The Nuclear Decommissioning Authority

  Data Packs for Use in the Elicitation of Solubility and Sorption of Carbon Species in a Cementitious Near Field and for Sorption in the Far Field J. Small, O. Thompson, and D. Trivedi. NNL (08) 9537 Issue 2  14844672 2011 (1.10mb)
The process of analysing the performance of a geological disposal facility and demonstrating that it will remain safe, to an appropriate level of confidence, is termed a performance assessment (PA). Probabilistic approaches to assessing data input uncertainties to PA require that a distribution of data ranges is defined. The Nuclear Decommissioning Authority (NDA) have developed a formalised approach of expert judgement to elicit data for PA. For this process a data pack of information is provided to the experts summarising experimental and other data and information. This data pack contains information and data for elicitation of solubility and sorption of carbon species in a cementitious near field and for sorption data in the far field. The data resulting from the elicitation are intended to be used to undertake PA of the impact of carbon-14 (14C) through a groundwater pathway in generic assessments of a geological disposal facility in different types of host geological formation. Unlike most other radionuclides 14C sorption and solubility is influenced by the much greater concentration of stable carbon isotopes 13C and 12C and interpretation of experimental studies which provide sorption and solubility data is more complex. In addition the representation of 14C sorption and solubility by PA models requires further consideration to account for isotope exchange and dilution. A further complexity concerns the possibility that 14C may be released from radioactive wastes in either inorganic or organic forms. With these points in mind this particular data pack provides a wide range of background information for the experts to consider in addition to a compilation of experimental data. For the relevant near field and far field conditions the data pack provides information and discussion on the following: ? the chemical forms of inorganic and organic 14C; ? carbon isotope exchange; and ? the mechanisms of removal of 14C from solution.

  Glass durability in high pH environments: A review of the literature C. Utton, R.J. Hand, N.C. Hyatt and S.W. Swanton SERCO / TAS / 003133 / 001  13859562 2011 (2.35mb)
Vitrification of some intermediate-level UK wastes is currently being investigated as a potential option for waste immobilisation and conditioning. Vitrification is being considered as it may offer the potential benefit of volume reduction compared to immobilisation with cement grouts. It may also reduce uncertainty associated with the long-term degradation of some wastes such as organic materials. One option for the disposal of the resulting vitrified ILW product would be to place it in a geological disposal facility (GDF) in a high pH environment with cemented ILW and a cementitious backfill. However, at present there is a lack of information on vitrified waste-cement interactions, in particular the consequences of the high pH of cement pore solution. Hence this report reviews the current understanding of the aqueous durability of vitrified and vitreous wasteforms with a particular emphasis on the effects of highly alkaline conditions as an input to future optimisation studies for a GDF. Durability test methods are reviewed and, as most durability studies on glasses have been conducted on vitrified high-level waste (HLW), the durability of vitrified HLW along with other vitrified and vitreous wastes is examined in detail. The performance of glasses in cement and concrete is also reviewed. Overall the literature suggests that highly-alkaline conditions, such as those provided by a cement-based near field, could have an adverse effect on the performance of vitrified ILW<br /><br />

  Implications of RWMD 500 year waste container integrity target compared with 150 years for container design and cost BT Swift, N Simpson, C-F Tso, NR Smart, PB Bamforth, M Jones and M Hubbert SERCO / 005084 / 001, Issue 1  15832227 2012 (2.95mb)
The Nuclear Decommissioning Authority (NDA) concepts for storage and disposal of packaged waste have evolved over the last few decades, so that both the maximum potential period of interim storage and the maximum potential period of exposure to an underground operational environment before a disposal facility is closed have been extended. Previously, containers were expected to maintain their integrity during interim storage for a period of up to 50 years, followed by 50 years in the operational period of a geological disposal facility (GDF) and 50 years after backfilling to allow for decay of short-lived radionuclides. This is consistent with the target of 150 years given by regulatory guidance. More recently, the maximum timescales have been extended. The current Generic Waste Package Specification (GWPS) calls for a target total container lifetime of 500 years, based on extended periods of up to 150 years of surface storage and up to a few hundred years after placement in a GDF prior to potential backfilling. The issue considered in this report is whether current designs of intermediate-level waste (ILW) containers will maintain their integrity under normal conditions for the extended total periods indicated by the current GWPS (i.e. 500 years compared to 150 years), and, if not, whether designing and manufacturing containers with the modifications required to ensure the required integrity under normal conditions has significant cost implications for waste producers.<br /><br />

  118366-09-Investigation-into-bolt-shear-i1-130911 - FINAL COPY (3.76mb)
Evaluation of lidbolt performance in Shear<br />

