HTGR Knowledge Base

Conference Article: Potential and limitations in maximizing the power output of an inherent safe modular pebble bed HTGR

Abstract

The past development of modular pebble-bed HTGRs in Germany led to two well-defined reactor designs, namely the 200 MWth HTR-MODUL and the 250 MWth HTR-100 by SIEMENS/Interatom and ABB/HRB, respectively. Recently the South African utility, ESKOM, decided to include the pebble-bed HTGR design as a future supply option. In contrast to the German designs, ESKOM prefers a direct cycle helium turbine system on the power conversion side. This imposes certain modified boundary conditions on the reactor design and enables a higher plant efficiency. Nuclear and thermal-hydraulic investigations have been performed at KFA-ISR to determine the potential and limitations of increasing the unit thermal power output of the reactor compared to the former german designs. In doing so an upper limit for the maximum fuel element temperature of 1600 deg. C was observed. The impact of all modifications in view onto the efficiency of the nuclear control and shut-down systems was also considered. The results obtained so far demonstrate the well-adapted and conservative design of the SIEMENS HTR-MODUL within a 10% safety margin to the higher region. The introduction of graphite noses has a remarkably positive influence on the shut-down and control systems, while the positive effect on the maximum accident temperature depends strongly on the fast neutron dose-related thermal conductivity of the nose graphite. Considering the fact that effective conductivity of the pebble-bed core is maintained at high temperatures, the temperature effect due to the noses are of secondary influence at this point.

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Reference:

Technical committee meeting on high temperature gas cooled reactor technology development. Johannesburg (South Africa). 13-15 Nov 1996.

International Atomic Energy Agency, Vienna (Austria)

IAEA-TECDOC--988, pp:229-246