SAFEGUARDS APPROACH
Mr. Richard Hooper

INTRODUCTION

International nuclear material safeguards consists of a complex control system based on material accountancy with the technical objective of providing for “ ... the timely detection of diversion of significant quantities of nuclear material from peaceful nuclear activities to the manufacture of nuclear weapons or of other nuclear explosive devices or for purposes unknown, and deterrence of such diversion by the risk of early detection” (para. 28, INFCIRC 153). Each non-nuclear weapon State party to the NPT undertakes to accept IAEA safeguards on all nuclear material within the State’s territory or under its jurisdiction or control. The basic procedural elements of the safeguards system are facility design review and verification, maintenance of facility operating records, reports on facility operations and on-site inspections. The system requires the concerted action of nuclear facility operators, state authorities and the IAEA inspectorate.

A Useful Analogy

The safeguards system based on nuclear material accountancy is directly analogous, both in concept and in basic procedural elements to a financial accounting system. The role of the inspectorate is analogous to that of the independent financial auditor.

Financial accounting is concerned with the collection of data describing the economic activities of a firm. These data are summarized in the form of financial statements. Auditing is the independent verification of the “fairness” (correctness) of the financial statements. The auditor collects data useful for verification from several sources and by different means. The acquisition of reliable audit information at minimum cost is a continuing aspect of the audit function.

Nuclear material accountancy records are maintained by facility operators for each facility under safeguards. basically two kinds of reports - comparable to financial statements - are made by facility operators, through the cognizant State authorities, the State System of Accounting and Controls of nuclear material (SSAC), to the IAEA:

a. The inventory change report (ICR) gives details, for each nuclear material category, of all receipts (credits) and shipments (debits) of nuclear material.

b. Periodically the facility operator performs a physical inventory taking (PIT), which results in a detailed list, again for each nuclear material category, of the nuclear material that exists in the facility’s inventory at a particular point in time.

These data provide the basis for the IAEA’s independent verification activities in exactly the same sense that the financial statements of a firm provide the basis for the auditor’s assessment of “fairness”. The strategy for independent verification of inventory changes and for the verification of the periodic statement of inventory by a facility operator are central to nuclear material accountancy. The strategy depends primarily on the type and design of the particular facility and the type and quantities of nuclear material being handled at it. The time period between successive inventory statements is called a material balance period. The verified inventory statement at the end of one period becomes the beginning “book inventory” for the period that follows. In a manner exactly analogous to the closing of financial records for a specific fiscal period, a statement of inventory by a facility operator marks the closing of material accounts for a material balance period.

The intensity (i.e., the frequency and extent) of the IAEA’s independent verification of inventory and inventory changes is determined by the values assigned to technical implementation parameters such as a significant quantity and timeliness (ref: “timely detection”). The IAEA has defined a “significant quantity” as the amount of a particular material (e.g., plutonium) that a State would need to make a nuclear explosive device. “Timeliness” is related to the estimated time needed to convert diverted material into the components of a nuclear explosive device. The uniform implementation of safeguards is maintained in all States with comprehensive safeguards agreements through application of technical implementation criteria. These implementation criteria provide detailed requirements and procedures for how safeguards are to be implemented in any given circumstance. New technical measures for improved and more efficient safeguards are under constant development and the implementation criteria are revised as new technical measures become available. Each year the IAEA produces a Safeguards Implementation Report which is submitted to the Agency’s Board of Governors. The report describes the implementation of safeguards in each facility and State.

THE DESIGN OF THE SAFEGUARDS APPROACH

The terms used in the definition of the safeguards objectives (significant quantities, timely detection, risk of detection) have to be “translated” by the IAEA into specific goals so that safeguards can be applied in an effective manner. These goals are not a requirement but serve as guidelines for the development of safeguards approaches and criteria which contain concrete instructions for inspection activities in the field. Design principles for such safeguards approaches have been developed during the last decade, starting from external factors and ending with inspection goals and procedures. The discussion which follows reflects these design principles and the resulting safeguards approaches currently used by the IAEA in safeguarding item-handling facilities and bulk-handling facilities. These approaches are provisional in the sense that they are constantly updated to take into account the experience of the inspectors, the development of new instruments and other equipment, and changes in the way nuclear plants are designed and operated.

The safeguards approach for a particular facility or facility type refers to the system of nuclear materials accountancy, containment, surveillance and other measures chosen for implementation of safeguards in a given situation. It is specially developed to satisfy the safeguards objectives of that situation. In designing the system, a model safeguards approach is developed for each type of nuclear facility; this is then adapted to specific facilities for implementation. The general scheme followed in designing a safeguards approach is illustrated in Fig. l.

In this session the relationship between external factors, Agency detection goals, design of the safeguards approach and inspection goals and procedures will be described and discussed. Safeguards implementation will be covered in later sessions but it should be stressed now that feedback of practical experience is the vital ingredient for improvement of inspection procedures.

