What Happened? Fukushima Nuclear Accident. ON March 11 this year, an. Cover Story K.S. PARTHASARTHY

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1 Fukushima Nuclear Accident What Happened? K.S. PARTHASARTHY Fukushima will now be remembered with Three Mile Island and Chernobyl, three places where nuclear accidents occurred. Apparently nuclear technology is on trial now. Though many reactors and related facilities are involved, the radiological impact of the incident is unlikely to be as much as that from the accident at the Chernobyl nuclear power station. ON March 11 this year, an earthquake of magnitude 9.0 on the Richter scale, followed by a 14-metre tsunami caused incalculable damage in Japan. According to Japan s National Police Agency, as on 3 April, 12,341 persons were dead and more than 15,000 missing. The economic losses are pegged at $239 billion, about 4 % of the Gross Domestic Product. The rarest of the rare, simultaneous occurrence of two natural phenomena, a powerful earthquake and a devastating tsunami, led to a serious situation at the Fukushima Atomic Power Station (Fukushima Daiichi). The staff of the Tokyo Electric Power Company (TEPCO) ably aided by other Japanese personnel is trying to mitigate the effects of the accident. Japan operates 54 nuclear power reactors that generate 30 % of the total electric power in the country. The accident is likely to retard the much talked about nuclear renaissance at least in some countries. However, we do not hear any talk of a moratorium on nuclear power generation from Japan. SCIENCE REPORTER, MAY 2011 Japan is earthquake prone. The Japanese include seismic factors in any construction activity, be it buildings, nuclear power reactors or other facilities. They keep track of the developments in this area far more seriously than any other country. The epicenter of the Tohoku- Taiheiyou-Oki earthquake was 130 km offshore of the city of Sendai in Miyagi prefecture, Japan, on the eastern coast of Honshu Island. The earthquake moved the island 4 metre east and apparently subsided the nearby coastline by half a metre (World Nuclear Association, 29 March 2011). The Nuclear Accident Eleven operating nuclear power reactors close to the region shut down automatically. They are TEPCO s Fukushima Daiichi 1,2,3, Fukushima Daini 1,2,3,4, Tohoku s Onagawa 1,2,3 and JAPCO s Tokai. Nuclear power reactors are equipped with earthquake sensors. If the ground acceleration at the location reaches above a preset value (90% of the design value), the reactor will shut down automatically. The full facts on what happened in Fukushima are not known. During 20 to 24 June 2011, the International Atomic Energy 8 Agency (IAEA) will organize a High-Level Ministerial Conference on Nuclear Safety to learn the right lessons from what happened on 11 March and afterwards at the Fukushima Daiichi nuclear power plant and to strengthen nuclear safety throughout the world. The Conference should provide an initial assessment of the Fukushima accident, its impact and consequences; consider the lessons that need to be learned; launch the process of strengthening nuclear safety, and strengthen the response to nuclear accidents and emergencies. The Fukushima reactor site suffered immensely. Hydrogen explosions, fires, radioactive releases to the outside Explosion at the nuclear reactor

2 All nations will consider that Japan s location and its proneness to earthquakes and tsunami are very peculiar and that those considerations need not come in the way of new nuclear build. environment, contaminated water in the reactor building, increase in radiation levels at the site, among other events. One worker died in a crane accident at Fukushima Daini. It was also reported that the dead bodies of two missing persons were located in the turbine building of Unit 4. Many workers are attending to the mitigation of the accident with stringent dose control procedures in place. None of them will receive doses more than the limits prescribed by the regulatory authority. Fukushima Daiichi plant has six Boiling Water Reactors (BWRs), Unit 1 of 460 MW capacity; units 2,3,4,5 are of 784 MW capacity and unit 6 has 1100 MW capacity. When the earthquake hit, the reactors 4, 5 & 6 were in shutdown stage for planned maintenance. The remaining reactors were shut down automatically during the earthquake. But then, a tsunami of 14 metres caused by the earthquake flooded the plant. When a reactor is shut down, power level due to fission reactions drops. But the fuel contains fission products and activation products. These decay at different rates. The energy released during decay will continue to heat up the fuel producing substantial quantities of decay heat. Just prior to shut down, the decay heat may be as high as 7%. It reduces exponentially to about 2% in the first hour. After one day, it will still be 1%. The decay heat is enough to heat the fuel, leading to its melting and cladding failure. The coolant flow must be maintained for a long time even after the reactor is shut down. In a nuclear power reactor, there are arrangements