Chapter 2

CHERNOBYL

The Chernobyl Nuclear Power Plant, officially known as the V. I. Lenin Atomic Power Plant during the Soviet era, began construction in 1970 in a remote region near Ukraine’s swamp-filled northern border, 15 kilometers northwest of the small town of Chernobyl. The desolate location was chosen because of its relative proximity to yet safe distance from Ukraine’s capital, a ready water supply - the River Pripyat - and the existing railway line running from Ovruc in the west to Chernigov in the east. It was the first nuclear power station ever to be built in the country, and was considered to be the best and most reliable of the Soviet Union’s nuclear facilities.71 Concurrent to the construction of the power station, the Soviet Union’s ninth Atomograd - Russian for ‘atomic city’ - named Pripyat was being erected 3 kilometers away, for the express purpose of housing the ambitious station’s 50,000 operators, builders, support staff and their families. Pripyat was one of the ‘youngest’ cities in the Soviet Union, with an average age of only 26.

To oversee the titanic operation, 35-year-old turbine expert and loyal communist Viktor Bryukhanov was plucked from his position as Deputy Chief Engineer at the Slavyanskaya thermal power plant in eastern Ukraine, and appointed as Chernobyl’s Director.72 It seems that he was genuinely liked and respected as a Director, with one of the plant’s original Deputy Chief Engineers commenting, “He is a great engineer. I really mean it.73” In his new capacity, Bryukhanov was responsible for overseeing construction of both the plant and city, and organising everything from the recruitment of workers to the procurement of machinery and masonry. Bryukhanov worked hard but, despite his earnest efforts, the construction suffered a plethora of problems typical of the Communist system. Thousands of tons of reinforced concrete were missing from orders, and specialist equipment was either impossible to source or of poor quality when it eventually arrived, forcing him to order the manufacture of replacements in makeshift on-site workshops.74 Although these complications put the plant two years behind schedule, the first reactor - Unit 1 - was commissioned on the 26th of November 1977, following months of tests. Three more reactors followed: Unit 2 in 1978, Unit 3 in 1981, and Unit 4 in 1983.

All four reactors were the relatively new, Soviet-designed ‘Reaktor Bolshoy Moshchnosti Kanalnyy’ (RBMK)-1000, or ‘High Power, Channel-type Reactor’ in English, which output 1000 Megawatts of electrical power via two 500MW steam turbogenerators. The RBMK-1000 is a graphite-moderated, boiling water-cooled reactor; an unusual and slightly outdated combination that was designed in the 1960s to be powerful, quick, cheap and easy to build, relatively simple to maintain, and to have a long service life. Each reactor measures a massive 7 meters tall by 11.8 meters wide.75 In 1986, fourteen of this type were in service, while another eight were under construction. Two of these were being built at Chernobyl on the night of the accident in 1986, with Unit 5 expected to be completed later that year. The four existing reactors together provided 10% of Ukraine’s electricity at the time and, had Units 5 and 6 been completed, Chernobyl would have been the highest capacity, non-hydro power station in the world.76 For reference, the world’s largest hydroelectric power station by installed capacity is the Three Gorges Dam in China, which is rated for an incredible 22,500MW.77

Nuclear reactors use a process called nuclear fission - sometimes called ‘splitting the atom’ - to generate electricity. All matter is composed of atoms, and each atom is mostly empty space, with a tiny centre of protons and neutrons joined together to form a nucleus, which gives an atom most of its weight. Much of the leftover space within an atom is occupied by electrons orbiting the nucleus in the middle. The differences between atoms come from the differing number of protons and neutrons in a given nucleus. For example, the element gold contains 79 protons, and is famous for being heavy. Copper has just 29 protons, and is far less dense than gold. Oxygen only has 8 protons. Every atom will have the same number of orbiting electrons as it does protons, but atoms of the same element can have different numbers of neutrons. These different versions of the same element are known as isotopes. You could think of isotopes as being like a car with optional upgrades. Mercedes has many cars - the elements - in their lineup, but these cars may have optional extras to add: a more powerful engine; different upholstery; an expensive paint job. The car remains the same vehicle, but is now in a different form. Stable isotopes - that is, isotopes which do not undergo spontaneous radioactive decay - are called stable nuclides, while unstable isotopes are collectively known as radionuclides. Together, these two groups that resulted from fission are known as ‘fission products’, almost all of which are the unstable radionuclide variety. These radionuclides are waste products of the reaction and are hot and highly toxic.

