Radionuclide observables for the Platte underground nuclear explosive test on 14 April 1962

The bioreduction of U(VI) and Pu(IV): Experimental and thermodynamic studies

The experimental and thermodynamic bioreduction of U(VI)aq and Pu(IV)am was studied in order to more accurately predict their transport velocities in groundwater and assess the contamination risks to the associated environments. The results obtained in this study emphasize the impact of carbonate-calcium and humic acids at 7.1 and anoxic solutions on the rate and extent of U(VI)aq and Pu(IV)am bioreduction by Shewanella putrefaciens. We found that the bioreduction rate of U(VI)aq became slow in the presence of NaHCO3/CaCl2. The more negative standard redox potentials of the ternary complexes of U(VI)-Ca2+-CO32- accounted for the decreased rate of bioreduction, e.g., [Formula: see text]  = -0.6797 V ≪ [Formula: see text]  = 0.3862 V. The bioreduction of Pu(IV)am seemed feasible, while humic acids accepted the adequate extracellular electrons secreted by S. putrefaciens, and the redox potential of Eh(HAox/HAred) was lower than Eh(PuO2(am)/Pu3+), e.g., Eh(HAox/HAred) ≦ Eh(PuO2(am)/Pu3+) if humic acids accepted ≧ 7.952 × 10-7 mol of electrons. The standard redox potentials, Eho(PuO2(am)/Pu3+) = 0.9295 V ≫ [Formula: see text]  = -0.6797 V, cannot explain the reduction extent of Pu(IV)am (8.9%), which is notably smaller than that of U(VI)aq (74.9%). In fact, the redox potential of Pu(IV)am was distinctly negative under the experimental conditions of trace-level Pu(IV)am (∼2.8 × 10-9 mol/L Pu(IV) if Pu(IV)am was completely dissolved), e.g., Eh(PuO2(am)/Pu3+) = -0.1590 V (α(Pu3+) = 10-10 mol/L, pH = 7.1). Therefore, the chemical factor of Pu3+ activity, leading to a rapid drop in Eh(PuO2(am)/Pu3+) at trace-level Pu(IV)am, was responsible for the relatively small reduction extent of Pu(IV)am.

Investigating the detection of underground nuclear explosions by radon displacement

A novel approach is proposed to detect underground nuclear explosions (UNEs) through the displacement of natural radon isotopes (²²²Rn and ²²⁰Rn). Following an explosion, it is hypothesized that the disturbance and pressurization of the sub-surface would facilitate the movement of radon from the depth of the UNE towards the surface resulting in increased soil gas activity. The resulting signal may be magnified by a factor of 2.0-4.9 by the decay of radon to its short-lived progeny. Increases in background activity may be useful for identifying locations to perform additional measurements, or as a detectable signal at monitoring stations. To validate this hypothesis, radon detection instrumentation was deployed at the Dry Alluvium Geology (DAG) site of the Source Physics Experiment (SPE) at the Nevada National Security Site (NNSS). Natural fluctuations in the soil gas activity due to barometric pumping, and the lower yield of the chemical explosions (1-50 t) made it difficult to confirm a displacement of radon from the explosions, and further study to validate the proposed hypothesis is recommended.

Rare observation of atmospheric 65Zn, 134Cs and 137Cs with possible relation to the 12 February 2013 test announced by North Korea

Abnormal particulate radionuclides (⁶⁵Zn, ¹³⁴Cs and ¹³⁷Cs) were detected at the CTBTO RN58 station which is located near North Korea between 12 and March 14, 2016. Detection ratio for caesium (¹³⁴Cs/¹³⁷Cs) shows that the product origin was nuclear explosion and dilution factors at RN58, released from DPRK test site, show clear correlation with radioactivity concentration of two samples. The detected radionuclides may be originated from the third nuclear test, February 2013. Half-life, radionuclides fractionation, MDC, and device design are attributed to no detection of other nuclides. Most of radionuclides have been decayed away and relatively long half-life nuclides might be in the third test site but they were displaced deep inside the area by fractionation during the explosion. Considering ⁶⁵Zn activity ratio to ¹³⁷Cs which is higher than historical ratios at Brunswick in 1968, there is a possibility that the third DPRK nuclear test was a "salted" nuclear bomb test using zinc as jacket instead of fissionable ²³⁸U around the secondary stage fusion fuel.

The detectability of the Wigwam underwater nuclear explosion by the radionuclide stations of the International Monitoring System

The Comprehensive Nuclear-Test-Ban Treaty (CTBT) bans all nuclear explosions, including those detonated from an underwater nuclear explosion. To improve the understanding of the radionuclide signatures of such an event, and whether it would be detectable under the verification regime of the CTBT, the 1955 Wigwam underwater nuclear explosive test has been modelled. Inventory calculations and atmospheric transport modelling has been performed to estimate the activity at the radionuclide stations (RN) of the International Monitoring System (IMS). This has utilized reported release values (0.92%) and meteorological data from the event. The research shows that there is a high probability that Wigwam would have been detectable at U.S. IMS stations at Wake Island (RN77) at 8.4 d, Upi, Guam (RN80) at 10.7 d and Sand Point, AK (RN71) at 13.7 d. At these locations, the majority of IMS relevant radionuclides were fission products, such that additional radionuclides from the seawater activation had largely decayed before reaching the stations.

Radionuclide observables of underwater nuclear explosive tests

There remain technical challenges for an On-site Inspection (OSI) in the high seas environment, which gathers evidence of a violation of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). For terrestrial nuclear explosions, the radionuclide observables are well defined and States Parties have chosen 17 particulate radionuclides that allow discrimination from other nuclear events. However, an underwater nuclear explosion generates induced radionuclides from the neutron activation of seawater, which has the potential to interfere with the measurement of the radionuclide observables using gamma-spectrometry techniques. To understand these effects the inventory of OSI relevant (6.0 × 10¹⁶ Bq) and activation (1.6 × 10¹⁹ Bq) radionuclides has been calculated for a 1 kT underwater nuclear explosion. The activation products consist predominantly of ³⁸Cl and ²⁴Na, which decay to 5.56% and 0.0007% of their initial activity within 1 and 14 days. Monte Carlo techniques have been used to assess spectral interferences within this timeframe. It is demonstrated that during this period they do not interfere with the measurement of the existing radionuclide observables. Additionally, ²⁴Na has been identified as useful for inspection purposes.

The 2014 Integrated Field Exercise of the Comprehensive Nuclear-Test-Ban Treaty revisited: The case for data fusion

The International Monitoring System of the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) uses a global network of radionuclide monitoring stations to detect evidence of a nuclear explosion. The two radionuclide technologies employed-particulate and noble gas (radioxenon) detection-have applications for data fusion to improve detection of a nuclear explosion. Using the hypothetical 0.5 kT nuclear explosive test scenario of the CTBTO 2014 Integrated Field Exercise, the intrinsic relationship between particulate and noble gas signatures has been examined. This study shows that, depending upon the time of the radioxenon release, the particulate progeny can produce the more detectable signature. Thus, as both particulate and noble gas signatures are inherently coupled, the authors recommend that the sample categorization schemes should be linked.