CRITERIA FOR NUCLEAR POWER PLANT SITE SELECTION Junaid Ahmad Trainee Scientific Officer-C Atomic Minerals Directorate for Exploration & Research, Hyderabad. ABSTRACT For any engineering project, geotechnical investigations, during site selection and preconstruction stage are most essential. This helps in improving the foundation conditions and provide adequate safety factor so that the structure remains stable during its life time and can withstand anticipated natural disaster. During the site selection of a site for Nuclear Power Plant geotechnical investigations play significant role in deciding merits and demerits of the sites. The process of evaluating the site involves conducting a site survey to identify one or more possible sites and then performing detailed evaluation of those sites. INTRODUCTION Siting, design, construction, operation, and de-commissioning are the five major stages during the life time of a nuclear power plant. Safety of the plant personnel, public and the environment from radiological hazard is the most important consideration for siting of nuclear power plants. Atomic Energy Regulatory Board (AERB) formulates safety requirements for nuclear and radiation facilities to assess their safety during siting, design, construction, commissioning, operation and decommissioning stages. Siting is the process of selecting a suitable site for NPP including appropriate assessment and derivation of the related design bases. Siting is required for following purposes: a) To construct and operate nuclear power plants safely. b) To provide protection of the public against radiological impact. c) Consideration for emergency planning. BASIC REQUIREMENTS For nuclear power plants, the site includes the area surrounding the plant enclosed by a boundary, which is under effective control of the plant management. Current mandatory requirement of AERB siting code is that an exclusion zone of atleast 1.5km radius around the plant is to be established and this area should be under the exclusive control of the station wherein public habitation is prohibited. A sterilized zone around the exclusion zone covering an Submitted By: Junaid Ahmad Page 1
area upto 5km radius around the plant is also established. Only the natural growth of population is permitted in the sterilised zone, but planned expansion of activities leading to enhanced population is regulated. Following criteria are studied during site selection procedures for Nuclear Power Plant sites: General Criteria Natural Events i. Geological Considerations ii. Seismic Considerations iii. Flooding of Sites iv. Shoreline Erosion v. Loss of Ultimate Heat Sink Man-Induced Events - Other Consideration - i. Aircraft Crash ii. Oil Slick iii. Blasting Operation iv. Mining, Drilling and Water Extraction i. Power Evacuation ii. Transport of ODC iii. Foundation Consideration iv. Radiological Impacts on Environments GENERAL CRITERIA General Acceptance Criteria during Preliminary Stage of Site Selection Sr. No. Criteria Desirable Parameters 1. Population density within 10 km radius Less than two-third of state average 2. Population within Sterilised Zone Less than 20000 3. Distance of population centres (> 10000 More than 10 km person) 4. Distance of large population centres (> More than 30 km 100000 person) 5. Terrain Reasonably flat up to 20 6. Distance from facilities involving storing handling inflammable, toxic, corrosive material and any mining activities. km More than 5 km. Submitted By: Junaid Ahmad Page 2
General Rejection Criteria during Preliminary Stage of Site Selection Sr. No. Criteria Rejection Standard/SDV Sites falling beyond Zone IV 1. Seismicity according to IS Classification (IS- 1893:1984) 2. Distance from capable fault Less than 5 km. 3. Distance from small airfield Less than 5 km. 4. Distance from major airports Less than 8 km. 5. Distance from military airfield Less than 15 km. 6. Distance from military installations storing ammunitions, etc. Less than 10 km. 7. Distance of historical monuments, 5 km. tourist interest. Geological Consideration NATURAL EVENTS The geological setting of a site is important and has to be carefully investigated. Information are collected from existing sources or relevant investigations should be carried out wherever necessary. Following information are required for geological considerations- 1) Regional and local Geology. 2) Faults, fracture, joints, shears, lineament and other discontinuities. 3) Dimensions of faults and information on their nature and degree of faulting. 4) Petrological studies of rock units are required to know the engineering properties of rocks. Presence of strained quartz is to be identified especially because it reacts with alkalis of silica and give rise to gel-silica and weaken the structure. It also helps in identification of terrain, fracture and shears. 5) Nature and depth of weathering to be observed in trial pits or boreholes. This gives information about depth upto which excavation is required to get fresh foundations. Slope Instability: The site and its vicinity shall be evaluated for slope instability such as landslide, rock fall, rock creep etc.,which could affect the safety of NPP. Submitted By: Junaid Ahmad Page 3
