Nuclear Terrorism

Introduction

Fig. 1: Damage of four reactor buildings of the Fukushima nuclear plant. (Source: Wikimedia Commons)

Broadly, nuclear terrorism refers to the use of radioactive material as a weapon with intent to harm individuals and/or the immediate environment. Under this definition nuclear terrorism encapsulates both the risk a group procures/develops a nuclear weapon and the risk an organization develops a method of dispersal such as a dirty bomb a weapon which spreads radioactive materials use a conventional explosive (i.e. not nuclear fission or fusion).

In this report we will focus on the procurement of nuclear material by a terrorist organizations and militant groups rather than a rogue state (such as North Korea). There is a degree of consensus within the academic community that the risk of terrorist organizations purchasing or building a nuclear weapon is low, and that the risk of a dirty bomb is more substantial. [1] Finally, we will conclude by discussing the possible damages of nuclear terrorism in this form.

Dirty Bombs and Radioactive Dispersal Devices

A dirty bomb employs conventional explosives to spread radioactive material emitting α, β or γ radiation. Table 1 depicts nine key isotopes which Argonne National Laboratory has identified as posing the highest threat for radiological terrorism given their concentration and availability. [2] Cs-137, Co-60 and Ir-192 are primarily gamma ray emitters, Sr-90 is a beta particle emitter and the rest are alpha emitters. Because human skin provides effective natural barrier against alpha particles and to a lesser degree beta particles, the health risks of radiation from external (i.e. not ingestion, inhalation) exposure of alpha emitters remains low. [2] Gamma emitters present a serious risk, with doses of over 4 Gy of radiation being fatal by way of damaging bone marrow and the intestinal tissues. [3]

The effectiveness of a dirty bomb is highly contingent on the physicochemical form of the radioactive materials and the design of the explosive. [4] An effective weapon will be able to aerosolize particles and spread them over a large area akin to the fallout cloud from a nuclear weapon detonation. Notably, Cs-137 can be packaged as a powdered chloride which is readily soluble, making it more prone to shock aerosolization. [5,6] Ir-192 and Co-60 are commonly found as metals and even when deployed with idealized detonation devices are estimated to achieve less than 1% aerosolization due to the requirement of a phase transition. [5,6] As such, development of dirty bombs may require chemistry to further process radioactive materials into more dispersal friendly states.

Its worth noting that γ sources present health hazards to those involved in procurement and bomb development which has led some to believe weaker sources may be of more interest to terrorists. [4] When ingested or inhaled, α sources can be up to 20 times more lethal than γ or β sources. [4] This has led some to speculate that terrorists may shy away from explosive dirty bombs and may instead opt for non-explosive dispersal methods of both γ and α emitters: driving a car that sprays a radioactive aerosols; dowsing victims in radioactive liquids; and polluting large volume of water. [4] While the chance of inhalation and exposure through these techniques is still low, they offer lower barriers to entry than developing an explosive and can could result in fatalities in the hundreds. [4,6]

Assessing the Security of Nuclear Material

Sources for procuring nuclear materials range from storage facilities of nuclear waste and spent fuel rods to industrial irradiators and radiography equipment at hospitals. A general rule of thumb is that α sources are subject to less regulation than β and γ sources. [4] In response to emerging reports in the 1990s that al Qaeda was attempting to procure nuclear materials, the International Atomic Energy Agency established the Incident and Trafficking Database (ITDB) in 1995. The database aggregates incident reports of nuclear material either leaving or entering regulatory control across its network of 139 countries. [7] Incidents are grouped according to health risk and suspected motives. Each radioactive source is categorized on a scaled from 1 - 5, depending on its potential to harm human health, with minutes-long exposure of category 1 being fatal. Three groups define the motive: incidents with malicious intent, incidents with unconfirmed motives and incidents without malicious intent including unauthorized shipment, unauthorized discovery and unexpected discovery of radioactive material (orphan sources). The ITDB's effectiveness at documenting incidents and providing an effective dataset for analysis has been questioned. [7] First, the ITDB has historically used ambiguous language to provide at best, course grain categorization of incidents. As an example, despite hundreds of reported incidents of malicious intent over the period from 2002 - 2012, only four cases of attempted sales of highly enriched uranium were recorded and all of them were to undercover officers. [7] Additionally, a lack of a standardized reporting procedures among participants has created significant fluctuations yearly incidents which present challenges for data analysis.

