Category Archives: Infrastructure and methodologies for the. justification of nuclear power programmes

Letter of invitation

The cornerstone of the BIS and written by the owner, the letter of invitation (LI) is addressed to the potential bidders, inviting them to submit their bids and briefly stating: [104]

• Plant location and main site characteristics (e. g. condenser cooling water method required)

• Contracting approach and scope of supply (base scope and options)

• Whether or not financing is to be arranged by the bidder

• Project scheduling forecast, and bid preparation and submittal schedule

• List of BIS documents enclosed with the LI

• Key BIS aspects that may be of special import to the owner and subject to special care from the bidders

• Request that the bidders formally notify, in writing and before the indi­cated date, of their intention to bid.

The LI should be brief (2-3 pages maximum) and avoid indicating details that are already covered in other BIS documents.

Licensing application and supporting technical documents

The licensee is required to prepare an extensive set of documentation cov­ering all aspects of the plant’s life cycle. Some of these documents are mandated by national laws and regulations, while others are required by the regulatory body for licensing or in response to specific requests. The content and number of documents will vary considerably from country to country depending on the national legal and regulatory systems and prac­tices. However, the IAEA has developed recommendations on the docu­mentation requirements that provide some common guidance, while recognizing that other systems may also be effective (IAEA, 2002a). Whatever system is used, the IAEA Guide states that:

The system of regulations should provide advance information to the operator on the requirements for each major stage of authorization. This will assist the operator to make sound plans and decisions with respect to safety in the siting, design, construction, commissioning, operation and decommissioning or closure of a nuclear facility.

While it is not possible to cover the specific documentation requirements that apply to all countries, Table 20.2 contains a representative sample of the types of information that might be required at each stage.

Conduct of operations

In successful organisations the operators do much more than simply operate the plant. The operators set standards and expectations for all aspects of the plant, from performance and material condition, to housekeeping and the conduct of staff involved in its operation and maintenance. It is important therefore that operations personnel exhibit, at all times, the values, beliefs and behaviours that support high standards.

WANO Guideline 2001-02, Guidelines for the conduct of operations at nuclear power plants, provides further insights into the setting of standards and expectations in the conduct of operations that are conducive to high performance.

5.9.1 Communication

Operators have to conduct their work across many interfaces, between the site and external bodies such as grid control centres and emergency services, between shifts and management and support organisations across the sites. Clear, concise and effective communication is an essential attribute of operations personnel in both verbal and written forms.

WANO and INPO have developed Good Practices and Guidelines for effective communication, based on insights and experience gained in peer — to-peer exchange programmes.

Plant operation

The operating organization responsible for an NPP has a staff that collec­tively has a variety of scientific, engineering and other technical back­grounds in fields needed to effectively and safely operate and maintain the plant. These include nuclear engineering, instrumentation and control, elec­trical engineering, mechanical engineering, radiation protection, chemistry, emergency preparedness, and safety analysis and assessment. There is a need to have access to national or international expertise to support the NPP operating organization and regulatory body in scientific areas such as neutronics, physics and thermohydraulics and in technical areas such as radiation protection, radioactive waste management, quality management, maintenance and spare parts management.

In addition to the required scientific, engineering and other technical education, normally the relevant staff need three or more years of special­ized training and experience prior to the initial fuel loading of an NPP. For
implementation of a first NPP project, much of this specialized training and experience can be included as part of the contract with the supplier of the NPP technology. It is necessary for the operating organization to establish the rigour, culture, ethics and discipline needed to effectively manage nuclear power technology with due regard to the associated safety, security and non-proliferation considerations (IAEA, 2007c).

Table 6.4 includes the specialization requirements during the stages of construction, commissioning and plant operation.

Construction quality

Towards ensuring high quality in construction, each piece of work must be carried out according to detailed procedures that are made available in advance. There should be an independent quality assurance agency with good participation of utility personnel to carry out quality checks at pre­identified stages or hold points. There should be formal procedures in place to deal with non-conformances from approved construction specifications, drawings and procedures, and the hierarchical levels at which their disposi­tion is to be decided shall be identified in advance. It is most appropriate to establish a formal mechanism for communicating such changes to the commissioning group and the O&M group and to associate them in the NPP construction activities to the extent feasible. This helps in making them thoroughly familiar with the as-constructed plant. Also it is frequently nec­essary to make mid-course changes in construction on account of factors such as unexpected interferences encountered while laying piping and cables or non-availability of specified materials. The O&M group must properly assess the impact of such modifications and the need for modifying operating and maintenance procedures or carrying out additional checks during commissioning.

