Full opinion text
Opinion for the Court filed by Senior Circuit Judge WILKEY. Opinion concurring in part and dissenting in part filed by Circuit Judge WALD. WILKEY, Senior Circuit Judge: On this appeal we review orders of the Nuclear Regulatory Commission granting licenses for low power and full power operations at the Diablo Canyon Nuclear Power Plant in San Luis Obispo County, California. Petitioners are groups and individuals who intervened in the licensing proceedings before the Commission; petitioners and their members live and work in the vicinity of the Diablo Canyon plant. Petitioners contend that, in granting licenses to Pacific Gas and Electric Company (“PG & E”) for operation of the facility, the Commission violated specific legal requirements of the National Environmental Policy Act, the Atomic Energy Act, the Administrative Procedure Act and numerous regulations promulgated pursuant to those statutes. Respondent Commission and intervenor PG & E characterize petitioners’ contentions as fundamental disagreements with the Commission’s factual findings. They defend those findings as lying well within the range of- agency discretion afforded the Commission under applicable statutes and regulations, and they urge this court to defer to the Commission’s scientific expertise in assessing the legality of the licensing actions challenged herein. After an exhaustive examination of the record in these prolonged and complex proceedings, we conclude that the Commission acted within the parameters of legal discretion in all but two minor respects. The Commission committed technical errors in licensing reactor operators who had been trained on computer simulators, and in denying petitioners a hearing on issues of construction quality assurance when it twice extended the term of Diablo Canyon’s license. The Commission has corrected its first error by amending its operator license requirements to recognize experience gained on computer simulators, and there exists no impediment to relicensing the Dia-blo Canyon operators under the new provision. The second error remains uncorrected, but we conclude that it would serve no discernible purpose to allow petitioners now to introduce the evidence they would have produced had they been properly accorded a hearing. Because that evidence was not material or safety-significant, we conclude that its exclusion calls into question neither the Commission’s decision to license Diablo Canyon nor the safe operation of the plant. Under these circumstances we believe a remand would be an empty gesture, and one with which we decline to burden the Commission. We therefore affirm the Commission’s decision to allow issuance of low power and full power licenses for the Diablo Canyon Nuclear Power Plant. I. The Limited Role on Judicial Review While our analysis necessarily critically examines individual decisions of the Commission and its boards, we recognize and respect the great deference due such expert determinations. The Atomic Energy Act of 1954 created a regulatory scheme which is “virtually unique in the degree to which broad responsibility is reposed in the administrative agency, free of close prescription in its charter as to how it shall proceed in achieving the statutory objectives.” As the Supreme Court has recently reminded us, “the Commission is making predictions, within its area of special expertise, at the frontiers of science. When examining this kind of scientific determination, as opposed to simple findings of fact, a reviewing court must generally be at its most deferential.” Just as we must not usurp the scientific role properly accorded the Commission by the Atomic Energy Act and other governing statutes, neither are we permitted to question this nation’s commitment to the development of nuclear power as a significant power source. On several occasions — often in the course of reversing decisions of this court — the Supreme Court has explicitly recognized Congress’s commitment to the careful nurturing of the nuclear power industry. In Vermont Yankee Nuclear Power Corp. v. Natural Resources Defense Council a unanimous Supreme Court described the limited mandate under which courts act in deciding questions of nuclear regulation: Nuclear energy may someday be a cheap, safe source of power or it may not. But Congress has made a choice to at least try nuclear energy, establishing a reasonable review process in which courts are to play only a limited role. The fundamental policy questions appropriately resolved in Congress and in the state legislatures are not subject to reexamination in the federal courts under the guise of judicial review of agency action. Time may prove wrong the decision to develop nuclear energy, but it is Congress or the States within their appropriate agencies which must eventually make that judgment. In the meantime courts should perform their appointed function. [The National Environmental Policy Act] does set forth significant substantive goals for the Nation, but its mandate to the agencies is essentially procedural. It is to insure a fully informed and well-considered decision, not necessarily a decision the judges of the Court of Appeals or of this Court would have reached had they been members of the decisionmaking unit of the agency. Administrative decisions should be set aside in this context, as in every other, only for substantial procedural or substantive reasons as mandated by statute, not simply because the court is unhappy with the result reached. On remand from the Vermont Yankee decision this court held that a “zero-release” assumption adopted by the Commission to describe the environmental impacts of radioactive waste storage violated both the Administrative Procedure Act (“APA”) and the National Environmental Policy Act (“NEPA”). Because the Commission had not factored into the licensing process uncertainties underlying its assumption, this court concluded that the assumption was arbitrary and capricious and a violation of NEPA. The Supreme Court reversed, holding that the Commission had not acted arbitrarily and capriciously in assigning a zero value to the environmental impact of radioactive waste storage. The Court again emphasized the limited nature of the judicial role in reviewing such Commission determinations: . We are acutely aware that the extent to which this Nation should rely on nuclear power as a source of energy is an important and sensitive issue. Much of the debate focuses on whether development of nuclear generation facilities should proceed in the face of uncertainties about their long-term effects on the environment. Resolution of these fundamental policy questions, lies, however, with Congress and the agencies to which Congress has delegated authority, as well as with state legislatures and, ultimately, the populace as a whole. Congress has assigned the courts only the limited, albeit important, task of reviewing agency action to determine whether the agency conformed with controlling statutes. In People Against Nuclear Energy v. Nuclear Regulatory Commission this court held that the Commission violated NEPA when it improperly failed to consider whether the risk of a nuclear accident at the Three Mile Island plant in Pennsylvania might cause harm to the psychological health and community well-being of nearby residents. Again the Supreme Court reversed. Emphasizing that “Congress [did not] intend[ ] to extend NEPA as far as the Court of Appeals has taken it,” the