Assessing the Likelihood of
Nuclear Terrorism Events
Steven S. Streetman
Data Architecture Solutions, Inc.
INMM, February, 2014
Overview
• Why Estimate Likelihood?
• Historical Estimates
• Principles for Estimating Likelihood
Estimating Likelihood
• Challenges
– Little to no historical data specifically about
radiological / nuclear terrorism
– Difficult to gain insight into terrorist intent and
capability
– Estimates will not only be highly uncertain, but
may vary significantly from one time to another
So Why Bother?
• Nuclear terrorism considered one of the greatest threats of
our time and could result in the highest consequences
• Must make decisions and prioritize defensive activities
– Any decision will be based – consciously or not – on an
estimate of likelihood
• The act of estimating teases out biases and assumptions and
forces better problem definition and characterization
• Estimates make the decision process more transparent and
repeatable
• Decisions should be informed by risk which requires
estimates of likelihood and consequence
How Has Nuclear Terrorism Risk Been
Estimated Before?
• Lugar (2005):
– 10% chance in next 5 years (~2%/year)
• Bunn (2006):
– 29% chance in next 10 years (~3%/year)
• Allison (2004):
– > 50% chance in the next 10 years (>5%/year)
• Mueller :
– <1 in a million chance of successful attempt (# attempts not estimated
but implication is <.001%/year)
• US Commission on Prevention of WMD (2008):
– “more likely than not by the end of 2013” (~5%/year – nuke or bio)
Do These Estimates Have a Bandwidth Bias or Are They Reasonable?
Political ‘Estimates’
•
•
•
•
•
•
•
•
Barack Obama, U.S. president (2010): “The single biggest threat to U.S. security, short-term, mediumterm and long-term, is the possibility of a terrorist organization obtaining a nuclear weapon.”
Mohamed ElBaradei, former director general of the IAEA and winner of the 2005 Nobel Peace Prize
(2009): “Nuclear terrorism is the most serious danger the world is facing.”
John Brennan, U.S. assistant to the president for counterterrorism and homeland security (2010): “The
threat of nuclear terrorism is real, it is serious, it is growing, and it constitutes one of the greatest threats
to our national security and, indeed, to global security.”
Hillary Clinton, U.S. secretary of state (2010): “The biggest nightmare that any of us have is that one of
these terrorist member organizations within this syndicate of terror will get their hands on a weapon of
mass destruction.”
Yukiya Amano, director general of the IAEA (2009): “The spread of nuclear weapons and nuclear
terrorism is an increasing threat for the international community.”
Ban Ki-moon, U.N. secretary general (2007): “Nuclear terrorism is one of the most serious threats of our
time.”
Anatoly Safonov, Special Representative of the Russian President for International Cooperation in the
Fight Against Terrorism and Transnational Organized Crime (2007): “We have firm knowledge, which is
based on evidence and facts, of steady interest and tasks assigned to terrorists to acquire in any form what
is called nuclear weapons, nuclear components.”
Alexander Bortnikov, director of the Russian Federal Security Service (2010): “We have information which
indicates that terrorists are continuing to try to get access to nuclear materials.”
Nuclear Terrorism Described as Biggest, Most Serious Threat
Principles for Estimating Likelihood
• Scenario Structure
– Make sure all the potential terrorism acts are considered
– Understand principle components of a nuclear terrorist
attack: adversary, material, device, attack logistics
• Uncertainty Analysis
– Consider best case, worst case, average, median
– Understand implications of alternative likelihood estimates
to prioritization decisions
• Sensitivity Analysis
– What would make your chosen course ‘wrong’?
Scenario Structure
• Scenarios should account for:
– Adversaries
– Acquisition of material, devices, or parts of
devices as well as device construction
– Likely device yields
– Potential detonation locations
– Response, mitigation, and recovery capabilities
• Scenarios may be specific or general, but
should cover the risk space
Contrasting Scenario Methodologies
Risk Scenario Space
(everything that
represents nuclear risk)
Common Approach
Better Approach
Scenario
The only risks represented are in
the dots. There may be important
risks that are missed in the white
spaces. There is no reason to
believe that all risks are covered.
Some risks are duplicated.
Each scenario is sufficiently abstract to
represent all the risk from the wedge. In
practice, the wedge is sampled multiple
times to get likelihood and consequences.
The approach for dividing into wedges is
the methodology.
Can Estimate by Dividing Likelihood into
Components
THREAT
VULNERABILITY
CONSEQUENCES
INTENT
CAPABILITY
LIKELIHOOD
SCENARIO
ADVERSARY
MATERIAL
TARGET
10
Relative vs. Absolute Likelihood
• Absolute likelihood much more uncertain and
difficult to estimate
– However, sometimes it must be included when comparing
to disparate threats (e.g., natural disasters, high frequency
security threats)
– Not necessary to include when only addressing rad/nuc
threats
• Relative likelihood (which attacks are more likely)
much easier – but still difficult – to estimate.
– Sufficient for resource allocation within the rad/nuc arena
Uncertainty Analysis
• Every value in a terrorism risk assessment is uncertain, but
the likelihood of a serious attempt is the most uncertain
quantity of all
• Combining multiple uncertainties is usually accomplished
with Monte Carlo estimation techniques
• Just as important as assessing the uncertainty is finding
appropriate ways to communicate it to decision makers
• Not all uncertainties are created equal. Sometimes
uncertainties are correlated and may be ignored
• In addition to uncertainties in values, must assess
uncertainties in model structure
– May need to look at different models
– May need to assess alternative futures
Sensitivity Analysis
• What if your estimates are wrong?
• Some estimates influence risk more than others:
risk is more sensitive to these estimates
• Knowing which ones are more sensitive is useful
in attempting to improve estimates over time
• In our risk assessments, the overall likelihood of
an attempt is usually the most sensitive
parameter
How Likely Must an Attack Be?
• Consequences: direct consequences often
estimated at around $1T
– Including cascading effects of the attack, a nuclear
detonation in the US is roughly a $10T event
• Risk is likelihood x consequences
• Suppose likelihood is in the range estimated
by previous experts (~1-5%/year)
• Then risk is $100B-$500B estimated annual
loss
What Should the US Spend Annually to Avoid a $500B Potential Annual Loss?