Radioactive contamination from the partially-burned former Santa Susanna nuclear research facility

Radioactive microparticles related to the Woolsey Fire in Simi Valley, CA SCience Direct, MarcoKaltofenaMaggieGundersenbArnieGundersenb Worcester Polytechnic Institute, Dept. of Physics, Fairewinds Energy Education, 8 October 2021.

Highlights

Wildfire in radiologically contaminated zones is a global concern; contaminated areas around Chernobyl, Fukushima, Los Alamos, and the Nevada Nuclear Test Site have all experienced wildfires.

Three hundred sixty samples of soil, dust and ash were collected in the immediate aftermath of the Los Angeles (CA, USA) Woolsey fire in 2018.

Radioactive contamination from the partially-burned former Santa Susanna nuclear research facility was found in the fire zone.

A limited number of widely scattered locations had evidence of radioactive microparticles originating at the research facility.

X-ray data showed that ashes from the fire could spread site contaminants to distant, but widely spaced, locations.

Abstract

In November 2018, the Woolsey Fire burned north of Los Angeles, CA, USA, potentially remobilizing radioactive contaminants at the former Santa Susana Field Laboratory, a shuttered nuclear research facility contaminated by chemical and radiochemical releases. Wildfire in radiologically contaminated zones is a global concern; contaminated areas around Chernobyl, Fukushima, Los Alamos, and the Nevada Nuclear Test Site have all experienced wildfires. Three weeks after the Woolsey Fire was controlled, sampling of dusts, ashes, and surface soils (n = 360) began and were analyzed by alpha- and beta-radiation counting. Samples were collected up to a 16 km radius from the perimeter of the laboratory. Controls and samples with activities 1σ greater than background were also examined by alpha and/or gamma spectroscopy or Scanning Electron Microscopy with Energy Dispersive X-ray analysis. Of the 360 samples collected, 97% showed activities at or close to site-specific background levels. However, offsite samples collected in publicly-accessible areas nearest to the SSFL site perimeter had the highest alpha-emitting radionuclides radium, thorium, and uranium activities, indicating site-related radioactive material has escaped the confines of the laboratory.

In two geographically-separated locations, one as far away as 15 km, radioactive microparticles containing percent-concentrations of thorium were detected in ashes and dusts that were likely related to deposition from the Woolsey fire. These offsite radioactive microparticles were colocated with alpha and beta activity maxima. Data did not support a finding of widespread deposition of radioactive particles. However, two radioactive deposition hotspots and significant offsite contamination were detected near the site perimeter……………………………

4. Conclusions

A significant majority of samples (97% of 360 samples) collected in the study zone registered radioactivity levels that matched existing area background levels. Nevertheless, some ashes and dusts collected from the Woolsey Fire zone in the fire’s immediate aftermath contained high activities of radioactive isotopes associated with the Santa Susana Field Laboratory (SSFL). The data show that Woolsey Fire ash did, in fact, spread SSFL-related radioactive microparticles, and the impacts were confined to areas closest to SSFL and at least three other scattered locations in the greater Simi Valley area. Alpha and beta counting, high-resolution alpha and gamma spectroscopy, and X-ray microanalysis using SEM/EDS confirmed the presence of radioactive microparticles in the Woolsey Fire-related ashes and dusts.

Most of the fire-impacted samples found near the SSFL site’s perimeter were on lands accessible to the public. There were, however, scattered localized areas of increased radioactivity due to the presence of radioactive microparticles in ash and recently-settled dusts collected just after the Woolsey fire. These radioactive outliers were found in Thousand Oaks, CA, and Simi Valley, CA, about 15 and 5 km distant from SSFL, respectively. The Thousand Oaks samples had alpha count rates up to 19 times background, and X-ray spectroscopy (SEM) identified alpha-emitting thorium as the source of this excess radioactivity. Excessive alpha radiation in small particles is of particular interest because of the relatively high risk of inhalation-related long-term biological damage from internal alpha emitters compared to external radiation.

The nuclides identified as the sources of excess radioactivity in impacted samples were predominately isotopes of radium, uranium, and thorium. These have naturally-occurring sources, but these isotopes are also contaminants of concern at SSFL and were detected at generally increasing activities as the distance from SSFL decreased. In addition, the number of radioactive microparticles per gram of particulate matter also increased strongly with decreasing distance from SSFL. These data demonstrate that fire and/or other processes have spread SSFL contamination beyond the facility boundary………..

……https://www.sciencedirect.com/science/article/pii/S0265931X21002277?dgcid=coauthor