Court concluded that the 1979 accident at Three Mile Island did not transform[ ] PANE’S contentions into “environmental effects.” ... NEPA is not directed at the effects of past accidents and does not create a remedial scheme for past federal actions. It was enacted to require agencies to assess the future effects of future actions. There is nothing in the language or the history of NEPA to suggest that its scope should be expanded “in the wake of” any kind of accident. The Supreme Court has recently detailed Congress’s historic commitment to development of a viable nuclear power industry. In Pacific Gas & Electric Co. v. State Energy Resources Conservation & Development Commission the Court described Congress’s intent in enacting the Atomic Energy Act, the Price-Anderson Act and the Energy Reorganization Act of 1974: There is little doubt that a primary purpose of the Atomic Energy Act was, and continues to be, the promotion of nuclear power. The Act itself states that it is a program “to encourage widespread participation in the development and utilization of atomic energy for peaceful purposes to the maximum extent consistent with the common defense and security and with the health and safety of the public.” The House and Senate Reports confirmed that it was “a major policy goal of the United States” that the involvement of private industry would “speed the further development of the peaceful uses of atomic energy.” The same purpose is manifest in the passage of the Price-Anderson Act, which limits private liability from a nuclear accident. The Act was passed “in order to protect the public and to encourage the development of the atomic energy industry The evident desire of Congress [in enacting the Energy Reorganization Act of 1974] to prevent safety from being compromised by promotional concerns does not translate into an abandonment of the objective of promoting nuclear power. The legislation was carefully drafted, in fact, to avoid any anti-nuclear sentiment. The continuing commitment to nuclear power is reflected in the extension of the Price-Anderson Act’s coverage until 1987, as well as in Congress’ express preclusion of reliance on natural gas and petroleum as primary energy sources in new power plants, [in the] Powerplant and Industrial Fuel [Use] Act of 1978. It is true, of course, that Congress has sought to simultaneously promote the development of alternative energy sources, but we do not view these steps as an indication that Congress has retreated from its oft-expressed commitment to further development of nuclear power for electricity generation. The foregoing passages clearly establish the limited nature of the role courts are to play in reviewing orders of the Nuclear Regulatory Commission. We are to determine whether the Commission’s decisions aré “arbitrary, capricious, an abuse of discretion, or otherwise not in accordance with law” — not to seize upon the fortuity of appeal to usurp those governmental functions properly accorded the political branches. Mindful of these unequivocal proscriptions against judicial overreaching, we turn to an examination of the orders issued in the present case and the legal deficiencies which allegedly taint them. II. Background Few forms of administrative adjudication are as prolonged and complex as the licensing proceedings for a nuclear power plant, and few nuclear licensing proceedings have produced a record as complicated and massive as that concerning the facility at Dia-blo Canyon. The parties have documented numerous significant actions taken by the Commission and its boards over the past fifteen years. The great majority of these decisions have little relevance to the issues raised on the present appeal; their chronological recitation would do more to obfuscate the issues with which we must deal than to clarify them. Accordingly, we set forth below only a capsule history of the Diablo Canyon proceedings; those facts bearing on specific issues are set forth in the appropriate sections of our opinion. The Atomic Energy Commission (“AEC”), predecessor to the Nuclear Regulatory Commission, issued construction permits to PG & E for Units 1 and 2 of the pressurized water reactor plant at Diablo Canyon in 1968 and 1970. Construction began shortly thereafter, based on the assumption that the nearest significant earthquake fault was a safe distance away. Four years later, however, offshore exploration for petroleum revealed the presence of the Hosgri Fault within three miles of the Diablo Canyon site. Petitioners, who had intervened in the administrative proceeding, requested that construction at the facility be halted until the implications of the discovery could be assessed. The AEC chose instead to authorize the continuance of construction, but it ordered an extensive reexamination of the plant’s seismic design. On 16 June 1981 the Commission’s Appeal Board approved the plant’s seismic design. In June 1980 PG & E applied for a license to load fuel and conduct low-power testing. On 21 September 1981 the Commission rejected claims of deficiencies in the quality assurance program at Diablo Canyon; it therefore issued the requested license for Unit l. Less than a week later, on the very eve of fuel loading, it was discovered that blueprints had mistakenly been reversed in the design of the facility’s reactor. Further investigations by PG & E and the Commission staff uncovered numerous other design errors, leading to the Commission’s decision on 19 November 1981 to suspend PG & E’s fuel loading and low power test license. To ensure that a functioning Diablo Canyon would be adequately protected against seismic disturbances, the Commission ordered PG & E, as a condition to reinstatement of the license, to institute an Independent Design Verification Program (“IDVP”). At the same time, the Commission staff imposed conditions on PG & E’s eligibility for a full power license: the additional requirements concerned seismic and other design verification issues. The ensuing reanalysis and modification of the plant’s design consumed more than 2,000,000 person-hours of professional effort before its completion in October 1983. Upon independent review of the IDVP by the Commission staff, the Commission progressively reinstated elements of the suspended low power license on 8 November 1983, 25 January 1984 and 13 April 1984. Reinstatement of the license was consistent with the findings of the Appeal Board on 20 March 1984 that “[t]he applicant’s verification efforts provide adequate confidence that the Unit 1 safety-related structures, systems and components are designed to perform satisfactorily in service and that any significant design deficiencies in that facility resulting from defects in the applicant’s design quality assurance program have been remedied.” On 10 August 1984 the Commission approved issuance of a license for full power operations at Diablo Canyon; before the license could issue, however, petitioners obtained a stay of the Commission’s order from this court. We heard oral argument on an expedited basis on appeals from both the low power and the full power orders on 30 October. On 31 October we lifted our stay, thereby permitting issuance of the full power license and the commencement of operations at Diablo Canyon. III. , Analysis . Á. Environmental Effects of a Core Meltdown Accident The National Environmental Policy Act requires that agencies prepare an Environmental Impact Statement (“EIS”) detailing