Applying risk informed methodologies to improve the economics of sodium-cooled fast reactors

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, February 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 94-97).In order to support the increasing demand for clean sustainable electricity production and for nuclear waste management, the Sodium-Cooled Fast Reactor (SFR) is being developed. The main drawback has been its high capital and operating costs in comparison with traditional light water reactors. In order to compete, the SFR must be shown to be economically competitive. This study makes use of the proposed Technology Neutral Framework (TNF) being developed by the U.S. NRC. By applying this risk-based approach to safety, rather than the traditional approach of applying deterministic requirements, it will be shown that significant savings can be realized without compromising fundamental safety. A methodology was developed using the Technology Neutral Framework to judge design alternatives based on risk significance that provide acceptable safety within the framework at less cost. The key probabilistic metrics of Risk Achievement Worth and Limit Exceedence Factor will be used to assess whether a system or component plays an important safety function. If not the system, structure or component either can be eliminated, modified or its safety grade can be reduced resulting in cost savings. In addition, assessments were made to determine how to improve thermal efficiency by raising reactor exit temperature and by applying other design alternatives to reduce costs as evaluated on a safety, reliability and economic basis.(cont.) This methodology was applied in a series of case studies demonstrating the value of the approach in design. The probabilistic risk assessment, the reference economic model and the Technology Neutral Framework tools required for this methodology are described. A reference economic model for a pool-type SFR was developed using the G4-ECONS model since it is an acceptable standard model for economic analysis. Since cost predictions for sodium cooled fast reactors are highly uncertain, the results of the economic analysis are used to estimate the relative improvement in cost as a function of the design alternatives proposed by the TNF methodology approach. This study used generic and comparative numbers for the ALMR and SPRISM reactors for cost of components of the SFR, to identify capital cost drivers for further study and cost reduction. For comparative purposes, the light water reactor (LWR) economic model in the G4-ECONS model was used and benchmarked to current LWR data. As a result of the case studies in which the methodology was applied, it was shown that the capital cost of the SFR could be reduced by almost 18% ($336 million) over the reference design and the levelized generating costs could be reduced by over 10% (almost 1 cent/kw-hr). These savings come largely from improvements in thermal efficiency, elimination of the energetic core disruptive accident as a design basis event and simplification of the reactor shutdown system based on risk analysis and safety significance. Should this methodology be applied to the entire plant design, it is expected that significant additional savings could be identified.by Christopher C. Nitta.S.M