Performance Assessment of a Repository for Intermediate-Level Radioactive Waste Using the Probabilistic System Assessmen
- PDF / 588,476 Bytes
- 8 Pages / 414.72 x 648 pts Page_size
- 97 Downloads / 214 Views
PERFORMANCE ASSESSMENT OF A REPOSITORY FOR INTERMEDIATE-LEVEL RADIOACTIVE WASTE USING THE PROBABILISTIC SYSTEM ASSESSMENT PROGRAM MASCOT J.E. SINCLAIR AND P.J. AGG AEA Technology, 424.4 Harwell, Didcot, Oxfordshire, OX 1 ORA, UK ABSTRACT UK Nirex Ltd is planning the deep geological disposal of intermediate- and low-level radioactive wastes. A site close to Sellafield in Cumbria in the north-west of England has been selected for evaluation, and an extensive programme of site characterization is underway. In support of this programme of characterization, and in preparation for presentation of a postclosure radiological safety case, performance assessment using mathematical modelling has been carried out by the Disposal Safety Assessment Team at AEA Technology, on behalf of UK Nirex Ltd. This paper describes recent developments of the assessment models relating to the groundwater pathway for return of radionuclides to the environment. INTRODUCTION Nirex is responsible for the development of a deep geological repository for the disposal of solid intermediate-level and some low-level radioactive wastes. In 1991, an area near Sellafield, West Cumbria was chosen as the focus for further investigations, following preliminary geological investigations of two sites. The Disposal Safety Assessment Team (DSAT), managed by AEA Technology (AEA) on behalf of Nirex, has been developing postclosure performance assessments in a progressive manner, as an increasing amount of information has become available. The Site Characterisation Programme is delivering information about the subsurface characteristics of the proposed site, and the Nirex Safety Assessment Research Programme delivers data concerning the fundamental physical and chemical processes affecting the safety performance, and mathematical models that can either be used directly in assessment calculations, or help to develop understanding of the system.
Figure 1
Schematic geological cross-section through the Sellafield area in the WSW-ENE direction.
Mat. Res. Soc. Symp. Proc. Vol. 353 01995 Materials Research Society
560
The safety performance requirements are defined by the authorising Departments [1]. These requirements are currently under review. The main quantitative requirement is a target for individual risk of 10-6 per year. To address this requirement, probabilistic system assessment (PSA) is used, and the present paper describes the approach taken. THE DISPOSAL CONCEPT AND SITE CHARACTERISTICS The Nirex concept for deep geological disposal involves excavation of caverns at depth in a stable geological environment; the wastes, set in steel or concrete packages, will be placed in the caverns, which will be backfilled with a cement-based material. For the Sellafield site, attention is being focused on disposal at a depth of about 750m below the surface, in the Borrowdale Volcanic Group (BVG) rocks. This concept makes use of multiple barriers, both engineered and natural, to provide adequate long-term isolation and containment of the waste. The steel or concrete p
Data Loading...
