                 FOR PUBLICATION
 UNITED STATES COURT OF APPEALS
      FOR THE NINTH CIRCUIT

PUBLIC CITIZEN; SAN LUIS OBISPO        
MOTHERS FOR PEACE,
                       Petitioners,        No. 07-71868
                v.                         NRC No.
                                              10CFR
NUCLEAR REGULATORY COMMISSION,
                      Respondent.
                                       

STATE OF NEW YORK,                     
                         Petitioner,       No. 07-72555
                v.
                                           NRC No.
                                             07-2052
NUCLEAR REGULATORY COMMISSION;
UNITED STATES OF AMERICA,                   OPINION
                    Respondents.
                                       
         On Petition for Review of an Order of the
             Nuclear Regulatory Commission

                Argued and Submitted
      November 17, 2008—San Francisco, California

                     Filed July 24, 2009

   Before: Cynthia Holcomb Hall, Thomas G. Nelson and
            Sidney R. Thomas, Circuit Judges.

                  Opinion by Judge Hall;
 Partial Concurrence and Partial Dissent by Judge Thomas



                            9615
                        PUBLIC CITIZEN v. NRC                       9619




                             COUNSEL

Adina H. Rosenbaum, Public Citizen Litigation Group, Wash-
ington, D.C., for the petitioners.

John J. Sipos, Assistant Attorney General, Albany, New
York, for the petitioner.

Steven F. Crockett, Special Counsel, Karen D. Cyr, General
Counsel, John F. Cordes, Jr., Solicitor, and E. Leo Slaggie,
Deputy Solicitor, United States Nuclear Regulatory Commis-
sion, Washington, D.C.; Ronald J. Tenpas, Assistant Attorney
General, Ronald M. Spritzer, Environment and Natural
Resources Division, United States Department of Justice,
Washington, D.C., for the respondents.

David A. Repka, Winston & Strawn, Washington, D.C., for
the intervenor-respondent.

Brian Hembacher, Deputy Attorney General, State of Califor-
nia, Los Angeles, California, for the amici curiae.


                              OPINION

HALL, Senior Circuit Judge:

  Petitioners Public Citizen, Inc., San Luis Obispo Mothers
For Peace, the State of New York,1 and amicus State of Cali-
  1
   New York’s petition for review was properly transferred to this court
and consolidated with the petition of Public Citizen pursuant to 28 U.S.C.
§ 2112(a)(5).
9620                PUBLIC CITIZEN v. NRC
fornia (“Petitioners”) challenge the Nuclear Regulatory Com-
mission’s (“NRC” or “Commission”) modification of the
Design Basis Threat (“DBT”) rule and partial denial of the
Committee to Bridge the Gap’s (“CBG”) petition for rulemak-
ing. Petitioners claim the Commission acted arbitrarily and
capriciously and contrary to law by refusing to include the
threat of air attacks in the final revised DBT rule. Petitioners
also claim NRC violated the National Environmental Policy
Act (“NEPA”) by not considering the risk of an airborne ter-
rorist attack in its Environmental Assessment (“EA”), and that
this risk creates a potentially significant impact on the envi-
ronment necessitating a full Environmental Impact Statement
(“EIS”). We deny the petition.

                       I.   Background

  A.   The History of the Commission and Development of the
       “Adequate Protection” Standard

   To better understand the complicated history of the DBT
Rule, we first outline the role of the NRC itself. In 1954, Con-
gress passed the Atomic Energy Act (“Act”). 42 U.S.C.
§ 2011 et seq. The Act created the Atomic Energy Commis-
sion, later renamed the Nuclear Regulatory Commission, to
regulate and develop the use of atomic energy. The Act is
“virtually unique in the degree to which broad responsibility
is reposed in the administrative agency, free of close prescrip-
tion in its charter as to how it shall proceed in achieving the
statutory objectives.” Siegel v. Atomic Energy Commission,
400 F.2d 778, 783 (D.C. Cir. 1968).

   When licensing nuclear facilities, the Commission is
charged with ensuring that the operation of those facilities is
“in accord with the common defense and security and will
provide adequate protection to the health and safety of the
public.” 42 U.S.C. § 2232(a). Although “adequate protection”
is not defined in the statute, legislative history “indicate[s]
that the Congressional concern with the common defense and
                    PUBLIC CITIZEN v. NRC                  9621
security related to such matters as the safeguarding of special
nuclear material; the absence of foreign control over the
applicant; the protection of Restricted Data; and the availabil-
ity of special nuclear material for defense needs.” Siegel, 400
F.2d at 781 (internal quotations omitted). “The public health
and safety standard, in like fashion, was said to be addressed
to the overall qualifications of the applicant and the design of
the facility to protect plant employees and the public against
accidents and their consequences.” Id. at 781-782 (internal
quotations omitted).

   The adequate protection standard has also acquired mean-
ing through subsequent case law. Union of Concerned Scien-
tists v. NRC, 824 F.2d 108, 117 (D.C. Cir. 1987) (Concerned
Scientists I), held that while the Commission could not con-
sider costs in determining the level of adequate protection
necessary, it could consider other factors, including the nature
and extent of the risks involved. The court declined to estab-
lish the scope of those factors, however, instead concluding
that “the ‘adequate protection’ standard may be given content
through case-by-case application of [the Commission’s] tech-
nical judgment rather than by a mechanical verbal formula or
set of objective standards” set by either NRC or an interpret-
ing court. Union of Concerned Scientists v. NRC, 880 F.2d
552, 558 (D.C. Cir. 1989) (Concerned Scientists II).

   Concerned Scientists I also made clear that “adequate pro-
tection” does not mean “absolute protection,” and that the
standard “permits the acceptance of some level of risk.” 824
F.2d at 114, 118. “Safe is not the equivalent of risk-free.” Id.
at 118 (internal quotations omitted). The Commission is
authorized to impose additional safety measures on licensees
above those required by adequate protection, and in doing so
may consider the economic costs of those extra measures. Id.
Siegel v. Atomic Energy Commission was the first case to
challenge whether adequate protection should extend beyond
the original congressional concerns to also encompass “the
risk of an enemy attack or sabotage against [the] structures.”
9622                PUBLIC CITIZEN v. NRC
400 F.2d at 783-784. The Siegel court held that there was no
indication that the “Commission was commanded to intrude
the possibility of enemy action into the concepts of ‘the com-
mon defense and security’ and ‘the public health and safe-
ty.’ ” Id.

