Материал: Крючков Фундаменталс оф Нуцлеар Материалс Пхысицал Протецтион 2011

[2–4]. Unlike the NM bookkeeping system, this mater ial balance system is based on NM measurements. Nuclear material is measured every time a major operation involving NM takes place, including, for example, transfers. This makes an allowance for the statistical nature of all NM measurements results. The basis of this NM accounting system will be looked at in the subsequent chapters hereof.

Computerization of NM accounting

There are different versions of computerized nuclear material (NM) accounting and control systems used nowadays by many nuclear industry entities in Russia. The explanation for computerized information technologies having been extensively introduced in accounting and control of NM is fairly simple. Lack of computers makes it rather difficult for large enterprises to determine highly accurately and rapidly where and in what quantity and state their nuclear material is. Furthermore, the requirements of the Federal Information System call for a phased transition to a system of reports based on material balance areas. Such volume of data cannot be acquired and handled with no computerized systems in place. It is exactly the absence of the sufficient choice of proven computerized NM accounting and control systems that leads to a simplified form of reports, that for the whole of the enterprise, being used nowadays. Finally, alienation and socialization of data on NM inventories and transfers, in the centralized database form, from the immediate operators, independent balance closings and other characteristics restrain to a great extent potential unauthorized use of NM and information on these. While contributing to achieving highlevel continuity and confidence of knowledge about NM, all these factors give a major impetus to a broad-scale introduction of computerized NM data handling technologies at enterprise, departmental and federal levels.

Continuity of knowledge about nuclear material

The requirement of controlling weapon-grade material necessitates continuous monitoring thereof. The key issue here is continuity of knowledge about inventories of NM, primarily, of weapon-grade NM. Solutions to this have been searched for technologically.

The ideal answer in the context concerned will be to keep NM continuously subjected to visual and instrumented monitoring. For NM at rest, this monitoring is achievable through access controls. Access controls have been heavily involved in accounting and control of NM. These include containment and surveillance measures (seals, TV monitors).

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Access control have been intensively developed and perfected in recent years. Aspects of access controls applications will be given a closer look in Chapter 10 hereinafter.

However, where NM is not at rest, no continuity of knowledge about NM can be achieved with the aid of access controls. There may be nuclear material thefts by personnel with access to NM. Such thefts may long be undetected not until the next physical inventory is taken. Still, a physical inventory taking may also fail to detect minor thefts because of an unavoidable uncertainty in the nuclear material balance.

It is exactly lack of secure technologies enabling continuity of NM monitoring in the conditions of operations that renders NM vulnerable to misuses by personnel. In this respect, facilities with a great deal of nuclear material in the form of small-size elements (e.g., the BFS with its large number of disks) are the point of the greatest concern.

A realistic technological solution to making continuity of knowledge about NM transfers substantially achievable is computerized near-real-time accounting of operations with NM involving as extensive use of containment and surveillance features as it can be.

The first ever realization of the near-real-time NM accounting concept was brought into being by Los-Alamos National Laboratory in 1991. This had the form of a standardized computer-aided NM accounting and control system called LANMAS (Local Area Network Material Accountability System). Near-real-time computer-aided NM accounting and control systems are also being created or have already been put into operation by a number of organizations in Russia.

References

1.Основные правила учета и контроля ядерных материалов. НП– 030–05. Утверждены Постановлением Федеральной службы по экологическому, технологическому и атомному надзору N 19 от 26 декабря 2005 года. М., 2005.

2.Глебов В.В., Измайлов А.В., Румянцев А.Н. Введение в системы учета, контроля и физической защиты ядерных материалов. М.:

МИФИ, 2001.

3.Основы учета и контроля ядерных материалов: Методические материалы / Под редакцией Б.Г. Рязанова. Обнинск: УМЦУК, 2000.

4.Training Course on the Fundamentals of MC&A. – O RNL, Oak Ridge, 1997.

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CHAPTER 2

BASIC CONCEPTS OF THE MEASURED NUCLEAR

MATERIAL BALANCE SYSTEM

2.1. Basis for categorization of NM

Accounting category of nuclear material is one of the basic NM-related concepts. A material falling into an accounting category is subject to certain accounting, control and physical protection regulations. A material that fails to fall into an accounting category does not have any stringent regulations it is subject to. The question of which material shall be categorized as accounted for arises so in connection with NM accounting categories.

Nuclear material subject to accounting and control

As defined by the General Rules for Accounting and Control of Nuclear Materials, the following material shown in Table 2.1 below shall be subject to accounting and control procedures.

Table 2.1

List of nuclear and special non-nuclear material subject to accounting and control

Apart from major elements of uranium-plutonium and thorium cycles, this list includes transuranium elements. Also, the list includes a range of

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special non-nuclear materials which have significance and can be used to produce weapon-grade material and nuclear explosives. Some of the examples are deuterium, lithium-6 and tritium used to make thermonuclear charges. Coming under international safeguards, as defined by the IAEA, is a list of nuclear material which is close to that given above.

Quantitative criteria for nuclear material to be put on and withdrawn from records

Nuclear material shall be subject to state accounting and control if the values of the masses held at the enterprise or carried by one vehicle are equal to or exceed the minimum quantities given in Table 2.2. For major elements of uranium-plutonium and thorium cycles, as evidenced by the data in the table, the minimum quantities thereof to be accounted for make 15 g. For uranium and thorium of a natural isotopic composition, the least quantity from which accounting starts is 500 kg.

In the event of an enterprise with more than one nuclear material, products or articles containing a mix of nuclear material presented in Table 2.1 are not subject to regulations unless exceed the limits given in Table 2.2.

State accounting and control are not applied to:

∙uranium contained in ore, as well as in intermediate products in mining or metallurgical processes,

∙thorium contained in ore, as well as in intermediate products in mining or metallurgical processes;

∙nuclear material in sealed ionizing radiation sources;

∙ neptunium–237, americium–241, 243 and californium–2 52 in irradiated products;

∙lithium–6 if its content in lithium is not more tha n 7.5 at. %;

∙deuterium contained in hydrogen-containing material where deuterium’s relative isotopic content does not exceed 50 at. %;

∙nuclear material in radioactive waste (RW) at RW storage points.

Where the mass of the nuclear material at an enterprise is less than specified in Table 2.2, material is accounted for and controlled subject to radioactive material accounting requirements.

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Table 2.2

Minimum quantities of nuclear material from which these are subject to state accounting and control

Categorization of nuclear material and facilities

A question arises, why one needs to categorize nuclear material? The answer is that NM is categorized to enable a differentiated approach to identifying techniques and instruments for accounting, control and protection of NM. In the first place, this makes it possible to focus on the nuclear material which is easy to convert to weapon-grade material.

We shall consider the principles to which nuclear material is categorized internationally with a nuclear material categorization system taken for illustration.

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