Leach Testing of Materials for Waste Acceptance

Transcription

1 Leach Testing of Materials for Waste Acceptance Presentation to: LLWR Customer Forum 2014 Date: 21st May 2014 Dr Frank Taylor - ESC Technical Manager

2 Overview Introduction Waste Acceptance Criteria Levels of control of non-radiochemical contaminants: Categories of control; Leach testing. What is leach testing? Introduction to the new leach testing methodology at the LLWR: When is leach testing required? Why have we changed how we do leach testing? Assessment model; How do we do leach testing now? Summary of developments. Conclusions.

3 Introduction Waste Acceptance Criteria Waste disposed of to the LLWR is controlled primarily by Waste Acceptance Criteria (WAC). The latest version of the LLWR WAC (Version 4.0, March 2014) became live on 31 st March This version of the WAC introduced new controls on nonradioactive contaminants present in waste, in line with Environment Agency (the Agency) requirements for the LLWR to manage the hazardous chemical properties of LLW by providing no less stringent protection than at hazardous waste sites.

4 Levels of Control of Non-radiochemical Materials Category 1 Materials not requiring control but the quantities of which must be recorded in the relevant section of the Waste Consignment Information Form (Reference: WSC-FOR-WCI). Examples of Category 1 materials include: Aluminium; Chromium, in metal as an alloy; Cobalt, as an alloy; Copper, as an alloy; Fluoride; Iron; Zinc, e.g. in galvanised metals.

5 Levels of Control of Non-radiochemical Materials Category 2 Materials requiring an allocation. These may be accepted for disposal subject to there being sufficient capacity for these materials at the Low Level Waste Repository. This will be assessed based on information in Waste Characterisation documents and in the UK Radioactive Waste Inventory. Examples of Category 2 materials include: Arsenic; Beryllium; Boron; Cadmium; Lead; Mercury.

6 Levels of Control of Non-radiochemical Materials Category 3 All other Hazardous Waste, Hazardous Substances and Non- Hazardous Pollutants (including asbestos and Man-Made Mineral Fibres). These may be accepted for disposal but the following information will be required: Details of the components that make the waste hazardous, their physical form and the levels at which they are present; Total weight of each such component in each Waste Consignment; Any treatment, conditioning or packaging taken to reduce their potential environmental impact and the results of any Leaching Test using a method agreed with LLW Repository Ltd.

7 Levels of Control of Non-radiochemical Materials Leach Testing The general requirement for leach testing hazardous substances and hazardous waste has been removed from the WAC and is replaced with a requirement to examine certain wastes by a Leach Test agreed with LLW Repository Ltd. This is a specific requirement under Subsections L1.7, L1.8, L1.17 and L3.9 of WAC v.4 (described later). A new leach testing methodology has been developed to support the WAC with regard to these Subsections.

8 What is Leach Testing? (1) Leach testing, in the context of radioactive (and other) waste management, supports WAC. It involves a laboratory procedure that measures the rate of loss of mobile contaminants from a body of waste. The determined rate of loss of contaminants informs the operator of a waste management facility if the waste intended for disposal can be managed safely.

9 What is Leach Testing? (2) Standard leach tests typically compare the concentrations of controlled contaminants in test leachates with: Environmental Quality Standards (EQS); or Drinking Water Standards (DWS). The new LLWR leach testing methodology does not make this comparison directly as it did in the past. To support WAC v.4 our leach testing procedures determine kinetic parameters required for our mathematical assessment models to enable us to manage non-radiological contaminant capacity as well as comply with all other aspects of the WAC.

10 When is Leach Testing Required? - 1 WAC v.4 Subsection L1.7: The non-aqueous content of any liquid in the waste shall be conditioned, prior to Consignment, such that no visible oil or grease will be released by leaching as demonstrated using a leach test agreed with LLW Repository Ltd.

11 When is Leach Testing Required? - 2 WAC v.4 Subsection L1.8: Soluble Solids present as Bulk Chemical Compounds greater than1 kg mass in a Waste Consignment may be accepted for disposal Such materials shall be fixed, prior to Consignment, in a Suitable Solid Matrix that will not readily release that component as demonstrated using a Leach Test agreed with LLW Repository Ltd.

12 When is Leach Testing Required? (3) WAC v.4 Subsection L1.17: Under Category 3 materials (Hazardous Waste, Hazardous Substances and Non-Hazardous Pollutants (including asbestos and Man-Made Mineral Fibres) - Any treatment, conditioning or packaging taken to reduce their potential environmental impact and the results of any Leaching Test using a method agreed with LLW Repository Ltd. It is envisaged that in most circumstances, where a capacity for the material concerned has been calculated, a leach test will not be required.

13 When is Leach Testing Required? (4) 4. WAC v.4 Subsection L3.9 (Transport Regulations): Classification LSAIII packages for consignment to the LLWR are acceptable, subject to confirmation of a Leach Test using a method agreed with LLW Repository Ltd

14 Why Have We Changed How We Do Leach Testing? We need a methodology that takes cognisance of the physical and chemical conditions of in the LLWR. We need a methodology that relates to our mathematical assessment modelling approach to capacity management.

15 Assessment Model - for Determination of the Capacity of the Repository for Contaminants Water through-flow Corrosion: Diffusion: f (t) = km B f (t) = k(c B -C N ) Bound f(t) Near Field Where MB is the mass of contaminant in the bound compartment, and CB and CN are contaminant concentrations in porewater in the bound and near field compartments, respectively. Leach tests can be used to determine k. A Simple Compartment Model Corrosion and Diffusion

16 Near-field Concentration Leach Tests Where Solubility Limitation Occurs X X X Solubility limit 0.14 X X 0.06 X 0.04 Gradient proportional to k 0.02 X Time Initially, the concentration increases approximately linearly with time. The gradient of the slope is proportional to the rate constant k. Once solubility limitation is reached, the concentration is held constant at the solubility limit. Batch static leach tests, such as the modified Tank Test used in our new methodology, can be used to provide estimates of the solubility limit and the rate constant k.

17 Near-field Concentration Leach Tests Where Solubility Limitation Does Not Occur X X X X X X X Time The initial gradient is once again proportional to the rate constant k, and can be obtained from static batch tests, as discussed previously. Following the peak in the near field concentration, the exponential decrease of concentration with time depends on a second rate constant (m) which can be estimated using a dynamic upflow leach test as used in our new methodology.

18 How do we do Leach Testing Now? Waste enquiry/variation form submitted Leach testing procedure agreed with LLWR Laboratory analysis conducted to determine required parameters Parameters modelled to determine the nonrad capacities required by the waste New 2-stage process Acceptability of the waste determined on the basis of capacity used

19 Leach Testing Methodology Summary of Developments We have retained three modified laboratory methods for the determination of required transport parameters: Static monolithic test; Static granular test; Dynamic up-flow test. We have developed a modelling process to calculate capacities required for contaminants in waste using constants determined using leach testing. The process of determining the appropriate test method and incorporating the results into capacity modelling is currently undergoing a trial (from March 31 st when WAC v.4 went live, until the end of July 2014). During the trial process period, LLW Repository Ltd will assist and advise consignors to procure leach testing and modelling services while a full formal service is developed.

20 Conclusions The new approach to non-rad management provides a proportionate level of control over non-radioactive contaminants; Is representative of conditions at the LLWR site; Eliminates the need to carry out leach testing of most wastes; Where leach testing is still required, the new testing methodology: Supports the WAC; Enables the generation of a database of information to inform future waste management decisions. The current methodology trials run from 31 st March to 31 st July 2014.