Nuclear safety and the perception of risk

A nuclear reactor core has to maintain two equilibria: the rate of neutrons produced has to be equal to the rate of neutrons lost, and the rate of heat generated has to be equal to the rate of heat removed. Both equilibria are linked through so-called reactivity coefficients, the values of which make the system stable or not. Perturbations in these equilibria may be intro­duced by internal or external causes and by human error. Consequently, the design of a reactor has to contemplate all the possible inputs and determine how the plant will react against them in such a way that no damage to the core is produced and no release of radioactive products should occur; under these circumstances, the reactor is declared safe.

Nevertheless, accidents may occur when not all the potential inputs (or a combination of them) have been considered, when their magnitude has not been measured properly, when multiple human errors have been com­mitted, or multiple safety equipment is unable to work due to common — cause failures. Combinations of all these are possible, although remote. When such accidents occur, there is a possibility that radioactive products will be released to the exterior, with the likelihood that the health and safety of people will be affected and that environmental contamination by radio­active products will occur.

The accident at TMI-2 was due to a combination of equipment failure, poor maintenance and human error, the accident at Chernobyl-4 was caused by human mismanagement of the reactor’s unstable condition (INSAG, 1992a), whilst the accident at Fukushima-1 had its origin in the multiple common-cause failures produced by an earthquake and a following tsunami, against which the plant was not designed. In TMI-2 the release of radioac­tivity was limited and the health and safety of people was not at risk; in Chernobyl the release was very large and the radiological consequences very serious; in Fukushima-1, the release from the three affected units was about one-tenth that of Chernobyl but the radiological consequences were limited, due to an efficient emergency management.

Relevant lessons have been learned from such events and these lessons have served to improve the safety of present and future nuclear power plants. These accidents demonstrate that absolute safety is not achievable, and that there will always be a residual risk, although that it should be as low as possible, and acceptable. Prevention of accidents and mitigation of their consequences is the main aim of nuclear safety.

The safety level of nuclear installations and activities that give rise to radiation risks can be improved and maintained by following the IAEA Fundamental Safety Principles (IAEA, 2006), which provide the basis for the safety requirements and safety guides and programmes which have been developed by the IAEA as part of its safety standards activities.

These principles apply to a nuclear power plant in all modes of operation and to its entire fuel cycle installations and activities, such as transporta­tion of radioactive waste and nuclear materials, and their final disposal. The principles recommend the creation of a series of administrative enve­lopes and technical barriers that prevent accidents and mitigate their consequences.

These administrative barriers assign the prime responsibility for safety to the licensee, as well as allocating to government the responsibility of enacting a complete and satisfactory legal and licensing system and the creation of a regulatory body with three major activities: the development of a consistent set of safety standards, the verification of compliance with applicable standards, and an enforcement authority to correct any devia­tion. The licensee is also obliged to develop leadership and management for safety, based on the promotion of a safety culture within the installations and all related activities, on the regular assessment of safety performance and on feedback from operating experience. These administrative and pro­cedural barriers are essential to achieve and maintain the required safety levels.

Technical barriers also help to prevent accidents and mitigate their con­sequences by adhering to the concept of defence-in-depth, through a com­bination of consecutive and independent levels of protection which would have to fail to cause the release of radioactivity to the environment. Such levels include conservative designs and use of materials of high quality and reliability; the introduction of control, limiting, protection and monitoring systems; the addition of technological safeguard systems to cope with acci­dental situations and to mitigate their consequences, including so-called passive systems; the application of well-developed and trained emergency procedures; and the availability of emergency measures to protect people outside.

The safety level of a nuclear power plant can also be measured through its complementary function: risk. A quantitative risk assessment method­ology for nuclear power plants was first introduced in 1975 by the Reactor Safety Study (NRC, 1975); the methodology was later repeated in Germany and an English translation produced (EPRI, 1981) and later refined to consider five specific nuclear power plants covering the nuclear technolo­gies used in the USA (NRC, 1990). This new methodology has been used widely (although covering only the first two levels of these studies) across practically all nuclear power plants in the world.

