An expression of the extent to which the performance of a system, facility, or device is expected to degrade in a given nuclear environment. 2. The physical attributes of a system or component that will allow survival in an environment that includes nuclear radiation and electromagnetic impulses (EMI. ) Note 1: Nuclear hardness may be expressed in terms of either susceptibility or vulnerability. Note 2: The extent of expected performance degradation (e.g., outage time, data lost, and equipment damage) must be defined or specified. The environment (e.g., radiation levels, overpressure, peak velocities, energy absorbed, and electrical stress) must be defined or specified. 3. The physical attributes of a system or component that will allow a defined degree of survivability in a given environment created by a nuclear weapon. Note: Nuclear hardness is determined for specified or actual quantified environmental conditions and physical parameters, such as peak radiation levels, overpressure, velocities, energy absorbed, and electrical stress. It is achieved through design specifications and is verified by test and analysis techniques.