Summary

The LILW repository at Baita Bihor (
Romania/>/>) was in operation under a license, which is lacking a long-term safety assessment relevant to standards and practices in the European Community.

A technical assistance was provided to experts of the National Commission for Nuclear Activities Control of Romania (CNCAN) by GRS (
Germany/>/>) and IPSN (France) within the framework of this project in order to address the following steps:

• Assessment of the current status of the Baita Bihor repository
• Development of scenarios and conceptual models
• Selection and transfer of relevant computer codes
• Transfer of information and training for utilization of computer codes
• Recommendations for the completion of the long-term safety assessment of the repository

The work performed began first by an assessment of the existing status of the site from regulatory and technical point of view and it was followed by a preliminary analysis al/>/>lowing determining the concerns that had to be more specifically addressed in order to complete the work.

In particular, a list of missing data related to the site and the repository itself (including characteristics of waste packages, buffer and backfill materials, and structures of the storage) was established and a collection of information was carried out in this way.

In parallel, after an on-site investigation and discussion between experts, a preliminary list of base case scenarios was established. These scenarios include particular features, events and processes (FEP) defined in so-called simplified FEP lists drawn up by experts and screened out on the basis of appropriate justifications.

Simplified models were developed and agreed upon and computer codes were then selected, in accordance with these models (EMOS code for migration of radionuclides in the engineered barrier and the surrounding rocks and ABRICOT code for the transfer in the biosphere).

A training session in GRS and IPSN offices allowed Romanian experts to get familiarized with utilisation of these codes, to make some necessary adaptations and to carry out some preliminary calculations dealing with the envisaged scenarios.

Finally, a strategy aiming at completing the assessment work was defined, displaying the main stages of the work still to be performed, in compliance with the requirements of CNCAN, and putting stress on the main features that should govern the project.

Main Results

From the assessment performed within the present project the following main results have been obtained. The results revealed several features, which are of importance for the continuation of the study.

a) Inflow rate

The inflow rate is a key parameter of the models proposed for the reference situation. If any, water enters the waste emplacement area at a given rate. To estimate the potential amount of contamination carried by water leaving the system, it is compulsory to have a right idea of the inflow rate, which is the only source of contaminant transport in the considered case

b) Sorption on backfill

Sorption on bentonite backfill in the emplacement galleries is one of the relevant safety factors in the repository. Thus, the sorption parameters (Kd values) for all relevant radionuclides should be known for the specific bentonite used in Baita Bihor repository. As the bentonite backfill in Baita Bihor does not fill up the entire open voids in the emplacement galleries, the effective amount of bentonite, i.e. the amount that actually takes part in the sorption process, is also a key factor.

In the future a more sophisticated method of backfilling could be applied, which might result in a tight enclosure of the waste packages, allowing only diffusive transport through the backfill. In this case, a key parameter will be the efficiency of the backfill. It depends on the type of selected bentonite and the quality of filling up the voids in the galleries. In particular, it must then be assured that the swelling of bentonite results in an effective enclosure of all waste containers and in a sufficient swelling pressure.

c) Strategy for the future

One of the major results of the present project is the development of a strategy for a future integrated performance assessment (IPA). It consists of the following iterative approach:

• First: Start with an assessment using simplified assumptions as proposed for the base case scenarios and with a set of mostly generic data. Comparison of the results of code calculations with appropriate target values.
• Second: Verification of the main assumptions made, improvement of the knowledge of parameter values and overall justification of the selected situations, including the likelihood of the reference scenario.
• Third: Assessment of the impact of more sophisticated scenarios, based on the results of the previous work. At this step, it is also proposed to consider a conventional scenario where the rock cover has been totally eroded, in order to investigate the impact of long-lived waste.
• />/>Eventually definition of a maximum waste content of the repository and of waste acceptance criteria.
• Depending on the outcomes, initiation of a further iteration step. In this step the list and the definition of scenarios should be completed and the set of parameter values be modified.