Quintessa Update June 2009 Header Image

Crowds flock to view the annual Royal Regatta in Henley-on-Thames, UK

Welcome to the June 2009 edition of Quintessa Update, the electronic newsletter of Quintessa Limited.

Dounreay Shaft Post-Closure Environmental Safety Case

Picture of the Dounreay shaft

The D1225 Shaft at Dounreay (right) is a historic facility for intermediate level radioactive waste that doesn't meet modern standards for these types of waste. Dounreay Site Restoration Limited (DSRL) is working towards retrieving the 800 m3 of waste. This has included isolating the Shaft from the surrounding groundwater by grouting the fissures in the rock to form an impermeable curtain - an engineering feat that has won widespread acclaim. Since 2003, Quintessa has been supporting the project by evaluating the long-term safety of the Shaft, including developing and updating a Post-Closure Environmental Safety Case (PCESC).

Graphic of contamination around the shaft

Information from over 200 grouting boreholes around the Shaft has now yielded a uniquely detailed picture of the contamination in the surrounding rock (left). This has been coupled with detailed analysis and modelling of the geological environment, and assessment of human health and environmental impacts, in the latest PCESC. The document, running to over 800 pages, presents a thorough evaluation of long-term effects of the contamination around the Shaft following retrieval of the waste, leading to robust conclusions about its safety. For more information, please contact James Penfold.

Modelling the Alteration of Clay at the Searles Lake Natural Analogue

Searles Lake (below), located near Death Valley, California, is an evaporite basin containing smectite mudstones that have been altered under mildly alkaline conditions (9

Photograph of Searles Lake, CaliforniaGraph of model results

Working with JAEA, Quintessa have developed a model of the system using Quintessa's general purpose modelling tool, QPAC. The model simulates the flows and reactions in the gradually forming sediment column, with flows varying with time as deeper-lying sediments undergo compaction and become more resistive to flow. To construct the model, the QPAC reactive transport module was coupled to a custom model for the evolving hydrogeology that includes a simplified effective stress model to simulate the compaction of the sediments. Due to the highly saline nature of the historic porewaters at Searles Lake, the Pitzer virial model for aqueous activities was incorporated into the model. Pitzer data from the Yucca Mountain database was used in the simulations. The results of the simulations compare well with core samples taken from the site. For more information, contact Steve Benbow.

CO2 Storage Risk Assessment

Graphic of risk assessment methodology

Quintessa's risk assessment tools are now being applied in CO2 storage projects throughout the world. In April 2009 Richard Metcalfe presented Quintessa's TESLA decision support tool and QPAC systems modelling tool at the fourth meeting of the IEA Risk Assessment Network in Melbourne, Victoria, Australia. The TESLA tool implements Evidence Support Logic (ESL) and is used to ensure that decisions are made in a structured and transparent fashion. Decision trees have been developed to help decide upon the suitability of sites for CO2 storage, and for analysing the associated uncertainties. QPAC is used to develop systems models that aid understanding of overall system performance. For more information, please contact Richard Metcalfe.

Sustainable Management of Disused Sealed Sources

Richard Little and Fraser King were invited by the International Atomic Energy Agency (IAEA) to an international workshop on "Sustainable Management of Disused Sealed Sources - Working Towards Disposal" in January 2009. The workshop was hosted by the IAEA, in collaboration with Government of Thailand, as part of its programme on the Safety of Nuclear Installations in South East Asia, Pacific and Far East Countries. Over 60 participants attended the workshop from 23 countries, representing national programmes, regulatory bodies, and implementing and source management organisations. Richard and Fraser presented the findings of the post-closure generic safety assessment (GSA) of the borehole disposal concept for disused sealed sources that they have undertaken on behalf of the IAEA. For more information, please contact Richard Little.

Graphic of borehole disposalPhotograph of people at the workshop

Long-Term Cement Studies

The use of cement and concrete as fracture grouting or as tunnel seals in a geological disposal facility for radioactive wastes creates potential issues concerning chemical reactivity. The elevated pH (>11) of pore fluids in such materials can lead to the instability of minerals in the host rock formation, increased solubility, and changes in the physical properties of the engineered barrier, such as porosity or permeability. The Long-Term Cement Studies (LCS) project is a collaboration between Posiva, JAEA, NDA and Nagra aimed at increasing the understanding of these high-pH cement interaction effects in a repository and surrounding geosphere, in order to develop confidence in the likely future system behaviour.

In the first stage of this project, Quintessa has been working in support of the NDA to model cement hydration reactions and the advective flow of hyperalkaline fluid through a column of fractured rock. The multiphysics code QPAC, including its geochemical reactive transport module, was used to produce models that can accurately replicate the experimental results of these lab-scale studies.

Graph of cement modelling results

The above figure shows results from a model of cement hydration, showing the percentage unhydrated of each of the main clinker components. Markers are experimental measurements; lines show the modelled results presented by Lothenbach and Winnefeld (2006) and the QPAC results. Differences between the modelled results are due to the thermodynamic dataset used by each modelling team.

Henley Schools Environmental Science Competition

Photograph of people at awards ceremony

The Awards Ceremony for the Henley Schools Environmental Science Competition, sponsored by Quintessa, took place recently in the Henley Town Hall. Children from Henley area primary schools presented their diverse range of environmental projects, including bird boxes, gardening, walking and school eco-status. The photograph shows the children together with from left: David Clenshaw (Henley Partnership), Dr. Richard Harding (CEH), Jenni Wood (Deputy Mayor of Henley), Dr. David Hodgkinson (Quintessa), Dr. John Thornley (HSESC) and Jackie Outram (Quintessa).

Three Peaks Challenge

James Penfold

James Penfold is aiming to ascend the highest mountains in Wales, England and Scotland in July, to raise money for Age Concern. What's more, the aim is to do it in just 24 hours! James has been training hard, including running a half-marathon, although he still thinks there will be some blisters involved. If you'd like to sponsor him, please visit