Dynamic simulation and verification of a compression-liquefaction system for material withdrawal from a uranium-enrichment plant

Dynamic simulation was used to evaluate the design of the Tails (depleted 235U assay) Withdrawal System for an uranium enrichment plant. Desirability of a simulation to check the design was indicated by requirements for a very high system reliability (99.95% availability) over a wide range of system throughput (85:1). Objective of the simulation included: evaluate alternate compressor anti-surge schemes, identify control system sensitivities, examine start-up and shut-down procedures, identify system limitations and testing of proposed design changes, and provide an understanding of system behavior. Three levels of process complexity were modeled: (1) compressions system, (2) combined compressor and liquefaction system, and (3) parallel operation of two compression/liquefaction trains. Two compressor train configurations were evaluated with the simulation mode. A FORTRAN based simulation methodology was used to implement and solve the mathematical models and plot the time history behavior for each test run. Results included discovery that that initial process steady state design would not operate stably. A new steady state was formulated which required some modifications to equipment sizing and control system philosophy. This new design was tested and proven with the simulation. Simulation objectives were achieved. Based on the simulation results, recommendations were made regarding: best compressor configuration, most effective anti-surge control scheme, changes to enhance system reliability and operability, control system sensitivities, control system design to achieve load sharing for parallel trains, and overall system operability with existing design