to cool the reactor. In an emergency, there are dedicated emergency core cooling systems. Normally, the line supply powers the pump. If it fails, the pump will not run, the core will heat up and melt, the fuel cladding may fail releasing radioactivity. To prevent this, there is a back-up supply in the form of diesel generators (DGs). There will be sufficient quantities of oil stored at the site to ensure that the DGs work continuously till the line supply comes back on line. If DGs also fail, Reactor Core Isolation Cooling (RCIC) pumps, which operate on steam from the reactor, will be used to replace reactor core water inventory; however, these pumps have their valves driven by batteries. At Fukushima, the battery-supplied control valves could not function for long One of the essential safety requirements in the case of nuclear power reactors is that the reactor core where the heat is generated must remain immersed in water all the time. There was some Wet Well (Torus) Fukushima Daiichi Unit-1 Cross Section evidence that due to lack of cooling, core meltdown occurred partially in reactors 1, 2 & 3. During the early hours, the pressure in the reactor pressure vessel of Unit 1 increased because of insufficient cooling. Normally the steam generated will get released through the suppression pool. The steam gets quenched partially depending on the efficiency with which the pool can condense steam. The remaining steam and non-condensable will reach primary containment causing pressure increase. Spent Fuel Pool Core Dry Well 9 SCIENCE REPORTER, MAY 2011

3 Generation of Nuclear Power A nuclear power reactor and a conventional power plant use steam to drive a turbine generator to produce electricity. The main difference between them is in the way the steam is produced. In a nuclear power reactor, energy released by nuclear fission produces steam. Most nuclear power reactors are fuelled by enriched uranium. When a reactor operates, fission of uranium-235 nuclei occurs at a steady rate. With each fission, two or more neutrons are also emitted. Some of these are emitted with some delay. These fast neutrons are slowed down as they travel through a moderator such as water. Uranium-235 nuclei absorb these moderated neutrons causing further fission and release of energy. The process continues at a steady rate causing a chain reaction. In a reactor there are arrangements to control the rate at which fissions occur. Each fission releases energy that heats up the core of the reactor. In Boiling Water Reactors (BWRs) the heat from the core is removed by water; the steam generated is made to drive a turbine to produce power. The steam in a BWR contains traces of radioactivity. Checking for radiation exposure (below); and Three Mile Island-site of another nuclear accident (right) Since suppression pool recirculation pumps, which are part of the emergency cooling system, were damaged by the tsunami waves, they were not available. This compromised the heat removal efficiency of the suppression pool its temperature increased. Hydrogen leaked from the primary containment to the secondary containment, reached the explosive limit, exploded and blew off the roof. Whether the operators vented the containment to reduce pressure is not clear. Hydrogen explosions occurring at different times destroyed the upper portions of the buildings that housed reactors 1, 3 & 4. An explosion damaged the suppression pool inside reactor 2; it must have affected the integrity of the primary containment of Unit 2. Multiple fires broke out at reactor 4. The fires died out subsequently. Radioactive releases occurred with the explosions. Since the temperature of the coolant water in the reactors was found to increase, the operators tried to pump seawater through the affected reactors. Apprehending that sea water may lead to clogging in the reactor internals and salt deposit may inhibit cooling of the fuel rods the rescuers pumped light water instead at quantities of 7 to 8 cubic metres per hr. This process is continuing. Present Status at Fukushima As on 5th April, the IAEA daily update continues to state that the situation remains very serious at the Fukushima Daiichi plant. The good news is that on April 3, line supply has replaced the temporary mobile power supply to pump water through the Reactor Pressure Vessels (RPV) of Units 1, 2 and 3. Also lighting in a part of Units 1-4 Explosive hydrogen concentration in secondary containment Turbine Building was restored on 2 April. Water containing high levels of radioactivity was seen in the containment Units of 1, 2 and 3 and in the drainage pits of Units 5 and 6. Regulatory authority has allowed the company to transfer 23,000 tonnes of water containing low level of activity from different locations of the plant to sea. The volume thus freed may be used to store highly contaminated water from the turbine buildings of the stricken reactors. After several unsuccessful efforts with different techniques, the TEPCO staff managed to stop flow of highly contaminated water from Unit 2 to sea by injecting coagulation agents (liquid glass). Spent Fuel Pools Spent or used fuel rods contain fission products and activation products such as plutonium. Once removed from the reactor, they remain in a specially constructed pool of water over 40 feet deep for one to three years. Water SCIENCE REPORTER, MAY

