|Year : 2020 | Volume
| Issue : 1 | Page : 1-5
Radiological safety and radiation emergency preparedness
Radiation Safety Systems Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India
|Date of Submission||23-Apr-2020|
|Date of Acceptance||23-Apr-2020|
|Date of Web Publication||12-May-2020|
Radiation Safety Systems Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Seshadri M. Radiological safety and radiation emergency preparedness. Radiat Prot Environ 2020;43:1-5
| Introduction|| |
Radiation is broadly categorized into ionizing radiation and nonionizing radiation. Our area of interest is on ionizing radiation, its effects, and personnel and environmental safety. Radioactivity is a natural phenomenon, in which high-energy radiation of ionizing nature is emitted. Radioactivity is expressed in terms of units Ci or Bq. Exposure to ionizing radiation is expressed in units – Gray, an absorbed dose of 1 J/kg of matter, earlier unit was Rad, an absorbed dose of 100 ergs per gram of matter. With knowledge on the type of ionizing radiation, suitable modifying factors for the effect of radiation (WR), cellular effects (WT), the equivalent dose, and effective dose to human system are estimated in dosimetric quantity – Sievert, the earlier unit was rem, an equivalent dose of 100 ergs per gram of living cellular matter. When dosimetric quantity is expressed in equivalent dose (unit: Sv), the type of radiation is already weighted, hence the type of radiation need not be referred again. 1 Gy of radiation exposure (internal) due to alpha radiation is equal to 20 Sv (committed effective dose), equivalent to that of 20 Gy of gamma radiation exposure. The natural radiation background, which leads to chronic human exposure of all age groups, does not result as radiation-induced effects in any clinically distinguishable form.
Radiation technology and radioactive material as radioisotopes are widely used in medicine, industry, agriculture, research, and in nuclear power production. Safety features are incorporated to minimize radiation hazard during normal operations, and also the emergency preparedness and response protocol has been developed to minimize the consequences during any abnormal event. Although there is a myth prevailing on ionizing radiation exposure of public near nuclear plant sites, epidemiological studies have not indicated any excess incidences or any genetic effects or other health effects attributable to radiation exposure in human inhabitants living in the vicinity of nuclear facility sites.
| Natural Background Radiation|| |
Natural background radiation observed at all places is due to both (a) cosmic radiation (extraterrestrial component) and (b) terrestrial radiation (primordial radionuclides226 Ra,232 Th, and40 K in earthen crust) prevailing in the earth. The prevailing radiation background dose rate at our environment is low, which is of few nGy/h. The background radiation level varies with respect to place, altitude, and latitude and is different at various places. Population of all age groups gets exposed to ionizing radiations, both internally and externally, and thus receive radiation dose. On an average, humankind is subjected to natural radiation exposure of 2400 μSv/year. In addition to the natural radiation background radiation, human exposure could also be due to medical diagnostic cases (voluntary), fallout of radioactivity from the nuclear tests carried out (earlier), and radioactivity released to the environment during normal operation of various nuclear facilities. This humanmade component of radiation exposure as world average is ~600 μSv/year.
| Radiation Technology and Nuclear Energy|| |
Radioisotopes are generated by neutron bombardment during irradiations (induced nuclear reactions: activation products) at operating nuclear reactors. Select target materials (stable isotopes) are irradiated for specified time duration to produce such radioisotopes, which after radio-chemical processing are used as nuclear medicines or tools of radiation technology. Operation of nuclear reactors and accelerators leads to the production of many such useful radioisotopes that are used in the diagnostic, therapeutic, as well as industrial applications.99 Mo,131 I,154 Sm, and177 Lu are few such radioisotopes used in nuclear medicines, whereas60 Co,192 Ir, and137 Cs as gamma-emitting radioisotopes find use in irradiators for sterilization of medical products, cancer therapy, and food preservation programs and industrial applications. Use of all these radioisotopes with inherent radiological safety, shielding, and transportation mechanism is the basis of the usage of radiation technology for wider applications in industry, medicine, and food processing and is more beneficial than the marginal hazard of radiation. Due to this, the applications of radiation in medical and industrial arena have been increasing. Nuclear power plants (NPPs) make use of the principle of controlled chain reaction (fission) of fissile material (natural uranium in pressurized heavy water reactors; enriched uranium in light water reactors/voda voda energo reactors; and uranium, plutonium mixed oxide fuel in breeder reactors) for electrical energy generation. Presently, India is operating twenty nuclear reactors with power output closer to 6780 MW of electrical energy. In a nuclear reactor, the fission reaction inside the reactor core leads to the generation of fission products which are well contained. Some activation products due to neutron reactions are generated, and radioisotopes used in various applications are obtained from operations of the nuclear reactors.
