Project Synopsis

Provide an independent engineering evaluation of various processes at a depleted uranium hexafluoride processing facility.

Project Summary

DUF6 CONVERSION PROCESS ANCILLARY SYSTEMS ENGINEERING EVALUATION

The client currently operates two plant sites where they convert depleted uranium hexafluoride (DUF6) to uranium oxide.  The client hired Process Engineering Associates, LLC (PROCESS) to perform a technical review of several of the systems peripheral to the DUF6 Conversion process, including reviews of the deionized water system, the offgas scrubber systems, the KOH Regeneration system, and the Waste Evaporator system. 

The overall Uranium Conversion process includes a multi-stage system for scrubbing the resulting off gas, which consists primarily of nitrogen, hydrogen, steam, and hydrogen fluoride.  The off gas from each Conversion Unit flows sequentially through:

  • a condenser/phase separator, where the bulk of the HF is collected as an aqueous solution
  • a demineralized water scrubber (DIW), consisting of a venturi / packed bed scrubber combination
  • a KOH scrubber and a venturi/packed bed scrubber combination
  • a backup packed bed scrubber, which is common to all of the processing lines.

The DIW scrubber removes the bulk of the HF remaining in the off gas after condensation; its sump is pumped out periodically to be combined with the condensed HF as a byproduct.  A solution of 20 wt% KOH is used in both the KOH and backup scrubbers; periodically, the “spent” KOH solution is transferred to the KOH Regeneration system (KRS) for reclamation and recycle.  Several operational concerns were identified during the initial startup runs which could hinder operation once the full on-line capacity is achieved. PROCESS researched these issues and both immediate and longer term recommendations were made to ease operations.

The Deionized Water System (DWS) consisted of a fairly complex arrangement of equipment in the original design, including: mixed media filters, chemical addition, reverse osmosis, water softening, and electro-deionization (EDI).  Following an involved period of testing and the discovery of some improperly designed piping arrangements, this system was isolated in place and deionized water was trucked in from a remote location for a period of time before a vendor-supported system was implemented.  The vendor provided system which consists primarily of cartridge filters, carbon adsorption, and a series of mixed bed ion exchange columns was installed.  Deionized water from the DWS is used at numerous locations within the plant, and it is imperative that the plant have a reliable and consistent supply of deionized water in order to remain in production.  Due to its simplicity of operation and the reliability of its water product, it was recommended to continue use of the vendor-supported system over the long term.

The KOH Regeneration system (KRS) is located in a building separate from the main Conversion Process.  The KRS system receives, via pipeline, the spent KOH solutions from all of the KOH scrubbers, the backup scrubber, and the HF Storage Tank fume scrubber.  Due to the batch nature of these processes, this is an intermittent flow throughout the time that the Conversion process is running.  The spent solutions are collected in a batch tank until a sufficient amount is collected to constitute a batch run of the KRS system, which consists of:

  • Mixing the spent KOH solution with hydrated lime to form a solid CaF2 precipitate
  • Adding a pre-coat slurry to enhance the filterability of the CaF2
  • Filtering the CaF2 out via a pre-coated filter press
  • Collecting the resultant filtrate in a holding tank
  • Adjusting the KOH concentration based on density
  • Recycling the regenerated scrubber solutions back to the main process use points.

At the time of the evaluation, this system had not been operated with process solutions. The assessment recommendations made by PROCESS included suggested improvements to instrumentation and process flows to streamline batch treatment of the spent KOH solutions.

The Waste Evaporator system is designed to receive the wastewater from the adjacent Ultrasonic cleaning sink and evaporate off the water content, thereby reducing the volume required for residue disposal. It is intended to operate as a batch process.  At the time of the evaluation, this system had been tested out successfully and, while it had not yet been operated with process materials, its operation appeared to be fairly straightforward.  Following a brief review of available process documentation, two relatively minor issues were identified for further operational confirmation.

 

Industry Type

  • Nuclear Materials Processing

Utilized Skills

  • Independent engineering process evaluation

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