Features | Environment | East Asia

Japan’s Underground Lab Wants to Solve the World’s Nuclear Waste Problem

A rare visit to the Horonobe Underground Research Laboratory, where Japanese researchers are testing options for storing radioactive waste.

Scientists visiting the Horonobe Underground Research Laboratory in Hokkaido, Japan.

Reindeer pastures and dairy farms stretch across the flat, windswept plain of Japan’s northernmost prefecture, giving little hint of what lies roughly 300 meters below. Inside the Horonobe Underground Research Laboratory, teams of engineers are trying to answer a question no country has fully solved: how to keep highly radioactive waste isolated from the environment for periods measured not in decades, but in tens of thousands of years.

In May, I gained special access to the facility through the Japan Atomic Energy Agency (JAEA), touring the underground galleries and observing several of the experiments currently underway.

Horonobe Underground Research Laboratory. Photo ©Piergiorgio Pescali.

A Rare Laboratory in Sedimentary Rock

Horonobe is one of only two underground research laboratories Japan has built to study geological disposal of high-level radioactive waste, and the only one still operating. Its counterpart, the Mizunami Underground Research Laboratory in Gifu Prefecture, was built in crystalline rock and was decommissioned in 2022 after its land lease expired. Horonobe, by contrast, sits in Neogene-era sedimentary rock, giving the JAEA a very different and, officials argue, complementary geological environment to study.

The project traces back to November 2000, when the governor of Hokkaido, the mayor of Horonobe town, and the president of the JAEA signed an agreement to permit research on the deep geological environment at the site. Construction and excavation followed over the next two decades, and the laboratory now includes shafts and galleries used to test how engineered barriers, groundwater, and surrounding rock interact over time – the same combination of natural and artificial safeguards that would, in theory, protect a real repository.

Two of the central experiments underway involve what the JAEA calls the “full-scale engineered barrier system performance experiment” and a “solute transport experiment,” both designed to test, at real scale, how bentonite buffers, canisters, and cement-based materials behave once water and pressure are introduced over years rather than months. The JAEA has also been testing how the surrounding sedimentary rock buffers natural disturbances, earthquakes, and groundwater shifts that could compromise a repository’s isolation over the long term.

Researchers conducting tests at Horonobe Underground Research Laboratory. Photo ©Piergiorgio Pescali.

The JAEA is emphatic on one point, repeated in nearly every briefing given to visitors: Horonobe is a research facility, not a candidate site for Japan’s eventual high-level waste repository. Japanese law formally separates the two functions, and the agency overseeing the actual site-selection process, the Nuclear Waste Management Organization of Japan, operates independently of the JAEA’s research program.

That legal separation has not entirely dissolved local unease. Horonobe is a farming town of roughly 2,000 residents, many of whom have lived for two decades with an underground laboratory in their backyard and, despite official assurances, the lingering question of what happens to the facility once the research concludes.

Japan’s broader search for a permanent repository has proven difficult everywhere it has been raised. Only two municipalities, Suttsu and Kamoenai in Hokkaido, have so far agreed even to preliminary literature-based surveys, and neither has committed to hosting a final site.

The outside view of Horonobe Underground Research Laboratory. Photo ©Piergiorgio Pescali.

An International Proving Ground

What distinguishes Horonobe today is its growing international role. In February 2023, the JAEA and the OECD’s Nuclear Energy Agency (NEA) launched the Horonobe International Project, bringing foreign research organizations into the underground laboratory to work on shared technical problems. The first phase ran through March 2025 with 11 participating organizations from countries including Australia, Bulgaria, Germany, South........

© The Diplomat