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Nuclear site planning: Site selection is first step in nuke safety

Nuclear site planning: Site selection is first step in nuke safety

Location of a nuclear power plant is the first step to its safety. Although not a single death has occurred in Fukushima so far because of radiation, questions are raised about why a modern nuclear plant in a high seismic and Tsunami-prone location proved so vulnerable. Sudhinder Thakur takes us through the process of site identification for India’s nuclear plants, but says seismic or other activity at a site location is less critical to safety than reactor design.

Statistically, per GW of electricity generated, the death rate is 0.04 for nuclear power, and 0.5 for thermal, 10 for hydro and 14 for gas. Statistics apart, conservatism is a preferred term in our circles. The more conservative our planning, the safer a nuclear plant is. A part of this conservatism involves planning where a nuclear plant will come up. In India, we have been conservative in this regard.

Japan is in an active seismic, earthquake-prone region. About 54 reactors are operational in the country, and all of them have withstood a several earthquakes through their lifetime. In Fukushima itself there were 13 reactors, of which 10 were in operation while three were down for maintenance. All the reactors automatically shut down even on the day of the incident—11 March. The reactors were supplied by various companies: General Electric, Hitachi and Toshiba. So there are no questions about the quality of the reactors’ vendors or technology suppliers.

Design conservatism

This reality also brings us to the fact that the criticality is not the seismic zone of any site or resulting Peak Ground Acceleration (PGA) of a particular site; it is to design the reactors for PGA at a particular site. The fact that reactors structurally withstood an earthquake of intensity higher than designed also reinforces conservatism in design, be it on account of uncertainties in design inputs or margins. The important consideration is that the reactor design has to withstand the PGA which is established for a site.

The robustness of nuclear is demonstrated by the earthquake’s severity, resulting in maximum ground accelerations of 0.52 g—well above the design basis. The vintage reactors, four decades old, withstood a seismic event much beyond design value. The containment integrity ensured that wide spread contamination is avoided. Though the full impact of the accident is still unfolding, the accident is closer to Three Mile Island rather than Chernobyl.

The geography

The seismic activity is region-specific, and it would be incorrect to extrapolate the intensities from one region to another. With an area of 3.3 million sq km, India’s area is 10 times that of Japan, with a long coastline of 7,500 km. Most of the Indo-Gangetic plains and peninsular regions of India are in Seismic Zone III or lower.

We have, therefore, no compulsions to go to locations with high seismic locations. However, even at those relatively seismically-safe sites, it is always possible to design a nuclear reactor suitable for high PGAs. An additional mandatory requirement is absence of active ground faults within five km of plant area.

Another consideration is the availability of water in the proximity, for reactor cooling purposes. Outside the stipulated 500 m distance from it, coasts are the most effective providers of cooling water. Cooler water is available at some depth and distance, and is pumped in. Apart from less work needed digging long canals to water sources (and for disposal of hot water), erecting a plant on the coast also reduces land requirement by nearly half, since we can plan a semi-circular campus rather than a circular one. The water is never in touch with any radioactive material.

In an inland plant, cooling towers become necessary—and a nearby water source is used (eg, Kaiga from the Kadra Reservoir, Narora from the Ganga, etc).

We plan for the worst possible earthquake in 10,000 years. In that unlikely event, the reactor shuts down by itself. Each plant needs to be sensitive to its geography; for example, a plant in the seismically more active North East needs a revalidated design, checks and re-enforcements.

The nuke land acquirers

The site selection is a first order assessment of the site to ensure that an engineerable plant can be set up. As with many infrastructure ventures, nuclear power stations are Central sector projects, but they are required to be established on land that belongs to a state. The Government of India has a Site Selection Committee (SSC) for the selection of sites in different zones in the country, as a first step for setting up nuclear power stations. Depending on the need for sites for future nuclear power plants (NPPs), a request is sent to all the state governments for their recommendations on the possible sites for consideration by the SSC. Many governments also request the Centre to start future nuclear power stations in their state. Such requests are also dealt with in the same manner.

At this stage, first order requirement of various inputs of land, water, demography, etc, alone are indicated and a state government agency for detailed interaction with SSC is identified. Thus, all sites selected by the Government of India have roots in the recommendation of the state governments.The proposals from the state governments are then evaluated by the SSC.

The SSC is constituted of experts from within the Department of Atomic Energy and representatives from other, related government agencies such as the Ministry of Power and Ministry of Environment and Forests (MoEF), who bring in valuable lateral inputs in the site selection process. The Atomic Energy Regulatory Board (AERB) provides the codes and guides for the site selection process.

Site requirements: Some of the parameters for requirements during the process of land identification are:

• Site falls within Seismic Zone 1-4
• Absence of capable faults within 5 km
• Distance from air fields/airports
• Military installations
• Storage of inflammable toxic or explosive materials
• Demographic details, particularly population density in adjoining locations

Proximity to water source: Availability of cooling water for all possible operational states of the reactor is also another important consideration. Being the first step in siting, reliance is on inputs already available with various institutions, government departments and fresh data generation is only to supplement the information gaps. The SSC also revisits the sites that were earlier recommended but could not be taken up in view of the nuclear programme. Based on the above evaluation, a panel of sites is recommended by the SSC.

The government considers SSC recommendations and conveys in-principle approval of the sites, depending upon the Nuclear Power Programme, the power situation between different regions of the country and relative priorities in setting up of nuclear power stations.

All clear? After an in-principle approval by the government, and before the establishment of the project, two statutory clearances are needed. While the environmental (other than impact of ionizing radiations) aspects are considered by MoEF, through the Environment Impact Assessments—carried out by the different institutions, public hearing, etc—siting consent in terms of nuclear safety is accorded by AERB. This is done through a detailed site evaluation report.

The consent for siting by AERB involves review of site related safety aspects and is done in accordance with AERB codes of practice. The salient areas of review are as follows:

• Geology and soil mechanics
• Topography
• Hydrology and hydro-geology
• Meteorology
• Natural phenomena such as earthquakes, floods, tsunamis and tornadoes/cyclones
• Potential external human-induced events, eg, plane crashes, fires, explosions
• Failure of humanmade structures such as dams and sea walls
• Availability of water for plant cooling and ultimate heat sink
• Reliability of off-site electrical power

Site reviews: During the life of the plant, periodic safety reviews are also conducted to ensure that the safety continues to be at an acceptable level. This review concerns the changes in land use around the site, population distribution, flood and seismic evaluation. The above comprehensive review of the site related factors, including periodic safety reviews for plants and operation, ensures that safety acceptability of the nuclear installations is ensued at all stages.

The site selection process is a multi-tier process involving various stakeholders, and is conducted in accordance with national codes and guidelines which are comparable to international codes and guides in this context. The fact that nuclear power is in government hands is a major advantage to an uncompromising stance on safety.

The author is Distinguished Scientist and Fellow, Nuclear Power Corporation India (NPCIL).

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