1. HRIBF Update and Near-Term Schedule
(J. R. Beene)
The six months covered by this report has been a difficult time for everyone involved with HRIBF, as we strive to recover from the Operational Emergency declared at HRIBF in July 2008. The events which precipitated that declaration were discussed in the August 2008 Newsletter. I will recap and update this discussion very briefly in the following paragraphs. Before I do that, I will skip to the bottom line and provide some information which must be of greatest interest to our users. When and how will we resume full operation of HRIBF?
ORNL line management agreed to allow us to proceed with a phased restart of the facility. The first step in this process was the resumption of stable-beam experiments in mid-September 2008. The next steps, in sequence, are (1) resumption of ISOL target R&D at the On-Line Test Facility (OLTF, based on the UNISOR facility), (2) resumption of RIB experiments using beams of long-lived isotopes (e.g., 7,10Be, 26gAl) employing what we refer to as batch mode operation, (3) resumption of ISOL target R&D with ORIC beams at HPTL, (4) resumption of ISOL RIB experiments employing selected proton-rich species, (5) resumption of target R&D at OLTF with actinide targets, and finally (6) full HRIBF operation including neutron-rich RIB production with ORIC beam on uranium carbide targets. We have initiated, or have permission to proceed with steps 1 through 3. Permission to proceed with steps 4 and 5 are expected soon. The final step is more problematic. It now appears that the set of requirements we must meet before resumption of neutron-rich operation cannot be completed before late May, or perhaps not until the first week in June.
I now return to a brief recap of the July event. The declaration of an Operational Emergency at HRIBF was made by the ORNL Laboratory Shift Superintendant following the evacuation of Building 6000 early on the morning of July 28. The evacuation resulted from the observation of airborne contamination on the first floor of Building 6000 near the door of the RIB production vault (C111S). The maximum dose rate observed outside of a radiological area was 4 mrem/h. Following this event, ORNL management commissioned a Management Investigation Team to probe the event, determine causes, and provide input to potential corrective actions. In addition, a Recovery Team was constituted, consisting primarily of HRIBF staff with the mission of preparing HRIBF for resumption of operation. However, our initial effort was largely devoted to carrying out physical on-site investigation and providing information to the Investigation Team.
The Investigation Team released a 150-page report on November 20, 2008. The direct cause of the event was determined to be release of radioactive noble gas into the air in C111S from a leak in the HRIBF off-gas system. The leak resulted from a small corrosion-induced hole in an oil-fill plug on the exhaust side of a mechanical roughing pump which served as a backing pump for the turbomolecular pumps that provide high-vacuum on the target/ion-source system (TIS) and the RIB production beamline. The plug was made of stamped-carbon steel approximately 1-mm thick, with threads cut into the 1-mm thickness. The corrosion-induced leak was on the threaded region of the plug. A contributing cause was found to be the failure of the belt driving an exhaust fan in the ORIC-shielded area HVAC system. This resulted in a slight positive pressure inside C111S (the RIB production vault), which pushed airborne contamination through the gaps around the shield door into occupied areas. An interlock on the exhaust fan motor was intended to prevent operation of the supply fan if any exhaust fan was not operating. However, the interlock was based on fan motor operation, rather than fan motion or room pressure.
The most important fact about the event was that no individual received a measurable radiological dose as a result of this incident. All personnel who entered Building 6000 on July 28 or the three preceding days had their thermoluminescent dosimeters (TLD) checked immediately. A number of scientists involved in the experiment that was underway were equipped with electronic dosimeters in addition to TLDs. Six individuals most directly involved with the event (scientists and radiological control technicians) were sent for whole body counts. All whole-body scans and dosimeter readings produced negative results.
A set of thirty-two corrective actions related to the event were established based on the Management Investigation Team Report. We have agreed with ORNL management on a mapping between closing of the corrective actions and the beginning of the various phases of the facility restart plan. Requirements for all phases except full facility operation to produce neutron-rich beams with ORIC beam on uranium carbide targets should be met before the end of March. An absolute prerequisite for full neutron-rich RIB operation is the completion of the Triennial Review of the HRIBF by the ORNL Accelerator Safety Review Committee (ASRC), a recommendation for resumption of operations by the ASRC, and formal approval by ORNL line management. This review was scheduled, before the July event, for the spring of 2009; its scope and significance are now enhanced. Unfortunately the earliest possible date for the start of this review is now mid April. Allowing time for the ASRC to draft its report, and for HRIBF staff to respond to any findings, we arrive at the estimate of full restart of neutron-rich beam operation quoted earlier.
Not all the news is bad. We are doing research with radioactive beams
again. The IRIS2 project
has proceeded extremely well over the past
year, in spite of a somewhat stretched-out funding profile. We are
well into FY2009 but are, yet again, operating under a Continuing
Resolution (CR), and are still uncertain what our actual budget for
the year will be. However, there is real optimism that funding for
science will see substantial increases over the next several years,
and that the budget process may become a bit less capricious, at least
for a few years.