Greaney, J.
Nuclear Metals, Inc. (plaintiff), filed a complaint in the Superior Court seeking, in count I, a determination that an assessment imposed on it by the Low-Level Radioactive Waste Management Board (board), acting pursuant to G. L. c. 111H, §§ 4A and 4B (1994 ed.), and corresponding regulations, 845 Code Mass. Regs. § 4.00 (1992),1 was unlawful. Count II of the complaint presented an appeal from a decision of an administrative magistrate, adopted with minor revisions by the board, concluding that the amount of the assessment charged to the plaintiff was proper.
The parties submitted the case on a statement of agreed facts and the record of the administrative proceedings. A judge in the Superior Court ordered entry of judgment for the board on the claim contesting the validity of the assessment. He vacated the decision of the board on the plaintiff’s administrative challenge to the computation of the assessment on the ground that the board lacked jurisdiction to hear the appeal, and he ordered that the claim in count II of the complaint be dismissed. Both parties appealed from the judgment, and we granted the board’s application for direct appellate review. We affirm that part of the judgment which declares the assessment to be a valid fee rather than an unconstitutional charge. We vacate that part of the judgment dismissing the plaintiff’s appeal from the administrative decision of the board, and remand the case to the Superior Court so that it may be returned to the board for administrative consideration of the plaintiff’s claim respecting the amount of the assessment charged.
1. Facts. The material facts are straightforward and undisputed. The plaintiff is a manufacturer licensed by the United [198]*198States Nuclear Regulatory Commission to receive, possess, use, transfer, or acquire radioactive materials. The plaintiff, which employs approximately 200 persons in the Commonwealth, uses depleted uranium in the manufacture of metal products for a range of applications, including kinetic penetrators used for armor piercing ammunition by the United States armed forces, and radiation-shielding components for medical, pharmaceutical, and industrial uses. As a byproduct of its manufacturing processes, the plaintiff produces low-level radioactive waste.2 Based on data collected by the board, the plaintiff was among the top four generators of low-level radioactive waste in the Commonwealth during the years of 1990 and 1991. The assessment at issue totals $102,103.76.
2. Statutory basis for the assessment. The Low-Level Radioactive Waste Policy Amendments Act of 1985, 42 U.S.C. §§ 2021a et seq. (1988) (Federal act), states as Federal policy that “[e]ach State shall be responsible for providing, either by itself or in cooperation with other States, for the disposal of . . . low-level radioactive waste generated within the State . . . .” 42 U.S.C. § 2021c (a) (1) (A). The goal of the Federal act is to decrease reliance on the few existing disposal sites, located in the States of Washington, South Carolina, and Nevada,3 by encouraging States to enter into cooperative regional compacts and develop disposal sites for [199]*199the low-level radioactive waste generated within each region. See 42 U.S.C. §§ 2021c, 2021e.
In New York v. United States, 505 U.S. 144 (1992), the United States Supreme Court interpreted the Federal act as providing to the States lacking in-State or regional disposal sites a series of strong incentives to comply with Federal policy concerning the disposal of low-level radioactive waste generated within their borders. Id. at 170. The Court explained that, in form, the Federal act is an “intricate” compromise between the States with, and the States without, disposal sites. Id. at 151. In effect, the Federal act authorizes burdens on interstate commerce that most likely would be unconstitutional absent express congressional authorization. See Philadelphia v. New Jersey, 437 U.S. 617 (1978) (law closing New Jersey’s borders to waste generated outside territorial limits unconstitutional burden on interstate commerce). States with disposal sites are granted the right to place escalating surcharges, beginning in 1986-1987, on disposal in their existing facilities, and, as of 1996, to deny access to the existing disposal sites to waste generators located in any State that has not met specific “milestones” set out in the Federal act. Those milestones mark progress toward the siting and licensing of an in-State or a regional facility for the disposal of a State’s low-level radioactive waste. Id. at 151-153. In the Court’s words, “any burden caused by a State’s refusal to regulate [in compliance with the Federal act] will fall on those [within the State’s borders] who generate waste and find no outlet for its disposal.” Id. at 174.
