The XeNRI project supports the development of the Helium-3 Enhanced Negative Reactivity Insertion (HENRI) prototype built and tested at Oregon State University. The HENRI prototype is being tested for the Transient Reactor Test (TREAT) Facility at Idaho National Laboratory (INL). The purpose of HENRI is to shorten the transients of TREAT to be more representative of a light water reactor Reactivity Insertion Accident (RIA) by injecting helium-3, a strong neutron absorber, into the core, which rapidly decreases the power of the reactor. To properly predict the effects HENRI will have on TREAT, the density evolution of helium-3 is crucial to understand completely. The XeNRI project looks to characterize the density effects due to the neutron absorption reaction. The density changes due to the gas physics have already been characterized by OSU with experimentation and computer modeling.

In an effort to characterize the density changes observed in helium-3, the XeNRI project aims to investigate the feasibility of breeding xenon-135 in the OSU TRIGA reactor; investigate the feasibility of using xenon-135 in the OSU TRIGA reactor to characterize the effects of helium-3 in the TREAT reactor; and design a HENRI-like system to be used in the OSU TRIGA reactor with xenon-135 to test the predictability, controllability, and reliability of the HENRI prototype.

Xenon-135 is a strong neutron absorber, like helium-3, but is radioactive and will decay if it does not absorb a neutron. This radioactivity means that it is not possible to store xenon-135 for a long period of time, but it is possible to breed xenon-135 in a reactor when it is needed. Xenon-135 does not produce a proton when it absorbs a neutron, which means the reaction deposits less energy in the gas, which changes the density less. If the density of the gas, either helium-3 or xenon-135, in the HENRI system is decreased by heating, the neutron absorbing effects also decrease. If the density were to decrease enough, the reactor could potentially see a power increase. This is very unlikely, but is still a possibility, which is why xenon-135 is such a great alternative to helium-3 for the HENRI system.