Strong link weak link
Encyclopedia
A Strong link/weak link and Exclusion zone nuclear detonation mechanism is a type of safety mechanism employed in the arming
and firing mechanisms of modern nuclear weapon
s. It is a form of automatic safety interlock
.
The safety mechanism starts by enclosing the electronics and mechanical components used to arm and fire the nuclear weapon with a mechanical and electrical isolation barrier, forming the Exclusion zone. This is insulated from mechanical, thermal, and electrical disruptions (such as static electricity
, lightning
, fire
).
Between the exclusion zone and the actual detonators, a normally disconnected link mechanism is used, such as a switch which has a built in motor to activate it. The arming system has to activate the switch in order to connect the firing circuits to the detonators in the weapon. This disconnection, which requires the arming mechanism to operate, is called the strong link
It is possible for an accident (rocket
explosion, airplane crash, accident while weapon is being moved) to disrupt the weapon and break the integrity of the exclusion zone. As a safety mechanism, a weak link is also built into the system. This is a set of components designed to fail at lower stresses (thermal, mechanical, and electrical) than will cause failure of the strong link mechanisms. The weak link acts to break the connection to the detonators before the strong link could be disrupted and fail by the stress of an accident.
These mechanisms do not prevent misuse of the weapon, which is restricted by Permissive Action Link
code systems, or an accident from physically causing initiation of the explosives or detonators directly from extremely high temperatures, impact forces, or electrical disturbance such as lightning. The risk of accidental direct detonation is significantly reduced by using insensitive high explosives such as TATB
, which is extremely unlikely to detonate due to fire or impact or electricity. While TATB may decompose or burn in a fire, it is extremely unlikely to detonate as a result of that decomposition or burning.
Fuse (explosives)
In an explosive, pyrotechnic device or military munition, a fuse is the part of the device that initiates function. In common usage, the word fuse is used indiscriminately...
and firing mechanisms of modern nuclear weapon
Nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission bomb test released the same amount...
s. It is a form of automatic safety interlock
Interlock (engineering)
Interlocking is a method of preventing undesired states in a state machine, which in a general sense can include any electrical, electronic, or mechanical device or system....
.
The safety mechanism starts by enclosing the electronics and mechanical components used to arm and fire the nuclear weapon with a mechanical and electrical isolation barrier, forming the Exclusion zone. This is insulated from mechanical, thermal, and electrical disruptions (such as static electricity
Static electricity
Static electricity refers to the build-up of electric charge on the surface of objects. The static charges remain on an object until they either bleed off to ground or are quickly neutralized by a discharge. Static electricity can be contrasted with current electricity, which can be delivered...
, lightning
Lightning
Lightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...
, fire
Fire
Fire is the rapid oxidation of a material in the chemical process of combustion, releasing heat, light, and various reaction products. Slower oxidative processes like rusting or digestion are not included by this definition....
).
Between the exclusion zone and the actual detonators, a normally disconnected link mechanism is used, such as a switch which has a built in motor to activate it. The arming system has to activate the switch in order to connect the firing circuits to the detonators in the weapon. This disconnection, which requires the arming mechanism to operate, is called the strong link
It is possible for an accident (rocket
Rocket
A rocket is a missile, spacecraft, aircraft or other vehicle which obtains thrust from a rocket engine. In all rockets, the exhaust is formed entirely from propellants carried within the rocket before use. Rocket engines work by action and reaction...
explosion, airplane crash, accident while weapon is being moved) to disrupt the weapon and break the integrity of the exclusion zone. As a safety mechanism, a weak link is also built into the system. This is a set of components designed to fail at lower stresses (thermal, mechanical, and electrical) than will cause failure of the strong link mechanisms. The weak link acts to break the connection to the detonators before the strong link could be disrupted and fail by the stress of an accident.
These mechanisms do not prevent misuse of the weapon, which is restricted by Permissive Action Link
Permissive Action Link
A Permissive Action Link is a security device for nuclear weapons. Its purpose is to prevent unauthorized arming or detonation of the nuclear weapon.The United States Department of Defense definition is:...
code systems, or an accident from physically causing initiation of the explosives or detonators directly from extremely high temperatures, impact forces, or electrical disturbance such as lightning. The risk of accidental direct detonation is significantly reduced by using insensitive high explosives such as TATB
TATB
TATB, or triaminotrinitrobenzene, is an aromatic explosive, based on the basic six-carbon benzene ring structure with three nitro functional groups and three amine groups attached, alternating around the ring....
, which is extremely unlikely to detonate due to fire or impact or electricity. While TATB may decompose or burn in a fire, it is extremely unlikely to detonate as a result of that decomposition or burning.