Strategic Guidance on the Management of LLW and ILW / LLW ...

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LLW Repository LtdNational Waste ProgrammeNWP/REP/011Issue 2.1 – Jan 2013Page 32 of 585.2.7. Chemical Decontamination (strong mineral acids) [Ref. 5]UsageLLWILW/LLWSurface contaminatedVolumetricallycontaminatedActivatedAluminiumCopperMild steelMild steel (coated)Stainless steelStainless steel (coated)Description of techniqueStrong mineral acids – such as sulphuric acid, hydrochloric acid, nitric acid or phosphoric acid – areparticularly useful for the removal of contamination from metals. The action of the strong mineral acid on themetal surface dissolves metal oxide films and improves the solubility of metal ions, thus removing surfacecontamination from the metal object. These may be applied as a solution, paste, gel or foam by a variety ofapplication methods including jetting, swabbing, wiping or spraying. The performance of the technique isdependent on the nature of the material to be decontaminated, the type of contamination and the geometryof the object.The technique is applicable to mild steel, stainless steel, aluminium and copper; and can be utilised fordecontamination of LLW or ILW/LLW. The technique is for surface decontamination and is not useful forvolumetric contaminated or activated waste, other than a precursor to other waste treatment.Outcomes Advantages Disadvantages• For LLW:o Waste metal decontaminated to EPRout-of-scope status; oro Waste metal decontaminated to enablefor further processing.o Secondary wastes – acidic liquidradioactive waste.• For ILW / LLW:o Waste metal decontaminated to LLWstatus to enable further processing ordisposal.o Secondary wastes – acidic liquidradioactive waste.A company owned by UK Nuclear Waste Management Ltd• Mature technology.• Potentially applicableto LLW/ILW borderlinewastes.• Generates a largevolume of acidicliquid radioactivesecondary wastesrequiring treatmentand disposal.• Technique poseschemical hazards –e.g. corrosivity,toxicity and adversechemical reactivity.• Not useful forvolumetricallycontaminated andactivated wastes(unless as precursorto other wastetreatment).NOT PROTECTIVELY MARKED
LLW Repository LtdNational Waste ProgrammeNWP/REP/011Issue 2.1 – Jan 2013Page 33 of 58• Potential forincompatibility ofmetal type with aspecific acid; e.g.copper waste canadversely react withnitric acid to generatetoxic NOx fumes.• Potential forgeneration of orphansecondary wastes.Technique used at:ILW/LLWCase Study C – Nitric acid decontamination at Hunterston AChallengeAs part of ongoing deplanting of the fuel storage pond at Hunterston A, 200 aluminium ILW pond skips wereidentified as requiring a waste management solution.SolutionA chemical decontamination technique using nitric acid was identified as a solution for the Hunterston A fuelskips. The skips were retrieved from the pond and decontaminated to LLW using a warm (60°C) solution of6% nitric acid, utilising existing equipment in the skip refurbishment plant. Following decontamination withthe nitric acid, the skips were size reduced and coated to meet the acceptance criteria for LLWR. Certaincomponents were compacted following coating to reduce the volume of the waste. The waste waspackaged into half-height ISO containers and transferred to LLWR for disposal.The process generated a significant volume (approximately 140m 3 ) of ILW contaminated liquid secondarywaste – the depleted nitric acid containing dissolved contamination and some dissolved aluminium. This hasrequired specialist interim storage in a purpose built acid storage facility pending encapsulation.A company owned by UK Nuclear Waste Management LtdNOT PROTECTIVELY MARKED
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