   The Siegel case dealt with the Commission’s decision
declining to require licensees to protect against possible mis-
sile attacks on nuclear facilities near Cuba. The court upheld
the Commission’s newly created “Enemy of the State” rule,
which insulated licensees from the requirement that they pro-
tect against the effects of attacks or destructive acts by ene-
mies of the United States (foreign governments or other
persons) or that they use or deploy weapons incident to U.S.
defense activities. 10 C.F.R. § 50.13. The court favorably
cited the Commission’s rationale animating the Enemy of the
State rule: “that [requiring] reactor design features to protect
against the full range of the modern arsenal of weapons [is]
simply not practicable and that the defense and internal secur-
ity capabilities of this country constitute, of necessity, the
basic ‘safeguards’ as respects possible hostile acts by an
enemy of the United States . . . . [t]he risk of an enemy attack
or sabotage against such structures, like the risk of all other
hostile attacks which might be directed against this country,
is a risk that is shared by the nation as a whole.” Id. at 783.

  B.    The Origin of the Design Basis Threat Rule

   The Commission, wholly of its own accord, decided in
1977 to promulgate the first Design Basis Threat (“DBT”)
rule to protect nuclear power reactors from industrial sabo-
tage. 42 Fed. Reg. 10,836 (Feb. 24, 1977). “Design bases”
are, generally speaking, applicant or licensee information
which identifies the specific functions to be performed by a
structure or system. 10 C.F.R. § 50.2. The “threat” is an
adversary characteristic, or what sort of threat against which
a licensee should be prepared to defend and engage. 72 Fed.
Reg. 12,705, 12,705, 708 (Mar. 19, 2007). The DBT rule
                    PUBLIC CITIZEN v. NRC                  9623
challenged in this action, 10 C.F.R. § 73.1, is the purpose and
scope section which defines included adversary chracteristics.
Other regulations implement specific physical protection
requirements to address these adversary characteristics once
they are included within the scope of the rule. See, e.g., 10
C.F.R. § 73.55 (outlining physical protection requirements to
protect against radiological sabotage).

   The regulation initially protected only against industrial
sabotage by individuals and groups with possible inside infor-
mation and hand-held weapons. But, the regulation stated:
“[t]he kind and degree of threat and the vulnerabilities to such
threats will continue to be reviewed by the Commission . . . .
the Commission [will] consider changes to meet the changed
conditions.” 42 Fed. Reg. 10,836, 10,836.

   In 1994, the Commission revised the DBT rule in response
to an intrusion at a nuclear power plant, the 1993 vehicle
bomb attack on the World Trade Center, and intelligence that
showed “a conspiracy with ties to the Middle East extremists
clearly demonstrated the capability and motivation to orga-
nize, plan, and successfully conduct a major vehicle bomb
attack,” 59 Fed. Reg. 38,889, 38,891 (Aug. 1, 1994). The
revised DBT incorporated the threat of adversaries utilizing “a
four-wheel drive land vehicle used for transporting personnel
and their hand-carried equipment,” and “a four-wheel drive
land vehicle bomb.” Id. The Commission explicitly denied
that these changes were necessary to meet the adequate pro-
tection standard. Instead, the changes were issued under the
Commission’s authority to outline additional safety measures
as a “matter of prudence” and represented a “substantial
increase in protection of the public health and safety.” 59 Fed.
Reg. 38,889, 38,891, 896; see also Concerned Scientists I,
824 F.2d at 118.

   To partially implement the 1994 DBT change, the Commis-
sion also revised 10 C.F.R. § 73.55 to require the installation
of passive vehicle barriers. These barriers were required to
9624                PUBLIC CITIZEN v. NRC
“protect against vehicle intrusion into protected areas,” but
the Commission believed that, if placed in the correct loca-
tions, they could also protect against a vehicle bomb. 59 Fed.
Reg. 38,889, 38,891. Because the changes were permissibly
made to “provide an additional, substantial increase in the
overall protection of the public health and safety,” rather than
statutorily required to meet the adequate protection standard,
the Commission engaged in a cost-benefit analysis of the pro-
tective measures. Id.; see also Concerned Scientist I, 824 F.2d
at 118.

   In that cost-benefit analysis, the Commission explicitly
rejected the argument from the nuclear industry that the
Enemy of the State rule insulated them from these measures.
The Commission reasoned “[t]here is a significant difference
in the practicality of defending against a missile attack and
constructing a vehicle barrier,” and that the scope of the
Enemy of the State rule was to “relieve applicants of the need
to provide protective measures that are the assigned responsi-
bility of the nation’s defense establishment.” 59 Fed. Reg.
38,889, 38,893. The Commission further explained that the
Enemy of the State rule “recogniz[es] that it [is] not practical
for the licensees of civilian nuclear power reactors to provide
design features that could protect against the full range of the
modern arsenal of weapons.” Id.

  C.   Post 9/11 and the Commission’s Response

   Following 9/11, the Commission again determined a
change to the DBT rule was necessary. Many studies were
conducted by both private and government entities, indepen-
dently and at the behest of the NRC, which showed that
nuclear facilities were not designed to withstand the impact of
a commercial jet plane. The studies showed that while “many
of [the] safety-related systems are well protected within har-
dened structures . . . some are not.” In the worst case, an air-
craft crash had the potential to set off an accident sequence
resulting in “serious damage if not total meltdown” of the
                     PUBLIC CITIZEN v. NRC                  9625
core, but such a sequence would “require[ ] the occurrence of
multiple failures, many of which are strongly plant-
dependent.” Additionally, many intelligence agencies, and the
NRC itself, closely monitored and acknowledged the credible
threat of a terrorist attack on nuclear facilities.

