Nuclear Power Plants: Vulnerability to Terrorist Attack
Nuclear Power Plants:
Vulnerability to Terrorist Attack
Mark Holt and Anthony Andrews
Specialists in Energy Policy
Resources, Science, and Industry Division
Protection of nuclear power plants from land-based assaults, deliberate aircraft
crashes, and other terrorist acts has been a heightened national priority since the attacks
of September 11, 2001. The Nuclear Regulatory Commission (NRC) has strengthened
its regulations on nuclear reactor security, but critics contend that implementation by the
industry has been too slow and that further measures are needed. Several provisions to
increase nuclear reactor security were included in the Energy Policy Act of 2005, signed
August 8, 2005. The law requires NRC to conduct “force-on-force” security exercises
at nuclear power plants at least once every three years and to revise the “design-basis
threat” that nuclear plant security forces must be able to meet, among other measures.
This report will be updated as events warrant.
Nuclear power plants have long been recognized as potential targets of terrorist
attacks, and critics have long questioned the adequacy of the measures required of nuclear
plant operators to defend against such attacks. Following the September 11, 2001, attacks
on the Pentagon and the World Trade Center, the Nuclear Regulatory Commission (NRC)
began a “top-to-bottom” review of its security requirements. On February 25, 2002, the
agency issued “interim compensatory security measures” to deal with the “generalized
high-level threat environment” that continued to exist, and on January 7, 2003, it issued
regulatory orders that tightened nuclear plant access. On April 29, 2003, NRC issued
three orders to restrict security officer work hours, establish new security force training
and qualification requirements, and increase the “design basis threat” (DBT) that nuclear
security forces must be able to defend against.
In the Energy Policy Act of 2005 (EPACT), Congress imposed a statutory
requirement on the NRC to initiate rulemaking for revising the design basis threat.1 The
DBT, a classified document, describes general characteristics of adversaries that nuclear
1 P.L. 109-58, Title VI, Subtitle D — Nuclear Security (Secs. 651-657). Sec. 651 adds Atomic
Energy Act Sec. 170E. Design Basis Threat Rulemaking.
plants and nuclear fuel cycle facilities must defend against, including radiologic sabotage
and theft of strategic special nuclear material. EPACT required NRC to consider 12
factors in revising the DBT, including but not limited to an assessment of various terrorist
threats, sizable explosive devices and modern weapons, attacks by persons with
sophisticated knowledge of facility operations, and attacks on spent fuel shipments. NRC
approved its final rule to amend the DBT (10 C.F.R. Part 73.1) on January 29, 2007.2
Plant Physical Security. Under the regulations in place prior to the September
licensed commercial nuclear power plants must have a series of physical barriers and a
trained security force. The plant sites are divided into three zones: an “owner-controlled”
buffer region, a “protected area,” and a “vital area.” Access to the protected area is
restricted to a portion of plant employees and monitored visitors, with stringent access
barriers. The vital area is further restricted, with additional barriers and access
requirements. The security force must comply with NRC requirements on pre-hiring
investigations and training.3
NRC published a proposed rule on October 26, 2006, to impose additional reactor4
security requirements. It would also codify in regulation various NRC security orders
issued since the 9/11 attacks and implement security provisions included in EPACT.
Design Basis Threat. The design basis threat is used by NRC licensees as the
basis for implementing defensive strategies of a specific nuclear plant site through
security plans, safeguards contingency plans, and guard training and qualification plans.
One of NRC’s April 2003 regulatory orders changed the DBT to “represent the largest
reasonable threat against which a regulated private guard force should be expected to
defend under existing law,” according to the NRC announcement.
NRC’s final rule for revising the DBT took effect April 18, 2007. As directed by the
Energy Policy Act, the final rule has the principal objective of making the security
requirements imposed by the April 29, 2003, DBT orders generically applicable.
