The deposition of fouling deposits on nuclear fuel rods combines the extreme conditions of high pressure, temperature, and fluid flow rates, with extreme radiation fluxes and water radiolysis. Previous attempts to study its deposition rates and mechanisms have relied on less extreme experiments, or on ex-situ measurements. These deposits, known as CRUD (Chalk River Unidentified Deposits), can create a variety of problems when operating light water reactors (LWRs), a few of which include; reduced heat transfer, CRUD induced power shifts (CIPS) and CRUD-induced localized corrosion (CILC). In light of this fact, the development and design of a prototypical pressurized water reactor (PWR) water loop, with in-situ water chemistry measurements and high-speed video capture through single-crystal sapphire windows, has been undertaken. Insights into the mechanisms and growth rates of CRUD deposition, heat transfer properties, resistant materials, and the validity of modeling CRUD as a fractal can now be obtained.