1 00:00:00,000 --> 00:00:10,000 [Music] 2 00:00:10,000 --> 00:00:13,000 Chain of events, cause and effect. 3 00:00:13,000 --> 00:00:15,000 We analyse what went right and what went wrong, 4 00:00:15,000 --> 00:00:20,000 as we discover that many outcomes can be predicted, planned for, and even prevented. 5 00:00:20,000 --> 00:00:23,000 I'm John Chidgey, and this is Causality. 6 00:00:23,000 --> 00:00:25,000 Causality is part of the Engineered Network. 7 00:00:25,000 --> 00:00:27,000 To support our shows, including this one, 8 00:00:27,000 --> 00:00:31,720 head over to our Patreon page and for other great shows visit https://engineered.network/ today. 9 00:00:31,720 --> 00:00:34,920 Chernobyl 10 00:00:34,920 --> 00:00:38,040 The fourth time is not a charm. 11 00:00:38,040 --> 00:00:47,160 On the 25th of April 1986, a cooling test began in Reactor 4 of a relatively new nuclear power 12 00:00:47,160 --> 00:00:54,440 plant called Chernobyl, near the town of Pripyat in northern Ukrainian Soviet Socialist Republic, 13 00:00:54,440 --> 00:01:00,840 the USSR in the Soviet Union. It would end the following day with what has become to date the 14 00:01:00,840 --> 00:01:07,480 most disastrous nuclear power incident in history, considered to be a Level 7 event on the international 15 00:01:07,480 --> 00:01:13,000 nuclear event scale. The only other event that has been classified as a Level 7 was covered in 16 00:01:13,000 --> 00:01:22,120 Episode 3 at Fukushima in 2011. It was an incident whose causes are hotly debated and it has been 17 00:01:22,120 --> 00:01:28,080 analysed by all and sundry for many many years since the event. One camp claiming 18 00:01:28,080 --> 00:01:32,160 that it wasn't caused by malfunctioning equipment but rather by human factors 19 00:01:32,160 --> 00:01:37,300 alone whilst others claim it was caused by a fundamentally flawed reactor 20 00:01:37,300 --> 00:01:42,560 design for which failure was inevitable at some point. Either way it wasn't 21 00:01:42,560 --> 00:01:46,400 caused by natural events that were inadequately prepared for, or for faulty 22 00:01:46,400 --> 00:01:51,600 equipment poorly serviced or monitored. But we're getting ahead of ourselves. 23 00:01:51,600 --> 00:01:58,500 The Soviet Union began a campaign in the 1960s of building towns to house the people 24 00:01:58,500 --> 00:02:02,340 that would construct and operate their power stations of the future. 25 00:02:02,340 --> 00:02:08,680 One of the nine so-called "Atom Towns" was the town of Pripyat, 104km or 65mi 26 00:02:08,680 --> 00:02:10,620 north of Kyiv. 27 00:02:10,620 --> 00:02:15,520 The construction of the new Chernobyl nuclear power plant began in 1970. 28 00:02:15,520 --> 00:02:20,880 Even after construction was well underway, debates continued through 1972 about the final 29 00:02:20,880 --> 00:02:28,040 design of the reactor. The two options considered were Pressurized Water Reactor (PWR) or Reaktor 30 00:02:28,040 --> 00:02:35,880 Bolshoy Moshchnosti Kanalnyy (or RBMKs for short), loosely translated meaning "High Power 31 00:02:35,880 --> 00:02:42,060 Channel Reactor". The RBMK design, specifically the 1,000 series, which is considered today 32 00:02:42,060 --> 00:02:47,220 to represent the second generation of large-scale nuclear reactor designs, was developed in 33 00:02:47,220 --> 00:02:51,980 Russia and was heavily favoured by nuclear scientists at the time as it was touted as 34 00:02:51,980 --> 00:02:57,060 having the lowest cost per MegaWatt of generated electricity. 35 00:02:57,060 --> 00:03:02,460 The downsides of the reactor design were instability in low power conditions and significantly 36 00:03:02,460 --> 00:03:07,060 higher radiation due to the fact it was a boiling water design. 