4 International Nuclear Events Scale The Fukushima incident has been elevated to level 7 on the International Nuclear Events Scale The earthquake moved the island 4 metre east and apparently subsided the nearby coastline by half a metre provides cooling and shielding. Each pool has systems to maintain temperature and level of water to provide cooling and radiation shielding. In Fukushima Daiichi, there are seven pools. One at each reactor and a shared pool. The used fuel pools at Fukushima Daiichi reactors are located at the top of the reactor building. This is as per design for easy handling of the fuel rods during de-fuelling operations. The pools are robust, steel and concrete structures designed to protect the used fuel from even the most severe accidents. Used fuel does heat up the water in the pool. This heat is continuously removed through heat exchangers in the pool. This helps to maintain the temperature of water in the pool at a low value. The safety status of the pools is unknown. Unlike reactors, they do not have a containment. If the fuel rods are left uncovered, they may come into contact with steam and air, oxidize releasing hydrogen. Hydrogen explosion will release radioactivity to the environment. At Fukushima, the spent fuel pools were losing water cover. Normally the temperature of the pool is about 25 degree Celsius. The water in the spent fuel pools in Fukushima had higher temperature of 58 degree to 84 degree Celsius. The spent fuel pool of Unit 4 suffered a hydrogen explosion and fire. We do not know to what extent fuel rods in the pool are exposed. Radiation Monitoring in Japan Japanese authorities started measurement of environmental radiation levels and concentration of radioactivity in foodstuffs right from the early days of the accident. They concentrated on the measurement of Iodine-131 and caesium-134/137 in various food items. Iodine-131 was implicated in childhood thyroid cancers in Chernobyl. On March 12, the Japanese authorities started evacuation of 170,000 persons from a zone of radius 20 km around Fukushima Daiichi and 30,000 from a zone of radius 10 km around Fukushima Daini. At the evacuation centres they distributed 230,000 doses of stable iodine. Flooding thyroid with stable iodine is a wellproven prophylactic method to prevent entry of radioiodine to the thyroid. It is very effective if used just ahead of any radioiodine entering the body. Various agencies were keeping track of radioactivity levels in different foodstuffs for the past several weeks. Initially high values were observed. As of 4 April, iodine-131 and cesium- 134/137 were detectable in drinking water in a few prefectures. All values were far below levels that would trigger recommendations for restrictions of drinking water. As of 6 April, one restriction for infants related to I-131 (100 Bq/l) remains in place as a precautionary measure in only one village of the Fukushima prefecture. A Bq is a unit of radioactivity. In a Bq one disintegration occurs every second. Since 23 March, gamma dose rates in the 45 prefectures have decreased. IAEA noted that values of dose rate for 6 April showed no significant changes. Gamma dose rates were reported for 45 prefectures to be between 0.02 to 0.1 microsievert per hour. In one prefecture the gamma dose rate was 0.16 microsievert per hour. These values are within or slightly above the natural background of 0.1 microsievert per hour. Background radiation at any location depends on the contribution from natural radioactive materials such as uranium, thorium and their decay products and potassium-40 in soil, some contribution from airborne radio-nuclides and cosmic rays. Cosmic ray contribution will depend on the latitude and to a greater extent on the altitude of the location. One notable feature of these results is the wide variation in the levels across various locations. The highest levels recorded are in Manvalakurichi. This is due to the higher concentrations of thorium in that area. Radiation Doses to Workers at Fukushima Unlike in Chernobyl, no worker in Fukushima died of radiation exposure. The media characterized rescuers as suicide 11 SCIENCE REPORTER, MAY 2011

