KASK: From a Single Channel to the Reactor Core, Making Safety Margins Visible

An engineer working on a reactor core usually has one question in mind: "How much margin do we have?" Getting to the answer is rarely a single step. Operating conditions are prepared in one place, the calculation runs in another tool, the charts are drawn separately, and the results are copied into a report by hand. Every hand-off copies a number, drops an assumption, and brings back the same question: "Which conditions was this result produced under?"

We built KASK to pull that scattered work together. Today it is a desktop application that examines the highest-power fuel channel and fuel assemblies in the reactor core, and calculates safety margins in normal operation and accident scenarios. But we got here by starting with a single channel.

One Channel, One Question

The first version of KASK was a single-channel thermal-hydraulic solver. The goal was simple: see, quickly and clearly, how coolant, cladding and fuel temperatures change along the hottest fuel rod in the reactor core.

Simple, but not easy. Getting the calculation right mattered, and so did making sure an engineer could set it up and read it. So from day one we didn't hide the solver behind a form. We treated it as a workspace that flows from setup to result.

We Entered the Competition As It Was

We took that first version of KASK to the TEKNOFEST 2026 Nuclear Energy Technologies Design Competition. After the final in September, we learned in October that we had taken first place in the Software Development Category.

For us, first place wasn't a finish line. It was a moment of confirmation: we had picked the right problem and started solving it in a way engineers could actually use. The real question came right after: how do we go beyond a single channel?

After the Competition: From Channel to Assembly

Not every fuel assembly in a reactor core produces the same power. Some work noticeably harder than their neighbours, and that is usually where the safety margin gets tight. A single-channel view explains the most limiting rod well, but it doesn't answer "where in the core?"

So after the competition we added subchannel-based hot-assembly DNBR screening to KASK. The analysis now starts from the core map. The engineer sees the power distribution on the map, the highest-power assembly stands out, and the study focuses there. That assembly is resolved into subchannels, and the result shows where the lowest safety margin to critical heat flux occurs. Not just a number, but where that number sits and what surrounds it.

Reading Accident Scenarios Over Time

A steady-state analysis is a photograph. An accident scenario is a film. In a loss of flow, the pumps coast down, coolant flow drops, fuel temperature starts to climb, and the time until the reactor's safety systems step in becomes what matters most.

KASK comes with built-in scenarios such as loss of flow, loss of coolant, loss of feedwater, rod ejection and power ramps. You pick the scenario, enter a few parameters and run it. One chart shows how temperatures and margin change through the scenario, and moving from the same operating conditions to a different scenario doesn't mean setting everything up again.

KASK Today

The tool that started with one channel now brings together:

• Hot-channel analysis: Coolant, cladding and fuel temperatures along the most limiting fuel rod, on one chart.
• Subchannel-based hot-assembly DNBR screening: From the core map to the highest-power assemblies, and from there to subchannels.
• Accident and transient scenarios: How a scenario evolves over time, with temperature and margin side by side.
• Built-in reactor templates: Starting points for designs ranging from large reactors to small modular reactors (SMRs).
• Clear reporting: Results and study conditions exported together as PDF, Excel and CSV.
• The same experience everywhere: Turkish and English interface, on Windows, macOS and Linux.

For us, the Turkish interface is more than a translation detail. Using natural Turkish terms for the reactor core, fuel assemblies and critical heat flux helps students and engineers get comfortable with the tool faster. KASK is now in academic pilot use at Hacettepe University, and the feedback from there keeps shaping the product.

What's Next

Our next step is to bring KASK to industry pilot users. Working with teams in the field will speed up the feedback loop we built during the academic pilot.

In parallel, we are working on YULA, the second Tengra Nuclear product. YULA is an original fuel performance code that follows a fuel rod's thermal and mechanical behaviour over its life in the reactor. The aim is to complement KASK's thermal-hydraulic view with the fuel's own story.

You can explore KASK's screens and capabilities on the KASK product page, and everything else we do in nuclear on the Tengra Nuclear page.