   The Commission responded to this information by issuing
emergency orders to licensees on February 25, 2002, January
7, 2003, and April 29, 2003. These orders, though non-public
and protected as “safeguards information” pursuant to 42
U.S.C. §§ 2167, 2201(i), required licensees to make a wide
variety of security improvements. See 70 Fed. Reg. 67,380,
67,381 (Nov. 7, 2005). Following the implementation of these
orders, the NRC “conducted detailed, site-specific engineer-
ing studies of a limited number of plants to gain insights on
[continued] potential vulnerabilities of nuclear power plants
to deliberate attacks involving large commercial aircraft.” 72
Fed. Reg. 12,705, 12,710. For the NRC, these studies “con-
firmed the effectiveness of the February 2002 NRC-ordered
mitigative measures” and “the low likelihood of both damag-
ing the reactor core and releasing radioactivity that could
affect public health and safety.” Id. The studies also “indi-
cate[d] that there would be time to implement the required on-
site mitigating actions” in the “unlikely event” that a terrorist
is able to use a large aircraft against a nuclear facility. Id.
“[A]dditional key radiological protection and mitigation strat-
egies” were imposed by the NRC on appropriate licensees by
order in June 2006. Id.; see also 71 Fed. Reg. 36,554 (June
27, 2006).

   The NRC also increased coordination efforts with other
government agencies. “[I]n early March 2006, the NRC
hosted an Interagency Aircraft Attack Tabletop Exercise at
NRC Headquarters . . . . reconfirm[ing] the respective respon-
sibilities of the participating organizations (NRC, DHS
[Department of Homeland Security], DOD [Department of
Defense], and FBI) in the event of a nuclear plant aircraft
attack and clarif[ying] protocols for response-related intera-
9626                    PUBLIC CITIZEN v. NRC
gency communication and coordination.” 72 Fed. Reg.
12,705, 12,710. The NRC and DHS also “worked together to
develop and improve EP [Emergency Planning] for a terrorist
attack through federal initiatives such as comprehensive
review programs and integrated response planning efforts”
including “State/local/tribal response capabilities.” 72 Fed.
Reg. 12,705, 12,712. Those efforts “include[d] prearranged
plans with local law enforcement and emergency planning
coordination.” 72 Fed. Reg. 12,705, 12,714.

   In June 2004, the Commission announced a proposed
amendment to the DBT rule “to incorporate the Commission
actions taken as a result of September 11, 2001,” making “re-
view and revisions as appropriate.” 69 Fed. Reg. 38,635,
38,636 (June 28, 2004). In July 2004, the Commission
received a rulemaking petition from Committee to Bridge the
Gap, PRM-73-12, which requested, inter alia: amending the
DBT to “encompass attacking forces equal to those of 9/11”
including attacks by boat and by air; amending the DBT
enabling regulations to mandate security plans, systems,
inspections, and force-on-force exercises; and requiring con-
struction of “beamhenge” shields2 to protect against air attack.3
Finally, as part of the Energy Policy Act of 2005, Congress
directed the Commission to initiate or complete rulemaking to
revise the design basis threats. 42 U.S.C. § 2210e (effective
August 8, 2005). Congress directed the Commission to con-
sider twelve non-exclusive factors in its rulemaking, including
“the potential for water-based and air-based threats.”
§ 2210e(b)(6).4
   2
     The “beamhenge” concept involves a shield constructed of I-beams
with steel or other cabling and netting between them at standoff distances
around      key     structures   at    nuclear    plants.   See     http://
www.committeetobridgethegap.org/beamhenge.html.
   3
     Attorneys General from seven states, including New York, filed writ-
ten comments in support of the CBG petition in January 2005.
   4
     The twelve non-exclusive factors the Commission was instructed to
consider are: “(1) the events of September 11, 2001; (2) an assessment of
                          PUBLIC CITIZEN v. NRC                           9627
  D.      The Current Revised DBT Rule

   The Commission issued the final revised DBT rule in
March 2007. See 72 Fed. Reg. 12,705. The rule significantly
increased the range of threats included within the DBT scope
and incorporated most of the factors Congress listed in
§ 2210e, including attacks by multiple groups attacking
through multiple entry points, individuals willing to kill or be
killed, water vehicles and water-based vehicle bomb assaults,
and cyber attacks. See 10 C.F.R. § 73.1. The final rule dis-
cusses: the 2002 and 2003 Orders in general terms, actions
taken by other Federal agencies in the wake of 9/11 to
increase national security and NRC’s efforts to coordinate
responses with these agencies, each of the twelve congressio-
nal concerns, public comments received, and the CBG peti-
tion. See generally 72 Fed. Reg. 12,705.

   The revised DBT rule elaborates on the purpose and scope
of the DBT rule, which the Commission explained was prem-
ised upon “adversary characteristics against which a private
security force can reasonably be expected to defend.” 72 Fed.
Reg. 12,705, 12,713. Relying on this “reasonable expectation”
standard, the Commission determined that the threat of an air-
based attack was beyond the scope of the DBT rule. The

physical, cyber, biochemical, and other terrorist threats; (3) the potential
for attack on facilities by multiple coordinated teams of a large number of
individuals; (4) the potential for assistance in an attack from several per-
sons employed at the facility; (5) the potential for suicide attacks; (6) the
potential for water-based and air-based threats; (7) the potential for use of
explosive devices of considerable size and other modern weaponry; (8) the
potential for attacks by persons with sophisticated knowledge of facility
operations; (9) the potential for fires, especially fires of long duration; (10)
the potential for attacks on spent fuel shipments by multiple coordinated
teams of a large number of individuals; (11) the adequacy of planning to
protect the public health and safety at and around nuclear facilities, as
appropriate, in the event of a terrorist attack against a nuclear facility; and
(12) the potential for theft and diversion of nuclear materials from such
facilities.” § 2210e.
9628                     PUBLIC CITIZEN v. NRC
Commission reasoned that “the responsibility for actively pro-
tecting against the threat lies with other organizations of the
Federal government, as it does for any U.S. commercial infra-
structures.” 72 Fed. Reg. 12,705, 12,710 (emphasis added).
The Commission explained that the public health and safety
was adequately protected, however, because of: 1) the active
protection of other Federal agencies, with whom the NRC
continues to coordinate; and 2) mitigative measures imple-
mented by the licensees that would limit the effect of an air-
craft strike. 72 Fed. Reg. 12,705, 12,711. Because the NRC
determined both that air-based threats were beyond the scope
of the DBT rule and that the adequate protection standard was
satisfied, CBG’s petition for rulemaking, as it pertained to the
beamhenge concept, was denied. Id.5

