Quintessa Update Autumn 2008

Welcome to the Autumn 2008 edition of Quintessa Update, the electronic newsletter of Quintessa Limited.

Performance Assessment framework for CO2 storage

C02 PA Framework

Quintessa's framework for integrated Performance Assessment (PA) of geological CO2 storage was presented at a session of the 33rd International Geological Congress in Oslo. Quintessa's methodology uses three existing computer codes: the decision support code TESLA; an online database of Features, Events and Processes (FEPs); and the general-purpose modelling code QPAC. Decision trees are constructed in TESLA to reflect the PA context, the relevant FEPs (via a link to the online database) and supporting evidence from a range of sources, including expert judgement, field and experimental observations, historical experience, and model calculations. The models cover the entire storage system (system-level) and specific system components (detailed level), which can be implemented in QPAC. Read the full story here, or for more information please contact Richard Metcalfe.

Generic Geological Environments for UK Radioactive Waste


In support of the NDA RWMD Disposal System Safety Case, Quintessa has developed system descriptions for a range of generic geological environments. The most recent report illustrated the approaches that might be used to model the groundwater pathway for each environment using the level of information that would typically be available at a desk study stage, such as that envisaged in the on-going MRWS programme, prior to any actual site investigation. The modelling illustrated the role of the geosphere in the post-closure safety case for advectively-dominated and diffusion-dominated environments. Read the full story here, or for further information please contact Sarah Watson or George Towler.

PHREEQC Pitzer database

Kenneth Pitzer

Quintessa was commissioned by NWMO to review the completeness of the thermodynamic database developed by the Yucca Mountain project and to develop software to convert the database format from EQ3/6 to PHREEQC format. The software was developed under Quintessa's ISO 9001:2000 approved software procedures that meet the TickIT software development standards. Read the full story here, or for more information please contact Steve Benbow.

ESL goes to Washington

Hanford RADWASTE storage

Mike Egan recently spent two weeks in Richland, Washington State, as part of a project for CH2M Hill Hanford Group to explore the use of Evidence Support Logic (ESL) for decisions relating to the clean-up of legacy operations at the Hanford site. This included a three-day technical workshop involving USDOE employees, contractors, regulators, and representatives of local and regional stakeholder groups, together with additional participants and observers from USDOE programmes across the USA, including Yucca Mountain, Savannah River and Washington DC. Quintessa's TESLA software was used as real-time support for the event. The visit also included facilitation of a workshop considering international best practice in the management of uncertainty within performance assessment, underpinned by a report written by Alan Paulley. The historical photo shows construction of radioactive waste storage tanks at Hanford. Read the full story here, or for further information contact Alan Paulley.

BIOPROTA Cl-36 Working Group

BIOPROTA Cl-36 Working Group

Within the BIOPROTA international cooperation framework, Laura Limer and Graham Smith are involved in the chlorine-36 working group, playing a key role in the group's recent study: Investigation of Cl-36 Behaviour in Soils and Uptake into Crops. Read the full story here, or for more information please contact Laura Limer.

Assessing Engineered Barrier Preservation - One Step at a Time

Wilhelm Ostwald

The chemical degradation of engineered barriers in radioactive waste repositories often proceed through what is known as an 'Ostwald Step Sequence', named after the pioneering Latvian/German chemist, Wilhelm Ostwald (right), whose eponymous rule states: "if a reaction can result in several products, it is not the stablest state with the least amount of free energy that is initially obtained, but the least stable one, lying nearest to the original state of free energy". Clays and zeolites, for example, tend to form poorly ordered precursors prior to the development of more crystalline forms. Growth of these metastable products may delay the attainment of true equilibrium for hundreds of thousands, or millions of years. Quintessa has used Ostwald's approach, incorporated in the QPAC code, to model the degradation of bentonite barriers, for example the alteration of clay by iron-rich solutions, where the formation of thermodynamically stable non-swelling sheet silicates such as chlorite is delayed by the formation of metastable products, such as berthierine and cronstedtite. For more information read the full story here .