Soil Liquefaction: Soil liquefaction is sudden loss of shear strength and rigidity of saturated cohesionless soil due to vibratory ground motion. If potential for soil liquefaction exists for vibratory ground motion S2, the site shall be deemed unsuitable. Site Surface Collapse or Subsidence: Area shall be examined for existence of caverns, karstic formation, mines or subsidence. SEISMIC CONSIDERATIONS The general seismic intensity expected in the region shall be carefully evaluated. Site falling beyond Seismic Zone IV shall not be considered for location of NPP. Faults in the region shall be investigated to determine their capability. A site closer than 5 km to a capable fault shall be deemed unacceptable. A Seismotectonic map of the area should be prepared. Consideration should be given to reservoir-induced seismicity for the dams existing or sanctioned to be built in the region. The design basis vibratory ground motion shall be based on S1 and S2 levels of earthquake. S1 Level Earthquake: S1 level earthquake is the level of ground motion which can be reasonably expected to be experienced at the site area once during the operating life of the plant. In the design of NPP the S1 level of earthquake should be the Operating Basis Earthquake (OBE). The Operating Basis Earthquake (OBE) is that earthquake which produces the vibratory ground motion for which the features of Nuclear Power Plant (NPP) necessary for continued safe operation are designed to remain functional. The return period of the S1 level event should not be less than 100 years. The peak ground acceleration for S1 level earthquake may be fixed using either a deterministic or probabilistic approach based on seismotectonic conditions. S2 Level Earthquake: It is that earthquake which produces maximum vibratory ground motion for which certain structures, systems and components are designed to remain functional. In the design of NPP the S2 level be referred to as the Safe Shutdown Earthquake (SSE). The S2 level event has a return period of the order of 10,000 Submitted By: Junaid Ahmad Page 4
years. The peak ground acceleration for S2 level earthquake should be determined using a deterministic approach. ACTIVE FAULTS If any fault is associated with following characteristics, then it can be termed as an Active Fault a) Faults which are associated with seismicity and neotectonism. b) Quaternary (2 or 3 million years old) or more recent movement at or near the earth s surface. An active Fault study is key element in seismic hazard assessment to identify and characterize seismic source. It gives information about shearing resistance along the fault. Rate of strain accumulation can be also determined. Size of Earthquake These are empirical formulas from which size of earthquake can be calculated. It is given by Wells and Coppersmith (1994) M = 5.08 + 1.16*log(SRL) Where SRL is surface rupture length in km. M = 6.69 + 0.74 * log (MD) Where MD is maximum displacement in meter. M = 6.93 + 0.82 * log (AD) Where AD is average displacement in meter. Preparation of Seismotectonic Map Seismotectonic of an area about 300 km radius around the site has to be examined. It gives idea about the potential sources of seismicity in the area. For preparation of seismotectonic map lineaments, earthquake event and hot spring data are required. The well defined and documented seismic sources are published in the Seismotectonic Atlas of India, GSI, 2000 and Tectonic Map of India, ONGC, 1968. Other sources are Geothermal Atlas of India, Aerial Photographs and Satellite Imageries and published literatures related to area of interest. Objectives: 1. Where the future earthquake will occur? 2. What will be the magnitude? 3. What will be the frequencies of these occurrences? Submitted By: Junaid Ahmad Page 5
4. What will be their impact on construction site? FLOODING OF SITE 1. Inland Flooding- Region shall be examined to determine the extent of flooding that could take place due to heavy precipitation. Dam failure shall be postulated taking into account the type and condition of the dam. 2. Coastal Flooding- Flooding may be caused due to tropical cyclones, tsunamis and wind waves. Frequency of occurrence and their intensity should be studied. Shoreline Erosion An investigation shall be undertaken to determine whether a potential for coastal instability exists in case of coastal sites. Sequential satellite data obtained from the previous years may be used in assessing the changes in shoreline. Loss of Ultimate Heat Sink The potential for loss of functions required for heat sinks shall be analysed. Availability of adequate quantity of water to maintain the reactor under safe shut down state for atleast thirty days shall be ensured under all circumstances. 1. Aircraft Crash: MAN-INDUCED EVENTS A study on the probability of occurrence of an aircraft crashing on the NPP shall be made. 2. Blasting Operation: Information regarding blasting operations in the site vicinity (less than 5km) shall be assessed. 3. Oil Slick: Information regarding movement of oil tankers in the nearby shipping channels in case of coastal sites shall be obtained. 4. Mining, Drilling and Water Extraction: Information related to mining, drilling and water extraction shall be collected which may affect safety of NPP. Submitted By: Junaid Ahmad Page 6
OTHER CONSIDERATIONS 1. Power Evacuation: Power evacuation scheme from the proposed plant is studied in detail considering transmission scheme, generation and load centres in the electricity network. 2. Transportation of ODC Some of the equipment used in NPP are heavy and having very large dimension. So, availability of transport route for movement of over dimension consignment (ODC) is checked. 3. Foundation Consideration: It shall be insured that the site has competent strata for transferring the design loads through the foundations. Adequate sub-surface investigations shall be carried out to verify the competency of the founding media. 4. Radiological Impacts on the Environments The radiological consequences due to NPP on environment should be as low as reasonably achievable for normal as well as accidental condition. Baseline data of atmosphere, hydrosphere lithosphere and biota in the site region is assessed prior to commissioning NPP. References 1) Code of Practice on Safety in Nuclear Power Plant Siting. AERB safety code no. AERB/SC/S.1990. 2) Monograph on Siting of Nuclear Power Plant, AERB. Roshan A.D., Shylamoni P., Sourav Acharya 3) New Empirical Relationships among Magnitude, Rupture Length, Rupture Width, Rupture Area, and Surface Displacement. Wells D.L. and Coppersmith K.J. Bull. of the Seism. Soc. of America, Vol. 84, No. 4, pp. 974-1002, August 1994 4) Nuclear Power Project Site Selection-Geotechnical Considerations Katti,V.J., and Banerjee,D.C.1997. AMD Training Course Handbook Vol.3, p.93-112. 5) Seismic Studies and Design basis ground Motion for Nuclear Power Plant Sites. AERB Safety Guide No. AERB/SG/S-11.1990. Submitted By: Junaid Ahmad Page 7