A new safety principle for the SLOWPOKE reactor

Slowpoke-2 (LEU core) is a pool type nuclear reactor with a maximum thermal power of 20 kW. It uses a pelletized uranium oxide fuel (19.9% enrichment) and provides a useful high neutron flux in the order of 1012 n.cm-2s-1. The key safety features built into the reactor design are the strictly limited amount of excess reactivity and the negative reactivity feedback characteristics, which provides a demonstrably safe self-limiting power excursion response to large reactivity insertions. However, the limited amount of excess reactivity also limits the continuous prolong reactor operation at full power. With a 3.7 mk excess reactivity, the reactor can operate for about one day at the full power, 20 kW, before this excess activity is lost due to temperature effects and Xe poisoning. A new safety concept is proposed in this paper to extend the continuous operation time to months by increasing the excess reactivity from 4 mk to 6 mk. This new concept has been demonstrated using a Matlab/simulink model of Slowpoke-2. (author)