Крючков Фундаменталс оф Нуцлеар Материалс Пхысицал Протецтион 2011

∙nuclear power and fuel cycles;

∙nuclear safety and radiation protection.

The department of nuclear sciences and applications studies global problems faced by the world, such as food and fresh water shortage, human health problems, etc.

The department of technical cooperation aims to facilitate transfer of nuclear energy knowledge to countries seeking it – primarily to the developing world. The technical assistance program covers:

∙personnel training (provision of training allowances, re-training courses);

∙consultancy missions to help in solving problems related to nuclear energy uses;

∙research contracts. Every year, the IAEA allocates $ 4 to 5 million for research activities. It supports studies under 1900 contracts and agreements in more than 90 countries, with the majority of them being developing economies.

The department of safeguards is the Agency’s largest unit with about 366 employees. This is explained by the fact that the department is entrusted with one of the most important tasks undertaken by the Agency, to wit, implementation of the international safeguards as a system of measures used by the IAEA to make sure that its member-states meet their obligations assumed in connection with the Agency’s Statute and the NonProliferation Treaty.

To this end, the safeguards department is staffed with about 250 inspectors. Inspection activities include independent measurements of nuclear material parameters on sites and use of containment and surveillance techniques to keep nuclear materials under control during inspection intervals. The IAEA inspectors have at their disposal up-to-date instrumentation and advanced systems. The safeguards-related data are processed by state-of-the-art computers.

The tasks of the safeguards department include inspections at national fuel cycle facilities; development of inspection/monitoring techniques and equipment; evaluation of safeguards information; cooperation with national authorities on matters of safeguards implementation. The safeguards department has six divisions (see Fig. 3.1). Three operations divisions carry out actual inspections in various regions of the world. The functions of the other three divisions are to support the activities of the operations staff.

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The division of information technologies analyzes and assesses the safeguards implementation activities by collecting and reviewing reports, questionnaires on design of facilities, and inspection results.

The division of technical services is responsible for development and use of equipment, instrumentation and computers. It provides the inspectors with up-to-date facilities.

The division of concepts and planning develops and improves safeguards implementation procedures and approaches, works out ways for enhancement of their efficiency, and deals with matters of standardization and statistical treatment of inspection results.

International legal framework for development and application of the IAEA Safeguards

Given below are definitions of some terms associated with the practice of international safeguards.

Source material is uranium (natural or depleted) and thorium in the form of metal, alloy, chemical compound or concentrate (other than ore).

Special fissionable material is plutonium–239; uranium–233; uranium enriched in U-235 or U-233; or other material containing one or several of the above substances.

The IAEA Safeguards constitute a system of technical measures taken by the IAEA in accordance with its Statute and the NPT for the purpose of non-proliferation of nuclear weapons.

1.The IAEA Safeguards were originally based on the Statute of this organization [2]. The principal requirements and conditions of the safeguards application were defined in Article III.A.5 of the IAEA Statute. Those requirements may be described as minimal. A state was required to make a minimum of efforts for providing access to nuclear materials at individual facilities chosen for inspection on agreement with the parties concerned.

2.In 1961, the IAEA Statute was taken as a basis for development of the initial safeguards system which is described in INFCIRC/26. At that stage, the inspection and verification activities of the Agency were limited to small research reactors and laboratory facilities.

3.As nuclear activities grew in scale, it became clear that the original system of safeguards was in need of extension and improvement. In 1965, the system was revised and extended to include nuclear power reactors, irradiated fuel reprocessing facilities, as well as nuclear materials found at

fuel fabrication plants. This system – INFCIRC/66 – amended in 1966 and

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1968 is in use up to now as a basis for agreements on safeguards concluded with the states that have no nuclear weapons and are not signatories to the NPT. Like all the earlier systems of safeguards, INFCIRC/66 was aimed at control over individual facilities in a country (such was, for instance, the agreement between the IAEA and Israel).

4. With the Treaty on the Non-Proliferation of Nuclear Weapons having come into effect in 1970, the IAEA acquired new significance in its role of consolidating the non-proliferation regime. It is very important that Article III.1 of the Treaty stipulates that the safeguards should be extended to all peaceful activities of the signatory states. Thus, unlike the safeguards imposed according to the IAEA Statute upon specific facilities, the safeguards arising from the NPT are full-scale and covering the whole nuclear fuel cycle in the states where they are implemented. The system described in the IAEA document INFCIRC/153, was set up 1971 and is still effective.

5. INFCIRC/153 [3] states that the main obligation assumed by a state in the framework of a safeguards agreement concluded in accordance with the NPT, lies in the fact that the safeguards should cover all the source or special fissionable materials involved in peaceful nuclear activities on the state’s territory for the exclusive purpose of making sure that such material is not diverted to production of weapons or other nuclear explosive devices.

