Another setback at Spallation Neutron Source

sns1Aerial view of the Spallation Neutron Source (ORNL photo)

SNS Building MarkerAnother target vessel has apparently failed at the Spallation Neutron Source, forcing the shutdown of systems only a week after they’d been restarted following two other problems. The SNS will be down for at least 2 1/2 weeks, once again requiring experiments to be rescheduled.

“It’s a big source of frustration for everybody,” Kevin Jones, director of Oak Ridge National Laboratory’s Research Accelerator Division, said this morning. “We’ve just got to work through it, solve the problem and move on. That’s what we’ve got to do.”

On Monday morning, sensors inside the stainless-steel target vessel — which holds and circulates 20 tons of mercury — indicated there was a potential mercury leak into the “interstitial region” between the mercury containment and the water shroud, Jones said. That is typically how the failure of a vessel is detected, although this one took place after only a very short run.

“That’s why we’re pretty puzzled,” Jones said.

“Per standard procedure, SNS was shut down to prepare for further inspection of this target and an anticipated target change,” he said. “All systems functioned as designed and there was no risk to personnel or the environment.”

The series of problems is playing havoc with the science endeavors at one of ORNL’s prized research facilities. Scientists come to Oak Ridge from around the nation and the world to use the streams of neutrons to explore the structure and properties of materials under various conditions.

The problems at SNS began in early September, only a few weeks after operations had resumed following a summer outage for maintenance and upgrades. The premature failure of the target vessel  forced the shutdown, but soon after the vessel was replaced — but before the operating systems could be restarted — another problem cropped up. A water leak in a section of the facility’s linear accelerator required extensive repairs and refurbishments and kept the SNS out of operation until Oct. 19.

According to Jones, the SNS operated for only 167 megawatt hours, the second shortest time in the facility’s nine-year existence.

This series of problems is reminiscent of a period in 2012 when the SNS had back-to-back failures with the target vessel. An investigation at that time determined that the source of the problem was related to welding during the manufacture.

Another investigation will be conducted this time around, and Jones said the team will involve experts from other areas of ORNL as well as some outside the lab.

Getting the SNS restarted in a timely way may be hampered by logistical issues.

When the target vessels are removed from the operating position, the vessels are hotly radioactive and must be kept in a shielded cell for a while to cool and also to provide time for evaluation. Currently, three formerly used vessels (Nos. 8, 9, and 10) are taking up all the room, so one of them must be shipped off-site for disposal before there will be room to take out the newly failed vessel (No. 11) and install No. 12.

Jones said it is hoped that vessel No. 8 can be shipped to the Nevada National Security Site on Friday.

Once vessel No. 12 is installed, there will only be one spare vessel available for backup.

The next one being manufactured is due to arrive in April 2015, Jones said. Each vessel costs about $1 million.

It’s conceivable that the SNS, once restarted, could be operated at a reduced power level in order to extend the lifetime of the target vessel, but Jones said that decision hasn’t been made yet.

The SNS had been operating with a beam power of about 1.1 megawatts.

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About Frank Munger

Senior Writer Frank Munger covers the Dept. of Energy's Oak Ridge facilities and many related topics — nuclear weapons, nuclear waste and other things nuclear, environmental cleanup and science of all sorts. Atomic City Underground is, first and foremost, a news blog, but there's room for analysis, opinion and random thoughts that have no place else to go.