As irony would have it, Fukushima in Japanese means the fortunate island. Sadly, it has been more than six years since disaster hit, and it is still unfolding. On March 11, 2011, an earthquake of magnitude 9.0 – the largest earthquake ever recorded in Japan – hit the Tohoku region causing a massive 13-15 meters high tsunami. The wall around the Fukushima nuclear power plant was designed to stop waves only as high as 5.7 meters.
The electricity supply had been shut down after the earthquake. The cooling of the reactors – a continuous process to stop them from overheating – were dependent on diesel generators. The impact of the tsunami disabled the generators as fuel tanks were swept away. With the cooling system knocked off, the extremely hot and radioactive reactor fuel started melting. Tokyo Electric Power Company (TEPCO) that operated the plant, started pouring sea water on to the reactors as a desperate attempt to keep their temperature under control. The steam inside reacted with the overheated zirconium foil sheath around fuel rods, producing highly explosive hydrogen and triggered the blasts.
Alarming volumes of radioactive substances like strontium, caesium, plutonium and iodine were released. According to the estimates made available, 20 to 40 trillion becquerels (the SI unit of radioactivity, corresponding to one disintegration per second) of radioactive Tritium got leaked into the Pacific Ocean. Everyone within a 20-kilometre radius of the plant was evacuated leading to displacement and unemployment for nearly 200,000 people. Compensation is being reduced or denied to them, and they are struggling with hardships, the psychological stress of developing radiation-borne diseases, social boycott and marginalisation.
The disaster isn’t over yet. TEPCO continues to pour hundreds of tonnes of water on the reactors to keep their temperature under control, and it has stored several hundred thousand tonnes of this highly contaminated water in over 1000 huge tanks. About 300 tonnes of this contaminated water leaks into the Pacific every day. TEPCO has officially announced, much to the shock and displeasure of the world, the release of nearly 1000 tonnes of ‘somewhat less contaminated’ water into the ocean. It could take 40 years and US$ 188 billion to decontaminate Fukushima. These are estimates for the plant site alone, not to forget the gargantuan ecological and social costs. According to a private think tank, the total cost of Fukushima disaster could reach a whopping US$ 626 billion. Many countries have banned sea food import from Japan altogether owing to the adverse effect of radiation on marine life. It’s a case of an entire ocean – the Pacific – getting polluted. Radiation has travelled all the way to North American shores, but scientists say that the levels are low enough to not pose any risk to public health in North American countries.
Another example is that of Chernobyl in Russia. Even after three decades, the 30-kilometre zone around Chernobyl has ghost cities like Pripyat which will remain ghost cities for several centuries. Namie, Futaba and Itate, three busy cities near Fukushima have turned into ghost cities as well. They have everything, the best of infrastructure – schools, hospitals, malls, office complexes etc. – but no human being owing to high levels of radiation. They are frozen in time, thick dust and moss has accumulated everywhere. The decontamination workers, cheap labour pushed into the hazardous job by the labour mafia with complete disregard to the impact of radiation on their health, is scrapping the top soil and cleaning the buildings 20-kilometers off the plant site. The highly radioactive top soil and waste are being dumped into temporary storage sites.
Even after six years of pouring water, they have not been able to get the reactors under control. Toshiba sent one of its most advanced robots inside the building to study the state of molten fuel but it died within hours because the reactors are still emitting radiation.
Let’s count the positives first. Kalpakkam has Prototype Fast Breeder Reactor (PFBR) which does not produce highly radioactive nuclear waste. It has also survived the Vardah cyclone and is in a relatively safe seismic zone too. The return period of the tsunami that hit the Indian shores in 2004 is 1000 years. Post-Fukushima, India has revisited the structural design and elevated the height level of backup diesel generators and their fuel tanks. The floor level of the island building of the Kalpakkam FBR is 9.6 meters above sea level, which is 5 meters higher than the 2004 tsunami water level. Hence, there is no possibility of water entering the complex. The submarine faults are located more than 1300 kilometres from Kalpakkam and therefore the simultaneous occurrence of natural disasters i.e. an earthquake followed by a tsunami as was the case in Fukushima is not foreseen.
Let’s look at issues of concern now. According to Swaminathan S Anklesaria Aiyar, regular nuclear reactors are cooled either by light or heavy water, but the Fast Breeder Reactors (FBRs) use liquid sodium as a coolant. Liquid sodium reacts explosively with both air and water and even a minute leak can cause fires. TEPCO used water cannons to bring the temperature of Fukushima reactors down but in the case of an accident in an FBR, water cannot be used as its reaction with liquid sodium coolant would trigger an explosion.