   As in 1994, the Commission again rejected the argument
that the Enemy of the State rule insulated the industry from
meeting the requirements of the revised DBT rule. The Com-
mission emphasized that “the DBT rule does not focus on the
identity, sponsorship, or nationality of the adversaries,” but
rather a “range of attacks and capabilities” against which pri-
  5
    The Commission continues to evaluate air-based threats even after the
revised DBT rule. In October 2007, the Commission issued a proposed
rule to amend 10 C.F.R. § 52 (Design Features) with the objective of “re-
quir[ing] nuclear power plant designers to perform a rigorous assessment
of design features that could provide additional inherent protections to
avoid or mitigate, to the extent practicable, the effects of an aircraft
impact, with reduced reliance on operator actions.” 72 Fed. Reg. 56,287
(Oct. 3, 2007) (emphasis added). The NRC issued a press release on Feb-
ruary 17, 2009, announcing it had issued its final rule requiring “appli-
cants for new power reactors to assess the ability of their reactor designs
to avoid or mitigate the effects of a large commercial aircraft impact.” See
http://www.nrc.gov/reading-rm/doc-collections/news/2009/09-030.html
(last visited May 15, 2009). The press release reiterates the NRC’s consis-
tent position that the new design features “will result in a margin of safety
far beyond that required to achieve reasonable assurance of public health
and safety,” and that the responsibility of preventing the impact of large
commercial aircraft rests with the federal government as it is a beyond-
design-basis event. Id. (emphasis in original).
                        PUBLIC CITIZEN v. NRC               9629
vate facilities can be “reasonably expected to defend . . .
regardless of whether it would or would not be deemed an
‘enemy of the state.’ ” 72 Fed. Reg. 12,705, 12,714-715.

   To comply with NEPA, the Commission completed an EA
for the final rule. Based upon the EA, the Commission con-
cluded that there would be no significant environmental
impact associated with the rule and therefore no EIS was nec-
essary. 72 Fed. Reg. 12,705, 12,718. The Commission also
concluded that NEPA did not require an evaluation of terrorist
attacks as “the consequences of a terrorist attack cannot be
said to be ‘an effect’ of this rule, and analyzing the effects of
a terrorist attack would be speculative at best.” 72 Fed. Reg.
12,705, 12,718-719. The Commission acknowledged this
court’s decision in Mothers for Peace, but distinguished a
licensing decision from the rulemaking action at issue. Id.; see
Mothers for Peace v. NRC, 449 F.3d 1016 (9th Cir. 2006).

                  II.     Standard of Review

   Under the Administrative Procedure Act (“APA”), agency
decisions may be set aside only if “arbitrary, capricious, an
abuse of discretion, or otherwise not in accordance with law.”
Earth Island Inst. v. U.S. Forest Serv., 442 F.3d 1147, 1156
(9th Cir. 2006) (quoting 5 U.S.C. § 706(2)(A)). “Review
under this standard is narrow, and the reviewing court may
not substitute its judgment for that of the agency.” Id. at 1156.
“We reverse under the arbitrary and capricious standard only
if the agency has relied on factors that Congress has not
intended it to consider, has entirely failed to consider an
important aspect of the problem, or has offered an explanation
for that decision that runs counter to the evidence before the
agency or is so implausible that it could not be ascribed to a
difference in view or the product of agency expertise.” Id.

   “[A]n agency’s interpretation of its own regulations is ‘con-
trolling’ unless ‘plainly erroneous’ or inconsistent with ‘the
regulations being interpreted.’ ” Long Island Care at Home,
9630                 PUBLIC CITIZEN v. NRC
Ltd. v. Coke, 127 S. Ct. 2339, 2349 (2007) (citing Bowles v.
Seminole Rock & Sand Co., 325 U.S. 410, 414 (1945)).

   This court is limited to a review of the reasoning the
agency relied upon in making its decision. Safe Air for Every-
one v. EPA, 488 F.3d 1088, 1091 (9th Cir. 2007) (citing SEC
v. Chenery Corp., 318 U.S. 80, 87 (1943)). “We will, how-
ever, uphold a decision of less than ideal clarity if the agen-
cy’s path may reasonably be discerned.” Motor Vehicle Mfrs.
Ass’n v. State Farm Mut. Auto. Ins. Co., 463 U.S. 29, 43
(1983). “Where . . . the agency’s course of action indicates
that the interpretation of its own regulation reflects its consid-
ered views [rather than merely post hoc rationalization] . . .
we have accepted that interpretation as the agency’s own,
even if the agency set those views forth in a legal brief.”
Coke, 127 S. Ct. at 2349; see also Global Crossing Tele-
comm., Inc. v. Metrophones, 127 S. Ct. 1513, 1525 (2007)
(noting that even if agency action is inadequately reasoned
initially, context and history of position can make agency’s
rationale obvious).

                       III.   Discussion

  A.   The Scope of the DBT Rule and the Reasonable
       Expectation Standard

   Petitioners first argue that the Commission’s explanation of
the scope of the DBT rule—as reaching only those threats
which a private force can reasonably be expected to defend
against—is a new standard which conflicts with and departs
from the Commission’s prior interpretations of the DBT rule,
and therefore represents an abuse of discretion. See, e.g., W.
States Petroleum Ass’n v. EPA, 87 F.3d 280, 285 (9th Cir.
1996).

