Year : 2011 | Volume
: 34 | Issue : 2 | Page : 144--146
30 th IARP conference on "Radiological protection and safety in nuclear reactors and radiation installations" Mangalore, Karnataka: Panel discussion
SK Prasad1, Pushparaja2,
1 RSSD, BARC
2 Ex. RSSD, BARC
Ex. RSSD, BARC
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Prasad S K, Pushparaja. 30 th IARP conference on "Radiological protection and safety in nuclear reactors and radiation installations" Mangalore, Karnataka: Panel discussion.Radiat Prot Environ 2011;34:144-146
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Prasad S K, Pushparaja. 30 th IARP conference on "Radiological protection and safety in nuclear reactors and radiation installations" Mangalore, Karnataka: Panel discussion. Radiat Prot Environ [serial online] 2011 [cited 2022 May 18 ];34:144-146
Available from: https://www.rpe.org.in/text.asp?2011/34/2/144/98404
The Panel Discussion was chaired by Dr. M. R. Iyer, former Head, RSSD, BARC, and Ex. IAEA.
Dr. K. S. Pradeepkumar of RSSD, BARC, introduced the subject and described the reasons for the worldwide fear psychosis created by the Fukushima and Chernobyl accidents. He explained that the combined effects of the high-magnitude earthquake and the ensuing tsunami on the Fukushima Nuclear Power Plant (NPP) site represent the most significant external challenges for any commercial nuclear reactor, and Fukushima type nuclear accidents cannot happen in India. Due to Chernobyl accident, 28 emergency workers died within a few days and there are a few cases of high radiation exposures. Fukushima nuclear accident did not lead to loss of life, and except the emergency workers, none had received dose more than 20 mSv. A few Fukushima emergency workers received doses of the order of 0.1-0.3 Sv which is less than 10% of the acute exposure received in the major radiological emergencies like Goiania, Mayapuri, etc. The international concern post Fukushima accident is mainly caused by radioactive contamination detected in the public domain due to the releases from those affected NPPs, though they did not lead to dangerous levels of exposures.
In Fukushima, an earthquake of magnitude 9.0 led to station blackout, and the unprecedented tsunami of 15 m height further affected the reactor site as well as the NPPs. The three reactors which were operating got into safe shutdown mode after detecting the seismic signals by the in-built safety systems. The fourth unit did not have any fuel in the core and spent fuels were stored in pond storage bay. Due to tsunami, DG power supply system got immersed in sea water ingress, which caused incapability to provide continuous cooling for the decay heat removal as required even after a safe shutdown. This led to temperature increase, melting of fuel, hydrogen explosion, and ultimately release of fission products, mainly noble gases, iodines, and cesium isotopes, to the environment.
Though Japan lost the four NPPs which were seriously damaged, the radioactivity released from the facility toward land was not significant to have any radiological consequences in spite of having had a very severe psychological impact partially because of the wrong interpretation of the risk from low-level exposure supported by the Linear No Threshold (LNT) theory. Environmental impact due to the atmospheric releases from Fukushima was further reduced as most of the time wind direction was toward sea (east) during the release time. Chernobyl reactor accident which had released much higher level of radioactivity to the environment, even after 25 years of the release, unlike the popular belief, has not led to any detectable increase in the cancer rates in public (except some marginal increase in thyroid cancers). Fukushima atmospheric release toward the land side, which is only a few percent of the release from Chernobyl reactor, is not expected to create any detectable health effects. At the same time, the lessons learnt from the Fukushima accident as well as from their emergency response experiences demonstrate the issue of addressing the public concern, requirement for monitoring of large number of people, food, water, environment samples, etc. to detect or to rule out radioactive contamination. Para-military and police forces which are being trained for national level emergency preparedness against radiological threats will be a big support for such situations. National Disaster Management Authority (NDMA's) decision in equipping police patrolling vehicles with radiation detection systems will act as a deterrent against radiological terrorism as well as for the prevention of inadvertent movement of radioactive material and will help in building up the confidence of the public even during trans-boundary nuclear emergencies like Fukushima.
Dr. Pradeepkumar concluded by saying that even though the sequence of events like those that led to Fukushima and Chernobyl accidents are unlikely to occur in Indian reactors, emergency preparedness and public awareness programs are to be given utmost importance, if clean and safe nuclear power is to be acceptable to the members of the public. He also proposed that in the absence of adequate scientific evidence, using the LNT theory for predicting risk for low radiation exposure cases should not be entertained by the radiation protection professionals.
Shri J. P. Gupta, Station Director, Kaiga Generating Station, said that Indian nuclear reactors are built in Zone 2 or 3, and hence earthquake cannot affect the reactors. The reactors designed for 0.25 g can withstand an earthquake between 3 and 5 in the Richter scale. Emergency power supply system, consisting of diesel generators, got submerged in the tsunami water and hence could not be deployed. Since the reactors tripped due to the earthquake, 6% of total decay heat remained which was enough to make the cooling water to boil, raising the pressure and causing steam to enter the drywell, and the water level came down in the reactor, resulting in the fuel meltdown. The metal-water reaction produced hydrogen and the secondary containment building exploded. Some contamination came out with the steam. As per New York Times, a lifetime dose of 25 mSv due to the accident is low. After earthquake, all NPPs in the US were reviewed. The modification of nitrogen blanketing available at TAPS 1 and 2 was not provided in Fukushima reactors.
