Over the past few years Sandia National Laboratories has been moving toward an increased dependence on model- or physics-based analyses as a means to assess the impact of long term storage on the nuclear weapons stockpile. It is particularly important to assist engineers in identifying potential problems well in advance of their becoming critical. An effort was therefore initiated in 1995 to evaluate the capabilities of existing probabilistic methods and, if required, to develop new analysis methods to support the inclusion of uncertainty in the classical design tools used by analysts and engineers at Sandia. Of critical importance was the need to develop the capability to predict the future impact of aging issues on the reliability of the nuclear weapons stockpile.
The primary result of this effort was a new uncertainty analysis software package. There are three major elements to this software: 1) the uncertainty analysis engine - Cassandra, 2) the user interface - CRAX, and 3) the physical model. The heart of the CRAX software is the Cassandra uncertainty analysis engine. This engine currently consists of over 22 different mathematical techniques for including uncertainty: 5 simulation methods, 14 analytical methods plus variations of a new hybrid technique being developed at Sandia. The specific methods are constantly being updated, validated and improved. Cassandra is written completely in C/C++ making the engine very easy to implement across a variety of computer platforms. The CRAX graphical user interface (GUI) is based entirely on the Tool Command Language (Tcl) and associated Tool Kit (Tk). The use of Tcl and Tk permits the software to be hosted on any platform (Win95, WinNT, Power Macintosh, Unix, Linux, etc.) and provides a great deal of flexibility in accessing the Cassandra uncertainty engine.
The fact that Cassandra is platform independent permits easy interface with many new and existing engineering design and analysis software packages. The use of a standard interface architecture permits the easy integration of new uncertainty methods into Cassandra and also interface with other software, e.g. SGOPT a comprehensive optimization package being developed at Sandia.
The CRAX/Cassandra analysis software is constantly being updated as additional proven analysis methods are incorporated into Cassandra and new techniques are developed. Each new problem brings with it a unique set of input, output and computational requirements. CRAX/Cassandra has been used with Win95, WinNT, Power Macintosh, Sun, Silicon Graphics and DEC operating systems. In addition, the software has been ported to one of the large tera-flop computers at Sandia. The flexibility of the CRAX interface and the extensibility of the Cassandra uncertainty engine permits the reliability and uncertainty issues to be addressed quickly and efficiently whatever the computational requirements might be. The software continues to provide new insights into issues related to stockpile surveillance that were not possible before.