Euradwaste '08 - EU Bookshop - Europa
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Euradwaste '08 - EU Bookshop - Europa

Euradwaste '08 - EU Bookshop - Europa Euradwaste '08 - EU Bookshop - Europa

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that provided by various national safety cases. Research as part of NF-PRO addresses the near-field processes for repository concepts in clay, granite and salt host rocks that are currently under investigation within the European Union and is focused on assessment of many of the most significant safety-related issues. The NF-PRO consortium consists of 40 leading European research organizations, waste management agencies/implementing organizations and technical safety organizations. The structure and areas of concern are shown in Figure 1. Fig. 1 NF-PRO’s main project components and structure 2. Complementarity – national safety cases vs. EU projects In recent years, substantial progress has been made in the scientific understanding of key processes affecting the overall performance of the near-field system. This has been achieved both within various EU projects that have focused on particular components or processes associated with disposal systems, and within national programmes where all aspects must be considered in a safety case. National projects typically work on a single system – a specific host rock (and often a specific site), with a particular design for the excavation and layout and for the EBS that are tailored to the rock engineering and geochemical requirements and to the relative contribution to isolation and retention required for the system components in question. The safety case integrates all this information and strives for completeness, full assessment of uncertainties and identification of areas in which more focused studies are needed for the next stage of repository licensing. One benefit of EU projects is that they demand, in contrast, a certain level of horizontal integration through cooperation of scientific groups across many national programs. Although there are clearly great differences in the EB materials, the repository design and the host rock in the various programs, there are also sufficient similarities in a number of areas that the cross-pollination is valuable. The exposure to studies done by other groups helps to counter the inward-looking tendencies of national safety cases. In addition, one may confront challenging new results that may bring into 214

question certain assumptions, as well as providing, eventually, a larger set of studies that aid in reaching scientific consensus on various issues. Unlike the national safety cases, EU Projects such as NF-PRO do not attempt to achieve completeness in the sense of covering all relevant areas at an appropriate level of depth. Instead, the project scope is a natural outcome of the respective interests of the organizations involved and the project must seek to develop appropriate shared goals and also accept the inability to tackle the completeness question, which is best left to the safety cases of the national programs that may put the NF-PRO results to further use. One of the distinguishing features of NF-PRO also lies in the communication that has been established in the project between groups doing detailed process investigations (the four hexagons on the sides in Figure 1) and those doing broader assessments of disposal systems (i.e. Performance Assessment)). Here again one sees the different roles played by those who are discipline-focused and seek ever greater detailed understanding, which complements the perspective of those who try to provide a balanced synthesis of information that clarifies how all the repository components and associated processes interact. 3. NF-PRO findings from a PA perspective The main findings of NF-PRO seen from the perspective of PA are summarised here. Specialists in the various scientific disciplines may have different views from PA specialists regarding the significance of various project achievements, but from the PA perspective, it is considered that both the quality of the scientific contributions and the impact on the system performance are relevant and these determine the emphasis presented here. It is emphasized that the summary of findings and recommendations for future work must be considered as guidelines that need to be evaluated in the context of the particular disposal system in question and that the absence of a comprehensive total system PA analysis in the project (due to the NF focus), requires that other considerations may also influence the focus and even the necessity for R&D in a given area. The details of the work are discussed in Grambow et al. [8], Arcos et al. [9], Villar et al. [10], Aranyossy et al. [11], and Johnson et al. [12]. 4. Release of radionuclides from the waste matrix HLW Studies performed within NF-PRO have improved understanding of the impacts of corrosion products and clay on the long-term dissolution rate of HLW. These studies indicate significant transient impacts on the rate (the rate may be initially similar to the high initial rate in distilled water), but a number of results suggest that the long-term rate will nonetheless be very low. During this transient only a relatively small fraction of the glass would dissolve before the residual rate is attained. The details of the transient are of interest to the extent that understanding something about the reactions involved may help to explain better the processes that control the long-term rate. The initial or transient glass dissolution rate (about 100 to 1000 times higher than the long-term or residual rate) is often used in assessment calculations, where it is applied to the entire duration of the dissolution process and is referred to as a “pessimistic” value or is used in a sensitivity analysis context. In the context of communicating the results of safety assessments, it appears that it would be consistent with the findings to use two dissolution phases accounting for the initial rate and then the residual rate. Use of the initial rate for the entire duration can be considered solely as an illustration of how the system behaves if the waste form dissolves very rapidly, i.e. as an illustration of 215

that provided by various national safety cases. Research as part of NF-PRO addresses the near-field<br />

processes for repository concepts in clay, granite and salt host rocks that are currently under investigation<br />

within the European Union and is focused on assessment of many of the most significant<br />

safety-related issues. The NF-PRO consortium consists of 40 leading European research organizations,<br />

waste management agencies/implementing organizations and technical safety organizations.<br />

The structure and areas of concern are shown in Figure 1.<br />

Fig. 1 NF-PRO’s main project components and structure<br />

2. Complementarity – national safety cases vs. <strong>EU</strong> projects<br />

In recent years, substantial progress has been made in the scientific understanding of key processes<br />

affecting the overall performance of the near-field system. This has been achieved both within various<br />

<strong>EU</strong> projects that have focused on particular components or processes associated with disposal<br />

systems, and within national programmes where all aspects must be considered in a safety case. National<br />

projects typically work on a single system – a specific host rock (and often a specific site),<br />

with a particular design for the excavation and layout and for the EBS that are tailored to the rock<br />

engineering and geochemical requirements and to the relative contribution to isolation and retention<br />

required for the system components in question. The safety case integrates all this information and<br />

strives for completeness, full assessment of uncertainties and identification of areas in which more<br />

focused studies are needed for the next stage of repository licensing.<br />

One benefit of <strong>EU</strong> projects is that they demand, in contrast, a certain level of horizontal integration<br />

through cooperation of scientific groups across many national programs. Although there are clearly<br />

great differences in the EB materials, the repository design and the host rock in the various programs,<br />

there are also sufficient similarities in a number of areas that the cross-pollination is valuable.<br />

The exposure to studies done by other groups helps to counter the inward-looking tendencies<br />

of national safety cases. In addition, one may confront challenging new results that may bring into<br />

214

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