The Government classifies nuclear weapons information
in various ways and maintains a number of different clearances to control access to it.
National Security Information (NSI): Information relating to U.S. foreign relations or military policy that requires protection against unauthorized disclosure and that has been determined to be classified in conformity with presidential executive order.
Unclassified Controlled Nuclear Information (UCNI): Used by the DOE to prevent the unauthorized dissemination of unclassified information on physical security for special nuclear material, critical installations, and equipment.
Restricted Data (RD): All data concerning the design, manufacture, and use of nuclear weapons; the production of special nuclear material; and the use of special nuclear material in the production of energy. According to the Atomic Energy Act, RD can be declassified as long as there is no "undue risk" to national security.
Formerly Restricted Data (FRD): Information relating to the military use of nuclear weapons protected under joint agreements by the DOE and DOD and information that the DOE has removed from the Restricted Data category. The two agencies protect it as classified national security information; in any releases to foreign governments, FRD are treated as restricted data. Declassification requires a determination that release of the information will not cause unreasonable risk to national security.
Q Sensitive: The highest clearance for access to Restricted Data. "Q Sensitive" provides individuals with access to the most sensitive categories of special nuclear materials (SNM) — those materials that are most readily weaponized, such as plutonium, uranium-233 or uranium-235. Individuals with this clearance have access to nuclear weapons design, manufacture, and use data. When working with this information, they have armed guards nearby because disclosure "could cause exceptionally grave danger to the nation." These individuals routinely have access to national security information and top secret formerly restricted data.
Q Nonsensitive: Individuals holding this clearance have access to less sensitive types of SNM. Individuals working with Q non-sensitive clearances also have armed guards stationed nearby.
L Clearances: Individuals with L clearances have access to secret national security information as well as confidential RD and secret formerly restricted data.
SIGMA Categories: Within the RD and FRD categories, Sigma designates differing degrees of access to information concerning the design, manufacture, or utilization of nuclear weapons or nuclear explosive devices:
— Sigma 1: Theory of operation (hydrodynamic and nuclear) or complete design of thermonuclear weapons or their unique components.
— Sigma 2: Theory of operation or complete design of fission weapons or their unique components. This includes the high-explosive system, and nuclear initiation system as they pertain to weapon design and theory.
— Sigma 3: Manufacturing and utilization information not comprehensively revealing the theory of operation or design of the physics package. Complete design and operation of nonnuclear components, but only information as prescribed below for nuclear components. Utilization information necessary to support the stockpile to target sequence. Information includes: (a) general external weapon configuration, including size, weight, and shape; (b) environmental behavior, fuzing ballistics, yields, and effects; (c) nuclear components or subassemblies that do not reveal theory of operation or significant design features; (d) production and manufacturing techniques relating to nuclear parts or sub-assemblies; (e) anticipated and actual strike operations.
— Sigma 4: Information inherent in preshot and postshot activities necessary in the testing of atomic weapons or devices. Specifically excluded are the theory of operation and the design of such items. Information includes: (a) logistics, administration, other agency participation; (b) special construction and equipment; (c) effects, safety; (d) purpose of tests, general nature of nuclear explosive tested (including expected or actual yields), and conclusions derived from tests outside of design features.
— Sigma 5: Production rate and stockpile quantities of nuclear weapons and their components.
— Sigma 9: General studies not directly related to the design or performance of specific weapons or weapon systems such as reliability studies, fuzing studies, damage studies, and aerodynamic studies.
— Sigma 10: Chemistry, metallurgy, and processing of materials peculiar to the field of atomic weapons or nuclear explosive devices.
— Sigma 11: Information concerning inertial confinement fusion which reveals or is indicative of weapon data.
— Sigma 12: Complete theory of operation, complete design, or partial design information revealing either sensitive design features or how the energy conversion takes places for the nuclear energy converter, energy director or other nuclear-directed energy weapon systems or components outside the envelope of the nuclear source with within the envelope of the nuclear-directed-energy weapon.
— Sigma 13: Manufacturing and utilization information and output characteristics for nuclear energy converters, directors, and other nuclear-directed energy weapon systems or components outside the envelope of the nuclear source, not comprehensively revealing the theory of operation, sensitive design features of the nuclear-directed energy weapon or how the energy conversion takes place. Information includes: (a) general external weapon configuration and weapon environmental behavior characteristics, yields, and effects; (b) component and sub-assembly design that does not reveal theory of operation or sensitive design features of nuclear- directed energy weapons categorized as Sigmas 1, 2, or 12; and (c) production and manufacturing techniques for components or sub-assemblies of nuclear-directed energy weapons that do not reveal information categorized as Sigmas 1, 2, or 12.
Critical Nuclear Weapons Design Information (CNWDI): A DOD category of weapons data that is analogous to "top secret" or "secret restricted data." Disseminated within the department and the armed services on a need-to-know basis, it includes information relating to the theory of operation or design of the components of a nuclear weapon. CNWDI excludes a number of less sensitive information related to the maintenance and operation of nuclear weapons.