New experiment holders accelerate nuclear fuel testing

The Minimal Activation Retrievable Capsule Holder (MARCH) test vehicle system was developed to provide rapid analysis and quicker turnarounds on smaller test samples of nuclear fuels and materials, and it simplifies the testing process by combining modularity and adaptability, INL said.

Small samples are placed inside a specialised holder, where experiments can be precisely tailored for neutron exposure, temperatures and the local thermal/cooling environment. The holders are then placed in a larger reusable safety capsule for insertion into TREAT. Once the transient test is complete, the holders can be easily extracted at the facility and the safety capsule can be reused for another round of experiments.

The low-activation material that is used for the safety capsules means the test vehicles do not become significantly radioactive during irradiation. This allows the experiment to be assembled or disassembled at the TREAT facility for rapid analysis.

The classic method for such testing required large-scale, fully-integrated experiments that took years to design and were costly to build, making it difficult for smaller federal agencies, industry and universities to take advantage of the USA's only transient test reactor. MARCH's modular design makes experiment cycles much faster and more affordable, INL said.

The accelerated process supports a "modernised" approach to separate effects testing, coupling scientific modelling with fuel performance data to produce quicker results. "A process that once took two to three years to complete, can now be accomplished in just one year," INL said.

TREAT can produce bursts of energy that are several times more powerful than conditions found in a commercial reactor, allowing fuel performance under extreme conditions to be studied. Exposing fuels to extreme conditions inside such a facility enables more resilient and long-lasting fuels to be developed. Such transient testing of nuclear fuels has been likened to high-impact car crash testing, which has helped to advance safety technologies in the automobile industry.

The TREAT reactor was restarted in November 2017 after more than 20 years on standby, and resumed testing of nuclear fuels in 2018. MARCH has taken three years to develop through a series of INL efforts supported by the DOE. MARCH-based irradiations have already been carried out to support the development, testing and licensing of accident-tolerant fuels and other advanced fuels.
 
NASA is also using the MARCH holders at TREAT to develop and test fuel composites to see how they perform under the harsh temperatures needed for nuclear thermal propulsion, INL said.