  1222g-1 v1 Neutron Poisons (909kb)
This report has been produced under the Upstream Optioneering work programme in support of RWMD’s work programme. The Upstream Optioneering project was set up to help identify and implement opportunities for improved management of higher activity radioactive waste in the UK. The aim of this document is to inform the Upstream Optioneering project by considering the potential use of neutron poisons as a criticality control in waste packages. It also aims to provide input to waste producers on potential opportunities available regarding neutron poisons and their uses in waste packaging. This study provides details of the potential business drivers that may be realised should such a strategy be adopted for waste packaging in the UK, highlighting benefits where relevant. Potential neutron absorbing materials which could be used as poisons are discussed and both ILW and spent fuel packages ultimately destined for a GDF in the UK have been considered in this work. Three generic scenarios that incorporate neutron-absorbing materials into waste packages have been identified: blending with the waste; use as an immobilisation matrix or package filler; and use as a package material. Other methodologies, e.g. strategic emplacement of wastes, have also been identified and alternatives to the use of neutron poisons which could be pursued for criticality control are presented

  124857-06 Breakup vs Flow i1 020911 - FINAL COPY (3.57mb)
Breakup vs Flow i1 020911 - FINAL COPY

  14500-TR-0006 Iss05 Approved June 2012 (1.56mb)
Human Factors and Behavioural Safety Approach for Managing Risks Associated with Nuclear Waste Repository Construction and Commissioning<br />

  18025TR001_Marine_Issue2 (6.83mb)
This report outlines the assessment model and associated data for a generic coastal (estuarine and open shoreline) and marine (nearshore and offshore) environment representative of the UK which complements RWMD’s post-closure biosphere assessment model for groundwater releases to terrestrial environments (Walke et al., 2013). Such a capability will (i) provide RWMD with quantitative evidence to support the principal focus on terrestrial releases (particularly for more generic assessments) and (ii) ensure that RWMD has the capability, if and when required, to undertake assessments for coastal sites that are more directly representative of specific locations. Assessment models for the marine environment need to strike a balance between being as simple as can be justified, erring on the side of conservatism, while also representing the features and processes required to reflect UK coastal systems. The approach to develop and justify the models is based on the guidance developed through the International Atomic Energy Agency’s BIOMASS programme and the European Union (EU) BIOCLIM project.<br /><br />

  2010-15-1B Peer Review of RWMDs DSSC Analysis of Comment Resolution Version 1 1 - 12 Jan 2011 (233kb)
RWMD has developed a suite of safety case reports for a future geological disposal facility (GDF), referred to as the generic Disposal System Safety Case (DSSC). The DSSC addresses the safety of waste transport and disposal operations, as well as the safety of the GDF in the long term after the facility has been closed. Because a specific site for a GDF has not been identified, the DSSC is based on a set of assumptions regarding possible host rocks and facility designs. In accordance with best practice in the development of such safety cases, RWMD has commissioned an external peer review of the DSSC reports. The peer review has been conducted in two phases by a multi-disciplined panel of suitably qualified and experienced reviewers. The first phase of peer review involved examination of draft versions of the DSSC reports during May and June 2010. In the first phase of its review, the peer review panel identified a large number of comments and some reservations on the draft DSSC reports and on some of the analyses they presented. A report from the first phase of peer review was completed and provided to RWMD on 1 July 2010. Following the first phase of peer review, RWMD continued to develop the DSSC documents to address comments received from the peer review panel and from various other groups and organisations. A second phase of peer review panel has been coordinated by TerraSalus Ltd. This involved reviewing later drafts of the DSSC documents, and examining the extent to which peer review comments had been addressed. RWMD has addressed most of the key peer review comments. The presentation of the aims, objectives and achievements of the DSSC has been improved and now seems appropriate. The DSSC collates and integrates a considerable body of information from across the waste disposal programme and for a wider range of wastes and potential waste materials than has been considered previously in the UK.

  3D thermal modelling of waste packages in backfilled vaults June 2010 (7.25mb)
AThe work described in this report is an extension of the earlier modelling: firstly, to take into account 3-dimensional (3D) effects in the waste packages, so that effects of the backfill, wasteform and packaging can be distinguished; secondly, to examine the effects of changing material property data; and finally to apply the 2D model to other storage configurations. The Finite Element code Abaqus (version 6.7.2) was used. This work includes detailed finite element modelling in 3D of three waste packages planned for emplacement in the repository: . a stillage containing four 500 litre Drums of cemented liquor waste . a side lifting (round-cornered) 3m3 Box containing cemented solid wastes . a corner lifting (square-cornered) 3m3 Box containing cemented sludge waste. Three variant cases of the 2D Reference model were then explored: . Variant 1: to examine the effect of assuming backfill 50% saturated with water (instead of fully saturated) . Variant 2: with 7 stacks of corner lifting 3m3 Boxes only, all with the same heat load (but different to the heat load in the Reference Case) . Variant 3: as Variant 2 but with a single ?hot? box containing limiting case inventory surrounded by all the other boxes with ?standard? inventory. Variant 1 gave results that were only 2 C hotter than the Reference case, again peaking within weeks of backfilling. Variant 2, however, gave a much higher and later peak of 44 C at 272 years from the start of backfilling, due to the different decay heat characteristics of the cemented sludge. For Variant 3 a simplified 3D model of the repository was created to study the local effects of a single hot box in more detail and hence derive correction factors which were then applied to the 2D model. The peak temperature of the hot box was predicted to be 57C at around 250 years.