| Radiological Safety in Radiation Technology and Nuclear Power Generation|| |
NPPs and other nuclear, radiological facilities consequent to their approval for commissioning from national regulatory body, namely, Atomic Energy Regulatory Board (AERB), safely handle the fissile or radioactive material, ensuring the protection of workers as well as public and environment. The end users of radiation technology can make use of radioisotopes, applications of the radiation technology in the field of industry, agriculture, or medicine, only after the peer review of safety systems and manuals and verification on the availability of trained set of radiation safety/operating personnel, after commissioning clearance is issued by the AERB. Besides, the AERB ensures safety during operation, transportation of radiation consignments, and handling of radioactive waste, with its stringent regulatory review, periodic inspection, and licensing of Radiation Safety Officers as radiation safety/protection personnel with their mandate to provide periodic reports of normal operations and in case of any abnormal events.
All the nuclear reactors in India are operated with multiple layers of safety – engineered safety systems, radiological safety, and under strict regulatory guidelines. Operation of a NPP/nuclear facility always ensures that there is no undue radiation exposure to the occupational workers, public, and environment. After due filtration, effluents in the form of liquids and gaseous phases are discharged into the environment, at activity levels of which are much below the regulatory authorized limits. Because the water and atmosphere could carry traces of radioactive discharges from the NPP site, an environmental survey lab is kept functional to assess the activity in environmental samples, namely, vegetative/air/soil/water and terrestrial/aquatic animals. The radioactivity estimate on all such samples from the environment is used to indirectly assess by using modeling techniques on likely public exposure of inhabitants at the site. The quantum of radiation exposure to a member of public in the vicinity of NPP site due to radioactivity discharged from a nuclear site during its normal operations is nearly 25–50 μSv/y. The exposure to public around the NPPs due to these environmental releases is a very small fraction (<1%) of the annual exposure from the natural radiation background and is negligible to cause any health hazards to be found in public domain. There has been no reported incident of human life loss attributable to radiation emergency from the Indian nuclear reactors, for the past 60 years of operations.
A scientific study by the GLOBOCAN – an international agency for cancer research – has shown that the international average death per thousand persons from cancer is 1.06 among the general population. As against this, the national average of deaths in India per thousand persons is reported to be 0.68. The Nuclear Power Corporation of India Limited (NPCIL) average is far lower, at 0.17/thousand. In addition to this, the most notable fact is that, there have been no incidences of death from thyroid, skin, and bone cancers among the NPCIL employees, which perhaps are the prime cancers attributable to radiation exposure. Thus, it is amply evident that there has been no measurable increase in the rate of cancers in the population as a result of operation of NPP/nuclear facilities.
| Radiation Emergency|| |
Although the radiation safety is prioritized and ensured during normal operations at facilities using radiation technology and a NPP, any abnormal situation cannot be ruled out, arising out of failure of safety systems, human error, or combination of both or a natural calamity as the cause of initiating an accident. The abnormal situation at the facility is termed as the “radiation emergency. ”
Radiation emergency is the terminology used to indicate any abnormal event during the utilization of radiation technology or NPP operation. Radiation emergency is broadly subclassified into:
- ”Nuclear emergency ” – wherein the accident/event is due to a fissile material with criticality and fission chain reaction as the cause. The probability of the nuclear accident is very low, due to inherent safety features, however the impact of the nuclear emergency could be higher (e.g., Chernobyl accident and Fukushima accident)
- ”Radiological emergency – wherein the accident/event is due to radioactive materials that are nonfissile or fissile materials that have not undergone criticality (fission chain reaction) as the cause. The probability of the radiological accident is marginally higher, due to the wide utilization of radiation technology in applications, however the impact of the radiological emergency could be lower (e.g., Goiania accident and Mayapuri incident).
