ISSN 2330-717X

Do Not Fear A Nuclear Power Plant In Your Neighborhood – OpEd

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If the Central Government agreed to build a nuclear power plant in your neighbourhood what will be your reaction? Many may support the decision. Looking at the past there will be strong opposition as well. The prolonged agitation against the setting up of the Kudankulam nuclear power plant is an instance in point. The perception on nuclear power by different sections of society is very different from the reality.

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In 1990, a survey carried out by the Atomic Energy Regulatory Board (AERB) on behalf of the Indian National Academy of Engineering has a revealed that a large proportion- 37% of the participants (Seven hundred and sixty two members of the faculty and students from the Indian Institute of Technology, Mumbai and Kanpur, Institute of Science, Roorkee University, Saha Institute of Nuclear Physics, and Tata Institute of Social Science; 162 of them with Ph.D)) believed that nuclear power generation makes the highest contribution to the radiation exposure to population from among the man-made sources of radiation, contrary to facts. These notions possibly reflect the irrational fear of radiation in the minds of even qualified people. Possibility of release of radioactivity during normal operation may be one reason for staying away from reactors.

The site of a reactor must satisfy several conditions including seismicity, availability of water, and proximity to airports among others. The site selection and site evaluation are important stages of setting up a nuclear power reactor.

Design of reactors

When a nuclear reactor starts operation, its fuel is mildly radioactive.  Radioactivity gradually accumulates as the reactor operates. The design of a nuclear power reactor and the operation of associated systems prevent uncontrolled release of that radioactivity in to the atmosphere.   Radioactive releases may reach the environment only if several barriers break.

These barriers include the fuel material, its sheath, the coolant, the primary heat transport system, filter and ion exchange system, water in the calandria or reactor vessel and the primary and secondary containment. The fuel and the sheath have high melting point. Rigorous quality control during construction ensures the integrity of each barrier. Each safety system is redundant and diverse to ensure high reliability. 

The primary and secondary containment structures are made of high quality, high strength concrete. The designers have kept the containment volume at negative pressure. If an accident occurs, the reactor operators can bottle up the containment volume. Radioactivity-bearing air has to go through filters of very high efficiency before it is released through 93-metre stacks to ensure dilution. Radioactivity is not released at ground level.

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 Additional safety features 

The reactors have redundant, diverse and thus reliable provisions to control nuclear reactions, to cool the fuel and to contain radioactive releases. They have built in safety features to handle any safety related event. If found necessary, neutron absorbers in liquid form flowing into the reactor core under gravity can rapidly bring down reactor power levels. Even after the reactor operating staff brings down the power levels, the active fuel will be hot because of decay heat, which can melt the fuel. Systems are in place to remove the heat by adequate flow of coolants to maintain the integrity of the fuel rods.

Reactor operations group analyze every event, which has any safety significance to ensure that they do not occur again. They report major events, if any, to the Atomic Energy Regulatory Board (AERB). The Board analyzes them independently and enforce measures to prevent their recurrence. There is a system in place to report safety related events to the International Atomic Energy Agency (IAEA)

Safety Reviews

Special committees with  experts in many relevant disciplines set up by the Nuclear Power Corporation and at times AERB reviewed major nuclear accidents such as the one occurred at the Three Mile Island in the USA, Chernobyl in USSR and Fukushima in Japan.  NPCIL has implemented their recommendations. AERB and NPCIL also reviewed reports on these accidents from the International Atomic Energy Agency (IAEA). Specialists from India have been actively participating in the activities of the IAEA .

AERB took restrictive regulatory actions on a few occasions; this included shutting down the reactors, restricting power levels, ordering retraining of reactor operating staff, directing NPCIL to carry out design changes to enhance safety among other measures. NPCIL can appeal to the Atomic Energy Commission against such AERB actions. NPCIL has never done it. It always complied with AERB directives.

Some safety features of Kudankulam nuclear power reactors

In Kudankulam nuclear power reactors, the nuclear fuel tubes are located in the 22 cm thick Reactor Pressure Vessel (RPV) which weighs 350 tonnes. RPV is kept inside a one-metre thick concrete vault.

The reactor has double containment, inner 1.2 metre-thick concrete wall lined on the inside with a 6 mm layer of steel and an outer 60 cm thick concrete wall. The annulus between the walls is kept at negative pressure so that if any radioactivity is released it cannot go out. Air carrying such activity will have to pass through high efficiency filters before being released through the stack. Multiple barriers and systems ensure that radioactivity is not released into the environment. 

Kudankulam reactors have many new safety systems in comparison with earlier models. They have many passive safety systems, which depend on never-failing    features such as gravitation, conduction, convection etc.

