Autonomous Hazardous Waste Inspection Vehicle

An Intelligent Mobile Sensing System (IMSS) has been developed for the automated inspection of radioactive and hazardous waste storage containers in warehouse facilities at Department of Energy (DOE) sites. Hundreds of thousands of hazardous, radioactive, and mixed waste drums are being stored at DOE sites throughout the country and the anticipated decommissioning of facilities will generate many more drums of waste. Federal regulations require that stored drums be inspected periodically for degradation and to verify inventories. Currently, these waste storage facilities are being inspected manually. The IMSS will reduce the risk of exposure to personnel and create accurate, high-quality inspection reports to ensure regulatory compliance. An autonomous robotic device with enhanced intelligence and maneuverability, capable of conducting routine multi-sensor inspection of stored waste drums has been developed. This device, based in part on a prototype for a wheeled Mars rover, includes five mission sensing subsystems, a relational site data base, a "partially ordered" scheduler/executive, omnidirectional wheels, autonomous landmark navigation, and a multilevel supervisory control interface. 1. 0 Introduction The purpose of the IMSS program is to create a system to automate the monitoring and inspection process for stored hazardous, radioactive, and mixed waste drums. The DOE has hundreds of thousands of storage drums stored in multiple facilities located at several sites in the United States (Figure 1). The Environmental Protection Agency (EPA) requires positive weekly inspection of each storage drum in a storage facility. This inspection process is time consuming and presents inherent health hazards. The IMSS system will automate the inspection process, lowering costs and providing safer, more accurate and more consistent inspections. Figure 1. Typical DOE Storage Facility The functional requirements for the system were developed from EPA requirements and from discussions with waste operations personnel at four DOE sites (Oak Ridge National Laboratory, Hanford Engineering Laboratory, Idaho National Engineering Laboratory, and Rocky Flats Plant). 1.1 Problem Most waste storage facilities contain 5,000 to 20,000 barrels per building. Barrel sizes inclue 35, 55, 87, 93, and 110 gallon drums; colors include white, yellow, silver, gray and black. Storage facilities typically have barrels stored four to a pallet, with pallets arranged in single rows. Observed stacking heights for pallets vary from two to five pallets with an average of three high. Aisle widths vary from facility to facility, ranging from 26 in. to 30 in. to 36 in. Aisle lengths also vary from 20 feet to hundreds of feet. In general, space is left between the last pallet in a row and the adjacent wall. Positive inspection of each barrel is required and operator response to flagged barrels is required within 24 hours. All drums must be inspected at least once every six days. Current methods used to inspect and monitor stored wastes are based on either passive detectors or on humans walking through the storage area with various instruments. Passive monitoring relies on fixed sensors dispersed within the containment building such as radiation or gas detectors. When an increase in radiation is measured, operators must enter the storage site and locate the leaking container. Walking inspections might include radiation detectors and gas detectors, but usually are only visual inspections. Visual inspection of the drums is required to detect dented, bulging, or rusting drums. However, visual methods are a function of operator acuity and fatigue level and may vary between operators and even between individual drums. Operators may receive varying radiation doses during their inspections and must be examined for contamination before site exit. Required drum inspection frequency and operator lifetime radiation limits raise the total cost of this monitoring process and introduces health and safety risks. In performing a visual inspection for mixed waste storage, a human operator evaluates the exterior condition of the drums to determine the integrity of liquid containment. Professional judgment is used to identify any negative conditions that may result in the escape of any liquids, or in the case of radioactive waste, any drum condition that may result in a release of air-borne contamination such as alpha particles. With these qualifiers in mind, the following extracted requirements for drum inspection were compiled (Table I). Table I Barrel Inspection Requirements Sharp or Pointed Dents No depth greater than one inch, width or length not critical. Rounded Dents Ignore unless the stability of the drum is in question. Surficial Rust (Paint Corrosion) Track diameter size; if rust is increasing, identify. Streaks of Rust Identify streaks; discriminate between streaks or rust and streaks of condensation in dirt or dust; quantify by length, width, and position. Nonsurficial Rust (Metal Corrosion) Identify by diameter. Tilted (Bulging) Drums If drums are banded, identify if base of drum is touching bottom storage surface (pallet, plywood, or floor); if drums are not banded, identify if tilted (any angle greater than two degrees); identify if ribs of drum cannot be distinguished. Stacking Levels For specific storage area, identify if stacking level is exceeded. Condition of Pallets Identify if broken. Location of Bar Codes Upper third of 55-gallon drums or top half of 35-gallon drums; the top of the bar code not more than two inches below drum seal, visible from the aisle. Note if missing. Location of Hazardous Waste Labels If the site requires hazardous labels, the label should be located in the center third of 55-gallon drums, or top half of 35-gallon drums. Quantitative numbers and/or conditions were selected to provide a decision making basis whether a barrel should be considered defective. These numbers and the system performance are discussed in section 6.0. Visual anomalies NOT to be mistaken or confused include: Ñ Accumulations of dust or dirt on ridges, rims, or seams; Ñ Condensation streaks in dust or dirt; Ñ Symbols or other labels that are not bar codes; Ñ drum seams. The inspection requirements are not standardized in general because of the differences of the various state and federal regulating agencies and various DOE facility policies. The report forms created by the IMSS system are the same as are currently created by the inspectors. In general, inspection reports will be completed automatically once per week per area. An operator must be positively called if a defective barrel is identified to ensure the condition is corrected within 24 hours. A map of the area is included in the report on which the defective barrel is identified to aid the operator in his response. 1.2 IMSS Program The IMSS program is a three-phase effort to develop an autonomous monitoring and inspection system/technology. The objective of the first phase was to demonstrate an integrated system performing all required functions; the objective of the second phase is to efficiently package the software and components and perform an actual hot demonstration in a full scale storage facility; the objective of the third phase is to develop the product into a certified, commercially viable system. The Phase 1 effort discussed in this paper assembled an integrated engineering demonstration model, including all components required to perform the functional requirements. The vehicle was integrated from subsystems some of which previously existed as part of a Mars rover prototype including the motion platform, the sensor mast, and the operator's console. Other components that were added included the ultrasonic obstacle avoidance system, the sensor suite, omnidirectional wheels, and the navigation software. The Phase 1 system was tested in a small-scale storage facility mockup to gather performance data for subsequent phase 2 design. The following portions of this paper discuss the design and performance of the engineering demonstration model beginning with an overview of the system architecture and then progressing through a discussion of the mobility base, mission sensors, and operator interface. The paper concludes with a presentation of measured system performance. 2.0 Architecture There are four main hardware components of the IMSS system: a mobile robot, the mission sensors, a control station, and support equipment (Figure 2). The vehicle portion includes the mobility base, navigation equipment, and onboard processing and power. The mission sensing functions run on three hardware subsystems: color vision system (corrosion inspection functions), structured light system (geometric inspection functions), and the bar code reader. The control station supervises vehicles in several buildings from a remote facility via ethernet commands to the docking station. The support equipment includes the docking station, battery recharger, and various vehicle recovery hardware.