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Students peer into the University of Wisconsin Nuclear Reactor pool to see the blue glow
May 14, 2025

Operation detect light: first year nuclear engineering students gain hands-on experience at the UWNR

Written By: Lili Sarajian

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You wouldn’t expect PVC pipes, plastic jars, and Gorilla Glue to be the makings of a device that measures nuclear reactor power. 

But for the first year students enrolled in NE 231: Introduction to Nuclear Engineering, a hands-on engineering project with budget constraints means getting creative with everyday objects. Each spring semester, the challenge is the same: design and fabricate a light sensitive detector to accurately measure light emitted from a nuclear reactor during operation.

The University of Wisconsin Nuclear Reactor. Looking down into the reactor pool, you can see the blue glow of the Cherenkov radiation.
The University of Wisconsin Nuclear Reactor (UWNR) is a 1 MW TRIGA research reactor. Looking down into the reactor pool, you can see the blue glow of the Cherenkov radiation.

When nuclear reactors produce power, they emit Cherenkov radiation, the characteristic blue glow produced when charged particles from the nuclear fuel move faster than light in water. As they regain equilibrium, the charged particles release photons in the visible spectrum–particularly at the wavelength and frequency corresponding to blue light. 

The intensity of this Cherenkov radiation is proportional to the reactor’s power level, allowing students to extrapolate light sensor readings at known power levels to determine an unknown power level. 

Students work in groups for the duration of the semester to come up with a design, purchase materials, and build their final product. With 10 groups of 6 students, this semester marked the largest enrollment in NE 231 to date.

“One of my favorite parts of this project was definitely the design process. It was great working as a team to come up with a design that all of us agreed on and were excited about,” says Maya Walker, a first year Nuclear Engineering student. 

One of the groups placing their floating light sensitive detector in the reactor pool.
This group designed their device to float on top of the reactor pool in a plastic container. Here they are determining the best location to take their light sensor readings.

For most teams, their designs went through multiple revisions informed by a series of tests. First, each group met with Reactor Director Bob Agasie to make sure their design choices and selected materials were safe to submerge in the reactor.

Buoyancy was another concern. Groups whose devices floated on the surface of the reactor pool made sure their designs were buoyant enough, while those that submerged their devices minimized buoyancy to ensure more accurate readings.

Waterproofing was another priority for all teams to protect their light sensors and electronics from water damage. Fortunately, the UW–Madison campus is conveniently situated on an isthmus, providing students with an ideal testing environment. 


“We went down to the dock as a team and tested it in Lake Mendota which was a lot of fun,” says Walker. 

This year, students were given the additional challenge of making their designs sustainable. 

Two students hold their device-a light sensor attached to a 12 ft scaffold pole-steady against the reactor wall while they collect data.
Two students submerge their device (a light sensor fixed to a 12ft scaffold pole) in the reactor pool and hold it steady against the wall while they collect data.

“This new constraint required them to think critically about each fabrication step and the reversibility of every action taken,” says Assistant Professor Charlie Hirst, the course instructor. This semester marks the fourth iteration of the upgraded NE 231 curriculum that was redesigned by Professor Adrien Couet in 2022. “It was fascinating to see how each team chose to approach this design problem, with solutions ranging from 12ft scaffold poles, to umbrellas, and even a recycled ramen pot!”

Aside from meeting safety and sustainability requirements, the groups were also evaluated on their ability to communicate their work, and not just in the classroom. 

In April, students presented scientific posters at the Undergraduate Research Symposium, a community event showcasing undergraduate research across all disciplines. Presenting at the symposium encourages students to convey their work to non-technical audiences, a vital skill for their academic and professional careers. 

a group of first year nuclear engineering posing in front of their poster at the Undergraduate Research Symposium
Students presented scientific posters at the Undergraduate Research Symposium in late April to share their research projects with the UW–Madison Community.

Finally, testing day arrived. All semester, students look forward to testing their devices in the University of Wisconsin Nuclear Reactor (UWNR), a 1 MW TRIGA research reactor that supports a wide range of research and educational endeavors.

Each group was allotted one hour to take light sensor readings at two known power levels (10% and 100%). Students then took a third reading at an unknown power level and extrapolated their data to determine the value.

“Working on a real-world nuclear engineering project let me learn the basic skills of any engineer, but in the context of what might be the coolest thing I’ve seen in my life–a real, legitimate, glowing nuclear reactor,” says Simon Katan, a first year Nuclear Engineering student. “I already had a strong idea that this is what I want to do, but this course let me confirm that!”

This unique course provides students invaluable hands-on experience, introducing important concepts related to nuclear reactor operation and regulatory compliance, while developing their engineering, communication, and problem-solving skills.