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Short answer: The Advanced Test Reactor (ATR) at Idaho National Laboratory is a pressurized, light-water, high-flux test reactor with a maximum operating power of 250 MW thermal. It has operated since 1967 and exists to expose reactor materials and fuels to intense neutron and gamma radiation, not to generate electricity. Since 2007 researchers outside the laboratory can use it through a proposal and peer review process.
What the Advanced Test Reactor is
The IAEA’s NEXSHARE facility profile (last updated 2 February 2024) describes the ATR as a water-cooled reactor at Idaho National Laboratory, operational since 1967, with the stated purpose of studying “the effects of intense neutron and gamma radiation on reactor materials and fuels”. The same profile says this supports extending the life of current plants, future reactor designs and new fuels. A test reactor is therefore an irradiation tool: samples are placed in the core, exposed under controlled conditions, then examined afterwards.
Key parameters
| Parameter | Value in the IAEA profile |
|---|---|
| Maximum power | 250 MW thermal |
| Maximum thermal neutron flux | 1.0 x 1015 n/cm2-s |
| Maximum fast neutron flux | 5.0 x 1014 n/cm2-s |
| Fast-to-thermal flux ratio range | 0.1 to 1.0 |
| Reactor pressure | 2482 kPa (360 psia), with independent pressure control for loops |
| Coolant temperature | 52 to 72 °C (125 to 160 °F) |
| Test positions | 77 in the core and reflector: 9 large flux traps plus 68 additional drop-in positions |
| Flux trap size | Up to 48 in (1.2 m) long and 5.25 in (13.3 cm) in diameter |
| Position diameters | 0.659 in to 5.00 in |
| Quality assurance standard | NQA-1 |
Source: IAEA NEXSHARE, “Advanced Test Reactor” (INL), 2 February 2024, read 2026-11-08.
How the core runs several experiments at once
The profile states that the ATR’s “unique serpentine core allows the reactor’s corner lobes to be operated at different power levels, making it possible to conduct multiple simultaneous experiments under different testing conditions”. It also lists a power tilt capability and a constant axial power profile. For an experimenter, this means the conditions at a test position depend on where it sits in the core, and different experiments can run side by side under different conditions rather than queued one after another. The size limits above (position diameters and flux trap length) are the first practical constraint when designing a capsule or loop.
How outside researchers get access
In 2007 the U.S. Department of Energy designated the ATR a National Scientific User Facility (NSUF). According to a 2011 INL conference paper (Marshall, Allen, Benson and Thelen, INL/CON-11-22431), this made test space and post-irradiation examination (PIE) equipment at INL available to approved researchers “via a proposal and peer review process”. The same paper describes a Partnership Program that added universities and one national laboratory, with reactor test space, PIE equipment and ion beam irradiation facilities. It also lists education activities: internships, a User Week and fellowships. That paper describes the program as it stood in 2011; the program is now called Nuclear Science User Facilities.
Checklist drawn from the sources
- Access is by proposal and peer review (Marshall et al., 2011).
- Irradiation is only half the work: PIE equipment is part of what the user facility makes available.
- Check sample geometry against the 0.659 to 5.00 in position diameters and the 48 in flux trap length.
- Experiments run under the NQA-1 quality assurance standard (IAEA profile).
- Per the IAEA profile, experimenters can interact under non-disclosure agreements, intellectual property can be protected under DOE CRADA rules, and publishable information can be shared. See also confidentiality agreements (NDAs).
Where it matters for materials and fuel research
The IAEA profile ties the ATR’s work to extending the life of current plants, future reactor designs and new fuels, which makes it relevant to anyone studying how materials and fuels respond to radiation. For the wider field, including regulation and funding, see What Is Nuclear Engineering?. For another large DOE user facility, see the Spallation Neutron Source guide, and for another DOE laboratory see Pacific Northwest National Laboratory.
Common misunderstandings
- It is not a power plant. The ATR is a test reactor; its purpose in the IAEA profile is research, not electricity generation.
- 250 MW thermal is a maximum. A 2007 World Nuclear News report said it usually runs at 110 to 120 MW thermal.
- It is not one uniform environment. Corner lobes can run at different power levels, so conditions differ by position.
FAQ
What is the Advanced Test Reactor?
A 250 MW thermal, pressurized light-water test reactor at Idaho National Laboratory, operating since 1967, used to study radiation effects on reactor materials and fuels.
Can university researchers use the ATR?
Yes, through the NSUF proposal and peer review process described above, which also includes partner facilities and post-irradiation examination equipment.
How many experiments can it host?
The IAEA profile lists 77 test positions: 9 large flux traps and 68 drop-in positions.
Can intellectual property be protected?
The IAEA profile says experimenters can work under NDAs and that IP is protectable under DOE CRADA rules.
Sources
- IAEA NEXSHARE, “Advanced Test Reactor”, Idaho National Laboratory, 2 February 2024: facility profile (PDF), read 2026-11-08.
- Marshall, Allen, Benson, Thelen, “Advanced Test Reactor National Scientific User Facility”, INL/CON-11-22431, 2011: INL Digital Library, read 2026-11-08.
- World Nuclear News, “DoE makes ATR available to others” (2007), read 2026-11-08.