5 The Chernobyl disoster (top) occurred 25 years ago; while thousands died due to the recent tsunami in Japan, no deaths were reported due to radiation exposure squads. This dramatized description made good copies. However, the workers were well-trained volunteers who wore protective gear. Their radiation doses were closely monitored and controlled. None of them exceeded the dose limit of 250mSv stipulated by the regulatory agency. Nineteen workers who belonged to the rescuer-team received over 100mSv. Three workers exceeded 170mSv. Two workers who worked in an area that had highly contaminated water received doses of 2000 to 3000 msv to the skin of their feet. Water seeped into their shoes. Based on further monitoring, they were discharged. Except for these workers, the doses were not unacceptably high for the type of operation they undertook. However, one worker died in a crane accident in Fukushima Daini plant; two workers who were missing were found dead in the turbine hall of Unit 4 presumably due to the tsunami. Fifteen workers were injured due to explosions in Units 1 and 3. Eleven of them returned to work. INES Rating Japanese officials rated the event at Fukushima at Level 5 in the International SCIENCE REPORTER, MAY 2011 Nuclear Events Scale (INES), which has now been raised to 7. INES is a useful tool to communicate to the public in consistent terms the safety significance of nuclear and radiological incidents and accidents. The Chernobyl accident was rated 7 in the INES; TMI Island accident was rated 5. The INES scheme classifies events at seven levels: Levels 1 3 are incidents and Levels 4 7 accidents. These levels consider three areas of impact: people and the environment, radiological barriers and control, and defence in depth. The scale is designed so that the severity of an event is about ten times greater for each increase in level on the scale. Events without safety significance are called deviations and are classified Below Scale/Level 0. Lessons from the Accident What are the lessons to be learnt from the accident? What has been done? What more has to be done? We have to wait till the entire events unfold themselves. We learnt many lessons from the accidents at the nuclear power stations at Chernobyl and Three Mile Island. Even the most ardent nuclear enthusiast cannot dismiss the recent accident, just because it resulted from the simultaneous occurrence of two rarest of rare natural disasters. AERB has already set up a specialist committee to review the capability of Indian Nuclear Power Plants to withstand earthquakes and other external events such as tsunamis, cyclones, floods, etc. The committee will examine the adequacy of provisions available to ensure safety in case of such events, both within and beyond the design basis. The Board has also set up a five member monitoring cell to monitor the events in Fukushima, maintain a database updated daily, and to coordinate with DAE and other support organizations to collect information on radiation levels, contamination levels in soil, air, water and food in Japan and India. The cell is also asked to prepare advice on actions to be taken by AERB in respect of radiation safety in public domain. The Nuclear Power Corporation of India Limited (NPCIL) set up four committees to study the event and its impact. The committees have already submitted interim reports. NPCIL will implement several significant safety short term and long-term recommendations to improve safety. 12 Earthquakes, Tsunamis and Floods in India We have some experience with the impact of earthquake, tsunami and floods on nuclear installations. The nuclear power plants at Kakrapar, Narora, and Rawatbhata operated normally during the Bhuj earthquake (6.9 on the Richter scale) on 26 January Their vibration levels were much below those for which they have been designed. In 2003, the International Atomic Energy Agency (IAEA) deliberated on the seismic safety features of reactors built as per earlier standards and published a document No 28 titled Seismic Evaluation of Existing Nuclear Power Plants. Specialists re-evaluated the seismic safety of Units 1 & 2 of the Tarapur Atomic Power Station (1969 vintage) and remedied the shortfalls by following the practices and guidelines of IAEA. The safety status of all reactors including Tarapur Units- 1 and 2 will now be reviewed again by AERB and separately by NPCIL. The NPCIL has installed seismic sensors at all plants as stipulated by the Atomic Energy Regulatory Board (AERB). Indian standard code IS 1893 Criteria for Earthquake Resistant Design of Structures categorises the country into four seismic zones and specifies the maximum possible earthquake in each zone. Rawatbhata, Kaiga, Kalpakkam and Kudankulam are in Zone II; Kakrapar, Tarapur and Jaitapur are in Zone III; Narora is in Zone IV. An AERB monograph lists the major earthquakes in India. All earthquakes magnitude 8 and above occurred in Zone V. AERB has issued a Code Practice on Safety in Nuclear Power Plant Siting. The Code prescribes the criteria for selection of sites for nuclear power plants (NPPs) and addresses the impact of natural events such as earthquakes, shore line erosion, flooding etc and man-induced events such as aircraft crash, chemical explosions, toxic gas releases and oil slick. AERB evaluates the general seismic intensity expected for earthquakes in the region by considering the seismic history and its potential as well as geological characteristics of the region. AERB stipulates that historical data relating to the past earthquakes in the tectonic province covering an area of about 300 km radius around the site in which the proposed plant has to be located should be collected and submitted for review.

