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Fast reactors exhibit some unique characteristics related to safety in comparison to thermal reactors. At first glance, it might appear that achieving exceptional safety in a fast reactor might be more challenging than in a thermal reactor, considering that sodium-cooled fast reactors (SFR) have a higher core power density, the neutron lifetime is shorter, the effective delayed neutron fraction is less, the core is not arranged in its most reactive configuration, the sodium void effect is usually positive, and sodium interacts rather violently with air or water. On the other hand, the boiling point of sodium is sufficiently high that the reactor can be operated near atmospheric conditions (eliminating the massive pressures required for water-cooled systems), sodium has a very high heat capacity and thermal conductivity, the neuron mean free path is sufficiently long that spatial power shifts are negligible, and xenon poisoning is a non-issue. Furthermore, it has been demonstrated that passive safety features can be more easily incorporated than in the thermal reactor systems. |