The system of INFCIRC/153 requires that a state should keep the Agency informed, or, more specifically, that it should:

∙supply the IAEA with information on the design features of its facility as well as with other, safeguards-related information;

∙keep accounting records for every material balance area;

∙submit to the IAEA reports on its nuclear materials as shown by the current accounting documents.

Thus, availability of a national system for accounting and control of nuclear materials is a prerequisite for implementation of efficient international safeguards, but cannot supplant the latter.

Agreements based on INFCIRC/153 will also stipulate that:

∙a state should set up and maintain its system for accounting and control of all nuclear materials to be kept under the safeguards;

∙a national system for NM accounting and control should be structured according to material balance areas;

∙a national system should provide for the availability and use of measurement systems and procedures to determine the actual inventory of nuclear materials (i.e. should allow taking a physical inventory at facilities).

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It is required that facilities submit to the IAEA reports of three types, which should be prepared on the basis of accounting documents:

∙a report on changes in the NM inventory (a detailed list of all materials received and dispatched);

∙a material balance report with indication of the inventory difference and the range of its statistical straggling;

∙a list of available nuclear material quantities.

The basis of the IAEA safeguards

The purposes of the IAEA safeguards are clearly stated under paragraph 28 of INFCIRC/153 as “timely detection of diversion of significant quantities of nuclear material from peaceful nuclear activities to the manufacture of nuclear weapons or other nuclear explosive devices or for purposes unknown, and deterrence of such diversion by the risk of early detection”. The words “for purposes unknown” are of importance for practical application of the safeguards as they imply that the IAEA should not try to find out the nature of the intended use of the diverted material, nor should it determine whether the material was diverted to the “manufacture of nuclear weapons or other nuclear ex plosive devices”.

The key principle of the Agency’s system of safeguards lies in comparison of the information submitted by the entity under inspection with the results of independent verifications and observations made by the IAEA.

Keeping to this principle in attaining the objectives of the safeguards, the Agency pursues its monitoring activities along the following three lines:

∙study of the data submitted by a state as part of the information on the design of national facilities, in its reports to the IAEA, and in preliminary notifications concerning international transfers;

∙collection of information during inspections to verify the states’ declarations, during routine and special inspections;

∙assessment of the information submitted by a state and collected during inspections to check it for completeness, accuracy and validity.

It should be emphasized that the IAEA safeguards are applied in a way to avoid impediments to the economic and technological development of countries, to their international cooperation for peaceful use of nuclear energy. The Agency avoids unjustified intervention in peaceful nuclear activities of states and operation of their facilities.

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Article XII of the IAEA Statute defines the types of activities undertaken to implement the safeguards. According to this article, the Agency has the right:

∙to verify the information on the design of nuclear facilities;

∙to demand that relevant national authorities keep records as required for NM accounting and provide access to such documents by the Agency;

∙to demand submission of the accounting documents to the Agency;

∙to send IAEA experts to the states that recognize the safeguards.

As mentioned already, for the purposes of the safeguards to be attained, the IAEA checks on the nuclear materials during inspections. To this end, it is necessary to know, first of all, which and how much material should be checked to allow a conclusion on the absence of NM diversion. Such verification involves three reference parameters:

∙significant quantity;

∙time of detection;

∙probability of detection.

Significant quantity of nuclear material

In the context of a national system of safeguards developed mainly to protect NM from theft or acts of terrorism, the word “significant” may be applied to a relatively small quantity of material, considering, for example, its high toxicity (plutonium). However, the international safeguards are intended primarily to make sure that governments do not procure nuclear weapons or other nuclear explosive devices (NED), and it takes a relatively large NM quantity to produce even one NED.

In practice, the safeguards apply to NM with various Pu and U concentrations and of various isotopic compositions. This fact suggests the need for defining the “Significant Quantity” (SQ) f or each material category, so as to indicate how much material should be looked for to determine whether there was a diversion in violation of the safeguards.

In general, the SQ is defined as an approximate quantity of nuclear material large enough to allow producing a nuclear explosive device, whichever conversion process is used.

The SQ varies depending on whether this material may be directly used for NED production, or it needs to be converted first, e.g., by enrichment (in which case it will be referred to as an indirectly usable material).

For directly usable materials, the Significant Quantities are established by experts of the Standing Consultative Group of the IAEA for Implementation of the Safeguards as follows:

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∙8 kg of Pu (containing < 80 % Pu–238);

∙8 kg of U–233;

∙25 kg of U–235 contained in HEU.

For indirectly usable materials, the Significant Quantities are:

∙75 kg of U–235 contained in LEU (10 t of natural ur anium);

∙20 t for depleted U and Th.

Significant Quantities in inspection practice

The actual purpose of inspections at a specific facility does not necessarily lie in detecting diversion of one SQ (nor is it practicable in some cases). For instance, checking on nuclear materials at reactors consists primarily of counting, identification and measurement of individual accounting items, i.e. fuel assemblies. Once such items are counted, the purpose of inspectors is to find whether at least one FA is missing. Before research reactors of the IRT type were converted to lowenriched uranium (LEU), fuel assemblies contained 300-400 g of highly enriched uranium (HEU). It means that the inspection target in counting such items is smaller that one SQ (25 kg) for HEU.

