Requirements for safeguarding nuclear materials exist both internationally and domestically. Nations involved with nuclear activities, either at a gov­ernmental or industrial level, must establish a regulatory framework to oversee aspects of the work including worker safety, environmental protec­tion, and nuclear safeguards. In the United States, domestic requirements are established through the Nuclear Regulatory Commission and the Department of Energy. Internationally, the IAEA is responsible for nuclear materials safeguards. According to the IAEA, “The IAEA is the world’s nuclear inspectorate, with more than four decades of verification experi­ence. Inspectors work to verify that safeguarded nuclear material and activi­ties are not used for military purposes” (IAEA 2005a).

In general, the goals of international nuclear safeguards are to detect proliferation and diversion of nuclear material from the civilian nuclear fuel cycle and to provide notification of potential diversion to the international community in a timely fashion so that the consequences of the diversion can be reduced. Nuclear material is specifically defined as either special fissionable material or source material. Special fissionable material is plu­tonium-239 or uranium enriched in either uranium-235 or uranium-233. Source material is material that can be used to produce special fissionable material, which includes natural uranium, depleted uranium, and thorium.

A goal of the IAEA is to detect diversion of significant quantities of nuclear material. In general terms, a significant quantity of material is con­sidered a “threshold” amount needed to make a weapon (IAEA 1975). For example, spent light water reactor fuel contains both uranium and pluto­nium. For the reprocessing of spent nuclear fuel, plutonium is the main special fissionable material of concern. A significant quantity of plutonium is considered 8 kg total plutonium (Thomas and Longmire 2002). If dealing with highly-enriched uranium, a significant quantity is considered 25 kg of contained uranium-235 (IAEA 1981).

Safeguards goals focus on both detection and timeliness. Timeliness goals are applied to the input spent fuel and separated products, and specific timeliness goals are established based on the attractiveness level of the material of concern. For example, a timeliness goal may be based on the estimated minimum time required to convert a specific material into a form that can be used in a weapon. Conversion times can range from weeks to months and in some cases may extend to over a year (OTA 1995). A general goal is to be able to detect the diversion or loss of one significant quantity of plutonium (i. e., 8 kg) within one month. Goals for the detection of mate­rial in spent fuel are lower because the attractiveness level of that material is much lower. Therefore, the timeliness goal for detection of a significant quantity of material from spent fuel is three months.

Low-enriched uranium is also recovered from the reprocessing of spent fuel. Low-enriched uranium contains less than 20% of the uranium-235 isotope. The timeliness goal for low-enriched uranium recovered from reprocessing is that no more than 75 kg of uranium-235 is unaccounted for within a one-year period (Thomas and Longmire 2002).

The two major components of nuclear safeguards are nuclear material accountancy and nuclear material containment and surveillance. Nuclear material accountancy is the system used to determine the amount of nuclear material present in a facility and to track the changes in the quantity of material as process activities are performed in the facility. It is basically an accounting system for keeping track of amount, type, form, and location of nuclear material in a facility. Measurement systems to establish these quantities are a major part of nuclear material accountancy.

Containment and surveillance complement nuclear material accountancy. Containment and surveillance are the methods used to ensure that move­ments of nuclear material are tracked. Containment specifically deals with ensuring that once nuclear material is placed into a physical container (whether a room, vault, enclosure, or container) that its location is known or tracked. Devices to support containment and surveillance include physi­cal barriers, cameras, detectors, high radiation environments, and tamper indicating devices.

Nuclear material accountancy and nuclear material containment and surveillance are the backbone of nuclear materials safeguards for both the national and international communities. Operators of nuclear facilities, like a spent fuel reprocessing facility, establish systems for accountancy, contain­ment, and surveillance. The data generated from these systems are provided to State agencies and the IAEA.

One function of the IAEA with respect to safeguards is to examine and evaluate the data provided by nations hosting nuclear facilities. The IAEA also has a significant role in data verification. They independently collect data and information from the facilities as well as perform inspections. IAEA inspections often include independent data collection and analysis using equipment that is independently designed, operated, and maintained by the IAEA. Inspections also provide verification of facility and process designs by ensuring that the facility is performing only the declared functions.

Since the nuclear material accountancy system relies on various measure­ments, the uncertainties associated with quantitative analytical measure­ments and mass, volume, and density measurements impact the interpretation of the data. The nuclear accountancy system should be able to determine the quantity of material at the facility that is not accounted for, which is termed Material Unaccounted For (MUF). The MUF is sometimes referred to as the Inventory Difference (ID). In an ideal situation where there is perfect accountancy, when the nuclear accountancy books for a facility are closed, the MUF will assume a value of zero. However, because measure­ment uncertainties always exist, the value of MUF must be compared against the value of the measurement uncertainty. The accountancy system needs to be able to distinguish, to a reasonable degree, if the MUF values are “not significant”, in which case they are indicative of the expected measurement uncertainties, or are “significant”, in which case they are indicative of possible diversion. Obviously, high uncertainties would make it impossible to detect diversion, regardless of the MUF value.

Facilities will have detection goals to determine if the MUF values are significant. In establishing these goals, detection systems can result in two types of error. The first type of error is a false positive, where an alarm is signaled, but in fact no loss of material has occurred. False positive alarms obviously have significant operational issues in a production facility, not the least of which is loss of credibility for the system’s integrity. The second type of error is a false negative, where an alarm is not signaled, but in fact a loss of material has occurred. This situation is much more serious because it results in a case where material loss or diversion is not detected. Typical IAEA thresholds are established at a 90% detection probability for detecting diversion of a significant quantity of nuclear material and 5% as the maximum accepted value for a false alarm rate (OTA 1995).

In the event that the IAEA receives evidence that diversion of nuclear material may have occurred, the protocol is for the IAEA Director General to deliver a report to the IAEA Board of Governors, which must then make an evaluation. If they are unable to verify that no diversion has occurred, the Board of Governors may take actions, which can include reporting to the UN General Assembly or the UN Security Council. The Security Council, the only UN body with executive powers, has authority to take action including the implementation of international sanctions.

There are presently 146 IAEA member states and 237 safeguards agree­ments in force in 163 countries. In 2007, 2122 safeguards inspections were performed. The IAEA’s detection and verification system is not perfect. To note from IAEA documentation, “safeguards can neither predict diversions ahead of time, nor physically predict them, nor be guaranteed to detect them 100 percent of the time, and they should not be expected to do so” (Thomas and Longmire 2002). Still the IAEA, working with individual nations, serves an extremely important function with respect to safeguards.

Transparency is also a critical component of safeguards and non­proliferation. Transparency consists of actions taken by a facility or nation to enhance the openness of activities to ensure other nations or organiza­tions like the IAEA that they are not performing clandestine operations. Transparency would include allowing inspectors greater access to facilities, more openness in the timing of inspections, and wider environmental sam­pling to potentially detect undeclared activities.