The American Centrifuge Demonstration Facility at the Piketon, Ohio, site is located in a portion of an existing process building that will ultimately house the American Centrifuge Plant.
In August 2007, USEC began the Lead Cascade test program at the facility, an integrated testing phase of the American Centrifuge technology involving multiple machines in a cascade configuration.
The license issued by the U.S. Nuclear Regulatory Commission for the demonstration facility specifies that the machines be operated in a closed-loop configuration where the uranium gas is enriched, depleted and recombined in a repetitive cycle. The demonstration facility license permits test samples of enriched uranium to be withdrawn through a mass spectrometer. The ability to separate uranium isotopes is tested by analyzing these samples.
In a centrifuge enrichment facility, a cascade is a group of centrifuge machines connected in a series and parallel arrangement to achieve an intended isotope separation capability. A commercial uranium enrichment facility that uses gas centrifuge technology is made up of multiple cascades.
The number and arrangement of centrifuge machines in a cascade can vary. The cascades tested so far during the Lead Cascade test program consist of fewer machines than would ultimately be in a commercial cascade. The proposed RD&D program would test operations of a full-sized commercial plant cascade of 120 machines.
Key Objectives
USEC has achieved a number of key objectives through the Lead Cascade test program, including:
- demonstrating the capability of the cascade to generate product assays in a range useable by commercial nuclear power plants,
- providing information on machine-to-machine interactions and integrated efficiency of the full cascade,
- confirming the design and performance of the centrifuge machine and cascade support systems,
- verifying cascade performance models under various operating conditions,
- providing information on the performance of centrifuge components over time, and
- giving operators and technicians hands-on experience assembling, operating and maintaining the machines.
Cascade Operations
The Lead Cascade test program in Piketon began operations in August 2007 and has accumulated more than 1,000,000 machine hours of runtime. Data from this testing program has provided valuable assembly, operating and maintenance information, as well as operations experience for the American Centrifuge Plant staff. The initial lead cascade test program involving USEC-produced prototype machines was completed in early 2010.
AC100 Series Cascade
The design for the AC100 machine reflects improvements learned during individual machine testing and integrated cascade testing of the prototype machine.
In parallel with the final operations of the prototype centrifuge machines, USEC began installing the first group of AC100 centrifuge machines. The AC100 series design has met the targeted performance goal of 350 SWU per machine, per year. USEC’s strategic suppliers manufactured parts for the AC100 centrifuge machines, replicating on a commercial basis manufacturing that USEC previously self-performed in building its prototype centrifuge machines. Installation of these AC100 centrifuge machines further demonstrated the ability of USEC’s suppliers to build components, assemble the machines and successfully bring them into operation. These centrifuge machines operated successfully in a cascade configuration beginning in March 2010 and demonstrated the ability to produce the full range of commercial product assays required by USEC’s customers for low enriched uranium.
In order to keep USEC’s supplier base intact, the company continued to manufacture AC100 centrifuge machines in 2011 that it used to replace the initial set of AC100 machines to optimize the use of the limited centrifuge machine positions available to the company in the lead cascade test program.
In June 2011, several lead cascade machines failed during an extended period of off-normal operating conditions. The off-normal conditions occurred as a result of a power interruption caused by an electrical fault in the lead cascade support systems and compounding issues experienced during the efforts to restore power. Following the June event, the centrifuges being operated in the lead cascade facility in Piketon, Ohio were not operated on uranium hexafluoride (UF6) gas, and USEC committed to the NRC not to reintroduce UF6 gas into these machines until the NRC completed its inspection of the event. In April 2012, the NRC completed its inspection and issued five Level IV violations, the least serious of the four levels of NRC violations, regarding the June event. No fines were assessed against the company. Two of these violations require no further response and we are responding to the three violations that require further action by USEC to resolve. USEC has conducted extensive reviews and taken comprehensive corrective actions that address issues raised by the NRC, including looking broadly at USEC’s conduct of operations, human performance, training and procedures and identified areas for improvement. After the NRC had completed its inspection of USEC’s response to the event and reviewed in detail USEC’s planned and completed corrective actions, USEC notified the NRC, and on April 18, 2012, resumed lead cascade operations with UF6 gas.
Beginning in the first quarter of 2012, USEC has been modifying the current set of AC100 machines in the lead cascade to install a safety enhancement in response to the June 2011 event. The safety enhancement does not impact SWU performance and is not expected to impact centrifuge reliability. Under the expected terms of the RD&D program, USEC would continue to manufacture and operate additional AC100 machines in 2012 and complete and operate a 120 machine commercial plant cascade configuration in 2013.
Continued lead cascade operations will accomplish two of the primary objectives of the proposed RD&D program. The first objective is to demonstrate sufficient run time on the AC100 centrifuges to establish the high confidence level in cascade reliability required by DOE to support loan guarantee financing for the commercial plant. A second objective is to build out and demonstrate the full level of balance of plant system redundancy designed for the commercial plant, which was not available for lead cascade operations during the June event.
