Y. Kim, “Computational Investigation of a Potential Uranium Diversion Scenario at an Enrichment Plan Due to Material Holdup inside Pipes”, M.S. Thesis, Nuclear Engineering, Texas A&M University, College Station, TX (2020).
Several studies have reported the effect of holdup on detectors and the magnitude of holdup in nuclear material processing facility. However, scenarios how diversion of special nuclear material occurs in the presence of holdup have not studied yet with respect to Gaseous Centrifuge Enrichment Plants (GCEP) safeguards perspective. The potential uranium diversion within the uncertainty of the NaI detector in the presence of holdup of uranium in the centrifuge pipe was analyzed. In addition, the possibility of an unnecessary inspection resulting from holdup of uranium was also studied. In order to accomplish the objectives, Monte Carlo N-Particle (MCNP) 6.2 code had been used. A centrifuge pipe modeled in MCNP 6.2 was NPS ½ and a 2” × 2” NaI detector was utilized and the detector was surrounded by 3cm thickness lead as a collimator. Given the condition holdup, UO2F2, is 0.7 at%, the simulations had been conducted for various cases ranging from 6 at% to 10 at% U-235 enrichments in increments of 1% contained in the pipe. The variations in the holdup thickness on the pipe wall are also studied through the simulations. Separative Work Unit (SWU) was also calculated to be compared the SWU values when nothing has changed with the SWU values when the U-235 enrichments of feed and waste has been manipulated. Load-Cell Based weighing System (LCBS) was introduced and considered to accomplish the uranium diversion scenario. Other simulations had been executed to figure the possibility of an unnecessary inspection. While holdup had 5 at% U-235 enrichments, the DUF6, NUF6, LEUF6 (1 at% to 4 at%) were assumed as the material flowing in the pipe and simulated.