Secondary Ion Mass Spectrometry Analysis of Materials to Develop In-core Safeguards Reactor Monitoring Devices

During reactor operations and fuel burn up, some isotopic abundances change due to nuclear reactions and provide sensitive indicators of neutron fluence and fuel burnup. Secondary ion mass spectrometry (SIMS) analysis has been used to directly measure isotope ratios of selected impurity elements in irradiated nuclear reactor materials. Direct in situ SIMS measurements were made in graphite and metal samples, following shaping and surface cleaning. Other elements such as Be must be chemically separated prior to SIMS analyses. Elements such as pre-existing impurity U, and Pu produced from the U, must also be chemically separated and are measured by thermal ionization mass spectrometry (TIMS). Studies combining SIMS and TIMS analyses demonstrate the value of this approach in determining reactor fluence profiles, power production, and other parameters. Future work proceeding from this analytical work will include developing monitoring devices designed for relatively easy placement and retrieval in a reactor, and direct SIMS analyses after exposure.