General Laws c. 111H (State act), inserted by St. 1987, c. 549, establishing the board and delineating its responsibilities, is the Commonwealth’s response to the Federal act. See Opinion of the Justices, 397 Mass. 1201 (1986). Under the State act, the board is charged with preparing and implementing a management plan to provide for the safe and efficient management of low-level radioactive waste produced in [200]*200the Commonwealth. G. L. c. 111H, §§ 11, 12.4 *In conjunction with the Departments of Environmental Protection and Public Health, the State act charges the board with the selection of a site for the disposal of low-level radioactive waste generated in the Commonwealth. See G. L. c. 111H, §§ 17, 33. The board has the responsibility for choosing among an in-State facility open only to generators of waste in the Commonwealth, a small regional disposal facility, or a large regional disposal facility serving waste generators in New England and offering disposal services to generators outside the region. See 345 Code Mass. Regs. § 1.74 (1994). See also St. 1987, c. 549, § 6. In the event that the milestones in the Federal act are not met and access to existing disposal sites in other States is denied to waste generators in the Commonwealth, the board is required by statute to develop interim or emergency plans for the temporary storage of low-level radioactive waste. See G. L. c. 111H, § 12 (6) (10).
3. The assessment. Pursuant to G. L. c. 111H, § 4A, the board must “annually assess each person licensed or registered to receive, possess, use, transfer or acquire radioactive materials in the Commonwealth, amounts sufficient to defray the costs annually incurred by the board” to implement its plan for managing the disposal of low-level radioactive waste generated in the Commonwealth. The total assessment is capped by statute at $500,000. That amount is to be reduced by any funds appropriated or obtained from other sources for implementing the management plan. See G. L. c. 111H, § 4A.5 The board is directed to apportion the total assessment among licensees and registrants,6 “based on the volume and classification of radioactivity of waste produced by each [201]*201licensee and registrant which is shipped for disposal off site or stored for later disposal; provided, however, that the board shall make a minimum assessment on all licensees and registrants.” Id. For purposes of apportioning the fiscal year 1992 assessment, the board first assessed a “minimum” flat fee of $75 to all licensees and registrants. The remainder of the total assessment was charged proportionally to licensees and registrants based on waste produced and shipped during 1990 and 1991. Excluded from the assessment calculation was data on waste produced during 1990 and 1991 and stored on-site for later disposal.
4. Validity of the assessment. The plaintiff challenges the validity of the assessment as a lawful fee. The plaintiff further argues that, if the assessment is viewed as a tax, it fails to pass constitutional muster. We agree with the judge, however, that the plaintiff has failed to satisfy its burden of proving that the assessment is not a lawful fee. See Southview Coop. Hous. Corp. v. Rent Control Bd. of Cambridge, 396 Mass. 395, 403 (1985). See also Bertone v. Department of Pub. Utils., 411 Mass. 536, 549 n.12 (1992).
“[T]he nature of a monetary exaction ‘must be determined by its operation rather than its specially descriptive phrase.’ ” Emerson College v. Boston, 391 Mass. 415, 424 (1984), quoting Thomson Elec. Welding Co. v. Commonwealth, 275 Mass. 426, 429 (1931).* *7 Fees generally fall into one of two categories. A fee may be categorized either as a user fee, charged by the proprietor of a particular instrumentality for its use, or as a regulatory fee, founded on the State’s police power to regulate a particular activity or business. Emerson College, supra at 424. As Justice Breyer (then Judge Breyer) recently noted, “The classic ‘regulatory fee’ is imposed by an agency upon those subject to its regulation. . . . [202]*202It may serve regulatory purposes directly by, for example, deliberately discouraging particular conduct by making it more expensive. . . . Or, it may serve such purposes indirectly by, for example, raising money placed in a special fund to help defray the agency’s regulation-related expenses.” (Citations omitted.) San Juan Cellular Tel. Co. v. Public Serv. Comm’n of P.R., 967 F.2d 683, 685 (1st Cir. 1992).
In the Emerson College case, this court observed that “fees share common traits that distinguish them from taxes: they are charged in exchange for a particular governmental service which benefits the party paying the fee in a manner ‘not shared by other members of society,’ . . . they are paid by choice, in that the party paying the fee has the option of not utilizing the governmental service and thereby avoiding the charge . . . and the charges are collected not to raise revenues but to compensate the governmental entity providing the services for its expenses” (citation omitted). Id. at 424-425, quoting National Cable Television Ass’n v. United States, 415 U.S. 336, 341 (1974). See Southview Coop. Hous. Corp. v. Rent Control Bd. of Cambridge, supra at 402; Berry v. Danvers, 34 Mass. App. Ct. 507, 510 (1993). A consideration of these factors, and the nature of the board’s regulatory responsibility, compels the conclusion that the assessment authorized by the act is a valid fee.