Decay heat removal

The reactor’s Passive Heat Removal System (PHRS) can remove decay heat of reactor core to the outside atmosphere. It works without any external or diesel power or manual intervention. The reactor designers have equipped them with passive hydrogen re-combiners to avoid formation of explosive mixtures .The reactors have a reliable Emergency Core Cooling System (ECCS).

Core catcher

Located outside the reactor vessel, a core catcher in the form of a vessel weighing 101 tonnes and filled with specially developed compound (oxides of Fe, Al & Gd) is provided to retain solid and liquid fragments of the damaged core, parts of the reactor pressure vessel and reactor internals under severe accident conditions. The probability for this to happen is extremely low.

The presence of gadolinium (Gd) which is a strong neutron absorber ensures that the molten mass does not go critical. The vessel prevents the molten material from spreading beyond the limits of the containment. The nuclear technologists have developed the filler compound to have minimum gas release during dispersal and retention of core melt.

Regulatory control of radioactive effluents

AERB permits the plant management to release some amount of radioactivity during normal operation. There are systems in place to measure this release and to ensure that it does not exceed the permitted limits. Any deviation is reviewed and appropriate corrective action taken promptly.  

Environmental Survey Laboratories set up outside the exclusion zone of each nuclear power station periodically collect representative samples of air, water and foodstuffs to evaluate radiation dose to the members of the public.  ESL scientists choose the sampling points and the frequency of sampling to ensure that the values obtained are representative. Scientists in ESL belong to the Health, Safety and Environment Group of BARC and are independent of Nuclear Power Corporation of India Limited, which operates the reactors

“The Radiation dose to members of the public near the operating plants is estimated based on gaseous release and measurements of radionuclide concentration in items of diet, i.e. vegetables, cereals, milk, meat, fish etc., and through intake of air and water. It is seen that the effective dose to public around all NPP sites is far less than the annual limit of 1mSv (1000 micro-sievert) prescribed by AERB” (Annual Report of AERB-2019).  Annual reports of AERB publish the values at the fence post of all nuclear power reactors, up to a distance of 30 km.

During 2015-2019, radiation dose at the fence post of different nuclear power reactors in India varied between 0.004 microsievert/year to 40.2 microsievert/year as against the dose limit for public of 1000 microsievert/y prescribed by AERB (Pages 60 and 61 AERB Annual report 2019). [Sievert represents the amount of radiation energy absorbed by living tissue and the extent of biological effects involved (IAEA 1997). Since sievert is too huge, millisievert (one thousandth) and microsievert (one millionth) are commonly used.] 

If accidents occur, the radiation levels can be high. That is why reactor designers provide diverse, redundant safety systems to ensure that an accident is entirely unlikely. That is also the reason for the robust design of the reactor with multiple barriers to prevent escape of radioactivity in to the environment.

Nuclear waste management

Generation of waste is an inescapable part of power generation. Indian scientists and engineers have developed technology to manage high-level radioactive waste. The first step in high-level waste management is to make them non-dispersible by incorporating them into glass, – a material which is virtually non-leachable for thousands of years. This property of glass has been well demonstrated. Relics of glass have remained intact for thousands of years. 

If any radionuclide escapes the glass matrix, it must penetrate several protective layers before reaching the biosphere. A stainless steel container, a cladding of lead, a casing of titanium alloy (corrosion rate 0.0013 mm year) several metres of backfill material such as clay. Each of this will last thousands of years. Waste repository will be a site, which will have negligible ground water flow. Even if water enters, and corrodes the barriers, radionuclides will be trapped in the backfill. Finland may start operation of  their geological repository by 2023. France and Sweden also made considerable progress.

India’s nuclear power programme is very modest now. NPCIL safely and efficiently operates twenty-one reactors with a total capacity of 6780 MWe at seven sites (Tarapur, Rajasthan, Madras, Narora, Kaiga, Kakrapara and Kudankulam). Projects with a total capacity of 4800 MWe are progressing at Kakrapara, (2X700 MWe), Rajasthan (2X700MWe) and Kudankulam (2X1000MWe). The Central government has plans for more.

Public must visit  nuclear power stations to see how engineers and scientists safely operate  them.  A visit to the Environmental Survey Laboratories will be reassuring. We need not be afraid of a nuclear power plant in our neighbourhood.

Dr. K S Parthasarathy

Dr. K S Parthasarathy is former Secretary, Atomic Energy Regulatory Board and a former Raja Ramanna Fellow in the Strategic Planning Group, Department of Atomic Energy, Mumbai. Dr. K S Parthasarathy may be contacted at [email protected]

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