A new technology for the retrieval of high-level nuclear waste (HLW) from storage tanks was demonstrated successfully at the Quarter-Scale Tank Test Facility at Hanford in July 1997 in order to determine the capabilities, limitations, and suitable applications of the tank retrieval equipment at U.S. sites.  In the fall of 1997, it was used to empty three tanks at a Russian site, and it is currently in use there.  Three sets of the Russian equipment were procured in November 1998 for deployment in the Oak Ridge GAAT tanks, which is expected to occur in June 2000.

Background Information

The Gunite And Associated Tanks (GAAT) located at the Oak Ridge National Laboratory (ORNL) were constructed in the early 1940s to collect, store, and transfer liquid radioactive and hazardous waste.  These tanks were to be in service for approximately five years.  However, they continued to receive nuclear waste until the early 1970s.  In the early 1980s, most of the sludge that had settled to the tank bottoms was removed using a water sluicing process.  A quantity of residual sludge and liquid remain, posing a potential threat to human health and the environment.

The Ministry of Atomic Energy for the Russian Federation faces a similar problem.  Russian decontamination and decommissioning plans for the radiochemical production complex at the Mining Chemical Association (Krasnoyarsk-26) made it critical to retrieve the sludge from their HLW tanks.  These 3000m³ tanks are similar to Hanford tanks, and they contain similar sludge.

Because of the successful use of the new Russian technology at Krasnoyarsk-26, it is expected that this technology will resolve the longstanding and serious problem of HLW storage tank sludge at ORNL.

Technology Description

The Russian device, the Pneumatic Pulsating Pump, has a productivity of 12-15m3/hr for sludge retrieval from a depth of 10-30m.  A pulsating monitor was also developed as part of the tank retrieval equipment tool kit.  The pulsating pump and monitor operate by drawing waste into a vertical cylindrical chamber through an immersed foot check valve and then expelling it.  The waste slurry is expelled through a riser stem-pipe and a check valve at the head of the riser into process piping on a holding tank.  The monitor, on the other hand, expels the waste through an array of nozzles at the bottom of the device that mobilize and mix the water and scour the tank floor.  The working fluid is atmospheric air delivered to the chamber in alternating pulses of a partial vacuum (-60kPa) and pressure (-400kPa) through a motorized rotary valve.  The vacuum is operating from the same compressor that supplies the pressurized air.

The equipment can recover from blockage to flow by means of back-flushing and valve-clearing techniques that are facilitated by the equipment design.  The design of the current control system limits operating pressure to 6 atm.  Planned engineering modifications will extend the range of applicability and extend the operating pressures to 30 atm (450psi).  The components of the system that are actually placed into the tank are simple, rugged, and inexpensive, making it economically feasible to leave the pump in the tank after use.  The more costly system components do not become contaminated under normal operating conditions and can be readily re-used without expensive decontamination operations.

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