In the Nuclear Security Enterprise (NSE), many high reliability components must be stored for long periods of time before being called on to function a single time. During dormant storage, changes in the performance of these components may occur due to environmental exposures. These exposures may enhance the natural degradation of materials or result in shifts in the performance of electronics. Ongoing assessment of these components is necessary to inform the need for upgrades or replacements to ensure high reliability requirements are being maintained. This paper presents several assessment methodologies that are used and have been proposed for this problem. We also present methods that we believe to be most appropriate for the assessment of nuclear weapons components subjected to dormant storage.
A reliability and availability model has been developed for a portion of the 4.6 megawatt (MWdc) photovoltaic system operated by Tucson Electric Power (TEP) at Springerville, Arizona using a commercially available software tool, GoldSim{trademark}. This reliability model has been populated with life distributions and repair distributions derived from data accumulated during five years of operation of this system. This reliability and availability model was incorporated into another model that simulated daily and seasonal solar irradiance and photovoltaic module performance. The resulting combined model allows prediction of kilowatt hour (kWh) energy output of the system based on availability of components of the system, solar irradiance, and module and inverter performance. This model was then used to study the sensitivity of energy output as a function of photovoltaic (PV) module degradation at different rates and the effect of location (solar irradiance). Plots of cumulative energy output versus time for a 30 year period are provided for each of these cases.
To determine whether a component is meeting its reliability requirement during production, acceptance sampling is employed in which selected units coming off the production line are subjected to additional environmental and/or destructive tests that are within the normal environment space to which the component is expected to be exposed throughout its life in the Stockpile. This report describes what these tests are and how they are scored for reliability purposes. The roles of screens, Engineering Use Only tests, and next assembly product acceptance testing are also discussed, along with both the advantages and disadvantages of environmental and destructive testing.