Although specific details of the revised DBT were not released to the public, in general
the final rule
!clarifies that physical protection systems are required to protect against
diversion and theft of fissile material;
!expands the assumed capabilities of adversaries to operate as one or more
teams and attack from multiple entry points;
!assumes that adversaries are willing to kill or be killed and are
knowledgeable about specific target selection;
!expands the scope of vehicles that licensees must defend against to
include water vehicles and land vehicles beyond four-wheel-drive type;
2 Federal Register, March 19, 2007 (vol. 72, no. 52), Nuclear Regulatory Commission, Design
Basis Threat, Final Rule, pp. 12705-12727.
3 General NRC requirements for nuclear power plant security can be found in 10 C.F.R. 73.55.
4 Federal Register, October 26, 2006 (vol. 71, no. 207), Nuclear Regulatory Commission, Power
Reactor Security Requirements, Proposed Rule.
!revises the threat posed by an insider to be more flexible in scope; and
!adds a new mode of attack from adversaries coordinating a vehicle bomb
assault with another external assault.
In 2006, the Government Accountability Office (GAO) reviewed the upgrades in
nuclear plant security and found a generally logical and well-defined process. GAO found
NRC staff trained in threat assessment who monitor information provided by intelligence
agencies and screen the information to evaluate particular terrorist capabilities for
inclusion in the DBT. However, the NRC produced a revised DBT that generally, but not
always, corresponded to the threat assessment staff’s original recommendations.5
The DBT final rule excluded aircraft attacks, which raised considerable controversy.
In approving the rule, NRC rejected a petition from the Union of Concerned Scientists to
require that nuclear plants be surrounded by aircraft barriers made of steel beams and
cables (the so-called “beamhenge” concept). Critics of the rule charged that deliberate
aircraft crashes were a highly plausible mode of attack, given the events of 9/11.
However, NRC contended that power plants were already required to mitigate the effects
of aircraft crashes and that “active protection against airborne threats is addressed by other
federal organizations, including the military.”6 Additional NRC action on aircraft threats
is discussed below.
Force-On-Force Exercises. EPACT codified an NRC requirement that each
nuclear power plant conduct security exercises every three years to test its ability to
defend against the design basis threat. In these “force-on-force” exercises, monitored by
NRC, an adversary force from outside the plant attempts to penetrate the plant’s vital area
and damage or destroy key safety components. Participants in the tightly controlled
exercises carry weapons modified to fire only blanks and laser bursts to simulate bullets,
and they wear laser sensors to indicate hits. Other weapons and explosives, as well as
destruction or breaching of physical security barriers, may also be simulated. While one
squad of the plant’s guard force is participating in a force-on-force exercise, another
squad is also on duty to maintain normal plant security. Plant defenders know that a
mock attack will take place sometime during a specific period of several hours, but they
do not know what the attack scenario will be. Multiple attack scenarios are conducted
over several days of exercises.
Full implementation of the force-on-force program began in late 2004. Standard
procedures and other requirements have been developed for using the force-on-force
exercises to evaluate plant security and as a basis for taking regulatory enforcement
action. Many tradeoffs are necessary to make the exercises as realistic and consistent as
possible without endangering participants or regular plant operations and security.
5 GAO, Nuclear Power Plants — Efforts Made to Upgrade Security, But the Nuclear Regulatory
Commission’s Design Basis Threat Process Should Be Improved, GAO-06-388, Report to the
Chairman, Subcommittee on National Security, Emerging Threats, and International Relations,
Committee on Government Reform, House of Representatives, March 2006.
6 NRC Office of Public Affairs, “NRC Approves Final Rule Amending Security Requirements,”
News Release No. 07-012, January 29, 2007.
NRC required the nuclear industry to develop and train a “composite adversary
force” comprising security officers from many plants to simulate terrorist attacks in the
force-on-force exercises. However, in September 2004 testimony, GAO criticized the
industry’s selection of a security company that guards about half of U.S. nuclear plants,
Wackenhut, to also provide the adversary force. In addition to raising “questions about
the force’s independence,” GAO noted that Wackenhut had been accused of cheating on
previous force-on-force exercises by the Department of Energy.7 EPACT requires NRC
to “mitigate any potential conflict of interest that could influence the results of a
force-on-force exercise, as the Commission determines to be necessary and appropriate.”