the possible environmental impacts of any proposed agency action that may significantly affect the environment. Only after an EIS has been prepared may an agency proceed with the action it proposes to take. The agency’s obligations under NEPA do not cease once the EIS has been prepared, however: both federal case law and regulations recognize a continuing duty' to supplement EISs which have already become final whenever the discovery of significant new information renders the original EIS inadequate. An EIS was prepared for the Diablo Canyon plant in 1973; it was supplemented in 1976. In neither the final nor the supplemental EIS was any significant reference made to the possible environmental consequences of a “core melt” accident. Petitioners contend that the failure to discuss such accidents constitutes a violation of NEPA. At the time the final and supplemental EISs for Diablo Canyon were prepared, the NRC employed a nine-part classification scheme for describing accidents that can occur at nuclear power plants. Class One accidents were considered so trivial as not to warrant inclusion in the Commission’s Environmental Impact Statements. Accidents of Classes Two through Eight were progressively more severe; with limited exceptions, discussion of their potential environmental impacts was required. Class Nine accidents were considered the most severe. The Class Nine designation represented a catch-all, or residual, category embracing those accidents not accorded lesser status. The most prominent type of Class Nine accident was the “core melt” accident, one in which the core of a plant’s nuclear reactor melts and radiation is released into the environment. The consequences of such an accident, should one occur, were conceded to be of potentially catastrophic proportions. At the same time, the probability that such an accident would occur was regarded as so low as to be scientifically and legally insignificant. The Commission therefore maintained a policy of not requiring detailed discussion of Class Nine accidents in its Environmental Impact Statements. As the Commission explained, [djefense in depth (multiple physical barriers), quality assurance of design, manufacture, and operation, continued surveillance and testing, and conservative design are all applied to provide and maintain the required high degree of assurance that potential accidents in this class are, and will remain, sufficiently remote in probability that the environmental risk is extremely low. For these reasons, it is not necessary to discuss such events in applicants’ Environmental Reports. This court upheld the Commission’s policy regarding Class Nine accidents in Carolina Environmental Study Group v. United States. “Viewing the record as a whole,” the court stated, we cannot say that the A.E.C.’s general consideration of the probabilities and severity of a Class 9 accident amounts to a failure to provide the required detailed statement of its environmental impact. That the probability of a Class 9 accident is remote and that its consequences would be catastrophic are undisputed. Neither the A.E.C.’s finding of low probability, nor its methodology or basis for that finding, are challenged here by appellant. Because each statement on the environmental impact of a proposed action involves educated predictions rather than certainties, it is entirely proper, and necessary, to consider the probabilities as well as the consequences of certain occurrences in ascertaining their environmental impact. There is a point at which the probability of an occurrence may be so low as to render it almost totally unworthy of consideration____ We find nothing in the instant record which would indicate that the A.E.C. findings regarding Class 9 accidents are clearly erroneous or that the A.E.C.’s compliance with NEPA Section 102(2)(C)(i) in this case was inadequate. Pursuant to the Commission’s policy, neither the final nor the supplemental EIS for Diablo Canyon discussed in detail the environmental impacts of a Class Nine accident. Two events in the late 1970’s led the Commission to consider revising its policy. In July 1977 the NRC commissioned a Risk Assessment Review Group to assess the “achievements and limitations” of a 1975 report which had concluded that the probability of a Class Nine accident was very low. In September 1978 the Risk Assessment Review Group issued its findings; it concluded that it was “unable to determine whether the absolute probabilities of accident sequences in [the 1975 study] are high or low, but believes that the error bounds on those estimates are in general, greatly understated.” The second event which prompted the Commission to reconsider its original policy was the 1979 accident at the Three Mile Island (“TMI”) nuclear power plant in Pennsylvania. While technically falling within the Commission’s Class Nine category, the TMI accident entailed no breach of the reactor containment vessel and no substantial release of radiation into the atmosphere. Despite its negligible environmental consequences, however, the accident at TMI was considerably more severe than any previous accident in the history of the American nuclear power industry. In light of these two developments, the Commission took the precautionary step of reassessing its assumptions regarding the probability of Class Nine accidents. On 13 June 1980 it published a Statement of Interim Policy, directing that future EISs include a discussion of “the site-specific environmental impacts attributable to accident sequences that lead to releases of radiation and/or radioactive materials, including sequences that can result in inadequate cooling of reactor fuel and to melting of the reactor core.” In departing from its practice of not requiring discussion of Class Nine accidents, the Commission noted the need for further study of the matter; it was not prepared to say, however, that the probability of such accidents was scientifically significant. Indeed, in the first sentence of its Statement the Commission referred to “the more severe kinds of very low probability accidents.” Because the Commission had not yet concluded that its earlier assumption was incorrect, it reaffirmed its faith in final EISs done under the old policy, holding that they need not be revised to conform to the new requirement: It is expected that these revised treatments will lead to conclusions regarding the environmental risks of accidents similar to those that would be reached by a continuation of current practices, particularly for cases involving special circumstances where Class 9 risks have been considered by the staff, as described above. Thus, this change in policy is not to be construed as any lack of confidence in conclusions regarding the environmental risks of accidents expressed in any previously issued Statements, nor, absent a showing of similar special circumstances, as a basis for opening, reopening, or expanding any previous or ongoing proceeding. Only for cases in which “special circumstances” existed was the Statement of Interim Policy to apply retroactively to EISs that had already become final. At issue on the present appeal is the validity of the Commission’s decision to exempt EISs that had already become final from the requirements of the Statement of Interim Policy, and its conclusion that the Diablo Canyon case does not involve “special circumstances” warranting special retroactive application. 