The International Atomic Energy Agency (IAEA) recently published a major technical report* on TRIGA research reactors (training, research, isotopes, general atomics), which it views as being in a “class of their own” among the many types in the world due to their fuel design and resulting enhanced inherent safety features.

Covering basic characteristics and historical developments, the IAEA report also reviews utilisation, fuel conversion and ageing management of TRIGA reactors. It also looks at the TRIGA research network and the potential issues that organisations need to address and solve in the near future.

While many TRIGA reactors have been shutdown, the report says that of those remaining 38 facilities across the world are being improved through upgrade and refurbishment, and have developed new utilisation plans and also scheduled development of future new applications and services.

“Thanks to their intrinsic safety features, TRIGA reactors will continue to be used in many different areas of education and training as well as for academic research and technology development,” says the report.

The training offered by one network of TRIGA research reactors, in particular – the Eastern European Research Reactor Coalition (EERRC), received an Nuclear Energy Institute (NEI) special award for hands-on training centred in Vienna but also involves central European facilities in the Czech Republic, Hungary and Slovenia. EERRC was established in 2008 with financial and logistical support from the IAEA.

But in its recent report on TRIGA reactors the IAEA further notes that the technology, and the scientific and engineering community involved with the reactors “have arrived at an era when knowledge retention and ageing management has become more crucial”.

With the potential for future gains from continuation and further investment in the research reactors at this juncture, and in light of needs around both front- and back-end fuel becoming increasingly more important, the IAEA hosted a technical meeting in 2013 to pull together a consolidated overview of the history, challenges and coming opportunities for TRIGA reactors. The TRIGA report is a key outcome of the work.

The focus on TRIGA reactors follows a run of reports on research reactors more widely from the IAEA, including: ‘Research Reactor Benchmarking Database (2015)’; ‘Applications of Research Reactors (2014)’; ‘Commercial Products and Services of Research Reactors (2013)’; and ‘Research Reactors: Safe Management and Effective Utilization (2012)’.

TRIGA – history

Born of a concept developed from the mid- 1950s, the TRIGA reactors were quickly developed across 23 countries over the following two decades to play key roles in both basic and applied nuclear research. The rapidly developed scientific and technological enterprise emerged from the ‘Atoms for Peace’ initiative launched by US President Eisenhower, and discussed at a UN conference on the Peaceful Uses of Atomic Energy, held in Switzerland.

A key company in the genesis and evolution of TRIGA reactors was US firm General Dynamics, through its General Atomic division which became known as General Atomics. 

The TRIGA reactors, though, are relatively small in power (100kW-16MW) and few in number (38 of 247 operating research reactors), according to the IAEA Research Reactor Data Base figures from 2015 (see Operational TRIGA reactors).

The operating reactors use UZrH homogeneous solid fuel, operate with uranium enrichment of less than 20% following the HEU-to-LEU conversion programme, and are light water cooled and use graphite or water as a reflector. Many can operate in pulse mode.

Almost the same number of reactors again (31) have been shutdown or decommissioned. The total number of TRIGA reactors built, therefore, is 69 according to IAEA data. The main geographic clusters of the reactors is the US, continental Europe and Asia to some extent. Most common power level range is 250kW-1MW for the reactors.

In its report, the IAEA outlines the progression of TRIGA reactor designs (Mark I – III, annular core pulsed, high power) before reviewing fuel designs, safety aspects, ageing management, advantages and disadvantages, respectively, and also reactor conversions and areas of applications.

Among key attractive features and relative advantages cited for the TRIGA reactors are: high degree of passive
safety; ease of operation, maintenance and conducting experiments – both for students and instructors.

Further, “typical irradiated samples are not highly radioactive” due to low flux levels and short irradiation times, which helps reduce handling restrictions and administrative requirements. Relatively large quantities of material can be irradiated without producing an excessive amount of radioactivity, says the report.

“Therefore, the actual insertion of samples for irradiation in reactor core positions can either be done by reactor staff or even by the experimenters themselves,” the report adds.

