In PNAS, Priyadarshi et al. (1) reported the detection of unusual levels of atmospheric 35 S in California related to releases from the Fukushima nuclear plant. The authors stated that the 35 S was generated by "leaking neutrons," activating the chlorine in the seawater that was used to cool the Fukushima reactors via the nuclear reaction 35 Cl(n,p) 35 S. The authors calculated "that 4e11 neutrons per m 2 were released," of which "2e8 neutrons per m 2 reacted with 35 Cl."Although we acknowledge it as probable that the detected 35 S originated from Fukushima, we have doubts about the proposed creation and release path. First, there are several possible alternative sources of 35 S:The primary coolant of light water reactors contains veritable amounts of 35 S, typically 0.07-2 MBq/m 3 (or, in other terms, about 7e11 to 2e13 atoms/m 3 ) (2). A typical concentration of Cl in the coolant is about 0.1 ppm, (i.e., 5 decades less than in seawater). However, a reactor at power level generates 1e18 neutrons/m 2 each second, 6 decades more than the calculated "neutron leakage." Hence, the 35 S content in the primary coolant alone could explain the calculated releases. Irradiated fuel itself also contains even more 35 S generated from Cl impurities of the fuel, about 1e19 atoms per ton. This is a huge reservoir of 35 S that might be released if coolant (whether primary or seawater) comes into contact with damaged fuel rods. Finally, the seawater contains dissolved atmospheric 35 S, which will be released immediately once the seawater has evaporated.Additionally, a calculation of the activation of the seawater used for cooling strongly depends on a number of unknown parameters that determine the "irradiation geometry" and reaction rate, most prominently the fuel and core geometry (i.e., the degree of fuel degradation), the water flow rate, moderation, and (self-)shielding effects. Also, the spent fuel pools have to be considered as possible origins, further complicating the analysis. Without any estimation of the size of these uncertainties, probably several orders of magnitude, the results are of little value. Furthermore, the term "neutron leakage" is misleading because its use is not in accordance with common understanding. As far as we understand it, the number given is a neutron fluence (i.e., the neutron flux integrated over the duration of the activation process). In any case, such a number does not provide any new insight as long as it is not compared with any typical value.To conclude, the attempt to gain insights into the accident at Fukushima from airborne radioactivity measurements is very interesting. However, given the uncertainties stated above, we doubt that meaningful quantitative statements are possible from such an analysis. The Fukushima accident is anything but a "well-defined 35 S source." The evidence appears to be too weak to gain "previously undescribed insight" into environmental transformational rates, simultaneously estimating the depositional time scale, oxidation time scale, and a neutron fluen...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.