  [1] Here, however, the Commission is not departing from
an established standard, but is merely elaborating on the inter-
pretation of its own regulation. See Coke, 127 S. Ct. at 2349
                       PUBLIC CITIZEN v. NRC                     9631
(holding that so long as interpretive changes create no unfair
surprise, as when an interpretation is codified in notice-and-
comment rulemaking, the agency’s interpretation of its own
regulations is controlling unless plainly erroneous). Though
the scope of the DBT has not previously been precisely defined,6
the NRC’s decisions have clearly been animated by consider-
ations of the credibility of the threat at issue and whether pri-
vate forces can reasonably be expected to actively engage that
threat. This rationale, while not previously articulated in any
one section of the rule, is easily ascertained from the history
and context of the DBT rule. See Global Crossing, 127 S. Ct.
at 1525.

   In both the 1977 and 1994 DBT rules, the Commission
evaluated the “kind and degree of threat” at issue in determin-
ing the scope of the DBT, illustrating that a threat must be
credible before it is included. See 42 Fed. Reg. 10,836,
10,836; see also 59 Fed. Reg. 38,889, 38,891. This is also
consistent with NRC’s decision to revise the DBT rule in light
of the changed threat environment created by the events of
9/11. See 72 Fed. Reg. 12,705, 12,705.

   In rejecting the Enemy of the State rule in both its 1994 and
2007 revisions when it was “practical” or “reasonable” for
private forces to defend against the included threats, the Com-
mission illustrated that a concept of reasonableness animates
both the DBT and the Enemy of the State rules. See 59 Fed.
Reg. 38,889, 38,893; 72 Fed. Reg. 12,705, 12,714-715; see
also Siegel v. Atomic Energy Commission, 400 F.2d 778, 783
(D.C. Cir. 1968) (noting Commission’s “recognition that reac-
tor design features to protect against the full range of the
modern arsenal of weapons are simply not practicable
. . . .”). Both rules have also been influenced by the reason-
able division of nuclear defense responsibilities between pri-
  6
    The Commission acknowledges a standard has intentionally not been
articulated so as to preserve the Commission’s flexibility. See 72 Fed.
Reg. 12,705, 12,713; see also Concerned Scientists II, 880 F.2d at 558.
9632                 PUBLIC CITIZEN v. NRC
vate and government forces. See Siegel, 400 F.2d at 783
(discussing defense and internal security capabilities in cre-
ation of Enemy of the State Rule); 59 Fed. Reg. 38,889,
38,893 (discussing that some protective measures are the
assigned responsibility of the nation’s defense establishment).

   Previous adversary characteristics have only been included
within the scope of the DBT rule if they represented a class
of threat that private forces could actively engage, such as
militant individuals or vehicles. See 10 C.F.R. § 73.1. Only
once a threat is determined to be within the scope of the DBT
do the implementing regulations contemplate passive protec-
tive measures as supplemental means of defending against the
threats. For instance, 10 C.F.R. § 73.55 required licensees to
install passive barriers to protect against vehicle intrusion
only after vehicle threats were added to the DBT rule. 59 Fed.
Reg. 38,889, 38,891. The NRC determined however, that nei-
ther the inclusion of vehicle threats, nor the decision to locate
barriers in a position where they could also maximize protec-
tion from vehicle bombs, was required to satisfy the statutory
adequate protection standard. Instead, the Commission illus-
trated that the requirements of the DBT rule could exceed the
requirements of adequate protection where the Commission
determined that private forces could reasonably defend
against the threat.

   [2] Applying this standard of reasonable expectation, the
agency did not act arbitrarily nor capriciously in concluding
that air-based threats were beyond the scope of the DBT rule.
An airplane attack is different in kind than attacks by militant
individuals or vehicles. Unlike other vehicles, airplanes are
not used as an intrusionary device to gain access to secure
portions of the facility. Instead, an airplane is used as an
explosive weapon, more analogous to a missile. When facing
an attack from a vehicle, a private force can engage those per-
sons who seek to intrude upon the facility. There are no sur-
viving crew members of an airplane for private forces to
engage following impact. Like a missile, the only means of
                        PUBLIC CITIZEN v. NRC                         9633
actively engaging an attack from an airplane is through the
use of anti-aircraft devices (prudently) unavailable to private
security forces. See 72 Fed. Reg. 12,705, 12,710. Thus the
rationale of the Enemy of the State rule applies to air-based
terrorist attacks, in that the defense against these attacks is
best left to government agencies. Once the Commission made
the general determination that air-based threats were outside
the scope of the DBT, the Commission was under no obliga-
tion to consider passive protective measures, such as the
beamhenge concept, as part of this rulemaking procedure.7

  B.     Adequate Protection from Air-Based Threats

   [3] Petitioners contend that the NRC’s decision to define
the scope of the DBT rule on what a private force can reason-
ably be expected to defend against, which excludes air-based
threats, does not ensure adequate protection of the public
health and safety. But, the Commission has an “overall statu-
tory mandate to provide adequate protection to nuclear
plants,” which is not abdicated by its failure to fully protect
against the threat of air-based attacks through an individual
regulatory decision. Riverkeeper, Inc. v. Collins, 359 F.3d
156, 169 (2d Cir. 2004). Here, while the NRC determined that
air-based threats were beyond the scope of the DBT rule, the
Commission provided two primary grounds to support its
determination that adequate protection was met: 1) active pro-
tection against airborne threats by other Federal agencies, and
2) the ability of mitigative measures to limit the effects of an
aircraft strike. 72 Fed. Reg. 12,705, 12,711. In its briefing, the
NRC further explained that its judgment was also informed
by: “threat analyses, by experience in the enforcement of
DBT orders, by knowledge about the robustness of nuclear
power plants, by a knowledge that nuclear power plants are
better guarded than any other private critical infrastructure,
  7
   The Commission has issued a final rule to modify the design features
of nuclear facilities to better withstand the impact of an air-based attack.
See supra n. 5.
9634                   PUBLIC CITIZEN v. NRC
and the guard forces subject to more oversight than any other
civilian industry security force, by new studies of how plants
might respond to an air crash, and by a knowledge of actions
that other Federal agencies have taken since 2001 to protect
against air threat.” Brief for Respondents at p. 46 (internal
citations omitted). Though set forth in its briefing, this reason-
ing is consistent with the reasoning included in the Commis-
sion’s final ruling and we accept it as the NRC’s considered
views. See Coke, 127 S. Ct. at 2349. Adequate protection may
be given content through a case-by-case application of the
Commission’s technical judgment, including its knowledge of
actions that other Federal agencies have taken since 2001 and
its active coordination with many of those agencies. See Con-
cerned Scientists II, 880 F.2d 552, 558 (D.C. Cir. 1989).8