1. Duty to Supplement Petitioners contend that the Commission’s decision to deny the Statement of Interim Policy retroactive effect (except when special circumstances exist) violates the Commission’s duty under NEPA to supplement final EISs. We believe that- petitioners fundamentally misconceive the nature of that duty. As a number of courts have held, Environmental Impact Statements need not address “remote and highly speculative consequences.” Under this well-established “rule of reason,” agencies need not discuss in detail events whose probabilities they believe to be inconsequentially small. It would be anomolous to apply a rule of reason to the preparation of final EISs but require that supplemental EISs address remote and highly improbable consequences. This would lead to the absurd result of a continuing agency requirement to supplement its EIS with consideration of effects that were not significant enough to require preparation of an EIS in the first place. Nothing in NEPA ... supports such a scheme, whereby a supplemental EIS is more easily triggered than an original EIS .... As our case law makes clear, this probabilistic rule of reason governs judicial review of both the preparation of an EIS and its supplementation. We conclude, therefore, that the Commission was under no obligation to supplement the Diablo Canyon EIS with a discussion of Class Nine accidents if the Commission reasonably believed that such accidents were highly unlikely to occur. As we have discussed above, the Commission did not conclude in its Statement of Interim Policy that its original assumption regarding Class Nine accidents was scientifically incorrect. Rather, it recognized, the need for renewed study of the issue. The clear import of the Commission’s Statement is that, until such time as its research yields a contrary result, the Commission continues to regard Class Nine accidents as highly improbable events. We do not consider that conclusion unreasonable. Neither the 1978 study by the Risk Assessment Review Group nor the accident at Three Mile Island established that the probability of a Class Nine accident with significant environmental consequences is anything but very small. The Risk Assessment Review Group concluded that the error bounds of an earlier study were greatly understated. As to the probability issue itself, however, the Group was unable to determine whether the estimates of the earlier study were too low or too high. Similarly, while the accident at Three Mile Island technically fell within the Commission’s Class Nine category, it resulted in no significant release of radiation into the atmosphere. Because the environmental consequences of Three Mile Island were scientifically and legally inconsequential, the fact that the accident occurred does not establish that accidents with significant environmental impacts will' have significant probabilities of occurrence. NEPA, therefore, does not require the consideration of Class Nine accidents in future EISs, nor does it require that final EISs be supplemented to take account of the Class Nine risk. The approach adopted in the Statement of Interim Policy — to include discussion of such accidents in future EISs — was a discretionary policy choice of the Commission. Because it need not have imposed upon itself the burden it did, the Commission was perfectly free to deny its new policy retroactive effect. We conclude that the Commission did not violate its obligations under NEPA by declining to supplement the Diablo Canyon EIS with a discussion of the environmental impacts of a Class Nine accident. 2. Worst Case Analysis Petitioners also contend that the Statement of Interim Policy is invalid under the “worst case analysis” regulation promulgated by the Council on Environmental Quality pursuant to NEPA. The Council was given authority, by Executive Order of President Carter in 1978, to direct the manner in which federal agencies comply with NEPA. Not only are the CEQ regulations binding on those federal agencies which they affect, they are also entitled to substantial deference by the courts. The worst-case-analysis regulation sets forth a'procedure for dealing with scientific uncertainty in the preparation of Environmental Impact Statements. It provides that: When an agency is evaluating significant adverse effects on the human environment in an environmental impact statement and there are gaps in relevant information or scientific uncertainty, the agency shall always make clear that such information is lacking or that uncertainty exists. (a) If the information relevant to adverse impacts is essential to a reasoned choice among alternatives and is not known and the overall costs of obtaining it are not exorbitant, the agency shall include the information in the environmental impact statement. (b) If (1) the information relevant to adverse impacts is essential to a reasoned choice among alternatives and is not known and the overall costs of obtaining it are exorbitant or (2) the information relevant to adverse impacts is important in the decision and the means to obtain it are not known (e.g., the means for obtaining it are beyond the state of the art) the agency shall weigh the need for the action against the risk and severity of possible adverse impacts were the action to proceed in the face of uncertainty. If the agency proceeds, it shall include a worst case analysis and an indication of the probability or improbability of its occurrence. Because the regulation is specifically designed to cope with the problem of scientific uncertainty, its provisions are triggered only when such uncertainty exists. No worst case analysis is required if an agency has carefully studied the potential environmental impacts of a proposed action and has determined, with a reasonable degree of certainty, the probability and consequences of such impacts. Where uncertainty exists as to either probability or consequences, however, a worst case analysis is mandatory if the agency decides to proceed with its proposed action. Most notably (and most controversially), the regulation requires such an analysis even where the probability of an impact is assumed to be very small. We do not believe, however, that the CEQ regulation governs the present case. The final Environmental Impact Statement for the Diablo Canyon facility was filed in 1973 and supplemented in 1976. The relevant CEQ regulations became effective on 30 July 1979; they provide that: These regulations shall apply to the fullest extent practicable to ongoing activities and environmental documents begun before the effective date. These regulations do not apply to an environmental impact statement or supplement if the draft statement was filed before the effective date of these regulations. No completed environmental documents need be redone by reasons of these regulations. Although the Statement of Interim Policy was issued after the CEQ regulations became effective, the final and supplemental EIS for Diablo Canyon was filed significantly before that date. By its own terms the CEQ regulation does not require the reworking of existing EISs. Nor do we find warrant in the language of the rule for applying its provisions to the duty to supplement final EISs. Were we to require such “worst case” supplementation, we would effectively circumvent the principle of finality underlying the quoted provision. We decline to construe the duty to supplement final EISs in a manner which would contravene the explicit language of the regulations. 