Overhaul gives test reactor new lease of life

The world’s most powerful and versatile test reactor is up for its sixth major overhaul since it began operating in 1967 and technological upgrades over the last five years mean the industry workhorse will be running for decades more.

INL's Advanced Test Reactor with the characteristic blue glow due to Cherenkov radiation. (Source: INL)

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During its over 50-year lifespan the Advanced Test Reactor (ATR), housed at Idaho National Laboratory (INL), has supported missions for the U.S. Navy, the Department of Energy’s (DOE) Office of Nuclear Energy, university research, the U.S. and international nuclear industries as well as providing isotopes for medical treatments and power for NASA space exploration.

From the last Core Internals Changeout (CIC) in 2004 to 2015, the ATR’s future beyond 2040 was uncertain, but the reactor’s versatility and continued relevance led the armed forces and the DOE to have a change of heart, says ATR Associate Lab Director Sean O’Kelly speaking from the INL labs.

“In 2015, the Navy and the DOE decided they were going to run this national asset much longer and started investing a lot more money needed to make that happen outside the reactor core itself, on the plant infrastructure. We’ve put in a $100 million worth of upgrades over the last 5 years,” O’Kelly says.

Wear and tear and, in some cases, obsolescence of parts were bound to take its toll after more than half a century of operations.

The ATR was designed to operate at low pressures and temperatures, unlike commercial reactors which are built to create heat, and produces neutrons at high levels with the help of beryllium metal reflectors which surround the reactor core.

Important data on how new materials and designs respond to long-term operations in high radiation environments is collected by exposing fuel and material samples to the bombardment of neutrons, called thermal neutrons due to thermal equilibrium with the temperature of the reactor at around 71 C (160 F), in the ATR.

However, as the neutrons are thrown against test materials, they are also gradually wearing down the essential components of the reactor itself which was built to allow for the periodic replacement of parts including the beryllium reflector blocks and other internal core components.

Core diagram showing ATR’s cloverleaf core design and control drum layout with test spaces available for research 

(Source: INL) 

Long due a upgrade

Originally, the ATR was to be overhauled every five years, but the changes became less frequent as reflector design changes and operational improvements helped extend each usage period.

After the 1994 CIC, with nuclear research funding dwindling and an eye to a possibly imminent decommissioning, the government ramped up its use of the ATR while its capabilities were still available.

“The US government wasn’t sure if they were going to run it for another 20-30 plus years after 2004 and, between 1994 and 2004, they were running it as hard as they possibly could. So, what happened was, we wore out not just the reactor, but also pumps and other parts were ran beyond design lifetime,” O’Kelly says.

In the years following the 2004 CIC, the reactor’s operational reliability dropped, and shutdowns for repairs increased as the previous decade’s heavy use and reduced maintenance and replacements prompted equipment failure.

By 2015, after the government decided that the ATR’s irradiation capabilities remained a relevant and useful asset for a new generation of nuclear power and radioactive isotope usage, it was clear that much of the sixties’ technology would need to be upgraded and a proper plant infrastructure update program was launched.

“Considering that the computers they had while it was being built were those mainframe, clunky machines which had less power in them than our handheld calculators today, it was an amazing story of design and innovation,” says O’Kelly.

In the case of the primary cooling pumps, the original machinery was already incredibly robust and needed little more than to be refurbished and rewound.

The analogue controls and computer hardware, meanwhile, needed a 21st Century reboot.

Sixties-era computing

One computer system ran on NEFF hardware, a trademark technology that has long since disappeared, though replacing it with modern electronics has posed its own challenge.

“We’ve gone in and used modern computing equipment and put in digital upgrades, but they have to go into an analogue system because that’s the basis for the safety cases and the logic and the relays and the controllers are set on these analogue backbones,” says Hans Vogel, ATR Strategic Irradiation Capabilities director.

The ATR also used the VAX operating system with computers designed by the Digital Equipment Corporation which went out of business in the late nineties. Fortunately, with the system’s supply chain all but dead, a one-man company which bought up all the VAX spare parts was, for a long time, the ATR team’s sole supplier.

Large, open-air relays, which would overheat and degrade, have been replaced by much smaller, much more reliable, enclosed systems, while many of the motor control centers have been upgraded with new electronics. Gearbox support beams that manipulate the control cylinders for reactor power, and haven’t been physically removed since the eighties, are due to be replaced by brand new pieces.

“If you were to go into the ATR control room today, we have big flat screen digital monitors on the walls, but that is just replicating an analogue system behind the scenes. So, it’s digital information, much more efficient than what was available in the sixties, but behind it there’s still relays closing and opening to provide those signals,” says Vogel.

Next lifecycle

While the core reactor and mechanical operations of the ATR are essentially the same today as they were over 50 years ago, the supporting infrastructure has been replaced by state-of-the-art technology and modernized operations and maintenance practices.

By integrating data from the Electric Power Research Institute (EPRI) and nuclear industry information, as well as adopting the MC21 software platform, the team has upgraded its modelling and predictive abilities to have a much clearer view of potential degradation of the valves, pumps and motors.

The test reactor simulates the environment of a pressurized water reactor, so the new, advanced reactors and small modular reactors, which use a range of generation technologies, may mean the ATR’s range sometimes fails to meet the experimental needs of newcomers in the nuclear industry.

For the moment, O’Kelly and Vogel say the ATR will be re-evaluated in 15-20 years’ time.

“Certainly, advanced reactors have changed since the sixties and demand for testing space continues to grow. In some cases even the ATR can’t do all the things we’re being asked to do. Discussions are happening, but absolutely no decisions about new irradiation capability have been made,” says O’Kelly.

By Paul Day