Oak Ridge National Laboratory (ORNL) reports it has tested a high-temperature fission chamber prototype built by Curtiss-Wright Nuclear that operated steadily at 800 degrees Celsius (about 1,472 degrees Fahrenheit) during a weeklong irradiation test at The Ohio State University Research Reactor. The successful trial addresses one of the hardest engineering problems facing advanced nuclear power: building sensors that can survive inside reactor cores running far hotter than conventional designs. With the U.S. Department of Energy accelerating its advanced reactor pipeline, the result lands at a moment when proven high-heat instrumentation could determine how quickly next-generation plants reach the grid.
Why Fission Chambers Matter at 800 Degrees Celsius
Fission chambers are the instruments that let operators start a reactor and track its power output in real time. They detect neutrons produced by nuclear fission, and without them a reactor cannot be safely brought online or monitored during operation. In conventional light-water reactors, these detectors typically operate at much lower temperatures than advanced high-temperature concepts, so established designs can be used. Advanced reactor concepts cooled by helium gas or molten fluoride salt (FLiBe) push core temperatures toward 800 degrees Celsius, a range that degrades standard detector materials, seals, cables, and fill gases. The ORNL publication on a high-temperature fission chamber for He- and FLiBe-cooled reactors describes why in-core fission chambers for these coolant types may need to operate up to roughly 800 degrees Celsius, establishing a clear design target for high-temperature instrumentation.
Until recently, the most reliable high-temperature fission chambers topped out well below that mark. A xenon-filled design documented in reactor diagnostics research demonstrated neutron-discharge discrimination in the 500 to 650 degrees Celsius range for sodium-cooled fast reactors, with fill gas choice between xenon and argon shown to affect partial discharge behavior at elevated temperatures. A broader review of irradiation-resistant neutron detectors published in the journal Sensors confirmed that reported fission chamber milestones clustered around 600 degrees Celsius, with only a handful of programs claiming results near 800 or 850 degrees Celsius. Reaching 800 degrees Celsius with stable, repeatable performance across varying power levels therefore represents a meaningful jump, not an incremental gain.
Inside the Weeklong Irradiation Trial
The prototype built by Curtiss-Wright was subjected to a weeklong irradiation campaign at The Ohio State University Research Reactor, known as OSURR. During that period, the device maintained expected performance across all power levels while operating steadily up to 800 degrees Celsius, according to an ORNL announcement describing the campaign. ORNL staff member Brandon Wilson led the evaluation alongside Curtiss-Wright engineers Chris Laidler and Heather Shave, all of whom were present at the OSURR facility for the test campaign, which paired the university’s flexible research reactor with national laboratory data acquisition and analysis capabilities.
The test built on years of planning documented in an ORNL technical report cataloged by the Office of Scientific and Technical Information at osti.gov, which identified operating environment targets for advanced reactors and high flux fields and evaluated candidate test facilities including OSURR. A companion version of that report, available through a separate technical memorandum identifier, laid out the specific thermal and radiation conditions the prototype would need to meet, meaning the weeklong trial was not exploratory but a structured confirmation of design targets. The fact that the chamber held up across the full power range, rather than only at a single set point, suggests the design can handle the variable conditions reactors experience during startup, ramp-up, and steady-state operation.
The Gap Between Testing and Deployment
Most coverage of this result has framed it as a straightforward win, but a critical distinction deserves attention. Validating a prototype under irradiation at a university research reactor is not the same as qualifying a sensor for commercial deployment inside a power-producing advanced reactor. Research reactors like OSURR operate at far lower power and neutron flux levels than a full-scale helium or FLiBe-cooled plant. The engineering challenges identified in the detector review, including long-term degradation of seals, cables, and gas media, play out over months and years of continuous operation, not a single week. No primary DOE record explicitly states approval of this fission chamber for deployment; what exists is testing validation, an important but earlier step in the qualification pipeline. It’s important to understand that gap before treating this as a finished product ready for installation.
That said, the result does clear a significant technical hurdle. Previous high-temperature fission chamber work had not demonstrated stable broadband performance at 800 degrees Celsius under actual irradiation conditions, even though laboratory studies such as the xenon-filled chamber experiments showed promise at somewhat lower temperatures. Curtiss-Wright and ORNL have now shown that the physics works at the target temperature inside a real reactor environment. The remaining questions are about endurance, manufacturing repeatability, and regulatory acceptance, all of which are engineering and bureaucratic problems rather than fundamental science barriers. Bridging that gap will likely require additional irradiation campaigns at higher flux, extended-duration tests, and coordination with regulators to define acceptance criteria for in-core detectors in advanced designs.
DOE’s Advanced Reactor Context and Next Steps
The fission chamber validation arrives as federal policy is actively pulling advanced reactors toward construction and commercialization. While the Department of Energy has not tied this specific detector program to a named demonstration project in public records, its broader emphasis on advanced reactor deployment means enabling technologies like high-temperature instrumentation will be watched closely. ORNL’s decision to document the test plan in reports indexed under federal technical archives underscores that the work is being positioned as part of a larger ecosystem of reactor R&D rather than a one-off industrial product trial. As developers refine helium- and salt-cooled designs, they will need proven in-core sensors before regulators can sign off on startup, shutdown, and emergency procedures.
Separately, DOE publishes policies meant to encourage reporting and disclosure of security issues across its digital and information systems. The department’s public-facing vulnerability disclosure policy is focused on reporting cybersecurity vulnerabilities, but it also reflects a broader emphasis on structured disclosure and corrective action. For high-temperature fission chambers, that could translate into structured pathways for vendors and researchers to surface issues discovered during extended irradiation or post-test inspections. As Curtiss-Wright and ORNL move from a single successful weeklong campaign to the multi-year data sets regulators will expect, the same openness that governs software and infrastructure vulnerabilities may help build confidence that the detectors will behave predictably under the most demanding reactor conditions.
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*This article was researched with the help of AI, with human editors creating the final content.