   [4] It is not implausible for the Commission to determine
that most attacks will be prevented in the first instance by the
coordinated efforts of multiple Federal agencies. It is also not
implausible, based on the evidence before the Commission,
for the NRC to conclude that, in the event that an airplane is
able to strike a facility, the mitigative and protective measures
imposed through the DBT Orders and the revised DBT would
likely prevent any serious harm from occurring. The adequate
protection standard need not prevent “each and every” poten-
tial attack, as advocated by amicus State of California,
because the standard “permits the acceptance of some level of
risk” and does not require “absolute protection.” Concerned
Scientists I, 824 F.2d 108, 114, 118 (D.C. Cir. 1987).

   [5] “[T]he NRC’s considered conclusion- right or wrong-
that [air-based threats were] being adequately addressed by
  8
   The extremely broad discretion granted to the Commission to ignore
the risks of enemy attacks and sabotage in assessing adequate protection
by the Siegel court, see 400 F.2d at 783-784, however, would not apply
today given the Commission’s own establishment of DBTs under the ade-
quate protection standard and Congress’s direction in 42 U.S.C. § 2210e.
See also Riverkeeper, 359 F.3d at 168 n.14.
                        PUBLIC CITIZEN v. NRC                       9635
other agencies of government and its consequent decision to
leave the matter to those agencies cannot amount to an ‘abdi-
cation’ of its statutory duty under the AEA to insure that the
public health and safety is adequately protected. Relying on
other governmental bodies to address a risk is not equivalent
to ignoring the risk.” Riverkeeper, 359 F.3d at 170;9 see also
42 U.S.C. § 2201(f) (authorizing the Commission to utilize
other Federal agencies to perform such functions on its behalf
as may appear desirable). Here the Commission is not merely
relying on other government bodies, but is an active partici-
pant in coordinating for protection of nuclear facilities. See 72
Fed. Reg. 12,705, 12,710. The NRC’s reliance on other gov-
ernment agencies, whose charge is to provide security and
defense of the nation against such attacks, is neither inconsis-
tent with its past practices nor an unreasonable interpretation
of its statutory obligations.

   Petitioners’ argument that the NRC’s inclusion of passive
measures to protect against vehicle threats in the 1994 revi-
sion necessitates the inclusion of passive measures against air-
borne threats now, is unavailing. In the 1994 DBT rule, the
Commission explicitly stated that its decision to include pas-
sive barriers against vehicle intrusions and explosions was not
based on adequate protection, but as a “matter of prudence”
to provide a “substantial increase in protection.” 59 Fed. Reg.
38,889, 38,891, 896. Thus, it cannot be said here that the
Commission is obligated to find, based on prior decisions,
that passive measures are necessary to provide adequate protec-
tion.10 And, as discussed above, the Commission was consis-
  9
    The Riverkeeper court also noted that the “FAA and Department of
Defense have acted more than once to protect airspace above nuclear
power plants from what were thought to be credible threats against spe-
cific sites.” 359 F.3d at 169.
   10
      It is also reasonable for the Commission to treat the interagency
response to air-based threats differently than in land vehicle or water-
based vehicle attacks. There are far fewer airplanes than either trucks or
boats, and they are far more regulated. Airspace is monitored by federal
agencies in a manner which cannot be duplicated on all of the nation’s
roadways and waterways.
9636                PUBLIC CITIZEN v. NRC
tent in including within the scope of the DBT rule only those
threats a private force can reasonably be expected to defend
against. The NRC’s determination that private forces can rea-
sonably defend against vehicle and water-based attacks does
not require the Commission to come to the same conclusion
regarding airborne threats. Once the Commission determined
that adequate protection was met, it was under no obligation
to further consider the beamhenge concept outlined in the
CBG petition.

   [6] Petitioners also argue that the Commission improperly
considered cost in its assessment. This allegation has no basis
in the record. The Commission has consistently stated that its
determination of adequate protection was not based on cost.
72 Fed. Reg. 12,705, 12,714. The NRC has provided suffi-
cient explanation of the reasonableness standard to show that
it is animated by considerations of practicality, feasability,
and the proper division of defense between government agen-
cies rather than cost concerns. For example, Petitioners argue
that any reasonableness limitation on the size of a private
security force must be driven by cost. This argument ignores
potential basic feasability concerns that may arise with main-
taining facilities for a private “standing army.” The Commis-
sion’s decision to limit the size of private security forces is
neither arbitrary nor an abuse of the Commissioner’s discre-
tion. Moreover, because the Commission found that the ade-
quate protection standard was satisfied through mitigation
measures and active defense by other federal agencies, any
decision to include air-based threats in the DBT could have
properly considered costs. When the NRC uses its permissive
authority to extend public safety measures beyond those
required by “adequate protection,” it may legitimately include
costs in its assessment. See Concerned Scientists I, 824 F.2d
at 118.

  C.   Compliance with Congress’s Directives in 42 U.S.C.
       § 2210e

   [7] Petitioners also contend that the Commission’s final
rule is contrary to law because the Commission failed to com-
                         PUBLIC CITIZEN v. NRC                         9637
ply with Congress’s directive to “consider” “the potential for
water-based and air-based threats.” § 2210e(b)(6). This argu-
ment is without merit. The Commission thoroughly discussed
its assessment of air-based threats in the final rule. The Com-
mission also implemented many mitigative measures to limit
the effects of an air-strike and coordinated with other agencies
to prevent an airborne attack. The direction to “consider” non-
exclusive factors does not necessitate including that factor in
the final rule, as Petitioners admit. The NRC’s interpretation
of the directive from Congress is reasonable. The statute has
no legislative history that could counter the Commission’s
interpretation, nor can it be assumed, given the “virtually
unique” authority of the NRC to achieve its statutory objec-
tives, see Seigel, 400 F.2d at 783, that Congress intended to
interfere with the Commission’s authority any more than is
facially clear from the statute.