The plaintiff’s primary contention is that the board functions as a planning agency and provides no service for which it may legitimately exact a fee. We disagree. Because of the risk posed by low-level radioactive waste, see New York v. United States, supra at 149-150, its disposal is a highly regulated activity. There may be means to reduce the amount of waste produced by the plaintiff, and alternative disposal technology may be, or may become, available for small amounts of waste having particular characteristics. Nothing in the record suggests, however (and the burden is on the plaintiff), that the plaintiff will be able to avoid reliance on disposal facilities like those in Washington, Nevada, and [203]*203South Carolina in the foreseeable future.8 The terms of the Federal act have the effect of conditioning the plaintiff’s access (and the cost of that access) to existing disposal sites (and to interim storage if the disposal sites are closed to Massachusetts generators) on the board’s performance of its functions. Only the board can meet the progress milestones in the Federal act, negotiate for continued access to existing facilities on behalf of waste generators in the Commonwealth, enter into a regional compact, or set in motion the siting process for a disposal facility in, or near, the Commonwealth. Thus, if it is to continue to engage in its current manufacturing activities, the plaintiff must rely on a service presently provided by the board, in the form of planning for disposal of low-level radioactive waste generated in the Commonwealth in compliance with Federal law and standards. See Mississippi Power & Light Co. v. United States Nuclear Regulatory Comm’n, 601 F.2d 223, 229 (5th Cir. 1979), cert. denied, 444 U.S. 1102 (1980).9 The assertion that the board has failed timely to meet certain of the Federal milestones is a complaint about the quality of the board’s services that does not affect their basic character as regulatory services essential to the plaintiff.
[204]*204The service provided by the board may, we think, reasonably be analogized, in some respects, to the service performed by the rent control board of Cambridge in the case of Southview Coop. Hous. Corp. v. Rent Control Bd. of Cambridge, supra. By statute, the city of Cambridge was entitled to regulate residential rental rates. A landlord dissatisfied with the maximum rent established for a particular unit could file a petition with the rent control board for an upward adjustment of the rent. As of 1981, the rent control board charged a fee in connection with the filing of such a petition, designed to compensate the board for the cost of processing a petition. Id. at 397, 402-404. The filing fees under consideration in the Southview case, which this court upheld as valid, obtained for the landlord a regulatory service that would have been unnecessary in the absence of legislation authorizing the city to control rental rates.10 Similarly, in this case, the regulatory and planning services of the board are made essential to the plaintiff by the policies and incentives of the Federal act.
As to the remaining aspect of the first factor, the board’s services provide a “sufficiently particularized” benefit to the plaintiff to qualify as a valid fee. While the safe disposal of low-level radioactive waste is a public benefit, see New York v. United States, supra, it is the plaintiff (and not the general public) which requires access to disposal facilities for low-level radioactive waste meeting Federal and State stan[205]*205dards. See Maine v. Department of Navy, 973 F.2d 1007, 1013 (1st Cir. 1992). The services of the board will be required in any event. It is appropriate that the entities which generate low-level radioactive waste (and not the taxpayers of the Commonwealth) should shoulder costs associated with protecting the general public from the hazards posed by the waste. Other States have taken an approach similar to the Commonwealth’s, passing on the cost of planning for its disposal to the generators of low-level radioactive waste. See, e.g., Conn. Gen. Stat. § 22a-164 (1993); N.Y. Pub. Auth. Law § 1854-d (2) (Consol. 1994).
