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| Fig. 1: The Smolensk Nuclear Power Plant site, which includes four reactors of the RBMK "soviet-type" design. (Source: Wikimedia Commons) |
As one of the first nuclear-capable nations in the world, the architects of the worlds first commercial nuclear power plant, and one of the two principle powers in the Cold War, the Soviet Union must be considered an early pioneer in the field of nuclear technology. [1] As the nation that gave us one of the most severe nuclear accidents in human history, this particular pioneer's approach to nuclear safety merits special examination. [2] This report aims to give a highly condensed overview, assuming no particular expertise, on Soviet nuclear safety practices, their development, and how they both led to and were fundamentally altered by the 1986 Chernobyl accident.
In the USSR, nuclear power was an appealing alternative to mineral fuel sources (despite the latter's relative abundance in the country) in large part because of geographical demands. While approximately 75% of the Soviet Union's population resided in the European part of the country, about 80% of the nation's energy resources were located in the nation's territories East of the Urals; in 1982, transporting fuel from its Eastern sources to its Western population centers represented about 40% of all rail freight turnover (a quantity determined by the product of the weight of cargo multiplied by the distance it is hauled, usually given in ton-kilometers). [3] As a result, the USSR's centrally planned economy emphasized the rapid development of nuclear power facilities in its European regions. [3] As part of this push to grow the nation's nuclear power sector, state organizations tasked with supervising nuclear safety were developed; starting in 1983 (after being formed from the merging of several previous agencies) and continuing through the Chernobyl accident, the primary organization fulfilling this role was Gosatomenergonadzor (a Russian syllabic abbreviation for "State Committee for the Supervision of Nuclear Power Safety"). [4] Crucially, Gosatomenergonadzor was not an independent organization, but instead was under the authority of existing Soviet bureaucratic institutions responsible for power production; in effect, the supervisors were the subordinates of the supervisees.
Compared to the precautions around nuclear power exercised in the West at the time, Soviet safety practices prior to the Chernobyl accident were substantially less rigorous (and, in light of the abject failure of these practices at Chernobyl, evidently woefully inadequate). Philosophically, Soviet safety policies centered around the idea that, when determining the Maximum Design Accident (MDA) of a reactor (the most extreme malfunction a reactor should be designed to cope with) consideration should be limited only to credible occurrences and not extended to far more dire, but only remotely possible, scenarios. [4,5] In practice, this philosophy resulted in plants that were significantly less well-equipped to deal with catastrophes than their Western counterparts. For example, Soviet plants were generally only equipped to safely handle a single break in the largest coolant-carrying pipe, and a melting of the reactor core (due to overheated fuel elements) was dismissed as virtually impossible. [5] US plants of the same era, meanwhile, were designed to cope with the possibility of both ends of the same coolant pipe breaking simultaneously, resulting in overheating severe enough to cause the type of core melting the Soviets dismissed as unrealistic. [5] Few Soviet plants possessed concrete secondary containment structures (to prevent radioactive materials from escaping into the general environment in a serious accident), compared with the near-universal presence of such structures in the West. [5] While it is easy to dismiss the Soviets apparent dearth of precautions as a consequence of carelessness and valuation of economy over basic safety, it should be noted that authorities on the subject did at least provide some rationalization for their design philosophy: As one Soviet writer claimed in 1970, "an excess of such backup systems, where the need or the reliability is not clearly assured, introduces operational complexity and reduces over-all safety." [6] While history would not bear out this particular writer's assertions, it is clear that the Soviet designers were approaching the problem of nuclear safety from a radically different philosophical foundation from that of their Western counterparts.
The danger posed by the Soviets relaxed attitude toward nuclear safety was compounded by the regime's extreme lack of transparency. By the late 1970s, Soviet experts were claiming that a single major failure had not occurred at a Soviet reactor in over 2,000 years of combined operating experience. [5] In fact, evidence that gradually emerged as the USSR collapsed suggests that this was far from the case; although poorly documented, it appears that major reactor accidents in the USSR included a rupture of a coolant loop in Leningrad which killed three individuals in 1974, a 1977 meltdown of half of the fuel assemblies in a reactor in Beloyarsk, and a 1985 explosion of a safety valve in Balakova which killed fourteen people. [4] In most cases, the regime (or in the case of more minor accidents, power plant workers and supervisors) did not just conceal these incidents from the Soviet public and foreign observers, but also kept the information from other Soviet nuclear power personnel, who might otherwise have used information from these accidents to correct severe engineering and procedural flaws. [4]
It is clear that despite being one of the world leaders in nuclear technology, Soviet safety practices around this technology were limited at best. However, while a lax approach to security certainly enables disaster, the Soviets' general safety practices did not lay the groundwork for the Chernobyl disaster alone. Rather, the design of the Chernobyl reactors, widespread in the Soviet Union but virtually nonexistent outside of it, introduced safety hazards unique to the Soviet nuclear power program, and hence this design, known as RBMK, must be discussed below.
