Scientists at the Swiss Federal Institute of Technology in Lausanne (EPFL) have devised and tested a new, gamma-noise method for monitoring nuclear reactors non-invasively and from a distance. The new method was tested on EPFL's CROCUS nuclear reactor. It can improve nuclear safety and treaty compliance.
Monitoring nuclear reactors around the world to ensure that they are in compliance with regulations in international treaties is essential for safety. However, while current monitoring methods are effective, they often involve invasive procedures that can disrupt reactor operations or pose security risks.
Nuclear technology is constantly evolving, creating new challenges for nuclear monitoring. Small modular reactors (SMRs) are compact and often installed in remote locations. Conventional monitoring methods are primarily designed for larger facilities and may not be sufficiently adaptable or sensitive to the workings of SMRs.
A team of researchers at EPFL and the Paul Scherrer Institut (PSI) have pioneered a non-invasive and more efficient technique using gamma noise to monitor reactors.
They just published a paper in Scientific Reports. In this report, they show that gamma radiation, as opposed to the neutron signals used by traditional monitoring methods, can provide accurate and timely data on reactor criticality and composition without actual, physical intrusion into the reactor vessel.
The study was led by Oskari Pakari. He is a scientist with EPFL's Laboratory for Reactor Physics and Systems Behavior and Professor Andreas Pautz with the PSI's Nuclear Energy and Safety Research Division.
In their new monitoring method, the researchers used two bismuth germanate scintillators. These were strategically positioned outside EPFL's CROCUS research nuclear reactor. This allowed them to non-invasively monitor gamma radiation emitted from its operation.
Gamma radiation is one of the types of electromagnetic radiation produced during nuclear reactions. Gamma rays carry information about the reactor's state, such as changes in criticality and composition of its fuel (e.g., uranium) without directly interfering with the reactor's operations.
The new method also utilizes statistical analysis of the variability of gamma ray detection over time. Unlike conventional methods, which rely heavily on neutrons, gamma noise analysis focuses on the fluctuations in gamma ray counts. These correlate to the fission chain reactions occurring inside the reactor. The degree of correlation provides insights into the reactor's operational state.
The new method can provide essential data within minutes. This is a significant improvement over traditional methods, which typically require longer measurement times and closer proximity to the reactor core. The gamma-radiation method uses computational tools to analyze the temporal and spatial variance of detected gamma rays, which allows for rapid and accurate assessments of the reactor's condition.
The researchers tested their method by extended experiments, successfully demonstrating its efficacy at distances up to several yards from the reactor core. The gamma-radiation monitoring detected prompt decay constants with minimal error. This reduced the need for direct contact with the reactor core and it also enhanced the speed and accuracy of data acquisition.
The new method provides reliable, non-invasive monitoring of a variety of nuclear reactor types, including SMRs. It could change nuclear safety protocols, facilitate better compliance with international treaties, and possibly be applied to other fields requiring radiation monitoring without direct sensor contact.