ORNL shuttered molten salt reactor made safer

May 12, 2023, 9:30AMRadwaste Solutions
For the first time in 26 years, work crews performed sampling of gaseous byproducts at the MSRE. (Photo: DOE)

The Molten Salt Reactor Experiment (MSRE) facility is one of hundreds of old, contaminated buildings at Oak Ridge National Laboratory and the Y-12 National Security Complex in Tennessee that are slated to be taken down.

Many of the structures will remain standing for years due to the large amount of work required to demolish them. Keeping them safe until then sometimes requires improvements to maintain their conditions and prepare them for deactivation, which will place them in a stable condition to minimize existing risks.

The Department of Energy’s Oak Ridge Office of Environmental Management is tasked with keeping these structures safe. The site’s cleanup contractor is UCOR.

Facility improvements: Upgrades to the MSRE's high bay—where the critical systems reside—are underway, and workers have improved infrastructure by installing electrical upgrades and an emergency generator, among other things.

In addition, and for the first time in 26 years, workers have conducted sampling at the reactor, measuring the amount of fluorine generated in gases that are byproducts from the salt tanks. Plans had long been underway to sample the gases, but concerns over brittle pipes and safe access presented challenges. Following installation of new robust piping and enhanced safety features, workers were able to start the project and have performed five samplings since December.

Demo preparation: Workers have been preparing for demolition by removing components in the MSRE, which has led to a downgraded radiological level in a work area there.

They have also installed a new portable maintenance shield that will enable the use of long-reach tools, reducing the risk of injury and radiological exposure. The shield, which is scheduled to go operational next year, will replace the current gas removal system. The shield is expected to minimize failure points in the MSRE and reduce hazards and required maintenance and oversight.

In addition, a study is underway to develop cleanup alternatives for the MSRE. The study evaluates alternatives that incorporate one or more basic types of remedial actions, including grouting and removal of contaminated equipment.

History: The MSRE operated from January 1965 through December 1969, logging more than 13,000 hours at full power during its four-year run. It was designated a nuclear historic landmark in 1994.

In October 1968, it became the first reactor ever to run on uranium-233, which acted as an economic proof of concept for nuclear power. Also, the reactor was fundamentally unlike most modern designs. The fuel did not sit in the reactor core while coolants circulated through; rather, the molten salts acted both as a carrier for the fuel and as a coolant.

After the reactor was shut down for good, it was observed that the graphite bars that lined the reactor core as its moderator showed little to no damage, either from heat, radiation, or chemical corrosion.

The molten salt program ended in 1973, when the Atomic Energy Commission decided to focus on other designs.

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