Concept Design of Pebble Catcher of Pebble Bed HTGR with Fast Pebble Discharge System

摘要

High temperature gas cooled modular reactor (HTGR) is an advanced reactor. It is passively safe against the loss-of-forced-cooling accident. In order to be passively safe, low mean core power density has to be adopted. This leads to much larger RPV and relevant surroundings comparing with PWR of the same power. Obviously, how to decrease size of RPV and relevant surroundings is a key to make HTGR more economical. One way is to increase the core power density. But this may compromise its inherent safety performance. In 2002, a new method was put forward to solve this problem. The basic idea is: 1) Under normal operation, the reactor core is of high power density; 2) When loss-of-forced cooling accident happens, pebbles are discharged into a pebble catcher by gravity, which make the reactor core in low power density; 3) Pebble catcher should prevent second criticality from happening and decay heat can be safely removed by passive ways. This paper presents the concept design of a pebble catcher. The result shows that the pebble catcher can prevent the second criticality from happening and decay heat can be removed passively.