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Indian Journal of Occupational and Environmental Medicine, Vol. 12, No. 3, September-December, 2008, pp. 122-127 Original Article Safety in nuclear power plants in India Deolalikar R Occupational Health, Narora Atomic Power Station Hospital, Type C, 11/2, N.A.P.S. Colony, N.A.P.P. Narora, Bulandshahr, Narora - 202 389, Uttar Pradesh Code Number: oe08032 Abstract Safety in nuclear power plants (NPPs) in India is a very important topic and it is necessary to dissipate correct information to all the readers and the public at large. In this article, I have briefly described how the safety in our NPPs is maintained. Safety is accorded overriding priority in all the activities. NPPs in India are not only safe but are also well regulated, have proper radiological protection of workers and the public, regular surveillance, dosimetry, approved standard operating and maintenance procedures, a well-defined waste management methodology, proper well documented and periodically rehearsed emergency preparedness and disaster management plans. The NPPs have occupational health policies covering periodic medical examinations, dosimetry and bioassay and are backed-up by fully equipped Personnel Decontamination Centers manned by doctors qualified in Occupational and Industrial Health. All the operating plants are ISO 14001 and IS 18001 certified plants. The Nuclear Power Corporation of India Limited today has 17 operating plants and five plants under construction, and our scientists and engineers are fully geared to take up many more in order to meet the national requirements.Keywords: Atomic energy act, atomic energy regulatory board, dose limits, emergency planning and measures, environmental radiological surveillance, epidemiological survey, nuclear facilities, nuclear power plants, radioactive waste management, radiological protection, safety, the disaster management act, zoning concept Introduction Safety in nuclear power plants (NPPs) is often less understood and more talked about and, thus, I wanted to share the facts with the readers. With reference to an article published in an earlier issue of this journal, [1] it became all the more pertinent to clear the myths. At the very start, may I state that any discussions on the Indo-US deal are outside the purview of this article. I would like to focus only on the safety aspects of the NPPs in India. Currently, all the NPPs in India are under the Nuclear Power Corporation of India Limited (NPCIL). Hence, any discussions regarding the NPPs in India will pertain to it. The NPPs in India are not only safe but are also well regulated, have proper radiological protection of workers and the public, regular surveillance, dosimetry, approved standard operating and maintenance procedures, a well-defined waste management methodology, proper well documented and periodically rehearsed emergency preparedness and disaster management plans. The NPPs have occupational health policies covering periodic medical examinations, dosimetry and bioassay and are backed-up by fully equipped Personnel Decontamination Centers manned by doctors qualified in Occupational and Industrial Health. Moreover, they have specialized training in handling radiological emergencies. Safety in NPPs in India is a very vast subject and would need reams of papers to cover it aptly. However, I have tried to summarize it to the best possible level. I hope that I would succeed in making the reader understand the magnanimity with which these plants are operated and that they are entirely safe. Safety is accorded overriding priority in all the activities. All nuclear facilities are sited, designed, constructed, commissioned and operated in accordance with strict quality and safety standards. Principles of defense in depth, redundancy and diversity are followed in the design of all nuclear facilities and their systems/components. The regulatory framework in the country is robust, with the independent Atomic Energy Regulatory Board (AERB) having powers to frame the policies, laying down safety standards and requirements and monitoring and enforcing all the safety provisions. The AERB exercises the regulatory control through a stage-wise system of licensing. As a result, India′s safety record has been excellent in over 277 reactor years of operation of power reactors. Nuclear power generation is governed by a legislation, the Atomic Energy Act, 1962. The Atomic Energy Act encompasses all the activities concerned with atomic energy, including electricity generation. Radiological Protection of Workers[2],[3],[4],[5],[6],[7],[8],[9],[10],[11],[12],[13],[14],[15],[16] Radiological protection of the workers is ensured by the following measures: Design aspects The design considerations that have a bearing on radiation protection in NPPs include :
A limit on the collective dose is specified at the design stage of each NPP so that adequate provisions for radiation protection are made in the design of the plant to keep radiation levels in different areas below design levels. Dose limits The AERB has prescribed the following dose limits for exposures to ionizing radiations for occupational workers:
In addition, investigation limits are also prescribed by AERB at which investigation of exposure cases exceeding these limits are carried out by an AERB committee. Effective dose means summation of the tissue equivalent doses, each multiplied by the appropriate tissue-weighting factor. Sliding scale of 5 years means the current year and the previous 4 years. Average dose over 1 cm 2 of the most highly irradiated area of the skin. For temporary workers, separate control limits, lower than that for regular workers, are prescribed. The external and internal exposures of all the plant personnel are assessed on a monthly basis. For assessing the internal dose in Pressurized Heavy Water Reactors, a bioassay program on a weekly basis and a dose estimation software are used. A computerized dose data management system is used, which helps in updating the data for effective dose control. Organization in radiation protection Each NPP has a Health Physics Unit (HPU), comprising of a group of trained and experienced radiation protection professionals, who, in coordination with plant management, implement the radiation protection program in the plant. The HPUs in all NPPs in the country are entrusted with the responsibility of providing radiological surveillance and safety support functions. These include monitoring of areas, personnel, systems, effluents, exposure control and exposure investigations. The HPUs are part of the Bhabha Atomic Research Center (BARC) and are independent of the NPP organization, and have direct channels of communication with the top plant management in enforcing the radiation protection program. The individual and the collective dose consumed in the plant is reviewed in detail and measures for reduction are devised at the plant level. These measures include engineering and administrative solutions such as shielding, ventilation, use of protective equipment, procedure adherence, work permit system, access control, display of placards, job planning, mock up, training, supervision, etc. In addition, a three-tier arrangement is in place to review and monitor implementation of recommendations pertaining to radiological safety. The first level review is carried out at the plant and the regulatory body performs the second- and third-levels reviews. There has been no case of annual exposure exceeding 20 mSv during the last 3 years in all the NPPs. The collective annual dose to plant personnel is kept below the annual dose budget approved by the AERB. Efforts are made each year to reduce this progressively [Figure - 1]. Steps for ALARA exposures In order to meet the objectives of the ALARA, working procedures and methods are examined with regard to the possibility of reducing doses resulting from radiation jobs. During the operational stage of the NPP, the exposures are kept ALARA by implementing the following operational aspects:
Radiation protection review by AERB The Atomic Energy (radiation protection) Rules, 2004, form the basis of regulatory control activities related to radiation protection. These rules are implemented by the utilities through various procedures. In addition, the AERB practices other measures to exercise control on radiation protection aspects for NPPs, which, among others, include the following:
Radiological Protection of Public The following measures ensure the radiological protection of the public due to the operation of a NPP. Design aspects
Dose limit The AERB has prescribed the following limits to a member of the public at exclusion distance due to releases of radioactive effluents from nuclear facilities at a site:. Effective dose (whole body): 1 mSv (1000 µSv)/year. The [Figure - 2] shows the environmental dose from various NPPs in India over the period 2002-2006, which is less than 10% of the prescribed limits. Equivalent dose (individual organs)
Radioactive Waste Management The performance of the radioactive waste management system established at NPPs is reviewed to ensure that appropriate methods and management practices continue to be in place and the generation of radioactive waste is kept to as minimum as practicable in terms of activity and volume.