Emergency Response. After the 1979 accident at the Three Mile Island nuclear
plant near Harrisburg, PA, Congress required that all nuclear power plants be covered by
emergency plans. NRC requires that within an approximately 10-mile Emergency
Planning Zone (EPZ) around each plant, the operator must maintain warning sirens and
regularly conduct evacuation exercises monitored by NRC and the Federal Emergency
Management Agency (FEMA). In light of the increased possibility of terrorist attacks
that, if successful, could result in release of radioactive material, critics have renewed
calls for expanding the EPZ to include larger population centers.
The release of radioactive iodine during a nuclear incident is a particular concern,
because iodine tends to concentrate in the thyroid gland of persons exposed to it.
Emergency plans in many states include distribution of iodine pills to the population
within the EPZ. Taking non-radioactive iodine before exposure would prevent absorption
of radioactive iodine but would afford no protection against other radioactive elements.
In 2002, NRC began providing iodine pills to states requesting them for populations
within the 10-mile EPZ.
Nuclear Plant Vulnerability
The major concerns in operating a nuclear power plant are controlling the nuclear
chain reaction and assuring that the reactor core does not lose its coolant and “melt down”
from the heat produced by the radioactive fission products within the fuel rods. U.S.
plants are designed and built to prevent dispersal of radioactivity, in the event of an
accident, by surrounding the reactor in a steel-reinforced concrete containment structure,
which represents an intrinsic safety feature. Two major accidents have taken place in
power reactors, at Three Mile Island (TMI) in 1979 and at Chernobyl in the Soviet Union
in 1986. Although both accidents resulted from a combination of operator error and
design flaws, TMI’s containment structure effectively prevented a major release of
radioactivity from a fuel meltdown caused by the loss of coolant. In the Chernobyl
accident, the reactor’s protective barriers were breached when an out-of-control nuclear
reaction led to a fierce graphite fire that caused a significant part of the radioactive core
to be blown into the atmosphere.
7 Government Accountability Office. Nuclear Regulatory Commission: Preliminary Observations
on Efforts to Improve Security at Nuclear Power Plants. Statement of Jim Wells, Director,
Natural Resources and Environment, Government Accountability Office, to the Subcommittee
on National Security, Emerging Threats, and International Relations, House Committee on
Government Reform. September 14, 2004. p. 14.
Vulnerability from Air Attack. Nuclear power plants were designed to withstand
hurricanes, earthquakes, and other extreme events. But deliberate attacks by large
airliners loaded with fuel, such as those that crashed into the World Trade Center and
Pentagon, were not analyzed when design requirements for today’s reactors were8
determined. A taped interview shown September 10, 2002, on Arab TV station al-
Jazeera, which contains a statement that Al Qaeda initially planned to include a nuclear
plant in its 2001 attack sites, intensified concern about aircraft crashes.
In light of the possibility that an air attack might penetrate the containment building
of a nuclear plant, some interest groups have suggested that such an event could be
followed by a meltdown and widespread radiation exposure. Nuclear industry
spokespersons have countered by pointing out that relatively small, low-lying nuclear
power plants are difficult targets for attack, and have argued that penetration of the
containment is unlikely, and that even if such penetration occurred it probably would not
reach the reactor vessel. They suggest that a sustained fire, such as that which melted the
steel support structures in the World Trade Center buildings, would be impossible unless
an attacking plane penetrated the containment completely, including its fuel-bearing
wings. According to former NRC Chairman Nils Diaz, NRC studies “confirm that the
likelihood of both damaging the reactor core and releasing radioactivity that could affect
public health and safety is low.”9
Although NRC’s final rule on the design basis threat (discussed above) excludes
aircraft attacks, NRC announced on April 24, 2007, that it would issue a proposed rule
requiring license applicants for new reactors to assess potential design improvements that
would improve protection against impact by large commercial aircraft. The proposed rule
would affect new reactor designs not previously certified by NRC.10 Westinghouse
submitted changes in the design of its AP1000 reactor to NRC on May 29, 2007,
proposing to line the inside and outside of the reactor’s concrete containment structure11
with steel plates to increase resistance to aircraft penetration.