THE EXTERNAL FACTORS

There are three external factors which influence the safeguards approach. Two of these, threshold amounts and conversion time, act through the Agency detection goals and the third, diversion strategies, directly affects the safeguards approach. All relate to the potential production of nuclear explosives from safeguarded nuclear material.

The threshold amount of special fissionable material is the approximate quantity required for a single nuclear explosive device. The amounts given in Table I were derived as a result of a special study done for the United Nations and published in 1968.

TABLE I. THRESHOLD AMOUNTS

Material Threshold amount
Pu (Pu-239>95%) 8 kg Pu-239
U (U-235>90-95%) 25 kg U
U-233 8 kg U-233


The time required to convert different forms of nuclear material to the metallic components of a nuclear explosive device is known as the conversion time. It does not include the time required to transport diverted material to the conversion facility, to assemble the device, or any subsequent time period. The diversion activity is assumed to be part of a planned sequence of actions chosen to give a high probability of success in manufacturing one or more nuclear explosives with minimal risk of discovery until at least one is manufactured. It is therefore assumed that all necessary conversion and manufacturing facilities exist, that processes have been tested, for example by manufacturing dummy components using appropriate surrogate materials, and that non-nuclear components of the device have been manufactured, assembled and tested. The conversion time estimates used at present are given in Table II.

The third external factor, diversion strategies, relates to the schemes which could be adopted by a State to divert material or to misuse equipment or facilities subject to IAEA safeguards. Diversion strategies postulated for safeguards planning purposes could include methods for:

- the physical removal of nuclear material or other materials from declared activities;
- the use of safeguarded facilities or equipment for the production of undeclared nuclear material;
- the use of diverted or undeclared nuclear material in safeguarded equipment or facilities; and
- the concealment of the above-mentioned activities.

TABLE II. ESTIMATED MATERIAL CONVERSION
TIMES TO FINISHED Pu OR U METAL


Beginning material form Conversion time

Pu, HEU or U-233 Metal Order of days
(7-10)

PuO2, Pu(NO3)4, or other pure Pu Order of weeks
compounds; (1-3)
HEU or U-233 oxide or other
pure compounds;
MOX or other unirradiated pure
mixtures containing
Pu, U[(U-233 + U-235) > 20%];
Pu, HEU and/or
U-233 in scrap or other
miscellaneous impure compounds

Pu, HEU or U-233 in irradiated fuel Order of months
(1-3)

U containing < 20% U-235 and Order of one year
U-233; Th


THE DETECTION GOALS

From a consideration of the threshold amounts and conversion time, together with the safeguards objective, the Agency derives its detection goals. Recall the objective of NPT safeguards as given in INFCIRC/l53 and quoted earlier (page 2). In order for quantitative goals to be formulated, it is necessary to specify the significant quantities of nuclear material required to be detected in a given time with a given probability and false alarm rate.

These detection goals are used as guidelines in designing the safeguards approach and establishing inspection goals. They form the basis for organizing safeguards activities and determining the need for technological improvements. They also constitute the point of reference from which to judge the adequacy of safeguards implementation.

Significant quantity (SQ) is defined as the approximate quantity of nuclear material in respect of which, taking into account any conversion process involved, the possibility of manufacturing a nuclear explosive device cannot be excluded. Significant quantity values currently in use are given in Table III.

TABLE III. SIGNIFICANT QUANTITIES

Material Significant quantity Safeguards apply to:

Direct-use nuclear material:
Pu* 8 kg Total element
U-233 8 kg Total isotope
U[U-235 > 20%] 25 kg U-235 contained

Indirect-use nuclear material:
U[U-235 < 20%]** 75 kg U-235 contained
Th 20 metric tons Total element

* For Pu containing less than 80% Pu-238
** Including natural and depleted uranium


Direct-use material is nuclear material that can be used for the manufacture of nuclear explosives components without transmutation or further enrichment, such as plutonium containing less than 80% plutonium-238, highly enriched uranium (HEU) and uranium-233. Chemical compounds, mixtures of direct-use materials such as mixed plutonium and uranium oxides (MOX) in fresh fuel and plutonium contained in spent nuclear fuel also fall in this category. Unirradiated direct-use material would require much less processing time and effort than irradiated direct-use material (contained in spent fuel).

Indirect-use material is all nuclear material except direct-use material, e.g. natural uranium or low-enriched uranium (LEU), which must be (further) enriched to be converted into HEU or inserted into a reactor to produce plutonium-239 which can be separated in a reprocessing plant, or thorium.

Detection time is defined as the maximum time that may elapse between diversion and its detection by IAEA safeguards. It is used as a parameter for timeliness and, according to the current guidelines, should correspond in order of magnitude to conversion time. The detection time is one of the factors used to establish the timeliness component of inspection goals, which is to be achieved by specified inspection and physical inventory frequencies and containment and surveillance measures. The timeliness goals in current use are given in Table IV.