The International Panel on Fissile Materials reports that Russia’s BN-350 FBR has had a big sodium fire. The improved version BN-600 FBR that was designed to contain sodium-water fires has had as many as 27 sodium leaks of which 14 resulted in sodium fires between 1980 and 1997. Monju, Japan’s FBR had a major sodium-air fire in 1995. The reactor was shut down, and recently Japan has announced that it has given up on it. The list does not end here. The Rapsodie, Phenix and Superphenix reactors of France as well as UK’s Dounreay Fast Reactor (DFR) and Prototype Fast Reactor (PFR), all of them have had sodium coolant leaks, some of which have resulted in big fires.
Besides the liquid sodium coolant limitation, there are other challenges as well. According to scientists MV Ramanna and Ashwin Kumar, the containment dome of the Kalpakkam reactor is not as strong as that of other reactors. One of the hallmarks of the accident-proof designs is to have physical barriers that can withstand severest of the accidents. Secondly, there is a problem with the core design of FBRs as they have a positive coolant void coefficient. Put simply, when operating normally the core of the FBR is not in its most reactive or energy producing state. An accident can lead to dramatic increase in its reaction rate leading to an equally dramatic increase in energy production. This large amount of energy produced is explosive and might rupture the reactor vessel and release radioactive substances into the environment.
It is possible to decrease this probability by designing a heterogeneous core as Russia is doing for its forthcoming BN-1600 reactor, but the Indian Department Of Atomic Energy (DAE) has not worked towards it. Reducing the sodium coolant void coefficient would have increased the fissile material requirement by 30-50%, making it a very expensive proposition. Even a stronger dome would have cost more. Both these factors, the dome not being as strong and the positive coolant void deficient bring down the cost of the FBRs and the unit cost of electricity produced. This aids in the rapid deployment of FBRs as well but Aiyar argues that this cost reduction should not be at the expense of high risk of catastrophic accidents.
The DAE has done some studies regarding fatality of a core-disruptive accident and the amount of explosive energy it would release. In the case of Kalpakkam FBR, DAE estimates that the worst core-disruptive accident would release 100 megajoules (MJ). Somehow, this seems to be an underestimation when compared to other FBRs and considering both its large power production capacity and the amount of fissile material to be used. This DAE estimate is based on assumptions that only one part of the core shall melt and only 1% of the energy released would get converted to mechanical energy that can damage the containment dome and lead to release of radioactive materials into the environment. Experiments done by British Atomic Energy Authority suggest that not 1% but 4% of the energy released gets converted into mechanical energy. Besides, there is no way that scientists can conduct a full-scale experiment to test the theoretical models used by reactor designers in their estimates.
Baldev Raj, Director, Indira Gandhi Centre for Atomic Research and Prabhat Kumar, Project Director, Bhartiya Nabhkiya Vidyut Nigam Limited, both based at Kalpakkam, answered Swaminathan Aiyar’s concerns immediately after. According to them, the Sodium-cooled Fast Reactors (SFRs) have attained adequate technological maturity. SFRs world over have gained more than 400 reactor years of operation. The technologies of sodium coolant and mixed oxide fuels lie largely mastered.
India has been pursuing FBR program since the ’70s by setting up a dedicated scientific organization, the Indira Gandhi Centre for Atomic Research. We have successfully operated the Fast Breeder Test Reactor (FBTR) for over 25 years. The Kalpakkam reactor design complies with robust national and international standards. Safety has been demonstrated through analytical and numerical analyses and experiments, more than 200 of them over three decades, under environments prevailing in the reactor. Design and safety aspects have been reviewed from design to component erection by competent experts under Atomic Energy Regulatory Board (AERB).
As far as Aiyar’s observations regarding the dome strength are concerned, one must understand that the dome design requirements for water reactors are different from SFRs and therefore it is inappropriate to draw comparisons. Water reactor domes, especially in case of pressurised heavy water reactors or PHWRs, are almost six times stronger because they are designed for pressure developed owing to loss of coolant accidents caused by rupture of heat transport pipes or steam line break. While in case of an SFR there is no such eventuality as sodium remains in liquid state at low pressure even at high temperatures. However, the dome of SFRs is designed to contain sodium fire and is strong enough for that.
When it comes to the second issue – the positive coolant void coefficient, there have been vast improvements like two independent and fast acting shut down systems; dedicated decay heat removal systems and provision for in-service inspection of the reactor vessel. There is no safety concern of sodium coolant voids during operation. In the case of a core-disruptive accident, other prompt negative reactivity feedbacks like Doppler and fuel expansion coefficients are in place. Overall, the reactor core safety has been adequately ensured.
