A transformational challenge: Making crack-free yttrium hydride

November 13, 2020, 12:00PMNuclear News

Fabricated yttrium hydride samples are pulled out of the system. Photo: ORNL

Oak Ridge National Laboratory scientists have developed a method to produce solid yttrium hydride for use as a moderator for the Transformational Challenge Reactor (TCR), a 3-MWt additively manufactured microreactor that ORNL aims to demonstrate by 2023. Lacking a commercial supply of the metal hydride, ORNL scientists developed a system to produce yttrium hydride in large quantities and to exacting standards.

The hydrogen density and moderating efficiency of metal hydrides—which combine a rare earth metal with hydrogen—could enable smaller reactor cores that can operate more efficiently and reduce waste products, according to ORNL. The material could be used in other advanced reactor designs, including space power and propulsion systems for NASA, and has been proposed as a shield component for thermalization and neutron absorption in fast-spectrum nuclear reactors.

The manufacturing challenge: “It’s easy to just form a hydride powder, but we want a crack-free solid, perfect hydride on a large scale,” said ORNL researcher Xunxiang Hu. “We experienced a lot of failures, but we learn from our failures. . . . We got it where we wanted it in the first two months.”

Hu used a modified static hydriding system with a high-temperature, high-vacuum furnace to fabricate crack-free disks, pellets, and hexagonal coupons with complicated geometries in ORNL’s Low Activation Materials Development and Analysis Laboratory.

Results: By the end of the project, researchers had perfected large-scale yttrium hydride production and established a database with detailed information on the thermal, mechanical, and neutron-scattering properties of the material.

According to ORNL, the machine can produce other hydride pieces up to 15 inches long and 3 inches in diameter, which could allow for broader application of the high-density hydrogen storage material. A report on the results explains that more work is under way to characterize the yttrium hydride samples and improve the quality of the products by reducing the metal yttrium content.

Related Articles