Technical Challenges in the Immobilisation of UKAEA ILW

1. Technical Challenges in the Immobilisation of UKAEA ILW Michelle Wise, Ann Goldsmith

2. Outline UKAEA Policy on Waste Management Overview of UKAEA Wastes Example Technical Challenge Waste Package Specifications embody general requirements on waste packages for them to be compatible with the Concept Formal documentation of the Concept fairly recent so are now undertaking a fundamental review of Specification against the ConceptWaste Package Specifications embody general requirements on waste packages for them to be compatible with the Concept Formal documentation of the Concept fairly recent so are now undertaking a fundamental review of Specification against the Concept

3. UKAEA Policy Compliance with regulator requirements and expectations Aim for passive safety Prioritise on basis of hazard, aim for progressive reduction Demonstrate BPEO/BPM as required Conditioned wastes consistent with future long term management

4. UKAEA Sites

5. Overview of Wastes- Solids Stored, Untreated Wastes Often incomplete records Inappropriate storage/ disposal arrangements silo & Dounreay shaft mild steel containers designed without sampling in mind Sea disposal packages Wastes from decommissioning old facilities Incomplete records Time drivers need to avoid creating new problems Fuels Early military and Magnox wastes are stored untreated in tanks and silos, as for wastes from reactor and weapons development programmes. Many of these wastes still have not been processed. Only some 12% of the expected 215,000m3 ILW has been conditioned, or will be conditioned, i.e. prepared for ultimate disposal, as it is generated. Both the specific problem storage methods and other old wastes (remember we're not just talking a few years old, but going back to 1950s) are exacerbated by incomplete and inadequate records. In the past, only criticality was considered in recording requirements. We don't know what exactly is in many of these stores, what form it was in, let alone what it might be like now, e.g. containers that have decayed. Retrieval and treatment systems have to be designed to cope with all foreseeable contents, so if there's only a rumour that a particular hazardous substance was placed in the "store", plans must be in place to deal safely with it if indeed it is found. We have also some specific decisions in the past, which have now come back to haunt us: At one time, certain LLW and lower-end ILW was disposed of by encapsulating in 200 litre drums using cement. These were then dumped at sea. The London Convention banned this practice, and eventually all disposals at sea, but when it came in we and other producers had thousands of drums prepared for disposal. We now have to take apart these containers and treat/ dispose of the contents appropriately. This is a difficult and potentially hazardous process. Some waste producers, including UKAEA, placed certain wastes in silos under water. This was perceived as safe, and indeed has not caused major incidents, but as this is not an adequate permanent solution, retrieval and conditioning of the wastes is now difficult. The Dounreay shaft was an old mine shaft into which UKAEA dumped a lot of their wastes. This has, unfortunately, caused safety concerns- there was an explosion that blew the concrete plug into the air, and now again UKAEA has problems in retrieving the wastes. Early military and Magnox wastes are stored untreated in tanks and silos, as for wastes from reactor and weapons development programmes. Many of these wastes still have not been processed. Only some 12% of the expected 215,000m3 ILW has been conditioned, or will be conditioned, i.e. prepared for ultimate disposal, as it is generated. Both the specific problem storage methods and other old wastes (remember we're not just talking a few years old, but going back to 1950s) are exacerbated by incomplete and inadequate records. In the past, only criticality was considered in recording requirements. We don't know what exactly is in many of these stores, what form it was in, let alone what it might be like now, e.g. containers that have decayed. Retrieval and treatment systems have to be designed to cope with all foreseeable contents, so if there's only a rumour that a particular hazardous substance was placed in the "store", plans must be in place to deal safely with it if indeed it is found. We have also some specific decisions in the past, which have now come back to haunt us: At one time, certain LLW and lower-end ILW was disposed of by encapsulating in 200 litre drums using cement. These were then dumped at sea. The London Convention banned this practice, and eventually all disposals at sea, but when it came in we and other producers had thousands of drums prepared for disposal. We now have to take apart these containers and treat/ dispose of the contents appropriately. This is a difficult and potentially hazardous process. Some waste producers, including UKAEA, placed certain wastes in silos under water. This was perceived as safe, and indeed has not caused major incidents, but as this is not an adequate permanent solution, retrieval and conditioning of the wastes is now difficult. The Dounreay shaft was an old mine shaft into which UKAEA dumped a lot of their wastes. This has, unfortunately, caused safety concerns- there was an explosion that blew the concrete plug into the air, and now again UKAEA has problems in retrieving the wastes.