At large facilities where nuclear material is found in bulk, it may be the other way around. In such cases, inspection will necessitate measuring large quantities of NM found in different physical forms and varying in chemical composition, including such material as waste. It may be tentatively assumed that the NM measurement error is about 1 % of the total measured quantity. It is clear, however, that 1 % of the inventory or throughput of a large facility with NM in bulk may exceed (by far in some cases) 1 SQ.

Let us consider a case where the IAEA safeguards cover several fuel fabrication facilities, with a large quantity of indirectly usable bulk material (LEU) being processed. Measurement errors and other factors make it necessary to set the inspection target at five SQs. In consequence, at such facilities there is no ruling out the possibility (with a credibility level of 90– 95 %) of one SQ diversion in the case of LEU. It does not mean, however, that diversion of one SQ is not detectable at all. Detection is possible even in this case, but its probability is lower. Besides, a high threshold of detection is offset by using additional means of control, such as containment and surveillance. Finally, it should be borne in mind that diverted LEU may be discovered at other stages of its conversion into a weapons-grade material.

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In countries with a well-developed fuel cycle, it is theoretically possible to divert a significant quantity of material by adding up under-SQ material quantities diverted at each one of many facilities. With such an approach, diversion would involve materials of different types and categories and would necessitate concerted actions of personnel from a large number of facilities. That is why the IAEA regards this scenario as unattractive for a rogue state and highly risky. Besides, an attempt to counteract such hypothetical diversion scenarios would necessitate an inspection regime much too cumbersome for implementation by either a state or the IAEA.

Early detection

Early detection is a notion of importance to the safeguards. The earlydetection requirement determines the frequency of inspections at facilities. The system of the IAEA safeguards is based on the assumption that diversion of a significant quantity of nuclear material should be detected at an early stage, irrespective of whether it is committed once or on multiple occasions. The practical implications of early detection depend on the type of the nuclear material covered by the safeguards. In order to determine ‘timely detection’ in quantitative terms it is nece ssary to have a notion of the ‘conversion time’. The time of NM conversion is the time required in optimal conditions for converting NM in a given form into a component of a nuclear explosive device. The following typical conversion time periods were established on recommendation of the Consultative Group:

Besides, following the CG recommendations, the IAEA established the ‘detection time’ to be of the same order of magnitu de as that of the conversion time. The ‘order of magnitude’ here is a factor equal to 1–3.

In practice, it is sometimes difficult to stay within a short time of detection. So, at some facilities where nuclear material is found in bulk it is a far from easy business to reconcile a short detection time with the requirements of normal operation. For plutonium and highly enriched uranium (whose conversion takes 7–10 days), inspect ion targets are set at the upper boundary of the permissible time range (3 weeks). In those cases where acceptable inspection frequency falls short of ensuring early

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detection, additional measures are taken to attain the required detectability, such as application of seals and surveillance.

Detection probability

Considering the global scale of the IAEA activities, it is an extremely difficult task to discover NM diversion with a 100 % probability and as early as required. That is why the Agency seeks to build such a system of safeguards that will meet these objectives with a certain probability. This probability should also be specified. Neither INFCIRC/66, nor INFCIRC/153 refers specifically to the level of confidence in detection, but the Agency interprets these documents as if this notion were covered there. From the viewpoint of the Agency, the detection probability should be so high as to keep a state from resorting to diversion and to ensure the

required confidence of the international community. The target detection probability was set by the IAEA at the level of 0.9÷0.95.

Extent of independent inspections

The effect of the probability of detecting a significant quantity of NM on the extent of IAEA inspection activities can be illustrated by a model case.

Suppose we have as many one-type articles as N = 12000. The SQ of the material under consideration (e.g., plutonium) is М = 8 kg. The mass of each article is m = 80 g. It is necessary to determine the number of articles to be verified during an IAEA inspection, if the probability β of attaining the safeguards purpose should not be less than 0.9.

The number of diverted components x in sample n is taken to be a random quantity whose distribution follows the hypergeometric law. The sample size is then determined by the formula:

Condition (3.2) implies that relatively large components are under consideration. Once fulfillment of this condition is checked upon, formula (3.1) will be used to find the number of measurements to be made during the inspection:

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n = 12000 × (1 – 0,1 1/100) = 276.

Apparently, the extent of sample measurements is vastly reduced in comparison to the initial scope, if the adopted SQ is largely in excess of the component mass, and the probability of attaining the purpose is noticeably smaller than 1.

Equipment involved in implementation of the safeguards by the IAEA

The complexity and diversity of NM-containing facilities call for use of various techniques and equipment [4]. Table 3.1 presents the main verification procedures carried out by the IAEA at such facilities.

Since the 1980s, inspection activities have tended to involve expanded means of containment and surveillance, as well as non-destructive test methods.

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