The Physical Protection of Nuclear Material and Nuclear Facilities INFCIRC/225/Rev.4 (Corrected)

Categorization of Nuclear Material

5.1.   Basis for Concern

5.1.1.   In determining the level of physical protection to be implemented for nuclear materials in use and storage or during transport account should be taken of the possibility that the unauthorized removal of plutonium, highly enriched uranium or uranium-233 could lead to the construction of a nuclear explosive device by a technically competent group.

5.2.   Categorization

5.2.1.   The primary factor for determining the physical protection measures against unauthorized removal of nuclear material is the nuclear material itself, categorized in accordance with the following table which gives a categorization of the different types of nuclear material and with the considerations given below.

NOTE: This table is not to be used or interpreted independently of the text of the entire document.

TABLE: Categorization of Nuclear Material
Category I
Category II
Category IIIc
 1.Plutoniuma  Unirradiatedb  2 kg or more  Less than 2 kg but more than 500 g  500 g or less but more than 15 g
 2.Uranium-235  Unirradiatedb

-  uranium enriched to 20% 235 U or more

- uranium enriched to 10% 235U but less than 20% 235U

- uranium enriched above natural, but less than 10% 235U

 5 kg or more  Less than 5 kg but more than 1 kg
10 kg or more
 1 kg or less but more than 15g
Less than 10kg but more than 1 kg
10 kg or more
 3. Uranium-233  Unirradiatedb 2 kg or more  Less than 2 kg but more than 500 g  500 g or less but more than 15 g
 4. Irradiated Fuel (The categorization of irradiated fuel in the table is based on international transport considerations. The State may assign a different category for domestic use, storage, and transport taking all relevant factors into account.)                  Depleted or natural uranium, thorium or low-enriched fuel(less than 10% fissile content)d/e        
a All plutonium except that with isotopic concentration exceeding 80 % in plutonium-238.
b Material not irradiated in a reactor or material irradiated in a reactor but with a radiation level equal to or less than 1 Gy/hr (100 rad/hr) at one meter unshielded.
c Quantities not falling in Category III and natural uranium, depleted uranium and thorium should be protected at least in accordance with prudent management practice.
d Although this level of protection is recommended, it would be open to States, upon evaluation of the specific circumstances, to assign a different category of physical protection.
e Other fuel which by virtue of its original fissile material content is classified as Category I or II before irradiation may be reduced one category level while the radiation level from the fuel exceeds 1 Gy/hr (100 rad/hr) at one meter unshielded.

5.2.2.   This categorization should be based on the potential risk of the material being used for a nuclear explosive device, which itself depends on: the type of material, e.g. plutonium, uranium; isotopic composition, i.e. content of fissile isotopes; physical and chemical form; degree of dilution; radiation level; and quantity. For example:

  1. The protection of nuclear material with a radiation level that exceeds 1 Gy/hr (100 rad/hr) at one meter unshielded, which is classified as Category I or II, may be reduced one category level below that determined by the fissile content of the material; and
  2. Nuclear material that is in a form that is no longer usable for any nuclear activity, minimizes environmental dispersal and is practicably irrecoverable, may be protected in accordance with prudent management practices.

5.2.3.   In determining the levels of physical protection in a facility, which may consist of several buildings, it is possible that the State's competent authority may identify part of the facility which contains material of a different category and which is therefore protected at a different level than the rest of the facility. Conversely, consideration may need to be given to adding together the total amount of material contained in a number of buildings to determine the appropriate protection arrangements for this group of buildings.

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