Defense-in-depth concept is used to minimize radiation exposure of members of the public from the reactor accidents. In Pressurized Heavy Water Reactors (PHWR), in the absence of normal power supply, core cooling is done by Emergency Core Cooling System (ECCS) by thermal syphoning, the core being at a lower elevation. Portable DGs may be required under situations where the installed DG power is not available for some reason. At Kudankulam, the DG/pump house is located above the 2000 tsunami levels. MAPS started operating at Kalpakkam after the earthquake; Kakrapar Nuclear Power Plant started operating after an earthquake of level 8. During Narora fire incident, the core cooling was maintained. All special precautions were taken. As Low As Relatively Safe (ALARS) concept is to be adopted.
Shri D. K. Goyal from Nuclear Power Corporation of India Limited (NPCIL) spoke on the issue of how to present and manage the public and environment. In view of the Fukushima accident, safety reviews of old stations were carried out. Four Task Forces were formed to analyze our NPPs in the light of Fukushima and the issues under review are: maintaining cooling in the absence of normal power supply; sources of cooling and power to activate for coolant supply; maintaining temperature and pressure; management of hydrogen formed under such situations; evacuation strategy for members of the public persons, etc. He brought out the issues connected with conducting emergency exercises and sensitization of local people on the methodology used during such exercises. Need for conducting public awareness program in universities was felt to remove any misconception about radiation and its effects.
Dr. D. N. Sharma, Health Safety and Environment Group, BARC, spoke about the earthquake plus tsunami at Fukushima, the death toll of 20,000 persons, and 300 million dollar economic loss. He said that one should not worry about exposures in the range of 10 mSv while no effect due to radiation exposure could be detected up to a dose level of 100 mSv. He further mentioned the need for considering formation of committees to look into the techniques available to handle total station blackout situations, such as portable DG sets to cool reactors. He also talked about reducing the generation of hydrogen. Massive training program is in place to train National Disaster Response Force (NDRF) and State Disaster Response Force (SDRF) personnel in each state and to train state police forces in detecting radiation levels higher than the background levels.
Dr. V. D. Puranik of Environmental Assessment Division of BARC talked about the economic aspects related with the emergency preparedness plans and emergency management. He said that the environment is not constant or stable in time. Earthquake, tsunami, etc. occurred a number of times and we are now in a comparatively stable period of time. He said a natural event of a meteorite falling in Russia about 6.5 million years ago caused the destruction of life such as of Dinosaurs.
The Environmental Survey Laboratories (ESLs) located in all nuclear sites continuously monitored the environmental levels of radioactivity/radiation after the accident at Fukushima. No activity was detected. Efforts are made to bring down the detection levels of the systems lower and lower. Modeling with data from internal sources at site, dispersion in atmosphere and in water body gives confidence to scientists and engineers, which makes us much better prepared for the future. He assured that lots of instruments for detecting radioactivity at different parts of the country have been installed and are operational.
Dr. M. R. Iyer, Ex. BARC, added that IAEA recommendations on the Fukushima were carried out by other agencies and not by Japan. In 1970, in Indian scenario, visionaries such as Late Dr. A. K. Ganguly, Director, Health and Safety, BARC, insisted on mounting the critical safety related systems at higher levels at Kalpakkam site. Due to prompt action by Japan, more than 95% evacuated persons got doses less than 5 mSv. There are lessons to be learnt from these efforts. In the post-accident scenario, some mistakes were done by Japan as per IAEA reports, for example, the judgment on the severity of the accident.
In Fukushima, about 70,000 TBq of activity was released, but due to high dilution factor, its impact is lower. When the evacuated persons are resettled in their own areas, they may have to face the problem of re-suspension of activity in the "decontaminated" areas. If one tries to estimate the impact of such low doses to large population groups, the total dose (collective dose) would be overestimated to a great extent. One should be careful in estimating cancer fatalities and genetic burden from such dose assessments. There is an inherent weakness in the LNT concept.
Responses from the audience
Dr. K. C. Pillai, Ex. BARC, opined that there is a tendency to calculate risk factor using trivial doses multiplied by large number of population. He also said that sometimes the emergency exercise is counterproductive.
Dr. Shivram, Prof. of Mangalore University, commented that we have failed in our attempts to convince the public about our nuclear projects. In Mysore, Rare Minerals Plant (RMP), we could not give right and convincing reasons for queries raised by the public. He suggested an integrated emergency preparedness program for the country.
Dr. K. S. Pradeepkumar of RSSD, BARC, replied that security concerns prevent the department from giving the information fully.
Shri S. K. Garai of RSSD, BARC, informed that out of the recent 29 earthquakes, 10 were severe. He expressed his concern why the Japanese government did not take care of the IAEA recommendation related to hydrogen recombination.
Dr. B. C. Bhatt, Ex. BARC, opined that the major concern of public is of nuclear waste disposal. Most people are not convinced of the safety of our disposal strategies. Dr. M. R. Iyer agreed with this comment.
Shri D. K. Goyal said that at Jaitapur, even though initially the public were not convinced, now the public seem to have understood about the safe radioactive waste disposal plans.
Shri S. K. Prasad of RSSD, BARC, commented that the explanation or clarification of wrong data or news published in newspapers, that too in front page, given by the department, comes very late to have any impact and is quite often not noticed by many readers.