3. “Special Circumstances” Petitioners contend that the EIS for Diablo Canyon is deficient in one final respect. In its Statement of Interim Policy, the NRC recognized an exceptional class of cases — those involving “special circumstances” — for which the Statement’s provisions would be given retroactive effect. Petitioners contend that the presence of the Hosgri fault within three miles of the Diablo Canyon site constitutes just such special circumstances as was envisioned by the statement. The special circumstances exception had precedent in the Commission’s pre-Statement practice. Although the Commission had generally not required consideration of the environmental impacts of core meltdown accidents prior, to adoption of the Statement, in certain exceptional cases the Commission had included a discussion of such accidents as a matter of discretionary policy. The Commission’s Statement cites three such exceptional eases: the Clinch River Breeder Reactor Plant, “a liquid metal cooled fast breeder reactor very different from the more conventional light water reactor plants for which the safety experience base is much broader”; the early site review for the Perryman facility, a site in an area of high population density; and the application of Offshore Power Systems to manufacture floating nuclear power plants, a proposal which entailed “potentially serious consequences associated with water (liquid) pathways leading to radiological exposures if a molten reactor core were to fall into the water.” The Commission’s decision in the Black Fox case, issued only three months prior to the Statement of Interim Policy, provides further insight into the meaning of “special circumstances.” In Black Fox the Commission identified “exceptional case[s] that might warrant additional consideration: higher population density, proximity to man-made or natural hazard, unusual site configuration, unusual design features, etc.” Such cases were those in which “the environmental risk from such an accident, if one occurred, would be substantially greater than that for an average plant.” The parties initially disagree as to whether the special circumstances exception speaks only to cases in which the consequences of an accident, if one occurred, would be unusually severe, or whether the exception speaks to exacerbated probabilities as well. Despite the silence of the Statement of Interim Policy and the ambiguous language of the Black Fox opinion, we believe that petitioners are correct in espousing the latter view. Both the probability and the magnitude of a nuclear accident contribute to its risk; unusual factors that exacerbate that risk demand special consideration, regardless of whether they make an accident more likely or more catastrophic. It is clear, however, that such special circumstances do not exist in the present case. Petitioners rely solely on the fact that Diablo Canyon is located near the Hosgri Fault; they contend that the concomitant earthquake risk greatly enhances both the probability and the expected magnitude of a nuclear accident. There are three possible ways in which petitioners’ argument might be said to have merit, but we believe that none is applicable to the Diablo Canyon plant. First, the existence of the Hosgri Fault might make a nuclear accident relatively more likely. After extensive studies and retrofitting of the plant, however, the Commission has determined that Diablo Canyon’s seismic design is more than adequate to guard against such a horrific possibility; significantly, petitioners have not challenged this conclusion on appeal. We must assume, therefore, that the likelihood that an earthquake will trigger a nuclear accident at the facility is so small as to be rated zero. Second, “special circumstances” might exist if there were a real danger that a core meltdown and an earthquake would occur — by coincidence — simultaneously. As we discuss in the following section, the Commission has determined that the chance of such a bizarre concatenation of events occurring is extremely small. Not only is this conclusion well supported by the record evidence, it accords most eminently with common sense notions of statistical probability. The third manner in which “special circumstances” might be said to exist is if a core meltdown were capable of triggering an earthquake. At oral argument petitioners disclaimed any reliance on this theory, and wisely so. We have been apprised of no studies suggesting that seismic disturbances may be precipitated by a nuclear accident, and we seriously doubt that any exist. We conclude, therefore, that the Commission did not violate NEPA by declining to discuss the possible environmental impacts of a Class Nine accident in the EIS for Diablo Canyon. B. Earthquakes and Emergency Planning NRC regulations require, as a prerequisite to issuance of an operating license for a nuclear power reactor, that “the state of onsite emergency preparedness provide[] reasonable assurance that adequate protective measures can and will be taken in the event of a radiological emergency.” By virtue of this provision, enacted in the aftermath of the accident at Three Mile Island, emergency planning is made an integral element of the licensing decision. In its 1981 San Onofre decision, the Commission held that its regulations do not require consideration of the impacts on emergency planning of earthquakes which cause or occur during an accidental radiological release. Whether or not emergency planning requirements should be amended to include these considerations is a question to be addressed on a generic, as opposed to case-by-case, basis. Relying on the San Onofre decision, the Commission’s Appeal Board declined to require consideration of the potential complicating effects of an earthquake on emergency planning at the Diablo Canyon facility. In December 1983 the Commission itself summarily declined review of the Appeal Board's decision. Further study of the matter by the NRC staff, however, prompted a Commission promise to address whether to reverse its former policy and allow consideration of the effects of seismic events on emergency planning “under the circumstances” of the Diablo Canyon case. Comments were submitted by the NRC staff, petitioners and PG & E in response to specific questions posed by the Commission. After considering the responses, the Commission issued a decision on 10 August 1984 reaffirming its holding in San Onofre. While it promised to initiate a rulemaking “shortly” to resolve the earthquake issue on a generic basis, “the issuance of a full-power operating license need not be delayed until the conclusion of any such proceeding.” In so holding, the Commission explained in detail the factors which weighed against individualized consideration of the issue for the Diablo Canyon facility: The focus of the emergency planning controversy among the parties is on the possible need to consider the contemporaneous occurrence of an earthquake and radiologic release from the plant. For the earthquakes up to and including the Safe Shutdown Earthquake (SSE), the seismic design of the plant was reviewed to render extremely small the probability that such an earthquake would result in a radiologic release. While a radiologic release might result from ah earthquake greater than the SSE, the probability of occurrence of such an earthquake is extremely low. In addition, as the NRC staff noted in its January 13,1984 