6. Harwell RHILW Historical waste in Tube Stores concerns over condition (mild steel containers) uncertainties over contents Accessibility retrieval machine, further requirements Waste Requiring Additional Treatment (WRATs) records may be misleading Assay

7. B462 Head End Cells UKAEA currently stores Remote Handled Intermediate Level Waste (RHILW) in a number of facilities in the B462 complex, principally in cans within below-ground storage tubes. The waste was received by UKAEA from operations on both the Harwell and Winfrith sites, and from the National Disposal Service (NDS). A new facility (B462.27) has been built to process these wastes, and store them in their disposal containers (500 litre drums) pending construction of a new encapsulation plant, which is currently in the design stages. Active commissioning of the plant was carried out in 2001. B462.27 consists of three principal operations areas: the Head End Cells (HEC), where the waste is analysed and repacked; the Vault Store, where the packaged wastes will be stored, pending encapsulation; and the crane maintenance area. A Flexible Waste Handling Facility (FWHF) is also proposed, which will be able to process certain wastes, such as powders, that require additional treatment before packaging. Within the HEC suite, a number of operations are carried out sequentially: The cans are identified from package markings, and the historical data on contents extracted from the HARWIN database. The cans are then weighed and assayed by Segmented Gamma Spectrometer (SGS), which measures the activity of gamma-emitting nuclides, and a Neutron Interrogator, which provides information on of fissile material. This assay record is compared with the package historical record using a purpose-designed computer system, which compiles all the necessary information on the wastes for record purposes. Any discrepancies are investigated. The can is then opened and placed on a tray for remote sorting, and suitable wastes are transferred to a 500 litre drum. Unsuitable wastes are posted out of the HEC for separate treatment. The cell operator always has a number of cans available so that he can choose appropriate combinations to put in the 500 litre drum to ensure that none of the contents limits are exceeded. When a 500 litre drum is full, an anti-flotation device is fitted to prevent wastes floating during encapsulation, an inner drum lid fitted and the drum is moved to the lidding cell where the outer lid is refitted. After checking the drum surfaces for contamination, it is normally moved to the vault store, but may be diverted out of B462.27. The drums used for the RHILW are of a special double-skinned design to give enhanced protection to the wastes, and reduce dose levels. The annulus between the skins is filled with concrete. UKAEA currently stores Remote Handled Intermediate Level Waste (RHILW) in a number of facilities in the B462 complex, principally in cans within below-ground storage tubes. The waste was received by UKAEA from operations on both the Harwell and Winfrith sites, and from the National Disposal Service (NDS). A new facility (B462.27) has been built to process these wastes, and store them in their disposal containers (500 litre drums) pending construction of a new encapsulation plant, which is currently in the design stages. Active commissioning of the plant was carried out in 2001. B462.27 consists of three principal operations areas: the Head End Cells (HEC), where the waste is analysed and repacked; the Vault Store, where the packaged wastes will be stored, pending encapsulation; and the crane maintenance area. A Flexible Waste Handling Facility (FWHF) is also proposed, which will be able to process certain wastes, such as powders, that require additional treatment before packaging. Within the HEC suite, a number of operations are carried out sequentially: The cans are identified from package markings, and the historical data on contents extracted from the HARWIN database. The cans are then weighed and assayed by Segmented Gamma Spectrometer (SGS), which measures the activity of gamma-emitting nuclides, and a Neutron Interrogator, which provides information on of fissile material. This assay record is compared with the package historical record using a purpose-designed computer system, which compiles all the necessary information on the wastes for record purposes. Any discrepancies are investigated. The can is then opened and placed on a tray for remote sorting, and suitable wastes are transferred to a 500 litre drum. Unsuitable wastes are posted out of the HEC for separate treatment. The cell operator always has a number of cans available so that he can choose appropriate combinations to put in the 500 litre drum to ensure that none of the contents limits are exceeded. When a 500 litre drum is full, an anti-flotation device is fitted to prevent wastes floating during encapsulation, an inner drum lid fitted and the drum is moved to the lidding cell where the outer lid is refitted. After checking the drum surfaces for contamination, it is normally moved to the vault store, but may be diverted out of B462.27. The drums used for the RHILW are of a special double-skinned design to give enhanced protection to the wastes, and reduce dose levels. The annulus between the skins is filled with concrete.

