Weigh and Leak Check System

The Nuclear Weapons Complex stores and handles hundreds of radioactive nuclear materials known as "pits" during annual operation. At the BWXT Pantex Plant in Amarillo, Texas, several stockpile inspection, evaluation, and maintenance programs require the handling and measurement of pits from a wide variety of weapons systems. These measurements are performed periodically to ensure stockpile integrity. Historically, these pit-handling operations were performed manually, resulting in a significant accumulation of radiation dose to the workers. However, with the successful development of the Weigh and Leak Check System (WALS), that is no longer the case.

WALS provides an automated robotic system capable of performing remote weigh and leak check operations on pits at Pantex. WALS uses a six-axis robotic arm on a 25-ft. linear track. The robotic arm is programmed to move pits to several custom tooling and automation stations, where the pits are unpacked from their containers, removed from their shipping fixtures, weighed, leak-checked, and repacked. WALS also has a suite of sensors and safety features necessary to operate the robot safely and reliably.

WALS was a joint effort by Sandia’s Intelligent Systems and Robotics Center (ISRC) who developed the robotic automation system and by Pantex who developed the weigh and leak check stations.

The WALS robotic system employs advanced automation technologies to provide safety in performing difficult operations and simplifies operator use of the system. For instance, computer vision is used extensively to determine the position of objects in the workcell, thereby eliminating the need for large numbers of precise fixtures.

Similarly, force control is used to allow the robot system to sense forces on the payload, thereby protecting the payload and providing an automated means to precisely and gently place pits in the workcell in spite of mechanical imprecision. Engineers have also included mechanical locks and sensors that ensure a sequence of events has taken place before a pit can be moved, and a redundant computer to independently monitor forces on the pit during robot motion.

Sandia is currently working on modifying the robot’s pit-handling tools so the system can accommodate new sealed insert (SI) containers, in addition to the several containers already used in WALS.

The primary benefit of WALS is the reduction of operator exposure to hazardous radiation by eliminating operator handling of pits. An important ergonomic benefit is the elimination of many of the manual lifting tasks that are required for unpacking and repacking the pits. Furthermore, the use of automation enforces the use of qualified, validated procedures, that will be executed the same each time. In addition, the sequence of performed operations automatically generates a log that can be retained and audited, thus improving quality.

Pantex is currently using WALS to perform remote weigh and leak check operations on its nuclear weapon pits. WALS is the first robot system ever to handle such stockpile pits.

The automation technologies developed for WALS can also be employed in a wide variety of areas where pits are handled. This will dramatically extend the scope of these technologies well beyond their original use in the weigh and leak check facility.

Contact:
Bill Drotning
(505)844-7934
email: wddrotn@sandia.gov