It is difficult to discuss nuclear safety in the USSR, or indeed Soviet nuclear power in general, without making some remarks on the rather unique RBMK-type (Reaktor Bolshoi Moshchnosti Kanalnyy, or High Power Channel Reactor) design; in Fig. 1, a plant employing the RBMK, still active today, is depicted. This reactor type possesses no clear counterpart in the West, and is so closely associated with the Soviets that it has been referred to simply as Soviet-type. [7] Prior to Chernobyl, these Soviet-type reactors enjoyed widespread use in the USSR; in 1980, RBMKs produced 64.5% of all electrical power produced in nuclear reactors in the country, despite the first such plant only being commissioned in 1973, and the commercial use of nuclear power (to the extent that anything in the Union of Soviet Socialist Republics can be referred to as commercial) in the nation dating back to 1954. [3] In contrast to more widely used pressurized water reactors, which employ water as both a coolant and a moderator (a material which slows down neutrons produced in fission events, increasing the probability of these neutrons precipitating more fissions and sustaining a chain reaction), an RBMK uses water as a coolant only, opting instead to use graphite as its moderator material. [3,7-9] This unique design choice offers a number of advantages which appealed to Soviet engineers. Most notably, the RBMK's solid moderator material allows for channels to carry coolant to each fuel assembly individually (a more difficult proposition when the coolant liquid is also serving as the moderator surrounding the fuel elements, as is the case in pressurized water reactors), which in turn permits a highly modular design. [3] As a result, fuel elements can be replaced while the rest of the reactor is running and the plants can be easily expanded by adding fuel assemblies after construction. [3,6,7] The existence of numerous small pipes delivering coolant, rather than a single large coolant line, even led Soviet experts to believe that it would be virtually impossible for the reactor to suffer a serious loss of coolant. [3] Beyond these supposed technical advantages, however, the RBMK possessed two additional characteristics that gave it a particular appeal to authorities in the Soviet government. First, the RBMK boasted a higher rate of plutonium production than pressurized light water reactors, making them more valuable in the production of weaponry. [7] Secondly, the RBMK's components were simpler to fabricate than those of their water-moderated counterparts, and did not require the construction of new, specialized manufacturing plants to produce. [3] In fact, some observers believe that it was ultimately the RBMK's ease of manufacturing, rather than any design advantages, that led to its heavy use by the Soviet Union; Soviet nuclear dissident Zhores Medvedev stated that "It was not so much considerations of economic efficiency, safety or institutional support which... gave priority to the RBMK system in the late 1950s and 1960s, it was simply easier for the Soviet industry to manage the less sophisticated design." [4]
In spite of the advantages of the RBMK design, reactors of this type (like the famous Chernobyl-4 reactor) possessed serious safety vulnerabilities. [9] Chief among these was a so-called positive void coefficient. In liquid cooled and/or moderated nuclear reactors, gas pockets (so-called voids) will form in the liquid (in the case of an RBMK, these are steam bubbles forming in the water coolant). Liquid water acts as a more efficient coolant and a more efficient neutron absorber than steam, so the reactivity (a measure related to the rate of growth of neutrons in successive generations of a chain reaction) of the reactor increases when these voids form, hence the void coefficient is positive. [8,9] In water-moderated reactors, this behavior is cancelled out by the fact that without liquid water to slow them down, the neutrons in the reactor are far less likely to precipitate fission events, resulting in a negative void coefficient. [8] A positive void coefficient, like that of an RBMK, is rare in the realm of nuclear reactors, because it can give rise to a catastrophic positive feedback loop: As the reactor power increases, the temperature of the coolant water increases, forming more steam bubbles, which in turn increase the reactor power further. [8] At reactors of the RBMK design, the positive void coefficient problem was compounded by a phenomenon known as a positive scram effect: The reactor control rods (rods of material that absorb neutrons and are inserted and withdrawn to regulate the reactivity of nuclear reactors) had graphite "displacer rods" attached to their ends, in order to keep the coolant water (a less effective neutron moderator than graphite) from occupying the space vacated by a control rod when it was withdrawn, maximizing the reactor reactivity when the rod is fully withdrawn. In the RBMK design prior to Chernobyl, when a control rod was fully withdrawn a 1.25 meter water-filled gap existed between the bottom of the control rod and the bottom of the reactor core. [8] When a scram order was given (requiring the immediate insertion of all control rods in order to shut down a reactor in an emergency), this water-filled gap would be quickly replaced with the graphite displacer, briefly increasing the reactivity at the bottom of the core, the precise opposite of the intended effect of a scram. [8] These two design characteristics, combined with user error, can lead to what could essentially be described as an uncontrolled atomic explosion, as occurred at Chernobyl. [10]