The second and third factors of the Emerson College test are also satisfied. The plaintiff is not “compelled” to pay the fee, even though it must pay the fee so long as it engages in manufacturing activities in the Commonwealth that produce as a byproduct low-level radioactive waste. The plaintiff has a Federal license, and therefore a right, to possess and use low-level radioactive materials, but “[f]ces are not taxes ‘even though they must be paid in order that a right may be enjoyed.’ ” Bertone v. Department of Pub. Utils., supra at 549, quoting Southview Coop. Hous. Corp. v. Rent Control Bd. of Cambridge, supra at 402. The plaintiff has a “choice,” in the sense that this term has been used in our cases, as to whether to engage in manufacturing activities resulting in the production of low-level radioactive waste. Cf. Emerson College v. Boston, supra at 426 (because of danger to public, plaintiff could not forgo firefighting services for which fee was charged). Just as the plaintiffs in the Bertone and Southview cases could have avoided the charges under consideration in those cases by forgoing the rights for which the charges were assessed, the plaintiff in this case could have avoided the, assessment imposed by the board, which was imposed only on current licensees and registrants.
We recognize that the “choice” presented in these cases cannot realistically be considered a free choice. In the Bertone case, the “choice” presented to the plaintiffs was to forgo the development of their property. In the Southview case, the “choice” presented to landlords in Cambridge was [206]*206to forgo obtaining what they considered a reasonable economic return on their investment in residential real estate. Here, the “choice” presented to the plaintiff is to cease engaging in activities that produce low-level radioactive waste. Several recent Federal cases we have examined do not mention the “voluntary” factor of the Emerson College test, but focus instead on whether the service in connection with which the charge is levied benefits the regulated entities in a way distinguishable from any benefit provided to the public at large. For example, in Maine v. Department of Navy, supra, the United States Court of Appeals for the First Circuit considered licensing and per-pound generation charges levied on the Navy by environmental authorities in Maine to provide for the safe disposition of hazardous waste produced at the Navy’s shipyard at Kittery. There was no way to avoid payment of the charges. The court found the charges to constitute a classic regulatory fee which raised funds to defray an agency’s regulation-related expenses and which benefited the Navy (and other regulated entities) by ensuring compliance with State environmental goals. Id. at 1012-1013. See Union Pac. R.R. v. Public Util. Comm’n of Or., 899 F.2d 854, 859-861 & n.11 (9th Cir. 1990). Here, the assessment made by the board is designed to raise funds to satisfy directives given the State by Federal law as a result of manufacturers within the State producing dangerous radioactive waste which must rely on the State to arrange for its proper disposal. The assessment is a classic regulatory fee, and the element of choice is not a compelling consideration which can be used to invalidate an otherwise legitimate charge.11
[207]*207Finally, the revenue derived from the assessment obviously is used to fund the particularized services provided by the board. The statutory authorization for the assessment requires the board to “annually assess . . . amounts sufficient to defray the costs annually incurred by the board for such purposes.” G. L. c. 111H, § 4A (a). The amount the board is permitted to raise is capped at $500,000; that amount is to be reduced by, among other funding sources, any part of a prior assessment that has not been expended to defray costs incurred by the board. No part of the monies raised by the assessment is treated as general revenue of the Commonwealth. Id. (“There is hereby established on the books of the commonwealth a separate fund, to be known as the Low Level Radioactive Waste Management Fund.”) See Union Pac. R.R. v. Public Util. Comm’n of Or., supra at 857.
We reject the plaintiffs argument that the board’s activities, all of which are funded by means of the assessments charged to waste generators, include services that are not of particular benefit to it. In connection with this point, the plaintiff singles out public information programs and the employment of a public participation coordinator. See G. L. c. 111H, § 4 (a) (6). As the board points out, an obvious purpose of such programs is to increase public acceptance of the need for a disposal facility for low-level radioactive waste, including the possibility that such a facility might be constructed in the Commonwealth. This service is essential to the board’s ability to meet its statutory obligations and directly benefits a generator of low-level radioactive waste. Because we conclude that the assessment is a valid fee, we need not consider the plaintiffs arguments that the assessment is improper when considered as a tax.
5. The computation of the assessment. On his own motion, the judge dismissed the plaintiffs appeal from the adminis[208]*208trative decision of the board on the ground that the board’s regulations did not permit administrative consideration of “the substantive validity of an assessment made pursuant to the Low-Level Radioactive Waste Board’s authority.”
