Pergamon o~,-4~9(gs)oools-6 Ann. Nucl. Energy Vol.23, No. 3, pp. 20%215, 1996 Elsevier ScienceLtd. Printed in Great Britain DESIGN PROCEDURES FOR SMALL PEBBLE-BED HIGH TEMPERATURE REACTORS P. H. LIEM National Atomic Energy Agency (BATAN) Center for Multipurpose Reactor, Puspiptek Complex, Serpong, Tangerang, Indonesia (Received 22 February 1995) Abstract--Design procedures for modularized, small-size pebble-bed high temperature reactors have been proposed for the existing fueling schemes, i.e. the multipass, O'VI'O and peu a peu fueling schemes. The well-established HTR-Module (200 MWth) is taken as the starting point in designing the small-size pebble- bed reactors, and its inherent safety features are conserved in the design procedures by imposing safety related, key design constraints derived from the HTR-Module. The burn-up characteristics of both uranium and thorium fuel cycles with fissile enrichment and heavy metal loading identical with the HTR- Module fuel composition are investigated for the small pebble-bed reactor design. Under the proposed design procedure for muitipass and OTTO fueling schemes, small-sized PBRs with fuel burn-up per- formance competitive to HTR-Module and satisfy the safety constraints can be satisfactorily designed. However, although the proposed design procedure for peu a peu fueling scheme can produce a safe small- size reactor design, the burn-up performance in general is inferior to the HTR-Module design. 1. INTRODUCTION Presently, the High Temperature Reactor (HTR) team of the Agency is conducting assessment and prefeasibility study on the utilization of high temperature gas reactor (HTGR) for future industrialization programs, particularly in the fields of: (1) process heat applications, (2) process steam and electricity co-generation, and (3) electric generation for isolated/remote islands (Subki et al., 1992). The modularized, small-size HTGR is yet considered since it could reduce the construction time and cost of manufacturing. Another reason for going to modularized, small-size HTGRs is that while the country has many major islands that need electric power for their economic development, integrating the electric grid might prove to be impractical. On top of that, islands far from the energy resources are burdened with high cost of fuel transportation and management. Several design basic requirements have been proposed such as 10 year continuous operation, small power, maintenance free and remote operation. The power scale is anticipated to be up to 50 MWe (or about 200 MWth) for each module and the reactors are planned for the eastern regions of the country which consist of many small islands. In the early phase of the assessment and prefeasibility study, intensive studies were conducted to investigate the behaviors of several important design parameters as the power and core go to small scale or dimension, respectively. The well-known and yet established design of HTR-Module (200 MWth) (Reutler and Lohnert, 1983) was used as the starting point to design small-size pebble-bed reactors (PBRs). Proper design procedures followed by systematic neutronic, fuel burn-up, and in-core thermal- hydraulic analyses are required in this phase of the study: (1) to ensure that these small-size PBRs still possess an acceptable neutron economic condition, good fuel burn-up performance and fuel utilization, and (2) to maintain the inherent safety features inherited from the HTR-Module design. Along with these efforts, computer code development was also conducted to support these quantitative analyses (Liem, 1994a and Liem, 1995). This paper gives the summary report on the results of the study mentioned above. Two conventional fueling strategies for PBRs, that is, the multipass and the Once-Through-Then-Out (OTTO) fueling schemes were investigated, although the HTR- Module design adopts the multipass scheme. In 207