Effect of Neutron Absorbers Mixed in or Coating the Fuel of a 1-MWt Lithium-Cooled Space Reactor

The goal of this study was to determine the effect of various neutron poisons (boron, dysprosium, erbium, and gadolinium) on a 1‐MWt, lithium‐cooled liquid‐metal reactor. The isotopes were considered to be in‐fuel poisons, as well as poisons coating the fuel. One way to quantify the effectiveness of a poison in meeting accident‐condition requirements is by defining the safety margin as the difference between keff at the beginning of life and keff during the accident scenarios. The isotope that showed the most potential in increasing the safety margin for the wet‐sand/water case was 157Gd. The safety margin was 10%–20% greater using 157Gd as an in‐fuel poison as opposed to a coating, depending on the poison quantity. However, the most limiting condition (i.e., the accident scenario with the highest keff, thus the lowest safety margin) is when the reactor is submerged in wet sand. None of the isotopes considered significantly affected the safety margin for the dry‐sand case. However, the poison isotopes con...