The RBMK, like almost all commercial nuclear reactors, uses uranium - which has 92 protons, making it the heaviest naturally occurring element - as a fuel source. Uranium contains a mere 0.7% of the fissionable isotope uranium235 (92 protons and 143 neutrons), and the 190 tons of fuel in a second-generation RBMK reactor like Chernobyl’s Unit 4 consists of cheap, and only slightly enriched, 98% uranium238 and 2% uranium235, contained within 1,661 vertical pressure tubes. During the nuclear reaction inside a reactor core, neutrons collide with the nuclei of another uranium235 atom, splitting it and creating energy in the form of heat. This atomic split creates an additional two or three neutrons. These new neutrons will then collide with more U235 fuel, splitting another uranium atom to form yet more neutrons, and so on. This process is called a fission chain reaction, and it is this reaction which creates the heat in a nuclear reactor. At the same time, additional new elements in the form of hot fission products are created.78

Nuclear power harnesses the same atomic reaction as a nuclear bomb, but is designed to ensure that it is physically incapable of causing a nuclear explosion, and instead controls the release of neutrons to generate the required heat. While a power station’s reactor contains barely-enriched uranium or plutonium fuel, dispersed over a large area and surrounded by control rods to restrain the reaction, a nuclear bomb is designed with the specific intention of causing this same reaction to occur instantaneously and with far greater intensity, by using explosives to force two hemispheres of 90%+ enriched uranium or plutonium together.

Preventing a radioactive release is the highest priority at any nuclear facility, so power stations are built and operated with a safety philosophy of ‘defense in depth’. Defense in depth aims to avoid accidents by embracing a safety culture, but also accepts that mechanical (and human) failures are inevitable. Any possible problem - however unlucky - is then anticipated and factored into the design with multiple redundancies. The goal, therefore, is to provide depth to the safety systems; akin to the way Russian dolls have several layers before reaching the core doll. When one element fails, there is another, and another, and another that still functions. The first barrier are the fuel ceramic pellets themselves, followed by each fuel rod’s zirconium alloy cladding. In an ordinary modern commercial nuclear plant, the nuclear core where the fission reaction takes place would be contained inside a third barrier: an almost unbreakable metal shield enveloping the reactor, called a ‘pressure vessel’. The RBMK forgoes a conventional pressure vessel and instead only uses reinforced concrete around the sides of the reactor, with a heavy metal plate at the top and bottom. Adding a proper pressure vessel, built to the standards and complexity required by the RBMK design, was estimated to double the cost of each reactor. The fourth and final barrier is an airtight containment building. It is well known that nuclear containment buildings are very, very heavily reinforced, with concrete and/or steel walls often several meters thick. They are built to withstand the external impact of an airliner crashing into them at hundreds of miles-per-hour, but their other purpose is to contain the unthinkable breach of a pressure vessel. Unbelievably, the RBMK’s accompanying reactor building is insufficient to be labelled as a true containment building, presumably as part of further cost saving measures.79

The RBMK’s stunning dual lack of the most crucial containment barriers is a glaring omission that should never have been considered, let alone designed, approved and built. Select Soviet Ministers were made aware of these inadequacies before the reactors were chosen, but still the RBMK design was selected over the competing ‘Vodo-Vodyanoi Energetichesky Reaktor’ (VVER, or ‘Water-Water Power Reactor’), a pressurised water reactor which was safer, but more expensive and marginally less powerful. Conventional wisdom at the time was that the RBMK could never cause a large-scale accident, because industry safety regulations would always be adhered to. Extra safety measures, they decided, were unnecessary.80

