New Criticality Safety Issues Pop Up at Y-12
NS&D Monitor
9/5/2014
Staff of the Defense Nuclear Facilities Safety Board recently identified several new criticality safety concerns at the Y-12 National Security Complex, which is under increased scrutiny because of the age of the plant’s production facilities. Such concerns include casting of slugs of highly enriched uranium. In a recently released reported dated Aug. 1, DNFSB staffers said there were two incidents that involved the casting of enriched uranium alloys. “Both events occurred at essentially the same time,” they reported.
Casting operations were suspended following the incidents. Y-12 spokeswoman Ellen Boatner said the operations for most casting resumed the next week. DNSFB staff members said Y-12′s nuclear criticality safety team identified one of the events as a “mis-pour,” with unusual quantities of molten uranium flowing outside the mold and crucible in “an uncontrolled geometry.” In the other event, “operators observed a crack in the crucible upon lowering the casting stack assembly from the furnace,” the report stated. “Shortly thereafter, both assemblies began oxidizing in a more energetic manner than typical. At that time, the cracked crucible broke into several pieces, creating another uncontrolled geometry situation. Operators later observed cracking in the mold for the other assembly.”
Officials: No Danger of Nuclear Criticality Accident
There reportedly was never a danger of a nuclear criticality accident. “During the critique, NCS (nuclear criticality safety) analysts indicated that these conditions, though unexpected, were bounded by the current analysis.,” the report stated. Boatner said the uncontrolled geometry of fissile material—such as highly enriched uranium—“means that the material has gotten into a shape or configuration that is not safe by geometry alone.” But other factors were not reportedly in place to facilitate an uncontrolled nuclear chain reaction. “NCS personnel instructed operators to isolate the cooling water and hydraulic systems in order to minimize sources of moderation in the furnace,” the DNFSB report stated. “Both assemblies took longer than typical to cool to an acceptable handling temperature. The assembly with the fractured crucible took several days.”
The presence of aluminum in the alloy material reportedly contributed to the situation, although that was not specified in the Aug. 1 DNFSB report. The report said Consolidated Nuclear Security, the Y-12 contractor, “indicated that a potential common contributor to the events was a failure to recognize a potential overflow condition, given that the operations involved some lower density metals at masses similar to those used for casting operations with pure uranium. The CNS casting subject matter expert also indicated that certain metals can react aggressively with the crucible and mold materials if exposed directly to these materials at the temperatures required for alloy casting.”
Supercomputer Awards Expected in October
The future of supercomputing at the Department of Energy is set to come more into focus by late October, when Oak Ridge National Laboratory plans to award a contract for its next-generation supercomputer as part of a three-lab effort known as CORAL (Collaboration of Oak Ridge, Argonne and Livermore). Buddy Bland, director of Leadership Computing Facility at ORNL, said the lab’s contract approval is still under review by the DOE, but he anticipates an award late next month. He said he couldn’t speak for the other labs—Argonne and Lawrence Livermore—but those awards are likely to come in the same time frame.
CORAL is a project that’s supposed to provide the next big jump in supercomputing before reaching the ultimate exascale capability—a thousand times more powerful than today’s best computers. Each of the three labs is supposed to have a next-generation supercomputer in or around the 2017 timeframe. The concept of the project is have the best companies in the supercomputing industry provide their best ideas for the computers of the future.
Ultimately, the plan is to have two different architectures among the three machines, with each capable of about 200 petaflops (about 200 million billion mathematical calculations per second). Proposals were submitted in February, and they have been in review ever since. According to earlier reports, Argonne and ORNL will definitely have computers of different architectures, with Livermore deciding its preference among the supercomputing options.