TABLE IV. TIMELINESS GOALS

Material Category Timeliness Goal
Unirradiated direct-use 1 month
Irradiated direct-use 3 months
Indirect-use 12 months


Detection probability and false alarm probability are statistical terms.

a, the false alarm probability, is the probability of concluding that a diversion has occurred when in fact there has been no diversion. It is necessary to keep this as low as possible to maintain the credibility of the system.

The non-detection probability, ß, is the probability of concluding that a diversion has not occurred when in fact there has been a diversion. The detection probability, (1-ß), is perhaps a more useful and more easily understood concept than the non-detection probability ß. It is the basic measure of the sensitivity of the safeguards system to diversion. The detection probabilities used for Agency verification purposes depend on the particular circumstances and will range from 10 to 90%.

DESIGN OF THE SAFEGUARDS APPROACH

In designing the safeguards approach, many elements are taken into consideration:

Design information is the information concerning the nuclear material subject to safeguards under the Safeguards Agreement and the features of the facilities relevant to safeguarding such material. The information is provided by the State to the IAEA.

Important features of the design information include a descriptions of the facilities; the types, quantities and forms of nuclear material being used; and the facility layouts and containment features. Design information is submitted to the IAEA by the States through answers to the questions in the IAEA’s Design Information Questionnaire (DIQ). There is a different questionnaire for each type of facility.

Facility practices are the set of management practices applied by the facility operator and required for the economic and safe performance of the nuclear activities at the facility. The management practices which are relevant to safeguards include material identification and measurement procedures, record-keeping procedures, inventory frequencies and procedures, designation of measurement points, and storage arrangements.

The State accounting system is that part of the function of the State System of Accounting for and Control of Nuclear Material (SSAC) which, at the facility level, fulfils the accountancy obligations set forth in the Safeguards Agreements and which enables the IAEA to meet its safeguards objectives. The Safeguards Agreements between the IAEA and the State specify appropriate requirements on establishing and maintaining national accountancy systems.

Diversion assumptions underlie the set of diversion paths which, from among all possible paths, is assumed by the IAEA in a given safeguards situation to be part of the plausible diversion strategies and which are therefore taken into account in designing, implementing and evaluating safeguards for that situation.

A key factor here is the diversion rate, which is the amount of nuclear material assumed to be diverted in a given unit of time. There are of course an infinite set of possibilities of diversion rate but two limiting cases are of special interest. Abrupt diversion consists of the removal of one significant quantity in a short time (hours or days). Protracted diversion consists of the removal of one significant quantity spread uniformly over the period of a year. The safeguards approach must consider the detection of both these types of diversion. For this purpose abrupt diversion is taken to mean the removal of a significant quantity in a period of time corresponding in order of magnitude to the conversion time appropriate to the nuclear material involved, more precisely to the removal within a period of time given by the timeliness goal for that particular material (see Table IV). The assumptions of abrupt and protracted diversion are applied to each facility separately and also separately to each type of nuclear material present in each facility.

Basic safeguards concepts are the underlying assumptions used in designing the safeguards approach. These concepts describe in general terms the strategies to be used in order to achieve the safeguards objectives.

As has already been emphasized, the fundamental concept is verification, as described in Article 7 of INFCIRC/153:

“... safeguards shall be applied in such a manner as to enable the Agency to verify, in ascertaining that there has been no diversion of nuclear material from peaceful uses to nuclear weapons or other nuclear explosive devices, findings of the State’s system. The Agency’s verification shall include, inter alia, independent measurements and observations conducted by the Agency ...”

This concept encompasses procedures such as:

- effective verification of the flow of source and special fissionable material by the use of instruments and other techniques at certain strategic points;

- the periodic closing of material balances by the taking of physical inventories, and the independent verification by the Agency of the entire inventory of nuclear material subject to safeguards, using chemical analysis and non-destructive measurements; and

- the use of containment and surveillance measures as important complementary measures to nuclear material accountancy to provide an additional or alternative verification method.

One of the important aspects of a safeguards approach is the selection of strategic points. These are locations selected during examination of design information where, under normal conditions and when combined with the information from all other strategic points, the information necessary and sufficient for the implementation of safeguards measures is obtained and verified. Strategic points may include any location where key measurements related to nuclear materials accountancy are made and where containment and surveillance measures are applied.

Technical capability is the expected performance of a system of safeguards measures consisting of accountancy, containment and surveillance. The achievable level of performance may be inherently limited, for instance, by the uncertainty in measurements, the degree of reliability of surveillance instruments, the resistance of seals to tampering, etc. These limits on the effectiveness of actual safeguards measures have to be taken into account in deriving practical inspection goals from IAEA detection goals.

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