A fission reaction is enabled by what is known as a neutron moderator, which, in an RBMK reactor, is comprised of vertical graphite blocks surrounding the fuel channels. Each RBMK contains 1850 tons of graphite. This graphite slows - moderates - the speed of neutrons moving in the fuel, because slowed neutrons are far more likely collide with uranium235 nuclei and split. When playing golf, for example, if your ball is a few centimeters from the hole, you don’t hit it as hard as you possibly can, you give it a slow tap to the target. It’s the same principle with neutrons in a reactor. The more often the resulting atomic split occurs, the more the chain reaction sustains itself and the more energy is produced. In other words, the graphite moderator creates the right environment for a chain reaction. Think of it as oxygen in a conventional fire: even with all the fuel in the world, there will be no flame without oxygen.

Using graphite as a moderator can be highly dangerous, as it means that the nuclear reaction will continue - or even increase - in the absence of cooling water or the presence of steam pockets (called ‘voids’). This is known as a positive void coefficient and its presence in a reactor is indicative of very poor design. Graphite moderated reactors were used in the USA in the 1950s for research and plutonium production, but the Americans soon realised their safety disadvantages. Almost all western nuclear plants now use either Pressurised Water Reactors (PWRs) or Boiling Water Reactors (BWRs), which both use water as a moderator and coolant. In these designs, the water that is pumped into the reactor as coolant is the same water that is enabling the chain reaction as a moderator. Thus, if the water supply is stopped, fission will cease because the chain reaction cannot be sustained; a much safer design. Few commercial reactor designs still use a graphite moderator. Other than the RBMK and its derivative, the EGP-6, Britain’s Advanced Gas-Cooled Reactor (AGR) design is the only other graphite-moderated reactor in current use. The AGR will soon be joined by a new type of experimental reactor at China’s Shidao Bay Nuclear Power Plant, which is currently under construction. The plant will house two graphite-moderated ‘High Temperature Reactor-Pebble-bed Modules’ reactors, which are expected to begin operation in 2017.

Because of the extreme heat fission generates, the reactor core must be kept cool at all costs. This is particularly important with an RBMK, which operates at an, “astonishingly high temperature,” relative to other reactor types, of 500°C with hotspots of up to 700°C, according to British nuclear expert Dr. Eric Voice. A typical PWR has an operating temperature of about 275°C. A few different kinds of coolant are used in different reactors, from gas to air to liquid metal to salt, but Chernobyl’s uses the same as most other reactors: light water, meaning it is just regular water. The plant was originally going to be fitted with gas-cooled reactors, but this was eventually changed because of a shortage of the necessary equipment.81 Water is pumped into the bottom of the reactor at high pressure (1000psi, or 65 atmospheres), where it boils and passes up, out of the reactor and through a condensator that separates steam from water. All remaining water is pushed through another pump and fed back into the reactor. The steam, meanwhile, enters a steam turbine, which turns and generates electricity. Each RBMK reactor produces 5,800 tons of steam per hour.82 Having passed through this turbogenerator, the steam is condensed back into water and fed back to the pumps, where it begins its cycle again.

There’s one major shortcoming inherent to using this method of cooling. Unlike in a typical PWR, the water entering the reactor is the same water that passes through the cooling pumps and then as steam through the turbines, meaning highly irradiated water is present in all areas of the system. A PWR uses a heat exchanger to pass heat from the reactor water to clean, lower pressure water, allowing the turbines to remain free of contamination. This is better for safety, maintenance and disposal. A second problem is that steam is allowed to form in the core, making dangerous steam voids more likely, and further increasing the chances of a positive void coefficient. In ordinary boiling water reactors, which use water as both a coolant and moderator like in a PWR, this would not be such a problem, but it is in a graphite-moderated BWR.