Environmental Radiological Surveillance An elaborate environmental survey program around each NPP site is carried out by the HPUs and the Environmental Survey Laboratories (ESLs) of BARC. The basic objective of the environmental monitoring and surveillance program is to assess the radiological impact under all states of the NPP and demonstrate compliance with the radiation exposure limits set for the members of the public by the AERB. This is achieved by carrying out a radiological surveillance of the environment by professionals of the ESLs. The HPUs and ESLs are part of the BARC and are independent of the utilities. They provide the regulatory body with periodic reports on radiological conditions of the NPPs and the results of environmental surveillance. The ESL is established several years before operation of a NPP. Extensive surveys are carried out around each nuclear power station to collect data on the dietary intake. During the preoperational phase, the annual intake of cereals, pulses, vegetables, fish, meat, eggs and milk are established by direct survey. Elaborate studies of the topography of the site, land use pattern and population distributions are carried out systematically during the preoperational phase. Also, a detailed epidemiological survey of the population is carried out in the preoperational phase. This is carried out by a neutral agency like the Tata Memorial Hospital or any closely located University Medical College. Along with the topographical and dietary studies, the ESL also carries out the work of establishing the preoperational background radiation levels. Extensive micrometeorological data such as wind speed and wind direction, temperature and rain fall are collected for a few years to identify the worst sector and critical population. The ESL continues its monitoring and surveillance program during the operation phase of the NPP. The samples for analysis are selected on the basis of potential pathways of exposure. The program undergoes modification based on experience. Generally, more samples are collected near the vicinity of the plant and from locations where population clusters exist, and the sampling frequency reduces with the distance. Areas up to a distance of 30 km are covered under the environmental survey program. Although the main emphasis is on samples that are relevant directly to the estimation of the dose, such as drinking water, edible food items, air, etc., a number of other samples are also assayed for radioactivity and used as trend indicators. From the radioactivity level in the environmental matrices, intake parameters and dose conversion factors, the population dose is estimated. The annual effective dose to members of the public in the vicinity of the NPPs have been estimated by ESLs and found to be only a few µSv. ESLs are accredited laboratories that take part in inter comparison studies conducted by the International Atomic Energy Agency.Emergency Preparedness General NPPs are designed, constructed, commissioned and operated in conformity with existing stringent nuclear safety standards. These standards ensure an adequate margin of safety so that NPPs can be operated without undue radiological risks to the plant personnel and members of the public. Notwithstanding these safety standards, it is necessary to develop, as a measure of abundant caution and in conformity with international practices, emergency response plans so that any eventuality, howsoever unlikely, with a potential to result in undue radiological risk to plant personnel and public, is handled effectively. The preparedness and response to emergencies are important responsibilities of the operating organization. All NPPs have established and documented emergency procedures by having an on-site emergency preparedness plan. Similarly, the plan with respect to off-site emergency is made available with the district authority. The role, responsibilities and action plans for various agencies required to act during an emergency are detailed in these plans. National laws, regulations and requirements The Government of India has enacted "The Disaster Management Act, 2005", which provides for the effective management of disasters, including accidents involving NPPs. As per the provisions of this act, the National Disaster Management Authority (NDMA) has been established at the national level, whose chairperson is the Prime Minister. The NDMA has the responsibility for laying down policies, plans and guidelines for disaster management for ensuring timely and effective response to any disaster. In line with the above national plan, a state plan and district plans are drawn up by the respective authorities constituted for the purpose. Specific requirements with respect to emergency preparedness in NPPs have been formulated by the AERB in the various regulations, as given in references. Zoning concept and emergency planning In India, a NPP is generally sited in a relatively low-population zone, with the basic objective of limiting the dose-received members of the public and population as a whole under normal and accident conditions to ALARA levels. In order to achieve the above objective, the area around the NPP is divided into the following zones:
Emergency measures The emergency measures consist of emergency actions in respect of notification, alerting personnel, assessment of situation, corrective actions, mitigation, protection and control of contamination. These are detailed in the emergency response manual.
References
Copyright 2008 - Indian Journal of Occupational and Environmental Medicine The following images related to this document are available:Photo images[oe08032f1.jpg] [oe08032f2.jpg] |
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