The regulations at issue provided (they have since been amended), in pertinent part, as follows. A licensee or registrant in receipt of a written notice of an assessment due and payable was required to “make payment in full on or before the due date . . . specified in the statement of assessment amount.” 845 Code Mass. Regs. § 4.03 (5). “Failure without just cause to pay any assessment when due” constituted a violation of 845 Code Mass. Regs. § 4.00 (emphasis added). 845 Code Mass. Regs. § 4.04 (1). Any licensee notified by the board of a violation of § 4.00 was entitled to request a hearing before being assessed civil penalties. 845 Code Mass. Regs. § 4.04 (4). The amount of the penalty was to be determined by the board based on consideration of a list of six factors. Id.12
The board interpreted its governing statute, and the regulations promulgated thereunder, as permitting it to consider, in an administrative proceeding, whether a licensee or registrant had “just cause” to decline payment of an assessment because the assessment had been computed in a manner inconsistent with the statute and regulations. “An agency’s construction of its own rules and regulations ‘is one to .which considerable deference is due.’ ” Boston Police Superior Officers Fed’n v. Boston, 414 Mass. 458, 462 (1993), quoting Northbridge v. Natick, 394 Mass. 70, 74 (1985). We accept the board’s position on this point.13 A waste generator might [209]*209reasonably be viewed as justified in declining to pay a wrongly computed assessment. We agree that it makes little sense to view the regulations as limiting administrative consideration to determining the amount of a penalty before it has been determined whether the assessment was legal and proper. The judge should have considered the substance of the plaintiffs challenges to the computation of the assessment.
Before the board and the judge, the plaintiff raised numerous challenges to the board’s method of computing its assessment. Before this court, the plaintiff presses, as its single contention, the board’s exclusion from the assessment computation data on low-level radioactive waste produced during the relevant period and stored on-site for future disposal. The parties join in requesting that we resolve this issue.
As a general rule, this court does not consider claims which were not addressed by the court below. “However, ‘[tjhere may always be . . . particular circumstances which will prompt a reviewing or appellate court ... to consider questions of law which were . . . [not] passed upon by the court. . . below . . .’ ” (footnote omitted). Cruz v. Commissioner of Pub. Welfare, 395 Mass. 107, 111 (1985), quoting Hormel v. Helvering, 312 U.S. 552, 557 (1941). The plaintiffs claim concerns the interpretation of statutory and regulatory language and the validity of the agency’s interpretation of its regulation. These are questions of law, appropriate for our resolution. The issue properly was raised in administrative proceedings. The agency has considered and passed on the point and an adequate record exists for its review. In these circumstances, as a matter of judicial economy, we shall address the merits of the plaintiffs challenge to the validity of the assessment.
[210]*210As was previously noted, the relevant legislation directs the board to apportion the total assessment “based on the volume and classification of radioactivity of waste produced by each licensee and registrant which is shipped for disposal off site or stored for later disposal.” G. L. c. 111H, § 4A (a). The applicable regulation provides that “[f]or each licensee and registrant, the volume of Class A, B and C waste shall be measured by the average annual amount of waste produced and shipped for disposal off site or stored for later disposal by such licensee or registrant. To establish this average, the Board shall utilize the yearly production figures given in the Board’s annual surveys for the two most recent calendar years for which, in the judgment of the Board, data sufficient for these purposes have been produced, except that, if the Board determines that such surveys-have not produced two years’ data sufficient for these purposes, it shall substitute whatever data, in its judgment, best approximates the data required.” 845 Code Mass. Regs. § 4.03 (2) (c) (l).14
The board based the fiscal year 1992 assessment on data it collected pertaining to waste produced by registrants and licensees during 1990 and 1991. Although its survey requested data on waste produced during 1990 and 1991 and stored for later disposal, the board computed the individual assessment of each licensee and registrant based solely on waste shipped for disposal off-site during 1990 and 1991. According to the deputy director of the board, data on waste stored for future disposal were excluded because the data available on waste produced and stored for later disposal were less reliable than the data on waste shipped off-site for disposal. In the board’s view, the “substitution provision” of 845 Code Mass. Regs. § 4.03 (2) (c) (1), permitted it to rely solely on data as to waste shipped off-site for disposal in ap[211]*211portioning the assessment among licensees and registrants. Nonetheless, according to the deputy director, the board anticipated relying on data as to waste produced and stored for later disposal in apportioning the annual assessment if and when licensees and registrants in the Commonwealth could no longer ship low-level radioactive waste out of State for disposal.