Planning to mitigate the consequences of potential accident scenario is carried out even at the precommissioning stage of any proposed radiation facility. In the Indian scenario, the commissioning clearance for the usage of radiation technology or operation of a nuclear facility is provided only when there is a document on “Plan for Response to Radiation Emergency. ” Based on the plan, there has to be a demonstrated capability on the preparedness for response to radiation emergency with technical capability, resources, systems/tools, gadgets, procedures, command and control center, and identified human capacity resource.
| Accidental Radiation Exposures|| |
The clinically observable early effects of ionizing radiation due to acute exposures in short time duration, include skin reddening (dose threshold 3–5 Gy), opacity of the eye lens (dose threshold 2–10 Gray), and permanent sterility (dose threshold 2.5–6 Gy). The effects range from relatively trivial (slight reddening of skin) to very serious (major burns and other injuries). At high radiation doses, death may occur. Generally, these effects appear in an exposed individual, referred as early effects. Whole-body exposure of radiation, to moderate/heavy doses, may lead to radiation sickness. The symptoms are nausea, vomiting, fatigue, etc., The duration of radiation sickness depends on the dose and the tissue receiving it.
Nuclear accident at a NPP site is highly remote in occurrence, its acute radiation could harm only a few workers, and it could be avoided with some reasonable procedure. From the set of available statistics, it could be concluded that the radiation detriment assigned and the results of radiation-induced effects on the follow-up studies have a large mismatch; the predicted values are gross overestimates based on modeling. Health effects of acute and chronic radiation are entirely different: 86,572 atomic bomb survivors in Japan had 5.4% increase in cancer mortality in 40 years, but 10,000 residents in Taiwan irradiated to fractionated dose had lower cancer incidences, a 97% decrease in cancer incidences. In more than 14,000 reactor-years of cumulative operation worldwide and a global commercial power generation history of 57 years, three significant accidents have occurred: Three Mile Island (TMI, 1979), Chernobyl (1986), and Fukushima (2011). With this extended operation history, there was no significant public radiation exposure possible from the TMI accident. The nuclear accident at the TMI was marked as Scale 5 event in the International Nuclear and Radiological Event Scale, whereas the accidents at Chernobyl and Fukushima were marked as Scale 7 events. The nuclear accident at Chernobyl resulted in radiation exposure with the death of 58 people and increased nonlethal thyroid cancer incidences, of which most were curable. However, no radiation-induced death had been reported due to the Fukushima nuclear accident and the accidental releases that followed, to the environment/aquatic bodies.
| Past Radiation Emergencies – lessons Learned|| |
The range of potential radiation emergency scenario is enormous, extending from a major reactor (nuclear) emergency to emergency involving lost or stolen radioactive (radiological) source.
The Chernobyl accident (1986) was the source of acute radiation due to the incident and chronic radiation due to accidental environmental releases over wide area. The meltdown of highly radioactive fission products released high doses of radioactivity abruptly into the reactor hall. As a result, 31 firemen and workers received high doses of acute radiation in a short time. Emergency workers and the evacuated public did not show any solid cancer deaths, though they had received quite high radiation exposure. The Fukushima accident (2011) led to nuclear emergency due to natural calamity wherein there was no reported life lost due to radiation accident; 167 workers at the plant have received over 100 mSv, with the highest dose being 680 mSv, and nearly 24,940 workers had taken part in response activities at the plant site. There were no cases of immediate radiation sickness in workers or in members of the public.
The radiological accidents where the radioisotopes are used for industrial, medical, and other gainful applications could lead to accidental situations during handling, transport, or inadvertent loss of regulatory control over the radiation sources. Such radiological emergencies which could happen even in the public domain, have marginally higher probability of occurrence; the radiological impact could be confined to a smaller area, with over 150 cases of life loss reported over the last few years.