   [8] Petitioner’s argument that air-based threats must neces-
sarily be within the scope of the DBT rule simply because
they were included as a § 2210e factor is also flawed. The
Commission does not argue that it could not have legally cho-
sen to include air-based threats within the scope of the DBT.
Section 2210e allowed the Commission the flexibility to
determine whether or not to include each individual factor in
the final rule. There is no indication that the Commission
could not exercise that discretion in determining a factor was
beyond the scope of the DBT rule, rather than excluding the
factor on any other discretionary basis.11 Petitioners cite no
authority to so limit the Commission’s discretion where a fac-
tor is not mandated by Congress and we decline to imply any
such limitation. Compare Public Citizen v. FMCSA, 374 F.3d
1209, 1216 (D.C. Cir. 2004) (finding agency rule arbitrary
  11
     Moreover, the first factor listed in § 2210e is “the events of September
11, 2001.” This illustrates that Congress could not have reasonably
expected the NRC to treat the factors as a sort of shopping list of threats
to include wholesale in the final rule, without further agency analysis and
expertise.
9638                 PUBLIC CITIZEN v. NRC
and capricious where the “agency neglected to consider a sta-
tutorily mandated factor” under its organic statute).

  D.    Reliance on Non-Public Information

   Petitioners next argue that the Commission improperly
relied on non-public information when engaging in the DBT
rulemaking. The cases relied upon by Petitioners, however,
involve cases where an agency relies on general factual infor-
mation not provided to the public, and do not govern this
case. See, e.g., Kern County Farm Bur. v. Allen, 450 F.3d
1072, 1076 (9th Cir. 2006). Here, the AEA specifically allows
the Commission to maintain “safeguards information” that is
not available to the public. 42 U.S.C. §§ 2167, 2201(i); see
also 10 C.F.R. § 73.21. The APA also exempts from the gen-
eral rule information it is specifically authorized to withhold
from public scrutiny. See 5 U.S.C. § 552(b)(3). The Commis-
sion cannot be required to reveal classified information about
nuclear facilities, nor would it be able to do so while fulfilling
its duty to maintain the common defense and security of clas-
sified information. See also Siegel, 400 F.2d at 786 (“When,
as here, a statute does not require that a particular kind of rule
making be on a record made after a public hearing, the Com-
mission is not confined to evidence presented in some formal
manner. It may act not only on the basis of the comments
received in response to its notice of rule making, but also
upon the basis of information available in its own files, and
upon the knowledge and expertise of the agency.”) (citing
Pacific Coast European Conference v. United States, 350
F.2d 197, 205 (9th Cir. 1965)).

   [9] We hold the Commission acted neither arbitrarily or
capriciously in excluding the threat of air-based attacks from
the scope of the DBT rule, nor contrary to law in finding that
adequate protection was satisfied without incorporating pas-
sive protective measures against air-based attacks in the DBT
rule.
                     PUBLIC CITIZEN v. NRC                  9639
  E.   NEPA Analysis

   Petitioners also challenge the sufficiency of the EA pro-
vided by the Commission, arguing that the NRC should have
analyzed its decision to exclude air-based threats from the
DBT rule and included that environmental analysis in the
alternative action portion of the EA. They argue that the deci-
sion to exclude air-based threats is an agency action that “in-
creases the risk of a successful terrorist attack,” and that that
decision produces its own adverse environmental affects. Peti-
tioners rely on this court’s decisions in Center for Biological
Diversity v. NHTSA, 538 F.3d 1172, 1216 (9th Cir. 2008), and
San Luis Obispo Mothers for Peace v. NRC (Mothers for
Peace), 449 F.3d 1016 (9th Cir. 2006).

   [10] “An EA shall include brief discussions of the need for
the proposal and the environmental impacts of the proposed
action and alternatives.” Center for Biological Diversity, 538
F.3d at 1215 (quoting 40 C.F.R. § 1508.9(b)) (internal cita-
tions and alterations omitted). Because the Commission acted
within its discretion in concluding that air-based threats were
beyond the scope of the DBT rule, however, it was unneces-
sary for the Commission to consider that decision as an alter-
native course within the scope of the rule. The Commission’s
determination that air-based threats were outside the scope of
the DBT rule distinguishes this case from a case like Center
for Biological Diversity, where we held an agency must con-
sider a broad range of alternative actions within the scope of
the rule at issue, beyond those alternatives the agency seri-
ously considered. We decline to extend that holding to create
a rule that ignores reasonable boundaries in the scope of an
EA alternative action analysis. The Commission did not
merely select among a range of options, but instead deter-
mined air-based threats were not properly addressed by the
DBT rule. As noted above, this decision was within the Com-
mission’s discretion and it need not include an analysis of air-
based threats within the EA alternative action section.
9640                PUBLIC CITIZEN v. NRC
   [11] By only highlighting one potential deficiency in the
EA that could impact the environment, petitioners implicitly
agree with the Commission’s argument that the rule was oth-
erwise only beneficial to the environment, because it reduced
the threat of a terrorist attack. Therefore, we do not address
whether the NRC violated this court’s holding in Mothers for
Peace, or whether the effects of an air-based attack (rather
than the possibility of a terrorist attack) were too speculative
to necessitate their inclusion in the EA. See Mothers for
Peace, 449 F.3d at 1033-1034. Because Petitioners have iden-
tified no effect of the revised DBT rule that “may cause sig-
nificant degradation of some human environmental factor,” no
EIS was necessary. Center for Biological Diversity, 538 F.3d
at 1219 (quoting Idaho Sporting Cong. v. Thomas, 137 F.3d
1146, 1149 (9th Cir. 1998)); see also Douglas County v. Bab-
bitt, 48 F.3d 1495, 1505 (9th Cir. 1995) (“[A]n EA or an EIS
is not necessary for federal actions that conserve the environ-
ment.”).