6 Japan operates 54 nuclear power reactors that generate 30 % of the total electric power in the country. AERB shall not allow NPPs to be constructed at sites falling above Zone IV. AERB prohibits construction of NPPs at sites with a fault located within 5 km. The designers estimate the seismic parameters for nuclear power plant structures conservatively. The analysis and design of these structures follow internationally accepted standards. The most important parameter is the peak ground acceleration due to earthquake at a site. This is expressed in units of acceleration due to gravity (g). As the nuclear power reactors at Narora are at seismic Zone IV, they have been designed by accepting a value of 0.3 g for the peak ground acceleration. A value of 0.1 g is taken for the reactors at Rajasthan and for other reactors a peak acceleration value of 0.2 g is taken. Standing up to the Tsunami The Madras Atomic Power Station (MAPS) withstood the tsunami disaster that hit the east coast of India on 26 December Unit 2 was operating at 215 MWe while Unit 1 was under long shut down. Following tsunami, the water level in the seawater pump house of the plant had arisen causing tripping of condenser cooling water pumps. The operator manually tripped the turbine generator noticing the unavailability of these pumps. Following this, the reactor tripped automatically. Subsequently, the reactor was brought to cold shut down state by following the emergency operating procedures. The increase in water level in the pump house during the tsunami made all the seawater pumps located in this area unavailable except one process seawater pump. This also became unavailable due to choking of the travelling water screen in the seawater pump house due to the heavy ingress of debris caused by the tsunami (AERB Annual Report ). Further, cooling of Unit 1 of MAPS and different loads were achieved by using fire water system. Though the offsite power remained available throughout the event, emergency diesel generators were started and kept running as a precautionary measure. What is a Safe Radiation Dose? The best answer is: It depends. There is no universally acceptable safe dose. For radiation workers, Atomic Energy Regulatory Board (AERB) wants the annual dose to be as low as reasonably achievable (ALARA); also it should not exceed 30 millisievert (msv) excluding the dose due to natural background radiation and medical exposure. AERB s annual dose limit at 30mSv for radiation workers is lower than 50 msv prescribed by USA. (Sv is a unit of biologically effective dose. Sv corresponds to absorption of one joule of radiation energy from gamma rays or beta particles or X- rays per kg of tissue. Since Sv is a big unit its submultiples such as milli (1/1000 th ) or micro (one millionth) or nano (one thousandth of a millionth) are normally used. I have received about 0.9mSv while recovering a lost radiation source used in industry. Twenty recovery workers in Fukushima accident received less than 200 msv; the dose limit decided by the Japanese regulatory agency was 250 msv. For members of the public, the dose limit is one msv. Pregnant workers may continue to work but the dose to the foetus should not exceed one msv. In medically justified procedures the following doses in msv may be considered as safe: Cardiac CT scan 12; angioplasty on an average 400, at times even 1000mSv; treatment of hyperthyroidism, 100,000; radiation treatment of cancer 60,000 msv to part of the body. In all cases doses must be ALARA without losing medical benefits. In USA, the dose limit for an astronaut is 250mSv per mission. In an offsite radiation emergency, sheltering and administration of stable iodine may start at a minimum dose of 20 msv; evacuation is mandated at 100mSv. The average natural background radiation dose is 2.4mSv annually. In England and Wales, residents of over 100,000 to 200,000 homes are exposed to more than 10mSv annually from radon, a radioactive gas found in nature. The maximum value is more than 100mSv. Millions of persons in countries with temperate weather receive doses ranging from 5 to10 msv or more from radon decay products. People seldom carry out remedial actions in their home. We accept different values of doses as safe and acceptable, depending on circumstances. One need not lose sleep over receiving a few tens of msv, if the occasion demands it. Exposing oneself to a few tens of millisievert in a reactor accident is no way different from receiving the same dose from radon at home. This is to place the issue in perspective and not to justify sloppy practices in reactor operation that may expose some people to unwanted doses of ionizing radiation. The tsunami damaged only the peripheral areas such as the cement brick wall at the plant periphery. It inundated roads on the east side of the turbine building. After detailed review AERB permitted operation of the unit on 1 January 2005 six days after the tsunami. There was no loss of life or significant loss of property due to the tsunami. Radiation levels in and around the plant were found to be normal. Vital areas such as the reactor building, turbine and service building switchyard, water treatment plant etc were unaffected by the tsunami. What is the likely impact of tsunami at other sites? Kudankulam reactors have an elevation of 7.5 metres above the mean sea level to take care of a potential tsunami. For Prototype Fast Breeder Reactor (PFBR) being constructed at Kalpakkam, the elevation is 9 metres. For Jaitapur, the elevation above mean sea level is about 25 metres. After excavation the elevation will be 16 metres. Specialists believe that these elevations are more than adequate to take care of potential tsunamis. Over the years, the designers of Indian nuclear power plants have introduced important modifications in the plants based on operating and other experience. However, they along with the regulatory agency must revisit the changes in the light of the accident at Fukushima. There have been instances of unprecedented floods that affected the functioning of the nuclear power plants at 13 SCIENCE REPORTER, MAY 2011