As inclined as the Soviet government might have been to conceal the catastrophic accident at the Chernobyl reactor (as the Soviet authorities' delay in admitting the severity of the event suggests), practicalities made such a cover-up impossible. [11] As a result, international and domestic pressure forced radical changes in the Soviet Union's nuclear safety policy in the few years between the 1986 accident and the 1991 dissolution of the USSR. On the technical side, the RBMK design was seriously reevaluated. The construction of all new RBMKs was scrapped, including the cancellation of four units that had been planned prior to the Chernobyl incident. [4] Existing RBMKs were retrofitted with a variety of new safety features, including 80-90 fixed neutron absorbers and the addition of more control rods, both of which reduced the magnitude of the design's positive void coefficient substantially (at the price, however, of RBMKs requiring fuel with a higher percentage of fissile material in order to sustain a reaction). [8] The responsiveness of emergency shutdown procedures in these plants was also dramatically improved, with shut down control rod insertion time cut from 18 seconds down to 12 seconds, and the graphite displacer rods were repositioned in the reactor in order to eliminate the positive scram effect. [8] These reforms have allowed existing RBMK plants to continue supplying power to consumers; 11 RBMKs are still operating, all of which are in the Russian Federation. [8] Beyond simply improving the safety of RBMKs, Soviet authorities also introduced measures to improve the safety of all nuclear facilities, including development of improved computer support of power stations, new personnel safety training, and heavy financial investment in new safety equipment for existing plants of all designs. [4]
Organizationally, the USSR also radically restructured its supervisory structure for nuclear power plant safety; in 1989, two years before the collapse of the USSR, Gosatomenergonadzor was supplanted by Gospromatomnadzor (State Committee for the Supervision of Safety in Industry and Nuclear Power), the regulatory powers of which were modelled off of the US Nuclear Regulatory Commission. [4] Significantly, unlike its predecessor, Gospromatomnadzor was completely independent of the organizations responsible for electricity production in the country. [4] Due to the short span of time between the Chernobyl accident and the collapse of the Soviet Union, radical restructuring of the nation's nuclear regulatory agencies was ongoing and did not achieve a stable state before the country ceased to exist; one Western commenter remarked that the process of reorganization in the Soviet nuclear industry is probably not yet over in a work published in June of 1991, a mere six months before the Union dissolved completely. [4]
Despite this organizational restructuring and new technical regulations, the Soviet Union suffered difficulties improving its safety practices after Chernobyl due to deeper systemic issues in the nation because wages for employees in the nuclear sector were not controlled by market forces but by government dictates. The quality of personnel the nuclear sector found was often inadequate for the jobs they had to perform; the chairman of the USSR State Committee for the Utilization of Atomic Energy stated in 1988 that nuclear specialists are paid less than a massive number of less qualified working people. An operator in charge of a reactor like the one at the Chernobyl AES (Atomic Energy Station) receives less than a city bus driver. [4] In fact, a number of Soviet critics (and some officials) lamented the inadequate incentive structure brought about by the USSR's centralized economy; even the deputy chairman of Gospromatomnadzor stated that a market economy could create the conditions for personal incentive and responsibility. [4]
The Soviet approach to nuclear safety, charitably described by various sources in the West as "different", could perhaps better be described as recklessly irresponsible, and in need of an earthshaking (or at least earth-irradiating) event such as the Chernobyl accident to force a change. [5,6] While the reforms made to the Soviet approach to nuclear safety certainly did offer significant improvement over the pre-Chernobyl state of affairs, particularly in technical deficiencies at reactors, ongoing issues with the fundamental structure of the USSR's state-run economy may have had a deleterious effect on the long-term efficacy of reforms to nuclear regulatory organizations and safety culture. As the USSR collapsed entirely in 1991, it is difficult to determine what the long-term results of the Union's nuclear reform process could have been, as the Union's former republics, newly endowed with market-driven economies and governments formed outside the USSR's Bolshevik political monopoly, were then tasked with the responsibility of continuing and building upon the Soviet Union's safety reforms.
© George Wojcik. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] S. Smith, "Obninsk Nuclear Power Plant," Physics 241, Stanford University, Winter 2017.
[2] M. Caballero, "The Chernobyl Disaster," Physics 241, Stanford University, Winter 2016.
[3] B. A. Semenov, "Nuclear Power in the Soviet Union," IAEA Bulletin, 25, No. 2, 47 (1982).
[4] W. C. Potter, "The Impact of Chernobyl on Nuclear Power Safety in the Soviet Union," Stud. Comp. Communism 24, 191 (1991).
[5] T. O'Toole, "Soviet Approach to Nuclear Safety is 'Different'," Washington Post, 8 Oct 78.
[6] P. R. Pryde and L. T. Pryde, "Soviet Nuclear Power: A Different Approach to Nuclear Safety," Environment 16, 26 (1974).
[7] J. T. Debardeleben, "Esoteric Policy Debate: Nuclear Safety Issues in the Soviet Union and German Democratic Republic," Brit. J. Polit. Sci. 15, 227 (1985).
[8] "INSAG-7: The Chernobyl Accident: Updating of INSAG-1," International Atomic Energy Agency, Safety Series No. 75-INSAG-7, 1992.
[9] A. Stephanus, "RBMK Reactors," Physics 241, Stanford University, Winter 2016.
[10] Z.W. Seh, "Causes of the Chernobyl Accident," Physics 241, Stanford University, Winter 2015.
[11] E.R. Chavez, "The Global Significance of Chernobyl," Physics 241, Stanford University, Winter 2017.