memorandum to the Commission on the generic subject of earthquakes and emergency planning, for those risk-dominant earthquakes which cause very severe damage to both the plant and the offsite area, emergency response would have marginal benefit because of its impairment by offsite damage. Thus, the Commission agrees with the NRC staffs conclusion that the expenditure of additional resources to cope with seismically caused offsite damage under those circumstances is of doubtful value considering the modest benefit in overall risk reduction which could be obtained. There remains only the possibility of a contemporaneous occurrence of both a radiologic release from the plant caused by an event other than an earthquake, and an earthquake that would complicate emergency response. NUREG-0654 does call for some consideration of site-specific adverse or emergency conditions on emergency response. In prior cases such frequently occurring natural phenomena as snow, heavy rain, and fog have been considered. With one exception, the focus has always been on frequently occurring natural phenomena. The Commission believes, based on the information provided by the parties, that earthquakes of sufficient size to disrupt emergency response at Diablo Canyon would be so infrequent that their specific consideration is not warranted. The Commission’s view that it need not give specific consideration to the complicating effects of earthquakes on emergency planning in this case is bolstered by the following consideration. Specific consideration has been given in this case to the effects of other relatively frequent natural phenomena. The evidence includes the capability of the emergency plan to respond to disruptions in communication networks and evacuation routes as a result of fog, severe storms and heavy rain. In the extreme, these phenomena are capable of resulting in area-wide disruptions similar to some of the disruptions which may result from an earthquake. Testimony in the Diablo Canyon record indicates that adverse weather conditions such as the effect of heavy fog could increase evacuation time to approximately 10 hours. Thus, while no explicit consideration has been given to disruptions caused by earthquakes, the emergency plans do have considerable flexibility to handle the disruptions caused by various natural phenomena which occur with far greater frequency than do damaging earthquakes, and this implicitly includes some flexibility to handle disruptions by earthquakes as well. The Commission also concluded that the Diablo Canyon site did not present “special circumstances” within the meaning of 10 C.P.R. § 2.758 that would require individualized consideration of the earthquake issue. The Commission noted the decision of its Appeal Board that the site was not one of high seismicity, despite its proximity to the Hosgri Fault. At most, the Commission concluded, the region surrounding the Diablo Canyon facility was characterized by “moderate seismicity.” Petitioners challenge the Commission’s decision on essentially three grounds. First, they contend that the earthquake issue is “material” to the licensing decision; as such, this court’s decision in Union of Concerned Scientists v. Nuclear Regula tory Commission would preclude its exclusion from the scope of the licensing proceeding. Second, petitioners assert that the earthquake issue is inappropriate for resolution through generic rulemaking: because the risk of seismic disturbance is significant for only two reactor sites in the United States (Diablo Canyon and San Onofre), petitioners contend that the issue should be addressed in the context of individual licensing proceedings. Finally, even if rulemaking were the proper avenue for agency resolution of the earthquake issue, petitioners contend that the failure of the Commission to commence rulemaking proceedings before approval of the Diablo Canyon license has effectively denied them an opportunity to participate in the decisionmaking process. The first contention raised by petitioners is by far the most significant, for the materiality or immateriality of the earthquake issue determines the extent to which petitioners possess a right to demand particularized agency consideration of the issue. The Commission has determined, both in San Onofre and in its 10 August decision, that the potential complicating effects of a seismic event on emergency planning are immaterial. We therefore confront a situation considerably different from that which this court was required to address in Union of Concerned, Scientists. In that case we held that section 189(a) of the Atomic Energy Act guarantees interested parties the right to a hearing on material issues; thus, an issue recognized by the NBC in its own regulations as material was found to require inclusion in hearings held under section 189(a). Here we are faced with precisely the opposite situation, for the Commission has twice held the earthquake issue to be immaterial. The Commission’s finding of immateriality does not close our inquiry, however, for otherwise the Commission could escape its responsibilities under section 189(a) by la-belling any scientific or environmental factor “immaterial.” Ultimate resolution of contested agency actions properly lies within the province of the courts. Because courts lack the scientific and technical expertise of regulatory agencies, however, the judicial role on review is limited to determining whether the agency has complied with relevant statutory and regulatory requirements. We must determine in the present case whether the NRC’s finding of immateriality is “arbitrary, capricious, [or] an abuse of discretion”; in doing so, we must accord great deference to decisions, such as the one at issue here, whose subject-matter lies “at the frontiers of science.” Applying these well-established principles of administrative law, it becomes obvious that the NRC’s decision to treat seismic issues as immaterial for purposes of individual licensing proceedings does not transgress the boundaries of agency discretion. The Commission’s decision was based on three well-articulated scientific conclusions, none of which warrant characterization as arbitrary or capricious. First, the Commission found that the probability of a radiological accident caused by an earthquake was extremely low. The plant has been designed to withstand earthquakes of a magnitude up to and including that of a hypothetical “Safe Shutdown Earthquake” (“SSE”); for Diablo Canyon, the SSE has been calculated to lie at 7.5 on the Richter scale. Moreover, because the SSE is chosen with reference to the region’s maximum earthquake potential, the probability that an earthquake greater than the SSE will occur is so low as to be legally insignificant. Second, the Commission considered the danger that an earthquake of significant magnitude would occur contemporaneously with a radiological accident precipitated by some other cause. The Commission concluded that, because Diablo Canyon is not located in an area of high seismicity, the probability that such a coincidence would occur is also extremely low. Finally, the Commission noted that the emergency plan for Diablo Canyon already possesses sufficient flexibility to deal with most disruptions that would be caused by an earthquake. While clearly not intended to be a complete justification for the Commission’s decision, this final conclusion is reasonable with regard to a wide variety of potential