8. Dounreay Silo and Shaft Retrieval even more difficult Throughput orders of magnitude higher Little or no link to records if contained, no numbers! Parallel sludge and solids treatment little sludge characterisation Criticality and analysis issues Have to think in completely different way

10. Overview of Wastes- Liquids Minor process residues organic solvents, may be in solid waste stream Floc from Effluent Treatment Harwell Sludges borderline LLW Specific Waste Streams Harwell Liquors Winfrith Sludges Dounreay Raffinates New waste streams e.g. from NaK/ sodium treatment

11. Harwell Sludges From floc treatment of low-medium liquors Accumulated over decades- settled Main problem is mobilisation of solid mass are samples representative New plant designed and built Incorporates active cementation lab

13. SGHWR Sludge Issues Variety of Sources ion exchange material (Powdex) filter aid decontamination operations Radionuclide Inventory analysis to date not comprehensive difficult to predict questionable how representative Chemical Inventory not comprehensive, e.g. wrt complexants

15. Resolution Trials to develop envelope using real samples takes into account ageing formulation based upon solids range Conservative scoping inventory estimates Scoping encapsulation trials to examine effect of complexants Comprehensive sampling and fingerprinting protocol for retrieved wastes Test blocks from each batch

16. Dounreay Process Liquors High Risk- Drive to Process Removal and Treatment of Liquors PFR Raffinate (203m3) DFR Raffinate (219m3) MTR Raffinate (807m3) currently being encapsulated in DCP ADU Floc (116m3) Heel in Tanks getting it out content chemical and radiological

18. HALS Tank

19. Example Challenge- PFR Raffinate PFR fuel reprocessed at Dounreay 1980-1996 Fuel in “basket” dissolved in conc. nitric basket introduces Zn and Cu Solvent extraction used to separate U/Pu PFR raffinate is the aqueous effluent from the first stage “washing” numerous “batches”, with different sources batches/ contents concentrated by evaporation

20. Composition of Raffinate Uncertainty only old samples- further additions/ removals analysis not comprehensive- e.g. no H-3, acidity or Tank 15- potentially inconsistent re-analysed/ re-assessed- found chloride re-sampling planned Previously considered as HLW on basis that future campaigns would process higher burn-up fuel and be concentrated further- this didn't happen

21. Options for Immobilisation Vitrification standard for HLW until recently reference strategy difficult to transport, or require >£40M plant! Cementation feasible because heat output is relatively low tanks incorporate cooling, but not required product would be within Nirex limits, i.e. can be considered as ILW, not HLW DCP unsuitable (inflexible), DCP2 required

22. Wasteform Development Lab at Harwell

23. Small-scale Scoping Trials Preparation of simulant cement mixes at ~150 ml scale use “Kenwood Chef” and “polypots” Determination of time to initial set Measurement of mix viscosity Measurement of bleed water Observation of change in physical appearance

24. Variables Examined Options for neutralising acid: NaOH solution Ca(OH)2 powder “mix” NaOH and Ca(OH)2 Cementation trials with (over) neutralised nitric acid solution neutralised worst-case simulant liquor effects of key cations independently 1:1 PFA:OPC and 1:1 BFS:OPC

25. Results PFA performed better than BFS 75% Ca(OH)2 (where precipitation started),25% NaOH sequence best- no excess Effect of cations varied with cement and with neutralising agent in one case, Zn delayed set >14 days Defined envelope for confirmatory tests Calcium (Ca) hydroxide is added as a solid. IN strong(ish) acid it dissolves readily, but once pH is near neutral and solids start to form, there is the potential for it to “clump” instead. Points to learn- can’t just look at constituents independently, all this gives is an indication. When you have a multi-anion system such as this raffinate, there are lots of potential combinations to consider- could go on indefinitely! Envelope required as plant additions, whether measured by volume or mass, will have a degree of error. Can’t risk this creating unacceptable wasteforms!Calcium (Ca) hydroxide is added as a solid. IN strong(ish) acid it dissolves readily, but once pH is near neutral and solids start to form, there is the potential for it to “clump” instead. Points to learn- can’t just look at constituents independently, all this gives is an indication. When you have a multi-anion system such as this raffinate, there are lots of potential combinations to consider- could go on indefinitely! Envelope required as plant additions, whether measured by volume or mass, will have a degree of error. Can’t risk this creating unacceptable wasteforms!

26. Formulation Working Envelope

27. Product Evaluation Tests Larger scale mixes of about 1 litre Profile of heat release Mix viscosity/ rheology Matrix density Compressive strength Dimensional stability measure expansion/ contraction Confirm previous measurements Bleed water, Initial set time

28. Calorimeter

29. Viscometer

30. Compression Testing Machine

31. In-situ Microstrain Measurement

32. Rate of heat release

33. Cumulative heat release

34. Microstrain measurements

35. Conclusions UKAEA has a range of historic wastes, and wastes from new operations design process to minimise WM problems Unique problems presented by relatively small-volume (sub)streams Frequently difficult to characterise Develop robust formulation envelopes Need for on-hand cementation and analytical facilities