Such ‘Probabilistic Safety Analyses’ (PSAs) are divided into three levels. Level 1 PSA determines the expected frequency of accidents producing core damages, the values obtained ranging from 1 in 10,000 to 1 in 100,000 per year and reactor. Level 2 PSA estimates the conditional probability of an early release of radioactive products by failure of the containment system within a damage core, with values found to vary from 1 in 10 cases to 1 in 100 cases. The accepted recommended values (INSAG, 1992b) are less than 1 in 100,000 per year and reactor for Level 1, and a conditional probability of 1 in 10 cases for Level 2 PSA. Level 3 PSA determines the complementary distribution function of the radiological consequences to the health and safety of the public and also the economic consequences derived from losing the plant and restoring the environment. When these results are compared with other technological risks and those from natural events, it is concluded that the risks of nuclear power plants are several orders of magnitude lower.

Although it may seem sufficient to estimate nuclear risks and put abso­lute, and also relative, values on acceptable risks, risks perceived by the individual and society are also a reality to be considered. In an analysis of perceived risks, it is necessary to consider, among the major aspects, the benefits obtained, familiarity with the type of risk, and the nature and time dependence of the harm produced.

The benefits obtained determine the perception of risk. Individuals accept high risks when the benefits are clear to them, which explains the acceptance of driving a car or smoking. The benefits from nuclear power are not clearly estimated by individuals and society: the need and apprecia­tion of the benefits obtained from electricity are well understood, but elec­tricity can also be provided by other means. Because of this, it is necessary to explain, once again, the worldwide, national and local socio-economic benefits coming from nuclear power. To make the picture complete, it would be necessary to compare the risks and benefits of the other sources generat­ing electricity, but such an analysis is outside the scope of this chapter.

Familiarity with the nature of a risk and its frequency is another major ingredient in the perception of risk. Although the use of radiation is now part of everyday life for many people, mainly through its use in medicine, fear of radiation is very high due to its peculiar nature, which is difficult to understand. An average individual receives doses, for medical purposes, which are much larger than those from natural radiation and orders of magnitude larger that those the most exposed person will receive from the operation of nuclear power plants and related fuel cycle activities. Nevertheless, society grossly exaggerates the risks perceived from nuclear power, despite the efforts made and the evidence presented to explain the real situation.

The timing of the harm produced is another aspect of interest. When damage done shows immediately, the perception of risk is different from when it may or may not come later in the life of the person, or if the risks may still exist for future generations. It is well known that high radiation doses may produce deterministic effects and that damage will show up soon after exposure but, most frequently, even in the case of severe accidents, most exposures produce low doses with the potential to produce stochastic effects, sometimes many years later. These circumstances have produced a considerable increase in perceived risk, with people believing that any exposure, however low, will produce the expected effects with certainty, despite efforts made to show that the probability of the effect is very low and proportional to the dose received.

Despite efforts made to increase safety, accidents cannot be completely discounted and preparation for them should be in place. Two instruments have been created to protect the health and safety of the public, and to protect private and public properties and the environment. The first is a legal instrument based on the concept of third-party liability for the damage caused. The second is the preparation and maintenance of emergency pro­cedures and the corresponding equipment needed to protect the health and safety of the individuals affected.

Seawater desalination

Due to water scarcity, total contracted desalination capacity (from both seawater and brackish water) has almost tripled in the past decade, reaching a global online capacity of about 50 million m3/d. Desalination has proven during the last 50 years its reliability to deliver large quantities of fresh water from the sea. Technological advances of the last decade have helped desalination to spread faster and to become a reliable way to supply water and consequently to promote sustainable development. Among the drivers for the growing interest in seawater desalination using nuclear energy are cheaper energy, less uncertainty on energy costs, higher load factor of the desalination plant, better load factor of the nuclear unit, utilization of the nuclear plant’s unused land, and reduction of the desalination carbon foot­print. The future requires effective integration of energy resources to produce power and desalinated water economically with proper consider­ation for the environment.

The principal desalination processes are based either on distillation or on membrane separation. The first group includes the widely applied com­mercial methods of Multi-Stage Flash Distillation (MSF) and Multiple Effect Distillation (MED). Still under development is Thermal Vapor Compression distillation (TVC) which is a promising process with a higher conversion ratio. The main characteristics of distillation processes are high energy cost, independence from feed water quality and simple technology with wide experience worldwide. The processes using membranes are char­acterized by having lower energy costs, dependent on the feed water quality, and simplicity. Major thermal energy in the range of 100-130°C is required to heat the feed water.