Spent Fuel Storage. When no longer capable of sustaining a nuclear chain
reaction, “spent” nuclear fuel is removed from the reactor and stored in a pool of water
in the reactor building and at some sites later transferred to dry casks on the plant grounds.
Because both types of storage are located outside the reactor containment structure,
particular concern has been raised about the vulnerability of spent fuel to attack by aircraft
or other means. If terrorists could breach a spent fuel pool’s concrete walls and drain the
cooling water, the spent fuel’s zirconium cladding could overheat and catch fire.
8 Meserve, Richard A., NRC Chairman, “Research: Strengthening the Foundation of the Nuclear
Industry,” Speech to Nuclear Safety Research Conference, October 29, 2002.
9 Letter from NRC Chairman Nils J. Diaz to Secretary of Homeland Security Tom Ridge,
September 8, 2004.
10 NRC Office of Public Affairs, “NRC Proposes Adding Plane Crash Security Assessments to
New Reactor Design Certification Requirements,” News Release No. 07-053, April 24, 2007.
11 MacLachlan, Ann, “Westinghouse Changes AP1000 Design to Improve Plane Crash
Resistance,” Nucleonics Week, June 21, 2007.
The National Academy of Sciences (NAS) released a report in April 2005 that found
that “successful terrorist attacks on spent fuel pools, though difficult, are possible,” and
that “if an attack leads to a propagating zirconium cladding fire, it could result in the
release of large amounts of radioactive material.” NAS recommended that the hottest
spent fuel be interspersed with cooler spent fuel to reduce the likelihood of fire, and that
water-spray systems be installed to cool spent fuel if pool water were lost. The report also
called for NRC to conduct more analysis of the issue and consider earlier movement of
spent fuel from pools into dry storage.12 The FY2006 Energy and Water Development
Appropriations Act (P.L. 109-103, H.Rept. 109-275) provided $21 million for NRC to
carry out the site-specific analyses recommended by NAS.
NRC has long contended that the potential effects of terrorist attacks are too
speculative to include in environmental studies for proposed spent fuel storage and other
nuclear facilities. However, the U.S. Court of Appeals for the 9th Circuit ruled in June
2006 that terrorist attacks must be included in the environmental study of a dry storage
facility at California’s Diablo Canyon nuclear plant. NRC reissued the Diablo Canyon
study May 29, 2007, to comply with the court ruling, but it did not include terrorism in
other recent environmental studies.13
Regulatory and Legislative Proposals
Critics of NRC’s security measures have demanded both short-term regulatory
changes and legislative reforms. A fundamental concern was the nature of the DBT,
which critics contended should be increased to include a number of separate, coordinated
attacks. Critics also pointed out that licensees are required to employ only a minimum of
five security personnel on duty per plant, which they argue is not enough for the job.14
Nuclear spokespersons responded that the actual security force for the nation’s 65 nuclear
plant sites numbers more than 5,000, an average of about 75 per site (covering multiple
shifts). Nuclear plant security forces are also supposed to be aided by local law
enforcement officers if an attack occurs.
Because of the growing emphasis on security, NRC established the Office of Nuclear
Security and Incident Response on April 7, 2002. The office centralizes security
oversight of all NRC-regulated facilities, coordinates with law enforcement and
intelligence agencies, and handles emergency planning activities. Force-on-force
exercises are an example of the office’s responsibilities.
12 National Academy of Sciences, Board on Radioactive Waste Management, Safety and Security
of Commercial Spent Nuclear Fuel Storage, Public Report (online version), released April 6,
13 Beattie, Jeff, “NRC Takes Two Roads on Terror Review Issue,” The Energy Daily, February
14 10 C.F.R. 73.55 (h)(3) states: “The total number of guards, and armed, trained personnel
immediately available at the facility to fulfill these response requirements shall nominally be ten
(10), unless specifically required otherwise on a case by case basis by the Commission; however,
this number may not be reduced to less than five (5) guards.”