new proactive engagement with Japanese society to realistically discuss eventual disposition of the processed water. With a frank and transparent discussion of the risks and benefits of all options, trust and confidence can be restored and an ultimate disposition path decided in an inclusive Japanese fashion.

There will still be some who will claim that any release of radioactivity is unacceptable because it will ruin the Japanese fishing industry in the area. I, for one, do not believe this, and someday I hope to be able to introduce my dear grandchildren to the fantastic seafood from the Tohoku coast. Assuming the Fukushima accident water has been properly processed and released, and that the Japanese government has declared the seafood safe for eating, I will gladly feed my own grandchildren these delicious delicacies without a moment’s hesitation.

Life is too short and precious to be marred by unnecessary fears and doubts.