disruptions. Many of the emergency planning problems that could be caused by an earthquake — the closure of roads, the disruption of communications, etc. — are already taken into account in Diablo Canyon’s emergency plans because they could also be caused by other, more frequently occurring natural phenomena. We conclude that the Commission did not exceed its discretion in finding that the complicating effects of a seismic event on emergency planning was not material for purposes of individual licensing proceedings. Having found that the earthquake risk was immaterial, the Commission was also clearly justified in deciding to treat the issue as a generic problem to be resolved through rulemaking rather than adjudication. Petitioners challenge the Commission’s decision on the ground that the earthquake risk affects only two nuclear plants, Diablo Canyon and San Onofre, both of which are located on the California coast. Rulemaking, they contend, is appropriate only for those issues which affect a large number of nuclear plants across the country, while specialized issues (such as the earthquake risk) should be dealt with in the context of individual licensing proceedings. As a general proposition petitioners’ analysis has merit: common issues should ideally be resolved through rulemaking, while unusual issues are best resolved through adjudication. This simple proposition, however, is incapable of being reduced to mathematical terms. One cannot say, for example, that an issue which affects 15% of the nuclear power plants in the country should be resolved generically, while one which affects only 10% of the nation’s plants is inappropriate for generic resolution. Determination of the best decisionmaking method must be made, in the first instance, by the agency; our review of that decision is circumscribed by the “arbitrary and capricious” standard. Particularly when agencies are dealing with probabilities — here, a risk which may or may not materialize — considerable deference should be accorded the agency’s decision. Even if it were currently believed that Diablo Canyon and San Onofre were the only nuclear facilities in America located in areas of significant seismicity, future research might reveal the existence of faults near other facilities. Indeed, the Hosgri Fault itself was unknown until the early nineteen-seventies. Because seismology remains a difficult and inexact science, we hesitate to conclude, as petitioners would have us do, that the earthquake risk is unique to Diablo Canyon and San Onofre. Petitioners’ final contention focuses on the Commission’s delay in instituting even rulemaking proceedings to address the earthquake risk. The Commission’s failure to institute such proceedings, petitioners argue, has effectively denied interested parties the right to present evidence on the seismic risk at Diablo Canyon. But we have already concluded that the Commission did not err in finding the earthquake issue immaterial for purposes of the Diablo Canyon proceeding; petitioners therefore did not possess the right they now assert. At most, their claim resolves to a contention that the Commission has unreasonably delayed in instituting rule-making proceedings. The Commission itself has admitted that it should have acted sooner in initiating a rulemaking. As it stated in its 10 August 1984 decision, [w]e previously indicated in San Onofre that this matter would be considered on a generic basis. Some time ago the NRC staff advised us that, in its view, generic consideration was not necessary. However, we were diverted from this issue by the press of other important Commission business, and we took no action in response to that advice. In retrospect, since we disagree with the NRC staff’s view, we should have acted sooner and initiated rulemaking. The need to address this issue in this case has again focused our attention on this matter. By this order we are indicating our desire to initiate rulemaking shortly, and directing the NRC staff to give priority attention to the matter. Taking into account the time period in question, as well as the fact that the Commission’s delay was occasioned in large part by the recommendation of its staff that generic consideration was not necessary, we conclude that the delay in instituting rulemaking proceedings was not so unreasonably long as to have violated the agency’s obligations under the Administrative Procedure Act or the Atomic Energy Act. C. Operator Licensing Requirements Before it may issue an operating license for a nuclear power plant, the Commission is required by its regulations to find that “the facility will operate in conformity with the application as amended, the provisions of the Act, and the rules and regulations of the Commission”; “[t]here is reasonable assurance ... that the activities authorized by the operating license can be conducted without endangering the health and safety of the public”; and “[t]he applicant is technically ... qualified to engage in the activities authorized by the regulations.” Essential to these findings is a determination that the plant’s reactor operators have been properly trained and licensed. In its 10 August 1984 decision the Commission concluded that the operators at Diablo Canyon were properly qualified. Petitioners now challenge that determination as contrary to the Commission’s own rules for the licensing of reactor operators. NRC regulations require that applicants for the position of reactor operator pass both a written examination and an operating test. These requirements may be waived, but only if the applicant “[h]as had extensive actual operating experience at a comparable facility within two years prior to the date of application.” The NRC regulations also provide for the administration of a simulated operating test to applicants, but only if the applicant “has had extensive actual operating experience at a comparable reactor.” The Commission has consistently construed its regulations to allow experience on a computer simulator to suffice in the absence of “actual operating experience.” The Commission’s rationale for doing so turns on an alleged inadequacy in the regulatory language: according to the Commission, great advances in computer simulation render anachronistic a literal reading of the rule. To correct the perceived anachronism, the Commission recently amended its regulations to permit experience on simulators to suffice in the absence of actual operating experience. That amendment came, however, long after reactor operators at Diablo Canyon had been licensed; many of the operators had received only computer-simulated training. Petitioners now challenge the qualifications of those operators who did not possess actual operating experience at the time of their licensing. It is quite obvious that the Commission’s “long-standing practice” was in direct contravention of the regulatory provision. It is true, of course, that “[w]ords ... do not have absolute and constant referents,” and that “a judicial belief in the possibility of perfect verbal expression ... is a remnant of a primitive faith in the inherent potency and inherent meaning of words.” But if words in a regulatory provision may be said to retain any meaning at all, we are convinced that “actual operating experience at a comparable reactor” cannot be said to encompass experience on a computer simulator. Courts must defer to the interpretation administrative agencies accord their governing