Safe and Secure Transport of Subcritical Experiment Assemblies

In support of the National Nuclear Security Administration’s (NNSA) Stockpile Stewardship Program (SSP), the Los Alamos National Laboratory has developed, manufactured, and transported a series of Subcritical Experiment (SCE) assemblies for stockpile reliability assessments. The latest SCE, named POLLUX, was successfully tested at the underground U1a complex located on the Nevada National Security Site (NNSS) in late 2012. The SCE examines the behavior of plutonium as it is shocked by forces produced by high explosives. The scientific data and technical information produced from the execution of the experiment will be used to support the safety and effectiveness of the nuclear weapons stockpile. POLLUX was the 27th SCE to date. In addition to high-powered x-ray radiographs from a device called Cygnus, data was also acquired from a new diagnostic technology developed called the Multiplexed Photonic Doppler Velocimeter. The PATRM paper will discuss the unclassified aspect of the SCE, the intricate transportation fixture, and the various analyses supporting the transportation certification and approval. The transport fixture utilized a complex metal structure for supporting and maintaining the SCE’s high fidelity tolerances and positional relationships. The design of the transportation fixture was challenging as the fixture was required to sufficiently support the SCE components, but also be flexible enough to preclude damage such as crushing, bending, or breakage. In addition, the SCE contained diagnostic components which were isolated to preclude damage to the SCE or the diagnostic component themselves. Various other elements of the fixture included inert gas compartments, leakage test connections, and shock mitigation devices. A full scale model of the SCE, fixture, and transport package was fabricated and assembled for testing certain aspects of the expected transport environment. The most significant concern of the transportation environment was vibration and shock during the loading/unloading cycle and during over-the-road transport. The design of the shock mitigation and clamping interface is very unique and could be applied to other contents where similar care is required.