Despite the “excellent performance” of all TRIGA reactors for nearly 60 years, however, the IAEA report notes there have been a few incidents due to ageing and also insufficient preventative maintenance (see Incidents box above).


While TRIGA reactors have their advantages, and like other reactors face generic issues, there are three particular challenges seen presently for them due, principally, from their limited number – fuel, utilisation and technical support, respectively, says the report. In other words, volume issues.


In terms of fuel, the challenges are primarily two-fold and arise at the start and end of the process: at the start, there is the challenge to obtain continuing supply of fuel over the long-term in light of “lack of sufficient demand to justify the costs of operating a fabrication facility”; and, at the end of the process, the challenge of returning spent fuel to the country of origin.

Based on survey data in 2014, the TRIGA reactors had enough stored and unused fuel to meet overall demand for the following five years to 2019, although case by case there are either instances of available supplies requiring reduced power/cycles or the possibility of transfer of fuel between reactors.

However, where reactors use different fuels the challenge rises further, possibly being added to with requirements for analyses and licence amendments should, for example, different uranium-weigh and dimensions combinations be brought together to achieve acceptable core configurations.

“Hence, the availability of unused fuel may not meet the needs of all facilities,” says the report.

It adds that to ensure sufficient fresh fuel supplies in later years there is a need of the TRIGA community to commit to and communicate their demand – which would help “make a clear business case” for ongoing life of a fuel fabrication facility.

In terms of spent fuel, the period has recently commenced to start preparing any return shipments to the US where required by May 2019, as required by the US Department of Energy (DoE) under its ‘Take Back’ programme. Fuel that is to be returned had to cease irradiation earlier this year. The wider TRIGA community would need to look at alternative spent fuel disposal options.


With respect to levels of utilisation of the TRIGA reactors, the majority have reported having low to only medium effective weeks of operation per year; only a few report relatively high use – classed as more than 20 effective weeks of operation annually, according to the IAEA Research Reactor Database.

Far more of the TRIGA reactors (yet only slightly more than ten) are reported as having only low use – classed as less than four effective weeks of annual operation; however, most of the reactors (yet still under 25) have an annual utilisation in the medium classification – between four and 20 effective weeks of operation per year.

While offering inherent safety benefits and flexibility for use across network partners in academic research, education and safety activities, the report notes that the low to medium power of the TRIGA reactors leaves them at a disadvantage – they “cannot compete” – with high power research reactors in a number of industrial applications (See Network and opportunities).

In this context, the report adds, international networking and cooperation becomes more important, and enables the use of TRIGA reactors to be “more flexible and more efficient when compared with large- scale production facilities”.

Further approaches noted to help overcome the limited utilisation of TRIGA reactors include a push to attract more users and industrial partners, working to enhance relationships with academia and research institutions, adding more experimental capabilities, and more broadly to work on the development of strategic utilisation plans.

Technical support

The issues around technical support are two-fold, concerning spare parts and knowledge transfer.

Dealing with spare parts, one aspect of the issue is that the TRIGA reactors have operated “with relatively little major maintenance or modernisation”, due to the robust fuel plus the simplicity of the control and safety systems. Those benefits and the limited numbers of reactors again present a challenge arising out of limited volume – there has not been a large demand for spare parts. Also, some facilities stocked some spares.

Consequently, for spare parts the solutions often arise with supplies being transferred between reactor operators or being sourced from some decommissioned facilities.

On the matter of knowledge transfer, this is the challenge of engaging sufficiently early to capture how and where possible, and to pass on as effectively, practically and retentively as possible, the key lessons, crucial wisdom and relevant nous won by older generations of engineers who have worked for years with the TRIGA reactors.

“It is of the utmost importance that a TRIGA facility deals with this problem at an early stage and before it is too late in order to be prepared for a smooth transition from one TRIGA staff generations to the next,” says the report. 

* ‘History, Development and Future of TRIGA Research Reactors; IAEA, Technical Reports Series No 482; 2016’.