HTGR Knowledge Base

Conference Article: Seismic behavior of the core cavern of a HTGR with pebble bed core

Abstract

The seismic response of a great pebble bed HTR has been examined theoretically by preliminary calculations. The total system to be considered, consisting of the core and the side reflector, is restrained by spring pack assemblies. The calculations of the natural frequency of the pebble bed based on different theoretical models led to values of 6 to 10 Hz or higher. This is close beyond the region of maximum magnification. The natural frequency of the system side reflector-pebble bed was found to be approx. 10 Hz or more, which assures rigid body behavior. The seismic behavior of the KLAK shut down system has been investigated experimentally. Most of the KLAKs will remain inside the pebble bed during an earthquake, they will be removed totally only from a flat layer of the pebble bed surface. To get more exact information about the pebble bed reactor seismic response the calculations shall be checked by model experiments with different scaled-down HTGR-core models. The main concerns of these investigations are: dynamic behavior of the pebble bed. Sloshing of pebbles at the core surface and at higher acceleration levels possibly inside the core. Dynamic response of the side reflector and its interaction with pebble bed and spring packs. Collisions between the blocks within the top reflector and between the outer blocks of the top reflector and the side reflector. And adaption of the parameters to different computer codes to calculate the dynamic behavior of the reactor more precisely.

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Reference:

IAEA IWGGCR specialists' meeting on gas-cooled reactor seismic design problems and solutions. San Diego, CA (USA). 30 Aug - 1 Sep 1982

International Atomic Energy Agency, Vienna (Austria).

IWGGCR--6, pp:119-132