All existing designs of nuclear reactors could be used to provide electric­ity, low-temperature heat and/or combinations of both as required for desalination. Relevant experience with nuclear desalination is already available. The use of nuclear heat requires a close location of the nuclear plant to the desalination plant, while the use of electricity generated by nuclear energy for reverse osmosis (RO) does not differ from any other use of electricity in that the energy source may be located far from the cus­tomer, with electricity being provided through the electricity grid. It should be noted, however, that electricity taken directly from the plant is cheaper than the electricity from the grid and that a distant location would not allow the use of warm water from a condenser for the RO feed.

Limited experience exists with nuclear desalination since the 1960s from nine nuclear units in Japan and one in Kazakhstan. The latter was a BN-350 fast reactor which produced 135 MWe and 80,000 m3/d of fresh water by MED over 27 years before it was removed from operation in 1999. In Japan, nuclear desalination is experienced in the form of having the desalination plants constructed on-site of the nuclear power plant with aim at supplying the required make-up cooling water to these nuclear power plants. Such desalination plants have in general small capacities of 1000-3000 m3/d. In India, a combined MSF and RO hybrid system connected to twin 170 MWe pressurized heavy water reactors has been constructed and is, presently, in the commissioning phase. With capacities of 1800 m3/d by RO and 4500 m3/d by MSF, it will become the largest nuclear-based desalination plant in the world. Optimization of water desalination using nuclear reactors has been analysed, and studies are still under investigation in several countries.

New developments in nuclear desalination are numerous as many coun­tries have consistently progressed almost simultaneously in three technical fields: the development of improved or new generation nuclear reactors, the improvements in desalination technologies and the adoption of many cost reduction strategies. An interesting feature of this development is that many countries, normally not considered as exporting countries, have begun to develop their own nuclear reactors. For example, Argentina is developing the CAREM reactor. China is pursuing the development of the dedicated heat only reactor NHR-200 providing relatively low-temperature heat for an MED process, with some electricity production to meet the local electric­ity needs. India is going along with a consistent evolutionary approach to develop its advanced PHWRs. The Republic of Korea continues with its program to develop the System-integrated Modular Advanced Reactor (SMART). South Africa is developing the PBMR which can be used for electricity generation, hydrogen production and desalination (although the project is currently frozen).

Defence in depth, defence in time

Defence in depth is a design philosophy that is applied universally in nuclear reactor design practice. Specific applications differ, of course, as reactor designs are quite different in their needs for protection against various hypothetical events such as sudden closure of turbine shutoff valves, pipe breaks, and accidental control rod ejection. In Canadian design philosophy, for example, each unit incorporates two independent, fully capable and physically diverse shutdown systems to reduce power quickly whenever necessary. There is a fast-acting emergency cooling system that would refill the heat transport circuit in the event of a loss of primary coolant. In addi­tion, the cool moderator water surrounding each fuel channel would remove the decay heat of fission remaining in the fuel, and so prevent fuel melting — as a result, broad dispersion of fission products would not occur. The containment structure features two independent means of sealing the ven­tilation systems, on receipt of one or more signals. These mechanisms are all kept in a ‘poised’ condition and are initiated by highly reliable detection and actuation chains with redundant components and ‘fail-safe’ design characteristics. An exclusion zone surrounds the plant. In this zone no per­manent residence is allowed, so that if radioactive materials were to be released in an accident situation there would be no measurable health damage to humans.

Defence in time is a new preventative concept, intended to specifically identify the need for regular attention to the possibility of sudden or wear — out failures of components and systems in use in an operating nuclear station. The basic idea is to establish a methodology requiring preventive maintenance for each component and system important to safety, at time intervals depending on the life expectancy of the item. Regular mainte­nance ensures that these components and systems are ready to perform their function if required during any possible accident. Testing of these systems is conducted on a regular basis; as a result the system is maintained in an essentially ‘as new’ condition for the whole operating life of the plant. Other jurisdictions have established similar formal structures, usually via some form of regulatory requirement; for an example, see USNRC (1991).


Exposure of the public

Подпись: Conversion factor (Sv Bq-1)

Public exposure to radiation arises not only from NPPs, but from natural background radiation and artificial sources such as medical diagnostic and therapeutic procedures, nuclear weapons testing, and many occupations that enhance exposure to artificial or natural radiation. All these sources

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Conversion factor (Sv cm2)

11.1 Interrelation among the radiation protection quantities.

deliver doses to members of the public, which are routinely estimated by UNSCEAR.

