Ensuring the Safety of Nuclear Waste Containers With LabVIEW and NI FlexRIO

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"With tools built using the real-time high data rate analysis capacity of the NI FlexRIO, we will be able to spot any dangers before they manifest, resulting in a safer tomorrow for us all."

- Pasi Karppinen, ProtoRhino Ltd., Finland

The Challenge:
Ensuring the safety of highly radioactive nuclear waste containers for at least 10,000 years.

The Solution:
Using NI FlexRIO hardware and NI LabVIEW system design software to measure the mechanics of copper cracking under stress in the millisecond timescale, to ascertain the suitability of copper containers for the storage of highly hazardous materials over long time spans.

Pasi Karppinen - Find this author in the NI Developer Community
Jari Tuovinen - ProtoRhino Ltd., Finland
Kimmo Mustonen - ProtoRhino Ltd., Finland
Juha Koivisto - Aalto University, Finland
Markus Ovaska - Aalto University, Finland
Mikko Alava - Aalto University, Finland

According to a report by the Swedish Radiation Safety Authority, copper containers planned for super long-term storage of nuclear waste in a deep geological repository may not retain their integrity until the radioactivity of the enclosed matter has subsided to low-enough levels.

The challenges of such long-term storage are unique. The containers face varying strain over thousands of years from geological stress and corrosion, which eventually causes cracks in the containers. The container design has to ensure the cracks do not compromise the integrity of the container until after a set time, such as 10,000 years.

While the cracking process progresses at a glacial pace, the resulting cracks are the combined result of a large amount of microscopic cracking events occurring locally over a time span of mere milliseconds. The mechanics of these events are still largely unknown. Our goal was to develop a measurement system to provide insight on these details.

ProtoRhino, a National Instruments Alliance Partner in Finland, was selected to tackle the issue because of the company’s experience in providing tailored solutions to challenges requiring high data acquisition rates and real-time analysis. The company also has a device template based on NI FlexRIO hardware in its product portfolio, which greatly expedites measurement device prototyping.

From Milliseconds to Millennia

We want to thoroughly inspect copper cracking mechanisms in the millisecond scale to attain a full understanding of the dynamics involved, thus determining the copper containers’ suitability for long-term hazardous waste storage. We can then extrapolate the durability of the copper containers over a timescale of millenia. This approach ensures that the encasement solutions chosen for long-term nuclear waste storage will not become hazardous for human generations yet to come.

Our method of measurement involves correlating acoustic emission from stress effects with optical observation of surface cracking to determine how structural failures progress under applied stress. We fixed the sample in a stress-strain apparatus and collected high-speed camera data (8,904 images per second) over a Camera Link connection through the NI 1483 Camera Link Adapter Module for FPGA Image Processing to analyze it in real time with the NI PXIe-7965R NI FlexRIO FPGA Module. We digitized the acoustic emission signals with an NI 5752 high-data-rate digitizer and analyzed the signals with a second NI FlexRIO module.

Synchronizing the NI FlexRIO modules was easy because the NI PXI Express chassis incorporated a timing bus that allowed for simple synchronization of the modules. The NI PXIe-8100 RT controller ensured uninterrupted operation of the measurement system. We processed the collected data on the PC using the NI Vision Development Module. The module contained preinstalled algorithms that made data analysis fast and simple.

Initially, we considered implementing our setup with traditional high-speed cameras that save the images to an internal memory with simple trigger options. In the end, these weren’t suitable for our needs because those cameras did not allow for enough customization with the trigger options and the internal memory can’t be read fast enough for real-time event detection. The NI FlexRIO with the NI 1483 module proved to be our best option. Implementing the Camera Link data collection was quick and easy because the built-in sample code worked with our camera out of the box.

The flexibility of the NI FlexRIO platform helped us easily collect data from measurements that spanned days or weeks by triggering both the camera and acoustic emission data collection only when either device observed a change in the sample that surpassed a given threshold value. The experiment could run nearly indefinitely by storing only the significant events. Programming the FPGA was effortless with the NI LabVIEW FPGA Module because we could use a high-level programming language and the available sample code. The inherent scalability of the NI FlexRIO peer-to-peer streaming feature helped us eventually upgrade our measurement setup to trivially accommodate any further increases to our data mining needs as we developed our real-time event detection algorithms.
Safer Storage Structures

We successfully monitored single event cracks in copper undergoing prolonged deformation well below yield stress. This is the groundwork for a comprehensive study, which will eventually result in a proven safe, long-term nuclear waste container. The NI graphical system design tools combined with flexible hardware made it possible for us to quickly transform an idea to complete implementation.

Looking forward, NI FPGA products will serve as a foundation for the development of tools that monitor stress-based degradation of critical structures, such as airplane wings and bridge supports, in real-time. The expected lifespan of such structures is usually years, decades, or at most, centuries, but the results of a freak critical structure failure can be devastating.

Author Information:
Pasi Karppinen
Find this author in the NI Developer Community

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