To control the release of energy by a nuclear reactor, ‘control rods’ are used. RBMK control rods are long, thin cylinders, composed mostly of neutron-absorbing boron carbide to hinder the reaction. The tips of each rod are made of graphite to prevent cooling water (which is also a neutron absorber) from entering the space the rod’s boron had occupied as it is withdrawn from the core, in order for that section to have a greater impact upon reactivity when reinserted. Chernobyl’s 211 control rods descend down into the core from above as necessary, and are aided in their role by an extra 24 special shortened ‘absorber rods’. These absorber rods ensure an even distribution of power across the entire width of the core by inserting upwards from below. The more control rods that are inserted into the reactor core, and the further they penetrate, the lower the levels of power will be. Conversely, fewer rods equals more power. Every control rod can be inserted together, penetrating as near or as far as the operator wishes, or they can be disconnected and inserted in groups, depending on requirements.83 The RBMK control rods are incredibly slow by Western standards, taking 18-21 seconds to fully insert from their uppermost position. Some, like Canada’s CANDU reactor, can take as little as 1 second.84

It is not well known that there was a severe accident at Chernobyl before the disaster of 1986, which resulted in the partial core meltdown of Unit 1. The incident occurred on September 9th, 1982, and remained secret for several years afterwards. Detailed and reliable reports are difficult to come by (especially in English), but it seems a coolant water control valve was closed, leading to overheating of a water channel and partial damage of the fuel assembly and graphite inside the reactor. A classified KGB report from the next day stated: “In connection with the planned overhaul of the 1st fuel unit of the Chernobyl nuclear power plant, which is scheduled to be completed on 13 September, 1982, a trial run of the reactor was performed on 9 September 1982. When its power was increased to 20%, there was a break in one of the 1640 pressure channels/loaded fuel assemblies. At the same time, the column where the fuel assemblies are located broke. In addition, the graphite stack became partially wet.85” This resulted in fuel and graphite being washed out through the pipes and fission products being vented from the chimney, which in turn prevented coolant from properly reaching the reactor, leading to the partial meltdown.

Operators were unsure of what was happening for a long time and ignored warning alarms for almost half an hour. Then the KGB accident investigation seemed to ignore negligent actions of plant staff (stopping the flow of coolant on purpose). The findings of two separate organisations measuring radioactive contamination outwith the plant wildly differed, too, with a government nuclear industry commission finding almost no contamination at all, while a team of biophysicists from the Institute of Nuclear Research from Ukraine’s Academy of Science found radiation “hundreds of times higher than permissible levels”.86 Two senior figures, who would later analyse the 1986 disaster, did not agree with the official description of events either. For their part, the reactor operators on duty that day denied any wrongdoing. “As an eyewitness of this accident and one of those involved in elimination of its consequences, I don’t have much to add [to] the version of NIKIET [the Scientific Research and Design Institute of Power and Technology] that blamed the Chernobyl ATS engineer for stopping completely [the] water supply into the [reactor, except that it] has never grown into anything else but a version,” writes Nikolai V Karpan, a senior engineer who worked at Chernobyl from 1979 to 1989. “Both the foreman and the whole team of servicemen that carried out flow rate adjustments that day have been repeatedly denying the error inflicted upon them. On that day they worked in the usual way, in strict compliance with the regulations, according to which that a guide plate was to be installed on the regulator that would mechanically prevent complete stopping of water supply into the channel.87” It is likely that a flaw in the reactor design or - more probable - poor manufacturing quality was identified as a principal cause of the accident, but the politicians chose to go with the easy option and blame an operating engineer instead. One instance of human error is more palatable than acknowledging that your brand new nuclear reactor, developed and built at enormous expense, and already operating at two other existing plants, has a flaw in its design. This unofficial version of events was supported by the plant’s Research Supervisor, who conducted an investigation of his own and reported: “It turned out that the zirconium channel pipes were destroyed due to residual internal stress in their walls. The manufacturing plant had, on its own initiative, changed the production process of channel pipes, and this ‘novelty’ resulted in the accident in the reactor.88”

