opinion: NORTHERN INDIANA PUBLIC SERVICE CO. v. PORTER COUNTY CHAPTER OF THE IZAAK WALTON LEAGUE OF AMERICA, INC., et al.
  No. 75-4.
  Decided November 11, 1975
  Per Curiam.
  An Atomic Energy Commission Atomic Safety and Licensing Board approved the issuance of a construction permit to Northern Indiana Public Service Co. (NIPSCO) for a commercial nuclear powered electrical generating plant proposed to be built on the south shore of Lake Michigan, in Porter County, Ind., RAI-74-4, p. 557 (1974). On appeal, an AEC Atomic Safety and Licensing Appeal Board, RAI-74-8, p. 244 (1974), sustained the approval. On petition for review by inter-venors in the administrative proceedings, a divided panel of the Court of Appeals for the Seventh Circuit set aside the approval on the ground that the Licensing Board and the Appeal Board failed to follow the Commission’s own regulations governing “population center distance” in the nuclear plant siting. 515 F. 2d 513 (1975). The petition for certiorari is granted, and the judgment of the Court of Appeals is reversed.
  Title 10 CFR § 100.10 (b) (1975) of the Commission’s regulations provides that “the Commission will take . . . into consideration in determining the acceptability of a [proposed nuclear plant] site” the “population center distance,” defined in 10 CFR § 100.3 (c) (1975) as “the distance from the reactor to the nearest boundary of a densely populated center containing more than about 25,000 residents.” At the time of NIPSCO’s application and also at the time of the Court of Appeals’ decision, 10 CFR § 100.11 (a)(3) (1975) further provided, in pertinent part, that “[a]s an aid in evaluating a proposed site” for a nuclear power plant a permit applicant should determine for the proposed unit a
  “population center distance of at least one and one-third times the distance from the reactor to the outer boundary of the low population zone. In applying this guide, due consideration should be given to the population distribution within the population center.”
  Two miles was the minimum allowable “population center distance” determined administratively pursuant to § 100.11 (a) (3). Accepting this determination, the Court of Appeals held that issuance of the construction permit violated the agency’s own regulations because the corporate boundary of the city of Portage, Ind. — projected to have a population in excess of 25,000 by 1980 — lay within 1.1 miles of NIPSCO’s proposed site. In reaching this conclusion the Court of Appeals rejected the agency’s administrative interpretation of its regulations as prescribing computation of “population center distance” for § 100.11 (a) (3) purposes, where the difference is critical to the siting decision, not solely to a political boundary but to the boundary of “that portion of the population center at which the dense population starts,” RAI-74-4, at 565. Under that interpretation of the regulations the “population center distance” was an acceptable 4.5 miles.
  The Court of Appeals erred in rejecting the agency’s interpretation of its own regulations. That interpretation is supported by the wording of the regulations and is consistent with prior agency decisions. The wording does not equate a “dense population center” with a city or other political entity, nor does it define a “boundary” in terms of pre-existing lines drawn for nonsiting purposes. Rather, the regulations require consideration of “population distribution within the population center” in applying the “population center distance” guide. Political boundaries, in contrast, may be drawn for many reasons irrelevant to safe reactor siting, and thus encompass areas never likely to harbor a significant population. But even if the meaning is not free from doubt, the agency’s reliance upon the actual boundaries of population density in its interpretation sensibly conforms to the purpose and wording of the regulations. In that circumstance, the Court of Appeals was “obligated to regard as controlling [such] a reasonable, consistently applied administrative interpretation . . . .” Ehlert v. United States, 402 U. S. 99, 105 (1971). See also Udall v. Tallman, 380 U. S. 1, 16-17 (1965); Power Reactor Co. v. Electricians, 367 U. S. 396, 408 (1961); Bowles v. Seminole Rock & Sand Co., 325 U. S. 410, 413-414 (1945).
  The judgment is reversed, and the case is remanded for consideration of other contentions against the issuance of the construction permit not decided by the Court of Appeals.
  So ordered.
  Porter County Chapter of the Izaak Walton League of America, Inc.; Concerned Citizens Against Bailly Nuclear Site; Businessmen for the Public Interest, Inc.; James E. Newman; Mildred Warner; and George Hanks.
  NIPSCO, the State of Illinois, and the city of Gary, Ind., intervened before the Court of Appeals.
  We do not understand the Court of Appeals' discussion of the evidence regarding population distribution within Portage to imply an alternative ground for the holding that the agency violated its own regulations.
  In re Consumers Power Co., 5 A. E. C. 214, 218 (1972) (although political boundary of nearby city was within low-population zone, “the reduced population distance was acceptable” since “populous areas” of the city were farther removed from the reactor site than one and one-third times the low-population zone radius); In re Consolidated Edison Co., 5 A. E. C. 43, 45 (1972); cf. In re Southern California Edison Co. (San Onofre Station), RAI-74-12, pp. 957, 960 n. 7 (1974).
  The Court of Appeals’ opinion also notes that the boundaries of 1970 census enumeration districts, including an area within Portage’s political limits, lay less than a mile from the proposed reactor site. The location of these boundaries, however, without more, has no greater significance than the location of the corporate border.
  Our decision does not rely upon a revision of 10 CFR § 100.11 (a)(3), 40 Fed. Reg. 26526 (1975), published after the decision of the Court of Appeals by the Nuclear Regulatory Commission, which, pursuant to the Energy Reorganization Act of 1974, § 201, 88 Stat. 1242, 42 U. S. C. §5841 (1970 ed., Supp. IV), now discharges the licensing responsibility formerly exercised by the Atomic Energy Commission.
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