  PETITION DENIED.



THOMAS, Circuit Judge, concurring in part and dissenting in
part:

   I join the majority in holding that the Nuclear Regulatory
Commission’s (“NRC”) use of a “reasonable expectation”
standard as a proxy for the division of responsibility between
public and private forces is not arbitrary and capricious, that
the NRC did not improperly withhold safeguarded informa-
tion, and that the NRC did not violate the National Environ-
mental Policy Act. However, I would grant the petition for
review as to whether the NRC acted arbitrarily and capri-
ciously in excluding air-based threats from the Design Basis
Threat (“DBT”) rule.

  No one disputes that there is a credible threat of terrorists
using commercial aircraft to attack nuclear power plants.
                       PUBLIC CITIZEN v. NRC                     9641
Nevertheless, the NRC concludes it was not necessary to
include air-based threats in its DBT rule because: (1) other
federal agencies will largely prevent such attacks in the first
instance, and (2) the effects of any successful attack will be
minimal, or at least minimized.

   The NRC claims it conducted “detailed, site-specific engi-
neering studies” that “confirm the low likelihood of [an air-
plane attack] both damaging the reactor core and releasing
radioactivity that could affect public health and safety.”
Unfortunately, this comforting conclusion directly contradicts
the unanimous findings of the studies available in the admin-
istrative record—some commissioned by the NRC itself—that
some of our nuclear facilities may not be able to withstand the
impact of a commercial jet airplane.

   One study found that an aircraft strike could cause radioac-
tive leakage along with “[e]xtensive destruction of [the] reac-
tor building.”1 One cautioned that a core meltdown could
result from even a light aircraft striking a nuclear plant’s con-
trol building,2 and another similarly concluded that even a
small plane could damage a plant’s reactor core.3 Still
another, performed by the Argonne National Laboratory,
warned that an airplane strike causing rapid depressurization
of the plant’s secondary cooling system might very well cause
“serious damage if not total meltdown.”4 Even the NRC itself
  1
     GERMAN REACTOR SAFETY ORG., PROTECTION OF GERMAN NUCLEAR
POWER PLANTS AGAINST THE BACKGROUND OF THE TERRORIST
ATTACKS IN THE U.S. on SEPT. 11, 2001, at 7-9 (Greenpeace Germany
trans.) (2002), available at http://www.greenpeace.org/raw/content/
international/press/reports/protection-of-german-nuclear-p-2.pdf.
   2
     POWER AUTH. OF THE STATE OF NEW YORK & CONSOL. EDISON CO.,
INDIAN POINT PROBABILISTIC SAFETY STUDY 7.6-3 (1982).
   3
     Ian B. Wall, Probabilistic Assessment of Aircraft Risk for Nuclear
Power Plants, 15 NUCLEAR SAFETY 276 (1974).
   4
     C.A. KOT, ET AL., ARGONNE NATIONAL LABORATORY EVALUATION OF
AIRCRAFT CRASH HAZARDS ANALYSES FOR NUCLEAR POWER PLANTS 51-52
(1982).
9642                    PUBLIC CITIZEN v. NRC
has recently determined that an airplane strike has a substan-
tial chance of causing “catastrophic” damage to spent nuclear
fuel pools.5 The studies referenced in the DBT rule, which appar-
ently6 “confirm” the low likelihood of radioactive release, are
the sole exceptions.

   Of course, we must defer to an agency’s expertise in
weighing evidence. However, there is no sign in this record
that the agency conducted that exercise here. Not only did the
NRC fail to rebut the multitude of studies that conflicted with
its own assessment, but it failed to even mention the contrary
studies. This failure alone is grounds to grant the petition. See
Motor Vehicle Mfrs. Ass’n v. State Farm Mut. Auto. Ins. Co.,
463 U.S. 29, 43 (1983) (noting that an agency’s failure to
offer an explanation for its decision that runs counter to the
evidence before it is arbitrary and capricious); Islander E.
Pipeline Co. v. State of Connecticut, 467 F.3d 295, 313 (2d
Cir. 2006) (observing that an agency’s failure to mention con-
trary scientific studies renders its conclusions arbitrary and
capricious).

   Moreover, the NRC’s determination that nuclear plants can
successfully withstand airplane strikes contradicts the agen-
cy’s own analysis. In its previous DBT rule, the NRC found
that truck bombs can inflict severe damage on nuclear power
plants. See Nuclear Regulatory Commission, Protection
Against Malevolent Use of Vehicles at Nuclear Power Plants,
59 Fed. Reg. 38889, 38891 (August 1, 1994) (stating that such
bombs’ “contribution to [nuclear] core damage frequency
could be high”). The NRC provides no explanation as to why
  5
     NUCLEAR REGULATORY COMMISSION, TECHNICAL STUDY OF SPENT FUEL
POOL ACCIDENT RISK AT DECOMISSIONING NUCLEAR POWER PLANTS at 3-23
(2001); see also NAT’L ACAD. OF SCICIENTISTS, SAFETY AND SECURITY OF
COMMERCIAL SPENT NUCLEAR FUEL STORAGE (2006).
   6
     We must accept on faith that the NRC’s studies actually stand for the
proposition for which they are cited, as the agency has not offered them
for our in camera review, even in redacted form.
                    PUBLIC CITIZEN v. NRC                 9643
we should fear the effects of a truck bomb attack, but not
those of a commercial airliner strike. Nor does the NRC
explain why the construction of passive structural barriers is
a critical component of defense against truck bomb attacks,
while it is completely unnecessary for the NRC even to con-
sider the installation of passive barrier defenses (such as
beamhenges) to attacks by air. The distinction the agency
draws between the risk of truck bombs and hijacked airliner
attacks is inconsistent with our nation’s recent tragic experi-
ences and common sense.

   Although we owe the NRC considerable deference, the
NRC owes the public a rational and reasonable explanation
why it would exclude from its rule consideration of terrorist
air attacks on nuclear facilities. In the face of near-uniform
scientific studies warning of serious risk, bare assurances by
the NRC that we are safe do not satisfy this minimal agency
burden.
