Impacts of future nuclear power generation on the international monitoring system.

Many countries are considering nuclear power as a means of reducing greenhouse gas emissions, and the IAEA (IAEA, 2022) has forecasted nuclear power growth rates up to 224% of the 2021 level by 2050. Nuclear power plants release trace quantities of radioxenon, an inert gas that is also monitored because it is released during nuclear explosive tests. To better understand how nuclear energy growth (and resulting Xe emissions) could affect a global nonproliferation architecture, we modeled daily releases of radioxenon isotopes used for nuclear explosion detection in the International Monitoring System (IMS) that is part of the Comprehensive Nuclear Test-Ban Treaty: 131mXe, 133Xe, 133mXe, and 135Xe to examine the change in the number of potential radioxenon detections as compared to the 2021 detection levels. If a 40-station IMS network is used, the potential detections of 133Xe in 2050 would range from 82% for the low-power scenario to 195% for the high-power scenario, compared to the detections in 2021. If an 80-station IMS network is used, the potential detections of 133Xe in 2050 would range from 83% of the 2021 detection rate for the low-power scenario to 209% for the high-power scenario. Essentially no detections of 131mXe and 133mXe are expected. The high growth scenario could lead to a 2.5-fold increase in 135Xe detections, but the total number of detections is still small (on the order of 1 detection per day in the entire network). The higher releases do not pose a health issue, but better automated methods to discriminate between radioactive xenon released from industrial sources and nuclear explosions will be needed to offset the higher workload for people who perform the monitoring.

Using STAX data to predict IMS radioxenon concentrations.

The noble gas collection and measurement stations in the International Monitoring System (IMS) are heavily influenced by releases from medical isotope production facilities. The ability to reliably model the movement of radioxenon from the points of release to these IMS samplers has improved enough that a routine aspect of the analysis of IMS radioxenon data should be the prediction of the effect of releases from industrial nuclear facilities on the sample concentrations. Predicted concentrations at IMS noble gas systems in Germany and Sweden based on measured releases from Institute for Radioelements (IRE) in Belgium and atmospheric transport modeling for a four-month period are presented and discussed.

Design considerations for future radionuclide aerosol monitoring systems.

Pacific Northwest National Laboratory (PNNL) staff developed the Radionuclide Aerosol Sampler Analyzer (RASA) for worldwide aerosol monitoring in the 1990s. Recently, researchers at PNNL and Creare, LLC, have investigated possibilities for how RASA could be improved, based on lessons learned from more than 15 years of continuous operation, including during the Fukushima Daiichi Nuclear Power Plant disaster. Key themes addressed in upgrade possibilities include having a modular approach to additional radionuclide measurements, optimizing the sampling/analyzing times to improve detection location capabilities, and reducing power consumption by using electrostatic collection versus classic filtration collection. These individual efforts have been made in a modular context that might constitute retrofits to the existing RASA, modular components that could improve a manual monitoring approach, or a completely new RASA. Substantial optimization of the detection and location capabilities of an aerosol network is possible and new missions could be addressed by including additional measurements.

Estimates of radioxenon released from Southern Hemisphere medical isotope production facilities using measured air concentrations and atmospheric transport modeling.

The International Monitoring System (IMS) of the Comprehensive-Nuclear-Test-Ban-Treaty monitors the atmosphere for radioactive xenon leaking from underground nuclear explosions. Emissions from medical isotope production represent a challenging background signal when determining whether measured radioxenon in the atmosphere is associated with a nuclear explosion prohibited by the treaty. The Australian Nuclear Science and Technology Organisation (ANSTO) operates a reactor and medical isotope production facility in Lucas Heights, Australia. This study uses two years of release data from the ANSTO medical isotope production facility and (133)Xe data from three IMS sampling locations to estimate the annual releases of (133)Xe from medical isotope production facilities in Argentina, South Africa, and Indonesia. Atmospheric dilution factors derived from a global atmospheric transport model were used in an optimization scheme to estimate annual release values by facility. The annual releases of about 6.8 × 10(14) Bq from the ANSTO medical isotope production facility are in good agreement with the sampled concentrations at these three IMS sampling locations. Annual release estimates for the facility in South Africa vary from 2.2 × 10(16) to 2.4 × 10(16) Bq, estimates for the facility in Indonesia vary from 9.2 × 10(13) to 3.7 × 10(14) Bq and estimates for the facility in Argentina range from 4.5 × 10(12) to 9.5 × 10(12) Bq.

Abatement of xenon and iodine emissions from medical isotope production facilities.

The capability of the International Monitoring System (IMS) to detect xenon from underground nuclear explosions is dependent on the radioactive xenon background. Adding to the background, medical isotope production (MIP) by fission releases several important xenon isotopes including xenon-133 and iodine-133 that decays to xenon-133. The amount of xenon released from these facilities may be equivalent to or exceed that released from an underground nuclear explosion. Thus the release of gaseous fission products within days of irradiation makes it difficult to distinguish MIP emissions from a nuclear explosion. In addition, recent shortages in molybdenum-99 have created interest and investment opportunities to design and build new MIP facilities in the United States and throughout the world. Due to the potential increase in the number of MIP facilities, a discussion of abatement technologies provides insight into how the problem of emission control from MIP facilities can be tackled. A review of practices is provided to delineate methods useful for abatement of medical isotopes.

Maximum reasonable radioxenon releases from medical isotope production facilities and their effect on monitoring nuclear explosions.

Fission gases such as (133)Xe are used extensively for monitoring the world for signs of nuclear testing in systems such as the International Monitoring System (IMS). These gases are also produced by nuclear reactors and by fission production of (99)Mo for medical use. Recently, medical isotope production facilities have been identified as the major contributor to the background of radioactive xenon isotopes (radioxenon) in the atmosphere (Stocki et al., 2005; Saey, 2009). These releases pose a potential future problem for monitoring nuclear explosions if not addressed. As a starting point, a maximum acceptable daily xenon emission rate was calculated, that is both scientifically defendable as not adversely affecting the IMS, but also consistent with what is possible to achieve in an operational environment. This study concludes that an emission of 5 × 10(9) Bq/day from a medical isotope production facility would be both an acceptable upper limit from the perspective of minimal impact to monitoring stations, but also appears to be an achievable limit for large isotope producers.

Neptunium(V) partitioning to uranium(VI) oxide and peroxide solids.

Metaschoepite, [(UO2)8O2(OH)12] x 10H2O, and metastudtite, UO4 x 4H2O, are alteration phases anticipated in a spent nuclear fuel repository following the moist oxidation of UO2 on a geologic time scale. Dissolved concentrations and hence potential mobility of other radionuclides in the fuel, such as the neptunyl cation (NpO2+), will likely be determined by the extent of their partitioning into these U(VI) solids. 237Np is of particular interest due to its potential high mobility and long half-life (2.1 x 10(6) years.) In this study, metaschoepite has been precipitated and subsequently transformed to studtite in the presence of dissolved Np. The metaschoepite and studtite solids that formed initially contained <10 and 6500 ppm Np, respectively. Batch dissolution studies of these solids at pH 6 demonstrate release of Np that exceeds congruent dissolution of U from metastudtite; furthermore, the released Np cation remains in solution. Thus, although the Np partitions into the metastudtite solid initially, it is released to solution over time, indicating that metastudtite is not likely to serve as a host solid for Np incorporation or sorption of the neptunyl cation on long time scales.