statutes and regulations, but such deference is appropriate only so long as the agency’s interpretation does no violence to the plain meaning of the provision. We would therefore be required to find Diablo Canyon’s reactor operators unqualified under NRC regulations, were it not for the recently-promulgated amendment to those regulations. The amendment addresses precisely the issue raised on this appeal: simulated experience is now considered sufficient to ensure that reactor operators are qualified to perform their crucial and demanding role. For us to remand the issue to the Commission would serve no discernable purpose: the Commission would clearly be justified in relicensing the Diablo Canyon operators under the amended regulation. We conclude, therefore, that the Commission practice under which Diablo Canyon’s operators were licensed was contrary to the plain meaning of the Commission’s own rule, but that the option of relicensing the operators effectively precludes the necessity of remanding the issue to the Commission. D. The Right to a Hearing Under Section 189(a) of the Atomic Energy Act The Atomic Energy Act grants to interested persons the right to a hearing in certain types of nuclear regulatory proceedings. Section 189(a) provides that [i]n any proceeding under this chapter, for the granting, suspending, revoking, or amending of any license or construction permit, or application to transfer control, and in any proceeding for the issuance or modification of rules and regulations dealing with the activities of licensees, and in any proceeding for the payment of compensation, an award or royalties under Sections 2183, 2187, 2236(c) or 2238 of this title, the Commission shall grant a hearing upon the request of any person whose interest may be affected by the proceeding, and shall admit any such person as a party to such proceeding. Petitioners contend that the Commission violated section 189(a) by refusing to grant them a hearing when it lifted a summarily-imposed suspension of Diablo Canyon’s license for low power operations, and when it amended that license to extend its term. The Commission defends its denial of petitioners’ request for a hearing on essentially two grounds. It first contends that the actions it took in the low power proceeding were not the types of actions for which Congress intended a hearing to be accorded under section 189(a). Neither the lifting of a license suspension nor the extension of a license term, it argues, automatically triggers the procedural protections of the Act. If section 189(a) is found to apply, however, the Commission contends that petitioners were in fact accorded a hearing by virtue of their ongoing attempts to reopen the record in the full power proceeding. Because the issues petitioners sought to raise in connection with the lifting of the license suspension and the extension of the license term involved questions of design and construction quality assurance, the Commission contends that it was justified in referring petitioners to their contemporaneous efforts to reopen the full power record with regard to those very same issues. Petitioners were ultimately successful in obtaining reopening of the record on design quality assurance, but they were unable to persuade the Commission to reopen on matters of construction quality assurance. In Section E below we conclude that the Commission was correct in denying petitioners’ request to reopen on the construction quality assurance issues. Our analysis of petitioners’ present claims under section 189(a) may be briefly summarized. We agree with the Commission that the lifting of a license suspension does not fall within any of the enumerated categories of Commission action for which a hearing must be held. We agree with petitioners, however, that the extension of the term of a license constitutes a license “amendment” within the meaning of section 189(a). Petitioners were therefore entitled to a hearing when PG & E sought two extensions of its low power operating license. We conclude that the Commission satisfactorily discharged its obligation to provide such a hearing on issues of design quality assurance when it referred petitioners to the reopened proceedings on that issue. The Commission violated section 189(a), however, when it denied petitioners a hearing on issues of construction quality assurance. The crucial distinction between construction and design issues stems from the fact that the full power record was never reopened on construction issues, as it was on matters of design. Because the Commission’s criteria for reopening a closed record are higher than the criteria for obtaining a hearing under section 189(a), the mere fact that a party can seek reopening is not a sufficient substitute for the hearing rights guaranteed by section 189(a). In light of the unique circumstances of the present case, however, we do not believe that judicial relief for the Commission’s procedural error is appropriate. Because we conclude in Section E that petitioners were not entitled to reopen the record on construction quality assurance, we must also conclude that none of the evidence petitioners would have presented on that issue, had they been accorded a hearing under section 189(a), would have been material or safety-significant. The Commission’s violation of section 189(a) therefore, does not call into question the decision to license Diablo Canyon or the safe operation of the plant, and it would be pointless for us to enjoin such operations as a result. Our analysis of petitioners’ claims under section 189(a) necessarily begins with a determination of whether the types of action taken by the Commission come within the ambit of the statutory provision. As an initial proposition, petitioners suggest that all actions by the Commission which bring about a “significant change” in the licensing status of a nuclear facility come within the mandate of section 189(a). That provision is quite specific, however, in its enumeration of agency actions which trigger the hearing requirement. No fewer than eight such types of action are listed, and among them no mention is made of actions which effect “any significant change.” An examination of the section's legislative history confirms the specificity and precision with which the section was drafted. When first proposed, the Atomic Energy Act of 1954 included no provision for hearing rights. After considerable discussion a new section 181 was ineorpo-rated in the substitute bill introduced in the House; it provided that “[u]pon application, the Commission shall grant a hearing to any party materially interested in any ‘agency action.’ ” The new provision was faulted, however, for being “too broad, broader than it was intended to be [be].” Senator Hickenlooper offered an amendment to restrict the hearing right to specific categories of agency action. The result, a new subsection within section 189, was the substantive equivalent of the modern provision. The Act’s legislative history, therefore, reveals the intent of Congress to guarantee hearings rights in certain classes of agency action, but not in others. We are aware that our decision in Sholly v. Nuclear Regulatory Commission may be read to suggest a contrary conclusion. In Sholly this court reversed orders of the NRC which had permitted the venting of radioactive gas into the atmosphere from the damaged Three Mile Island nuclear plant. The petitioners in Sholly contended that the