The ultimate heat sink in SFRs during decay heat removal condition is air, not water. During the reactor shut down, even after an off-site power failure, the heat generated in the core will be removed comfortably by a set of dedicated heat exchangers. These heat exchangers will pass on the heat to the atmospheric air by way of natural convection without any external power supply. Sodium has high heat transfer properties. The operating temperature is 820 K, and the boiling point of sodium is 1200 K, and this difference can accommodate temperature rise without vaporisation. The ambient air being at 310 K and hot sodium being at 820 K lead to heat exchange via convection. Therefore, there is no need for any additional emergency core cooling system.
For sodium fires, the welding points in pipes have been reduced significantly by adopting two, the minimum possible number, primary and secondary sodium loops; use of improved stainless steel grade pipes; advanced nondestructive examination techniques with sensors and instruments for detecting defects, etc. The sodium to air contact is prevented by surrounding the pipes with guard pipes carrying inert nitrogen, and incorporating a safety vessel surrounding the main vessel with inert nitrogen in the space between the two vessels. Innovative self-extinguishing materials and technologies have been deployed as well.
Initial sodium fires in FBR reactors world over have provided experience to improve the design. The Russian BN-600 has operated for 30 reactor years, and the last sodium fire was almost two decades ago. French Superphenix and Japanese Monju have been shut down because of political reasons, not scientific, just like Germany decided to close nuclear reactors as a policy decision after Fukushima nuclear disaster. Other reactors like Phenix, PFR (UK) etc. have completed their design life and shut down,but none due to sodium fires.
India has a wealth of experience of more than 40 years in managing sodium coolant. There has been only one sodium leak in Kalpakkam test reactor which did not result in any fire, and the reactor was back in operation within 60 days. Even in PFBR at Kalpakkam, more than several hundred tonnes of sodium has been transferred from tankers to various storage tanks without any incident whatsoever. China, France, Japan, Russia and South Korea are in an SFR race with us and admire our track record and safety measures. We have been appreciated in international journals as well.
The nuclear industry in India is non-transparent and unaccountable. It comes directly under the Prime Minister’s Office (PMO) and therefore is insulated from scrutiny. The archaic Atomic Energy Act of 1962 related to national security is quoted as the reason for rejection of RTIs. In the case of Kundankulam, DAE refused to divulge the site selection and safety assessment reports which are made public the world over. Chief Information Officer’s letter to the Prime Minister received no response.
We have a toothless regulator, the Atomic Energy Regulatory Board (AERB) which monitors the Atomic Energy Commission (AEC) but it depends on AEC for salaries and expenses. How and why will the regulator then bite the hand that feeds it? Dr. A.K. Gopalakrishnan, the AERB chairman, had ordered a safety audit, but the central government shelved the report calling it a state secret. The government chose to set aside post-Fukushima recommendations of AERB for getting a green signal for Kundankulam from the Supreme Court. AERB was forced to call its recommendations advisory, not mandatory.
The government has assured of evacuation and post-accident plans, but DAE in most cases does not reveal anything about emergency preparation management. Unlike Fukushima, the 20-30 km area around Kalpakkam is densely populated. Emergency drills before commissioning a reactor seem hollow – relocating 50,000 people to a school complex while only a few hundred are packed in buses and taken to nearby villages.
We need to have a safety culture, reliable civic administration, people centric mechanism for an adequate response but what we have instead is a system that’s answerable to none. Why would it reveal its shortcomings? In the US, private companies operate the nuclear power plants, and a government regulator keeps an eye on them. In India government operates them and the government regulates them. No questions regarding safety assessment, monitoring and evaluation are entertained because these are state secrets. It’s time we have an independent regulator like TRAI, IRDA, etc. that asks relevant questions and directs the government agencies that operate nuclear plants to ensure absolute safety.
If one were to define accidents, they are unanticipated happenings despite all precautions. Even a developed country like Japan with advanced technologies and the responsive administration has not been able to manage a nuclear accident. Fukushima has been an eye opener as it has told the world in no uncertain terms that every nuclear reactor can undergo an accident and nuclear disasters are long-term, irreversible, genetic and uncontrollable. There is absolutely nothing that we, despite all the scientific and technological developments, can do to check it. Also, nuclear accidents should never be compared with industrial or other accidents because in those cases reconstruction and relief can start almost immediately while nuclear disaster sites become ghost sites for decades and at times, centuries.