The measures implemented by operators under the National Inspection framework are based on three fundamental points: physical protection, physical monitoring and accounting, which are complementary, reinforce each other and form a coherent whole.
By physical protection we mean measures to prevent, detect, hinder or forestall any unauthorised or unjustified access to nuclear materials and any unauthorised or unjustified removal of such materials from the locations where they are held. In the event of unauthorised action being detected, these measures should provide for the authorities to be alerted in order to initiate action by the police if required.
The physical protection of facilities comprises the technical, organisational and human resources aimed, firstly, at restricting and controlling access to nuclear materials, secondly, at establishing protective areas to ensure that nuclear materials remain under control. These measures insert a sufficient number of "lines of defence" between such materials and outside the installation, and to check the integrity and effectiveness of these lines of defence.
Physical monitoring means measures to authorise the movement of nuclear materials, and to inspect them, where required, in order to detect attempted dishonest behaviour during any such movement. These measures are based on constant and precise knowledge of both the quantity and quality of all nuclear materials brought in and removed, as well as knowledge of the location, use, movement and changes in these materials. The physical monitoring applies to all nuclear materials held:
- those present in the form of articles, that is to say nuclear materials forming individual countable objects: monitoring is based on an individual tally of the articles
- to those produced in the processes  carrying out physical and/or chemical transformations of these: monitoring is based on knowledge and control of physical flows (quantities and qualities of materials inserted or removed during these processes) and, where possible, quantification of the materials at specific points of the process.
Accounting means measures to allow independent monitoring of physical inspection, inspection based on daily awareness, accounting for each area, of the volume of nuclear materials held and all insertion and removal of nuclear material (a location that is ‘accounted for’ may be all or part of a facility in terms of the activities carried in the said facility).
Local accounts, held by each facility’s operator, record and track work with nuclear materials, as well as the evidence from the monitoring of nuclear materials in order to control them.
The centralised accounts, held by IRSN, complement the local accounts and centrally stores all information recorded in the accounts of each local operator. Regular comparison of these two sets of accounts ensures that errors are detected and prevents any possible falsification. It also helps to check the consistency of statements made by different operators and reconcile them with the data reported separately by those responsible for transport.
Regular physical inventories (annually at least) are carried out to verify the consistency between the physical reality, physical monitoring and the inventory of nuclear materials derived from the accounts. These inventories include a check of the qualities and quantities of nuclear material where this is practicable. They are complemented by a review of nuclear materials coming in and out of the process locations in order to detect any possible diversion of nuclear materials
Different operators are in charge of physical monitoring from those responsible for local accounting. The former are allowed to move nuclear materials, but without access to accounts, while the latter, who are responsible for local accounts, are not authorised to deal with the transport of materials. This helps reduce the risk of materials being diverted.
Finally, all of these measures are monitored at two levels:
- first by the operator personally, who is primarily responsible for the security of the nuclear materials in his/her possession;
- secondly, by the government via a national inspection system.
1- An industrial process is a set of systems and mechanical and/or chemical equipment designed to produce goods or to synthesize products in large quantities.