Projected Health and Economic Impacts of a Dirty Bomb Attack

An analysis of hypothetical dirty bomb attacks at the Long Beach Port in Los Angeles California estimated a 50,000 Ci (curie) release (assuming 20% of the material aerosolized in the attack) would cause between 0 and 20 fatalities from the blast, acute radiation and latent cancers, while causing up to 200 million USD in losses from a port shutdown and 100 million USD in decontamination costs. [8] A 1,000,000 Ci release would be responsible for up to 50 fatalities from the blast, and up to 500 fatalities from latent cancers. The necessity for serious decontamination would result in an estimate 10 to 100 billion USD cleanup cost and 100's of billions USD in property and business losses. The authors caution the likelihood of such scenario is exceedingly low and the impacts are subject to an error bar, the implication is that economic harms heavily outweigh any harms to human health.

To give an order of magnitude estimate of how long the damage of a nuclear terrorist attack could persist we can look at the 2011 Fukushima Daiichi nuclear disaster which released up to 14.5 PBq (PetaBecquerel)of Cs-137 and Sr-90, of which Cs-137 was the main contributor. [9] In the scenario where Cs-137 was used in a radiological terror attack, the expected fallout and atmospheric deposition could mimic the aftermath of the Fukushima disaster. After the disaster, Cs-137 atmospheric deposition rates increased by six order of magnitudes in the immediate area, and to a lesser but still noticeable degree around the world (facilitated by atmospheric transport). Fig. 1 depicts the birds eye images of the damaged reactors after the disaster. Although the half-life of Cs-137 is 30.2 years, the rate of decline can be accelerated by natural environmental and weather processes. A recent study estimated the effective half-life of Cs-137 atmospheric deposition is 4.7 years at a site approximately 70 miles from the Daiichi power plant, which would require roughly 42 years until deposition rates reached the background rate proceeding the incident. [9] While this estimate is not synonymous with the time required for the immediate surroundings of the Fukushima plant to be habitable again, it underscores the time scales of Cs-137 persistence in the environment.

Conclusion

Ultimately the risk of nuclear terrorism from radioactive dispersal devices and dirty bombs remains low. Although unaccounted isotopes are not synonymous with stolen isotopes, the minor amount of illicit trafficking suggests a nuclear black-market of some form exists. Should the world be subject to such an attack, acute and long-term health effects from exposure will be minimal. Economic costs from lost business, quarantine and decontamination will dominate.

© Alexander Conklin. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.

References

[1] R. M Frost, Nuclear Terrorism after 9/11 (Routledge, 2017).

[2] J. P. Peterson et al., "Radiological and Chemical Fact Sheets to SupportHealth Risk Analyses for Contaminated Areas," Argonne National Laboratory, March 2007.

[3] T. J. Cerveny et al., "Acute Radiation Syndrome in Humans," in Medical Consequences of Nuclear Warfare, ed by. R. Zajtchuk, T. J Cerveny and R. J. Walker (Dept. of the Army, 1989).

[4] J. M. Acton et al., "Beyond the Dirty Bomb: Re-Thinking Radiological Rerror," Survival 49, 151 (2007).

[5] K. G. Andersson et al., "Requirements for Estimation of Doses from Contaminants Dispersed by a Dirty Bomb Explosion in an urban area," J. Environ.Radioact. 100, 1005 (2009).

[6] F. T. Harper, S. V. Musolino and W. B. Wente, "Realistic Radiological Dispersal Device Hazard Boundaries and Ramifications for Early Consequence Management Decisions," Health Phys. 93, 1 (2007).

[7] S. Kondratov, "Illicit Trafficking in Nuclear and Other Radioactive Materials: Separating Myths From Realities," Int. J. Nucl. Governance, Economy and Ecology 4, 180 (2019).

[8] H. Rosoff and D. von Winterfeldt, "A Risk and Economic Analysis of Dirty Bomb Attacks on the Ports of Los Angeles and Long Beach," Risk Anal. 27, 533 (2007).

[9] K. Takeshi et al., "Temporal Variations of Sr-90 and Cs-137 in Atmospheric Depositions After the Fukushima Daiichi Nuclear Power Plant Accident With Long-Term Observations," Sci. Rep. 10, 21627 (2020).