7 operation and the station policies are approved by AERB. Further, for monitoring of the environment around the nuclear power plants, Environmental Survey Laboratories (ESL) are stationed at each site. The sampling and analyzing of the radioactivity in the environment matrices like water, air, soil, sediment, vegetation, milk etc. are done by these ESLs regularly. Each ESL is equipped with modern nuclear, meteorological and chemical instruments and operated by trained and experienced scientists. Also Environmental Thermo Luminescent Dosimeters (TLDs) are located at various locations surrounding the plant to measure the integrated environmental dose over a period of time. Moreover, as a measure of abundant caution, prior to the issuance of a license for the operation of a nuclear facility, AERB ensures that the facility has the Site-specific Emergency Preparedness and Response Manuals for radiological emergencies. These Emergency Response plans include the emergency response organisations, their responsibilities, the detailed scheme of emergency preparedness, facilities, equipments, coordination and support of various organizations and other technical aspects. No nuclear power plant can operate without approved and tested emergency response plans which are rehearsed periodically at every site. HJK: In case of radioactivity leakage what are the steps taken by government agencies and what precautions should the general public be aware of? R. BHATTACHARYA: An accidental release of radioactivity confined to the exclusion zone constitutes a Site Emergency. An assessment of such a situation would imply that protective measures are limited to the site boundary only. In case the radiological consequences of an emergency situation originating from NPP are likely to extend beyond the site boundary (exclusion zone) and into the public domain, district government officials have the overall responsibility of deciding and implementing the appropriate protective actions for the public during a nuclear power plant radiological emergency. They are responsible for notifying the public to take protective actions, such as evacuation, sheltering in safe places or taking potassium iodide pills as a supplement. State and local officials base their decisions on the protective action recommendations by the nuclear power plant operators. Evacuation is an extreme measure taken after evaluating the risks and benefits of this countermeasure in terms of the averted dose. If radiation levels in the affected zone continue to exist beyond acceptable levels, then relocating the affected population is resorted to. Residents living in the vicinity of a nuclear power plant should increase their awareness about radiation by attending the training sessions conducted by NPP units. In the unlikely event of a nuclear power plant accident, members of public living in vicinity of a nuclear power plant should follow the instructions of the district government officials. These instructions include directions for intake of prophylactics, sheltering or for evacuating to reduce any possible exposure to radiation. HJK: How would you allay the fears expressed by those opposing the Jaitapur nuclear reactor? R. BHATTACHARYA: Today s nuclear power plants are designed with very high level of safety. During normal operation the radiological impact from these plants to the environment is negligible. Possibility of accidental release harmful to the public is extremely rare. However, clearance will be given for any project for different stages like siting, construction, commissioning and operation after in-depth review of all safety aspects through a wellestablished three-tier review system of AERB. After several unsuccessful efforts with different techniques, the TEPCO staff managed to stop flow of highly contaminated water from Unit 2 to sea Rajasthan and Kakrapar. NPCIL and AERB may revisit the modifications made to verify their adequacy. Some design features of PHWRs On 31 March 1993, a serious fire incident occurred at the Narora Atomic Power Station leading to a black out (loss of all power supplies) for 17 hrs. Thermosiphoning took place. Thermo-siphon refers to a method of heat exchange based on natural convection, which circulates liquid without the necessity of a mechanical pump. It is a physical phenomenon and not an add on system. It is obviously a passive method of cooling. Active cooling depends on use of pumps to drive the coolant. During the incident, there were no fuel failures or related consequences. Based on this experience, NPCIL initiated remedial actions to prevent such incidents in all reactors. Earlier, BARC scientists led by Dr V. Venkat Raj demonstrated experimentally the thermo-siphoning capability of Indian PHWRs. PHWRs have an important advantage. PHWR of 220 MW capacity has an inventory of 210 tonnes of heavy water; besides this, the calandria vault has about a few hundred tonnes of ordinary water. Large inventory of heavy water and light water will serve as a possible heat sink in a loss of coolant accident. Fukushima Accident: Measures taken in India Soon after the Fukushima accident there was public concern that radioactive material from Fukushima may be carried to the Indian continent by various atmospheric processes and may cause increases in background radiation levels. 15 SCIENCE REPORTER, MAY 2011