For as long as they have been on the planet, humans have been exposed to radiation from natural sources, and such exposure has been continually modified by human activities. The main natural sources of exposure are cosmic radiation and natural radionuclides found in the soil and in rocks. Cosmic radiation is significantly higher at the cruising altitudes of jet air­craft than on the Earth’s surface. External exposure rates due to natural radionuclides vary considerably from place to place, and can range up to 100 times the average. An important radionuclide is radon, a gas that is formed during the decay of natural uranium in the soil and that seeps into homes. Exposures due to inhalation of radon by people living and working indoors vary dramatically depending on the local geology, building con­struction and household lifestyles; this mode of exposure accounts for about half of the average human exposure to natural sources. It is now recognized that a very large number of workers are exposed to natural sources in their working places.

Concerns on nuclear test explosions in the atmosphere were the original reason for the UNSCEAR conception. They had been conducted at a number of sites, mostly in the northern hemisphere (the most active testing being in the periods 1952-1958 and 1961-1962), and the radioactive fallout from those tests represents a source of continuing exposure even today, albeit at very low levels. The most dominant peaceful exposure is medical exposure. Irrespective of the level of health care in a country, the medical uses of radiation continue to increase as techniques develop and become more widely disseminated; about 3.6 billion radiological examinations are conducted worldwide every year. (In countries with high levels of health care, exposure from medical uses is on average now equal to about 80% of that from natural sources.)

By contrast, radiation doses due to the generation of electrical energy by NPPs are extremely small in spite of the fact that this type of generation has grown steadily since 1956. Moreover, the doses due to the production of energy in the nuclear reactor are in turn a small part of the doses due to the nuclear fuel cycle, which includes the mining and milling of uranium ore, fuel fabrication, storage or reprocessing of irradiated fuel, and storage and disposal of radioactive wastes. The doses to which the public are exposed vary widely from one type of fuel-cycle installation to another, but in any case they are generally small and they decrease the further the distance from the facility. Moreover, they have been markedly reduced over time because of lower discharge levels. For instance, Fig. 11.2 presents the reduc­tion of normalized noble gas releases for different periods and types of reactor. Over the period 1970-2002, radioactive releases (expressed as 1012 becquerels per 109 watts of electrical energy produced) of noble gases were

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Подпись: 100 000Подпись: 10 000Подпись: 1 000Подпись: 100Подпись: Periodimage07311.2 Normalized noble gas releases for different periods and types of reactor.

reduced from 13,000 to 112; those for tritium were reduced from 448 to 43, and for iodine from 0.047 to 0.0006 (UNSCEAR, 2011).

In sum, the doses due to the nuclear fuel cycle in general and to NPPs in particular are a tiny fraction of the doses incurred by the population. Table 11.3 presents the latest UNSCEAR estimates of global radiation doses from different sources (UNSCEAR, 2011).

International conventions and standards on emergency planning

In most countries, the nuclear emergency plans are governed by specific regulations that establish the national regimen of civil protection and radia­tion safety. These regulations allocate responsibilities to different actors taking part in the emergency management, set up requirements for emer­gency preparedness and response, and establish criteria for intervention in case of emergency.

The national civil protection legislation, which is mainly addressed to the off-site emergency plans, usually establishes the basis for planning, empha­sizing the right of citizens to their own protection and their obligations in the event of emergency, as well as allocating the responsibilities of all organizations participating in the preparedness and response to nuclear emergencies. Civil protection legislation is strongly conditioned by national political and administrative structures since it sets up rights and obligations for citizens and public and private organizations, as well as the basic respon­sibilities and procedures to take decisions.

The national regulations on radiation safety are usually based on the standards and recommendations issued at international level for the safe and secure use of nuclear energy and its applications. Emergency prepared­ness and response have been taken into consideration by international standards and recommendations on radiation safety and nuclear liability, since the very beginning of the use of nuclear power for peaceful purposes. But it was in the late 1980s, as a result of the lessons learned from the Chernobyl accident, when this subject was treated by the international com­munity as a common concern at the highest level of internationally legally binding instruments. It is too early to conclude lessons learnt from the Fukushima event, but there is no doubt that this accident will be the starting point to review some safety criteria related to facility siting and to recon­sider some hypotheses usually accepted for on-site emergency plans. It is also probable that off-site emergency plans are revised to take into account the special difficulties that are expected to implement countermeasures when a big nuclear accident occurs simultaneously with a natural or anthro­pogenic disaster.

396 Infrastructure and methodologies for justification of NPPs