Even89 before the Chernobyl incident of 1982, there was another serious accident involving the RBMK design at the Leningrad Nuclear Power Plant in November 1975, when its Unit 1 suffered a partial meltdown. Detailed information is more challenging to find than the 1982 Chernobyl accident, but Viktor M. Dmitriev, a Russian nuclear engineer from the Institute of Nuclear Power Operations in Moscow, has a web page explaining what happened. The accident bears some remarkable similarities to Chernobyl’s 1986 disaster. Leningrad’s Unit 1 was restarting after routine maintenance and had reached 800MW when operators disconnected one of its two turbines due to a fault. To keep the reactor stable, power was reduced to 500MW and then the evening shift handed over the reins to the night shift. At 2am, someone in the control room disconnected the only remaining turbine by accident, tripping the emergency computer system and automatically shutting down the reactor. Reactor poisoning began (I’ll explain this in more detail later), leaving the operators with a choice of battling the reactor back to full power or allowing it to shut down, but there would be repercussions for allowing it to happen at all. They chose - just as at Chernobyl over a decade later - to raise the power. It didn’t go well. “During rising to power after shutdown, without any operator’s actions to change reactivity (without lifting any rods) the reactor would suddenly reduce acceleration time by itself, i.e., inadvertently accelerate; in other words, it would try to explode,” says V. I. Boretz, a trainee from Chernobyl who happened to be on this shift. “The reactor acceleration was stopped twice by the emergency protection system [in fact, the emergency protection was triggered more than twice, both on excess of power and on speed of its growth - Viktor M. Dmitriev]. Attempts of the operator to reduce capacity growth velocity by standard methods, lowering at the same time a group of manually controlled rods, plus four automatically controlled ones, failed, and rising to power was increasing. It was only stopped by triggering the emergency protection system.” The reactor eventually reached a power of 1,720MW - almost twice its rated capacity - before it was brought under control.90

A government commission into the accident found serious faults with the design, and in 1976 recommended that the void coefficient be lowered, the control rod design be altered, and for ‘fast-acting emergency protection’ to be installed. New designs were drawn up for the rods, but were never installed on any reactors. On October 16th, 1981, a report was submitted to the KGB highlighting several concerns over the quality of construction and equipment at Chernobyl. It stated that there had been 29 emergency shutdowns during the plant’s first 4 years of operation - 8 of which were caused by personnel errors, the rest from technical faults - and that, “control equipment does not meet the requirements for reliability.” These faults had been brought to the attention of the Ministry of Power and Electrification and the design institute responsible for the reactor, “several times,” by the date of the report, according to the KGB, yet nothing had been done.91

In late 1983, Lithuania’s brand new Ignalina Power Station began commission testing its first RBMK reactor and soon encountered a problem: control rods entering the reactor together caused a power surge. This is basically what caused the Chernobyl disaster a few years later. At Ignalina, the fuel was brand new, the reactor was stable, and the rods travelled down the entire height of the core, allowing boron to be introduced and the reaction to be brought back under control. This critical discovery was passed around the relevant nuclear Ministries and Institutes, but again nothing changed. Another KGB report dating from October 1984 highlighted complications with the cooling system experienced by Unit 1. The necessary information had been sent to the relevant Ministries at the time, “but even on Units 5 and 6 that are now [in 1984] under construction, these comments are not taken into account.92” In light of all these repeated, wilful examples of negligence, I find myself agreeing in many ways with Chernobyl’s Deputy Chief Engineer Anatoly Dyatlov, when he said years later that, “the RBMK reactor was condemned to explode”.93