8 The Indian Environmental Monitoring (IERMON) network collects data from 85 locations in different parts of the country and transmits them to a central unit in BARC. Background radiation levels at different locations are published by AERB, DAE and NPCIL in their website. These radiation monitors have not recorded any detectable increases in back ground radiation levels. Doses are shown in nanogray per hour in AERB website. This unit is equal to nanosievert per hr. BARC scientists detected radioiodine released from the accident (26 April 1986) at the Chernobyl nuclear power station by measuring the radionuclide in goats thyroid. Radionuclides such as iodine-131 will deposit on the surfaces of grass. Goats thyroid will concentrate iodine 131. The activity concentration in goats thyroid gives an idea about iodine-131. Radioiodine appeared in goats thyroid samples at various power stations on or around May 14. The concentrations increased steadily reaching the highest value of 26.7 Bq per gm on May 27 at Rawatbhata. The radioiodine content in goats thyroid was significantly less in Kalpakkam compared to that in Rawatbhata and Tarapur. Notable depletion of radioactivity occurred during its transit from northern to southern regions of India. So far, the goats thyroid has not registered any increase in activity due to SCIENCE REPORTER, MAY 2011 radioiodine from Fukushima. We are able to detect extremely small amounts of radioactivity as our measuring techniques and instruments are very sensitive. It does not mean that these radiation levels are harmful. Public was concerned about the possibility of foodstuffs contaminated by Fukushima fall out getting imported into India. Indian scientists have attended to a similar issue in 1987 when there was wide spread apprehension that foodstuffs, particularly dairy products, contaminated with Chernobyl fallout may be imported into India. AERB acted proactively by organizing the collection of imported food samples from ports with the help of public health officers and its activity assessment by the laboratories of BARC. Only those foodstuffs that were below the AERB s limit were allowed into the country. In 2003, AERB initiated a programme that accredited a few laboratories to measure radioactivity in foodstuffs. Six laboratories in various parts of the country are ready to assist the importers of food items. The Nuclear Path Fukushima is a serious accident, caused by the highly improbable simultaneous occurrence of a very severe earthquake and a devastating tsunami that left persons dead and over 15,000 missing. Unlike Chernobyl, Fukushima did not kill any 16 An AERB monograph lists the major earthquakes in India. All earthquakes magnitude 8 and above occurred in Zone V. one due to radiation exposure. Because of prompt administration of stable iodine (potassium iodide) there may not be any thyroid cancer among children. In spite of the fact that six reactors and seven spent fuel pools were involved, the radiological impact will be localized. Of the six reactors, three with partially melted core may have to be decommissioned. Handling the partially exposed rogue fuel rods in dry spent fuel is a unique challenge. Unit 4 may have to go the same way because its fuel pool suffered fire and explosion. We do not know anything about its status. Unit 5 and 6 may be operable; chances are that the provincial authorities may be too hostile to allow their continued operation. TEPCO will have to suffer humongous economic losses. Scrubbing the place clean (if they attempt) may take decades and may cost billions of dollars. The media has been doing an excellent job in putting radiation effects into perspective. When the dust settles down, public will be more comfortable with radiation effects than in the past. The events at Fukushima are still unfolding, and complete analysis and understanding will become available only in due course. Nuclear energy will continue to play a significant role in the energy mix of all countries. India s programme to maintain 10% of its power nuclear by 2035 is very modest. While recognising the seriousness of the Fukushima accident, all nations will consider that Japan s location and its proneness to earthquakes and tsunami are very peculiar and that those considerations need not come in the way of new nuclear build. India is likely to follow the same path. Dr K.S. Parthasarathy is Former Secretary, Atomic Energy Regulatory Board (AERB). Currently, he is Raja Ramanna Fellow, Department of Atomic Energy. Address: Flat 302, Mangal Prabha, Sector 9, NERUL, Navi Mumbai ; ksparth@gmail.com; Ph.: (O), (Mobile), (R)