NRC’s Supporting Role in NASA’s Mars 2020 Launch

Don Helton
Senior Reliability and Risk Engineer

global-color-views-mars-pia00407-full“Outer space” may not come to mind when you think about the NRC. But we’re excited to be involved with NASA in the planning for a 2020 launch of another Mars rover.

As explained by NASA:

The Mars 2020 rover mission is part of NASA’s Mars Exploration Program, a long-term effort of robotic exploration of the red planet. Designed to advance high-priority science goals for Mars exploration, the mission would address key questions about the potential for ancient life on Mars. The mission would also provide opportunities to gather knowledge and demonstrate technologies that address the challenges of future human expeditions to Mars. The mission would take advantage of a favorable launch opportunity in 2020 when Earth and Mars are in ideal positions in their orbits for a Mars landing in early 2021.

So what does planetary exploration have to do with the NRC? Well, like past missions of this type, the Mars 2020 mission will use a Multi-Mission Radioisotope Thermoelectric Generator – which goes by the fancy acronym of MMRTG. That’s a fancy name for using the radioactive decay of plutonium to produce electrical power needed to run the rover and its instruments.

mars-2020-rover-cad-diagram-pia20759-fullSince the NRC regulates the safe use of radioactive materials, we are part of the Mars 2020 Interagency Nuclear Safety Review Panel that NASA has convened to assure the safety of the launch. This process was originally put in place by Presidential directive and is used each time the U.S. prepares for this type of launch. In addition to NASA and the NRC, the panel includes members from the Department of Energy (which builds and owns the MMRTG provided to NASA), the Department of Defense and the Environmental Protection Agency.

I am honored to serve as the NRC-appointed technical advisor to the panel. The panel’s job is to prepare a Nuclear Safety Evaluation Report — which will be delivered to the White House’s Office of Science and Technology Policy as part of NASA’s request for the President’s authorization of the launch. The panel will evaluate the potential radiological hazards associated with the launch, and the methods used to mitigate the risks.

The NRC has served a similar role in other NASA launches over the past several decades, most recently with the 2011 launch of the Mars Science Laboratory mission and its rover, Curiosity. In addition to this important activity, the NRC and NASA share knowledge in safety, reliability, and risk analysis methods and applications though a Memorandum of Understanding and other interactions.

NRC policy requires other federal agencies to reimburse us for providing services that aren’t part of our statutory mission. So NASA will reimburse us for labor and travel costs associated with our service on the launch safety review panel. In other words, NRC’s licensees (such as nuclear power plants) don’t end up footing the bill for NRC’s participation in this activity.

More on the Mars 2020 mission can be found at NASA’s website, and in the associated Final Environmental Impact Statement associated with this mission.

REFRESH — Where There’s Steam, There’s … a Steam Generator

Kenneth Karwoski
Senior Advisor for Steam Generators

refresh leafWhen the NRC talks about “steam generators,” we’re not talking about teakettles. Steam generators provide vital technical and safety functions at many U.S. nuclear power plants.

In the United States, steam generators are only found in pressurized-water reactors, one of the two types of U.S. reactors. There can be two to four steam generators for each reactor unit. The generators mark the spot where two closed loops of piping meet. The first loop sends water past the reactor core to carry away heat, and this loop is at such high pressure that the water never boils. The second loop is at a lower pressure, so the water in this loop turns to steam and runs the plant’s turbine to generate electricity.

The steam generator’s main technical job is to let the first loop pass its heat to the second loop as easily as possible. To do this, a steam generator packs thousands of small tubes closely together, allowing the maximum area for heat to pass through the tubes and into the second loop’s water.

At the same time, the steam generators provide an important safety barrier – the first loop can contain radioactive material, so the tubes must keep the two loops of water separate. NRC rules require plants to closely monitor the second loop and immediately shut the reactor down if a tube leak exceeds very strict limits.

pwr[1]The NRC’s rules for inspections, maintenance and repair of steam generator tubes help ensure the tubes continue providing the safety barrier. If an inspection shows a tube is starting to get too thin, the plant will repair or even plug a tube to maintain safety.

Steam generator tube material has improved over time. The first steam generators had tubes made from a type of stainless steel that experience showed could be corroded by the chemicals, temperatures and pressures in the first and second loop. Over time, plants have replaced those steam generators with ones using more advanced alloys that are less likely to corrode.

Steam generator replacement only happens when the reactor is shut down for refueling, and plant owners bring in hundreds of specialized workers to safely remove the old generators and install the new ones. The old generators have to be safely disposed of as low-level radioactive waste.

REFRESH is an occasional series where we revisit previous posts. This first ran in July 2013.