Training Centre / Centre de formation Fundamentals of Power Reactors Module Two Nuclear Reactor Systems Copyright Notice ©HER MAJESTY THE QUEEN IN RIGHT OF CANADA (1993) as represented by the Atomic Energy Control Board All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, electrostatic, magnetic tape, mechanical photocopying, recording or otherwise, without permission from the Atomic Energy Control Board of Canada. Training Centre / Centre de formation Training Centre / Centre de formation Site Selection Training Objectives On completion of this lesson for a CANDU Station the participant will be able to: • Name the site characteristics which are important for design safety • Identify the three phases in a typical site selection process • Identify the natural site factors affecting design safety • Identify the human-related site factors affecting design safety • Name the site characteristics which are important in determining the impact of the plant in the region in which it could be located. Table of Contents 1 Overview of Siting Requirements for CANDU Nuclear Power Plants......................................................... 2 2 First Stage of Site Selection Process ...................................................... 4 3 Site Parameters Affecting Design Safety.............................................. 5 4 Site Selection - Natural Factors............................................................... 6 5 Site Selection - Human-Related Factors................................................ 8 6 Site Characteristics Influencing Plant Impact on the Region........... 8 Site Selection - Page 1 Training Centre / Centre de formation 1. Overview of Site Requirements for CANDU 6 Nuclear Power Plants The siting of Nuclear Power Plants differs from that of conventional plants in that the safety and protection of the public and the environment against the radiological impact of normal and accidental releases of radioactivity must be taken into account and are considered of primary significance in the site selection. The site characteristics which are important to plant design, and the site characteristics which, when the plant is operational are important in terms of occupational and regional public safety, must be investigated. This means that considerably greater effort must be taken in Nuclear Station site selection than for a standard large industrial plant or a conventional fossil fired station. A large number of Codes and Standards by Environment Canada, Canadian Standards Association (CSA), Atomic Energy Control Board (AECB) of Canada, U.S. Nuclear Regulatory Commission (NRC) and International Energy Agency (IAEA) are available which address in detail the various aspects of site selection for nuclear power plants. A summary of the more significant aspects of a nuclear plant site selection is given here. Space and Water Requirements The space requirements for the plant are determined by factors such as, the number of units intended for the site, exclusion zone requirements, construction methods, waste storage technology and transportation methods. The site, if possible, should be selected to accommodate future units. This allows the extensive cost and schedule of site selection activities to be spread over a large amount of power generation. It is also easier, from the point of view of public acceptance to site further units on an existing site. A modular construction concept is used in the construction of new stations. On- site and off-site module fabrication are both possible. For on-site module fabrication the selected site should accommodate a fabrication facility area of 50 x 100 m. For off-site module fabrication, the space and transportation access should be adequate for the shipping of large size modules to the site. Certain major pieces of equipment such as the reactor structure (calandria), the steam generators and fuelling machines require special technical knowledge in their production and will be built off-site on the suppliers premises. The site must therefore be suitable for shipment of these major components. Figure 1.1.1 shows a steam generator being shipped overseas. Site Selection - Page 2 January 1996 Training Centre / Centre de formation Figure 1.1 Loading a Steam Generator for Shipment Overseas Exclusion Zone The exclusion zone, in which no permanent habitation is allowed, is presently chosen as a circle of 1.0 km with its centre at the centre of the reactor building, (Figure 1.1.2). Radiation protection design criteria will then ensure that individual doses within the exclusion zone and individual and population doses outside the exclusion zone are within the legal limits set by AECB. Radioactive Waste Storage Requirements Space is required at the site for waste storage facilities for radioactive waste produced in the lifetime of the plant. The material requiring storage may range from highly radioactive irradiated fuel to material of low radioactive level such as used clothing, tools, debris, etc. CANDU stations currently provide water pool storage facilities for the irradiated fuel for a number of years of operation. For longer term storage a dry storage method in which irradiated material is placed within above-ground concrete containers is utilized by some of the existing CANDU stations. Site Selection - Page 3 Training Centre / Centre de formation Figure 1.2: Typical CANDU Layout Showing Exclusion Zone Cooling Water Requirements Present CANDU stations use an open circuit cooling water system using sea water, lake water, or river water as the coolant for the turbine steam condenser. If adequate water from such sources is not available, a design with a closed circuit cooling water flow, employing cooling towers, can be used to reduce the cooling water flow to that required for make-up of loss from the system. 2 First Stage of Site Selection Process The first stage of three stages of site selection is the site survey which leads to identification of one or more preferred candidate sites from consideration of both safety and non-safety factors. The phases involved in this stage are: Phase 1 - Regional analysis to identify potential sites. This phase consists of simple rejection criteria based upon information which is readily available such as cooling water availability, population density, surface faulting, volcanic activity, seismicity. Phase 2 - Screening of potential sites to select candidate site. This phase will involve visits to potential sites and application of simple comparison methodologies. Site Selection - Page 4 January 1996 Training Centre / Centre de formation Phase 3 - Screening, comparison and ranking of candidate sites to obtain the preferred candidate site. This phase requires limited field work and use of sophisticated scaling and comparison techniques. During the site survey stage, disciplines such as the following are required: • Power Engineering • Seismology • Nuclear Engineering • Soil Mechanics • Radiological Protection • Geology • Ecology/Radioecology • Hydrology • Demography • Meteorology • Emergency Planning • Civil Engineering Much of the expertise in the above disciplines is required for siting conventional plants. However a more specialized level of expertise is required in nuclear plant siting. A well balanced site survey team should include a nuclear engineer, a geologist with seismic expertise, a soil mechanics engineer, a hydrologist, a meteorologist, and an expert on siting. Starting with this stage, all screening data which will be necessary for safety purposes should be subjected to a Quality Assurance (Q.A.) program as specified in the applicable codes. For each site, the availability of labour and the existence of infrastructures such as housing, airports, schools, etc. should also be considered as they affect the construction cost and schedule. 3. Site Parameters Affecting Design Safety There are two major classifications of the external factors (that is, factors not stemming from the plant itself), which must be considered in siting: 1. Natural Factors; included in this category are: • Surface faulting • Seismic Conditions • Subsurface (Foundation) Stability • Flooding • Climactic Conditions • Blockage of Cooling Water Sources Site Selection - Page 5 Training Centre / Centre de formation 2. Human-Induced Events; included in this category are: • Aircraft Crashes and Impact of Missiles • Chemical Explosions • Release of Hazardous Materials 4. Site Selection - Natural Factors Surface Faulting The site should not be close to known capable geological faults. Proximity to known capable faults imposes extensive analytical and licensing efforts if a decision is made to use the site. Seismic Conditions For nuclear stations the seismic requirements that must be met are much more rigorous than those given in building codes. Areas of high seismic activity should be avoided. Site specific seismicity studies are required for the selected site. These studies include historic earthquake records, regional tectonics and seismological characteristics and micro-earthquakes monitoring. Using these data, probability analysis will be carried out in order to determine the Design Basis Earthquake at the site. These studies will have to be carried out regardless of the earthquake zoning defined in the National Building Code for the area. Standard plants such as CANDU 6 are designed for a defined maximum ground acceleration which will meet the requirements of most Canadian and