There was a radiological emergency at Goiania, Brazil (1987), wherein during the relocation of a medical facility using137 Cs tele-therapy unit as an irradiator, the unit was stolen, the radioactive source (19.3 g of CsCl) was removed, and the incident resulted with reported four losses of human life, with very large volume of radioactive waste generated (3500 m3) due to the incident. The radiological emergency in Mayapuri, New Delhi, India (2010), due to mishandling of60 Co at a non-Department of Atomic Energy (DAE) facility, resulted in a single case of reported human life loss. Due to expertise and response from the DAE, the situation could be brought to normalcy quickly.
| Preparedness and Response to Radiation Emergency|| |
The increasing use of radiation technology has led the DAE, India, to strengthen its preparedness and response to any potential radiation emergency involving nuclear/radioactive material. In India, the AERB is the national regulatory body, which regulates the nuclear/radiation facilities as per its regulatory framework in line with international codes/guides. Requirement for preparedness and response to radiation emergency in any state is guided as per the GS-R-2 guidelines, specifying all requirements for adequate level of preparedness and response to any radiation emergency by the state. Implementation of these requirements is intended to minimize the consequences in public, property, and environment during any radiation (nuclear or radiological) emergency. Because the nuclear facilities are governed by robust regulatory aspects, operated under defense in-depth approach with fail-safe engineered safety systems, the probability of any accident is remote. Off-site emergency plan documents for response to any nuclear emergency from the operating NPPs have been drafted, revised, and periodically exercised. The preparedness and response to any radiation event is focused on the potential radiological emergency in the public domain.
At the national level, the National Disaster Management Authority has prepared the guidelines for prevention, preparedness, and response to nuclear or radiological emergencies. The AERB or DAE's Crisis Management Group, on receipt of any information on suspected elevated radiological conditions in the public domain, intimates the National Radiation Emergency Response Director (RERD). The RERD will draw available expertise from the DAE to constitute emergency response teams to supervise and direct the response during radiation emergency, if any, in the public domain. Bhabha Atomic Research Centre, DAE, has established emergency response centers (ERCs) at 25 different locations, for response to any radiological emergency in the public domain. Standard operating procedures for response and mitigation of consequences for potential scenarios of radiation emergencies are drawn, approved, and circulated. The DAE-ERC at Mumbai as the nodal ERC has adequate trained workforce, radiation-monitoring devices, and mobile-monitoring systems; has developed few software tools for the prediction of radiological impact, personnel, and area decontamination methodologies; and has designated teams and other logistics. In addition, there are DAE-ERCs which take part in the exercises of NPP, communication exercises, and human capacity-building activities to demonstrate their preparedness to respond quickly.
A network of radiation-monitoring devices, Indian Environmental Radiation Monitoring, a self solar-powered radiation-monitoring network, at around 520 different locations pan India, is in operation. Mobile radiological monitoring of major rail/road route of the Indian cities is being carried out to generate the baseline radiological data. These radiological data could be used for observing the changes/trends in radiological status, if any, due to the presence of any abnormal situation or during any radiological emergency.
Training of the resource personnel involved in various response activities – first responders, law enforcement agencies of various Indian states, medicos, para-medical staff, defense personnel, security and fire safety agencies both at DAE and non-DAE units, and training of trainers in National Disaster Response Forces personnel – has been carried out in various layers in a large scale. It has resulted in the availability of trained workforce for response activities during radiation emergency. The discussion meet of DAE-ERCs coordinators, sharing of their experience during the past exercises, has led to the enhancing of preparedness and response measures for radiological emergencies. Expert personnel identified with on field experiences as leaders, has given confidence to the trained team of response personnel (including security and medicos) to any radiological emergency anywhere in the country.
| Conclusions|| |
With radiological safety accorded priority at radiation facilities and NPPs, health effects and risk assessment based on dose estimation, indicate that no health effects are attributable to low radiation that were observed among the workers in nuclear industry, among children of their family or any other member of the population due to normal release from NPP/nuclear facility. Normal release from operational activities at NPP/nuclear facilities and during the uses of human-made radioisotopes, the hazard due to radiation is much smaller compared to the prevailing natural radiation background. By the use of proper safe procedures and following the regulatory guidelines, radiation can be used as a gainful tool to the advantage of humankind. The preparedness and response to radiation emergency has been evolved over the past decades; with the establishment of response centers, procedures, monitoring systems, and available trained resource personnel (human capacity).
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