On Wednesday morning my student Weixiong Zheng successfully defended his Masters thesis entitled “Physics-Based Uncertainty Quantification for ZrHx Thermal Scattering Law”.  His thesis work is partially covered in this American Nuclear Society Transactions paper.

His work centered on how low-energy neutrons scatter off zirconium hydrate (ZrHx — the x varies from 1 to 2). For those not nuclear engineers, most nuclear reactors use fission caused by thermal (low energy) neutrons.  In some reactors, especially research reactors like we have here at TAMU, there is zirconium hydride in the fuel.

It turns out that how thermal neutrons scatter of the zirconium hydride is very important to the reactor behavior, in large part because this scattering can effect the fission rate and how the reactor behaves.  It also happens that the “standard” model for how neutrons scatter off of ZrHx is based off of a model formulated in the 1960’s.  This model is not based on some heroic experiment performed in the 60’s, as a lot of nuclear data is.  Rather the model is based on a 1960’s computational model.  Now I’m a big fan of the computational work done early in the age of computers (von Neumann and Ulam did some awesome work with minimal computational power), nevertheless, I think we can do better now.

What Weixiong’s thesis looks at is how we can create models similar to the standard model.  Assuming the standard model is not the “truth”, it stands to reason that one would like to see how sensitive real calculations for reactors are to variations in the scattering off ZrHx.

Obviously it get’s much more complicated than this, but the gist of the story is that using some experiments we can calibrate or estimate what is the best scattering formula (or law) for a reactor.