The plaintiff contends that the board was required to apportion the assessment based on waste produced in the calendar period and either shipped off-site for disposal or stored for later disposal and that the board’s interpretation of its regulation fails to comport with the governing legislation. We agree.
“ ‘A state administrative agency in Massachusetts has considerable leeway in interpreting a statute it is charged with enforcing.’ A. Celia, Administrative Law and Practice § 747 (1986). See Consolidated Cigar Corp. v. Department of Pub. Health, 372 Mass. 844, 850 (1977); Cleary v. Cardullo’s, Inc., 347 Mass. 337, [344] (1964); Massachusetts Nurses Ass’n v. Board of Registration in Nursing, 18 Mass. App. Ct. 380, 389 (1984). Regulations properly adopted by an administrative agency stand on the same footing as statutes and all rational presumptions are to be made in favor of their validity. Greenleaf Fin. Co. v. Small Loans Regulatory Bd., 377 Mass. 282, 293 (1979). Massachusetts Nurses Ass’n, supra. Such regulations are not to be declared void unless their provisions cannot by any reasonable construction be interpreted in harmony with the legislative mandate, Massachusetts Nurses Ass’n, supra at 389 n.19 . . . .” Berrios v. Department of Pub. Welfare, 411 Mass. 587, 595-596 (1992). These principles of deference, however, are not principles of abdication. See Warcewicz v. Department of Envtl. Protection, 410 Mass. 548, 550 (1991). When an agency’s interpretation of its regulation cannot be reconciled with the governing legislation, that interpretation must be rejected. See Consolidated Cigar Corp. v. Department of Pub. Health, 372 Mass. 844, 855 (1977).
[212]*212General Laws c. 111H, § 4A (a), requires the board to apportion the assessment among waste generators “based on the volume and classification of radioactivity of waste produced by each licensee or registrant which is shipped for disposal off site or stored for later disposal.” “The word ‘or’ is given a disjunctive meaning unless the context and the main purpose of all the words demand otherwise.” Eastern Mass. St. Ry. v. Massachusetts Bay Transp. Auth., 350 Mass. 340, 343 (1966), and cases cited. See Bello v. South Shore Hosp., 384 Mass. 770, 782 (1981). The language of § 4A is unambiguous and includes both waste produced within the given calendar period that is shipped for disposal off-site or stored on-site for later disposal. Both categories of waste are subject to the assessment required to be apportioned among generators of low-level radioactive waste in the Commonwealth. There is nothing in the statute which suggests that the board has been granted discretion to eliminate from its computation of the assessment data concerning waste which is stored on-site for future disposal.
The testimony before the administrative magistrate was that the board considered the data on waste stored for future disposal to be somewhat less reliable for purposes of determining volume and activity of waste that should be subject to the assessment. The board admitted, nonetheless, that it would be relying on data concerning waste stored for later disposal in calculating its annual assessment once out-of-State disposal facilities closed their doors to waste generators in the Commonwealth. Thus, there was no contention that the board could not conform to the legislative directive. In these circumstances, we conclude that the board’s interpretation of the “substitution provision” of its regulation cannot be reconciled with the language of G. L. c. 111H, § 4A. The board will have to recompute the plaintiff’s fiscal year 1992 assessment. In so doing, the board may use actual 1992 data and any other information that has become relevant since this controversy began.
6. Commerce clause violation. The plaintiff also contends that the assessment is in violation of the commerce clause of [213]*213the United States Constitution. This contention is based on differing treatment accorded by the board, for purposes of calculating the assessment, to waste shipped for disposal off-site and waste stored on-site for future disposal. In the view we take of the case, which is that the Legislature has not authorized differing treatment for these two categories of waste, we need not consider the plaintiff’s challenge to the assessment based on the commerce clause.
7. Disposition. We affirm the judgment as to count I of the plaintiff’s complaint, declaring the assessment charged by the board a fee and not an unconstitutional tax. We vacate that part of the judgment which vacates the administrative decision of the board and dismisses the plaintiff’s appeal from that decision. We remand the case to the Superior Court so that it may be returned to the board for recomputation of the plaintiff’s fiscal year 1992 assessment in accord with the principles expressed in this opinion.
So ordered.