Plasma Waste Vitrification

PLASMA WASTE VITRIFICATION

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Dr Bryony Livesey*, Dr Tim Johnson+, Mark Rogers*

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*Costain, +Tetronics International

• International Workshop on Plasmas for Energy and Environmental Applications

Meeting national needs through people and innovation

Nuclear waste – long term storage

Plasma Waste Vitrification

Objectives

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• Demonstrate flexibility of plasma system to treat multiple waste streams:

• Two types of sludge• Future decommissioning waste

• Demonstrate maximum passivation and stabilisation of vitrified product

• Maximise volume reduction• Demonstrate maximum retention of caesium in the vitrified product• Investigate factors affecting plasma vitrification process

performance: volume reduction, process stability, homogeneity, throughput, off gas treatment demand, etc.

• Confirm that critical components deliver their process and safety functions

Basis of Safety

• System is always a net-consumer of energy (i.e. no thermal runaway)

• Process prevents accumulation of explosive gases• Standard nuclear ventilation and shielding suitable for dealing with

radiological hazard• Criticality hazard managed by geometry• Multi-layer containment of melt• Avoidance of melt pouring – solidification in-situ• Replaceable furnace refractory lining• Melting crucible suitable for loading directly into final waste

container for ultimate disposal

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Design of Demonstration Plant

• Based on concept design and corresponding safety case

• Key design features include:

• Remote loading of crucible into cooling jacket• Remote vertical and horizontal movement of

crucible• Monitoring of furnace seal integrity• Furnace clamp mechanisms• Replaceable roof refractory

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Demonstration Plant

• Feeding of sludges and fluxes

• Twin electrodes

• Plant cell (cage)

• Plasma furnace

• Water-cooled ‘clam shell’ and base

• Remote loading and unloading of crucible

• Simulated final waste container

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Product

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Single-skinned waste container

Vitrified waste

Grout

Crucible liner

Refractory

Slag Composition Control

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• Fluxes are added to ensure low melting point and good fluidity

• Allowing the material to solidify in-situ reduces accuracy of composition control required

Species SIXEP Magnox FD wasteRaw waste simulants 100 % 59% 92%Silica sand, flux - 30% -Aluminium oxide, flux - 11% -Calcium Carbonate, flux - - 8%Total 100 % 100 % 100 %

Mass Balance – SIXEP Sludge

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Inputs: Mass, kg % of Input

Solid in waste simulant 553.51 63.0%

Water in waste simulant 325.08 37.0%

Flux in blended waste simulant 0.00 0.00%

Total mass input 878.59 100.0%

Outputs:

Vitrified slag 446 50.8%

Furnace exit duct dust 1.51 0.2%

Combustion chamber dust 0.12 0.0%

Filter bag-house dust 9.14 1.0%

Total solid mass output 456.77 52.0%

Volume Reduction

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SIXEP Trial No SIXEP001 SIXEP002 SIXEP003 SIXEP004 SIXEP005Feeding method Batch Continuous Continuous Continuous Continuous

Sludge fed during trial, m3 0.112 0.112 0.112 0.112 0.139

Vitrified slag volume, m3 0.076 0.043 0.043 0.043 0.065

Volume reduction (without crucible) 32% 61% 61% 61% 53%

Maximum vitrifed slag volume, m3 0.108 0.108 0.108 0.108 0.108

Sludge volume required, m3 0.158 0.280 0.280 0.280 0.231

Maximum final wasteform volume, m3 0.278 0.278 0.278 0.278 0.278

Volume reduction (with crucible) -76% 1% 1% 1% -20%

These values are following initial demonstration trials designed with conservative assumptions and limited optimisation studies. Further design modifications for specific waste streams will result in improved volume reduction performance.

Summary of Results

• ~60% bulk waste volume reduction

• >95% of caesium retained in the wasteform (single pass)

• Uniform unreactive monolith

• Key engineering achievements include:• Making a provable crucible seal• Making a provable electrode seal• Furnace can be dismantled remotely

Next Steps

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• Pursuing low hazard industrial implementation opportunities at full scale

• Pursuing funding for active demonstration as the next step towards commercial-scale implementation

• Developing the existing business case to explore the benefits of this approach across the nuclear industry

Summary

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