37 00:03:07,060 --> 00:03:12,060 Ultimately the RBMK design was chosen for its cost effectiveness and the first unit 38 00:03:12,060 --> 00:03:20,100 was brought online in 1977, with a second following in 1978. In 1982, Unit 1 experienced 39 00:03:20,100 --> 00:03:24,940 a partial meltdown, however this is not directly related to what was to happen in subsequent 40 00:03:24,940 --> 00:03:30,800 years and therefore it's beyond the scope of this episode. The fact that details about 41 00:03:30,800 --> 00:03:36,820 this partial meltdown in Reactor 1, and the quantity of reactor issues that were covered- 42 00:03:36,820 --> 00:03:43,420 up by the Soviet Union in that time period is cause for some concern. 43 00:03:43,420 --> 00:03:47,980 In this case, the extent of the meltdown in 1982 wasn't released to the public until 44 00:03:47,980 --> 00:03:53,700 1985, long after the damage was repaired and the unit was returned to service. 45 00:03:53,700 --> 00:03:59,260 Unit 4, in this case, however, was brought online on the 20th of December 1983. 46 00:03:59,260 --> 00:04:04,220 An interesting side note was that three months prior to the incident, in the February 1986 47 00:04:04,220 --> 00:04:10,540 edition of Soviet Life, Vitaly Sklyarov, the Minister of Power and Electrification of Ukraine 48 00:04:10,540 --> 00:04:16,400 was quoted as saying "The odds of a meltdown are one in 10,000 years. The plants have safe 49 00:04:16,400 --> 00:04:23,060 and reliable controls that are protected from any breakdown with three safety systems." 50 00:04:23,060 --> 00:04:28,980 The power plant itself had a three-shift rotation, with 8 core hours of work per shift and 51 00:04:28,980 --> 00:04:34,180 a 30-minute handover between the shifts. Night shift ran from midnight to 8 in the morning, 52 00:04:34,180 --> 00:04:38,380 day shift from 8 in the morning to 4 in the afternoon, and evening shift from 4 in the 53 00:04:38,380 --> 00:04:41,380 afternoon to midnight. 54 00:04:41,380 --> 00:04:45,420 Like all nuclear fission power plants, the fission reaction of fissile material, in this 55 00:04:45,420 --> 00:04:51,820 case was U235, releases large amounts of heat, and that heat in turn converts liquid water 56 00:04:51,820 --> 00:04:56,380 to steam, which in turn drives a turbine, and this turbine drives a generator, which 57 00:04:56,380 --> 00:04:58,260 produces electricity. 58 00:04:58,260 --> 00:05:02,380 Beyond the usual need to condense the steam for recycling through the system, cooling 59 00:05:02,380 --> 00:05:06,060 water is also essential for keeping the temperature of the reactor under control, 60 00:05:06,060 --> 00:05:11,460 especially when the core is shut down to control decay heat generated. 61 00:05:11,460 --> 00:05:15,820 Decay heat has been covered in previous Episodes 3 and 17 if you want more information about 62 00:05:15,820 --> 00:05:17,340 that. 63 00:05:17,340 --> 00:05:23,980 Reactor 4 specifically had 1,600 fuel rods that required 28,000 litres per hour which 64 00:05:23,980 --> 00:05:27,820 is 7,400 gallons per hour of coolant flow. 65 00:05:27,820 --> 00:05:31,420 The cooling pumps that regulated the core temperature relied on steam created by the 66 00:05:31,420 --> 00:05:37,980 reactor to drive a turbine to create electricity to, in turn, drive those pumps. 67 00:05:37,980 --> 00:05:42,820 The backup diesel generators took 15 seconds to start once triggered, and between 60 and 68 00:05:42,820 --> 00:05:47,860 75 seconds in total to start, come online and ramp up to the minimum power required 69 00:05:47,860 --> 00:05:50,320 to run the cooling pumps. 70 00:05:50,320 --> 00:05:55,060 The idea was that the residual momentum of the steam turbine could continue to generate 71 00:05:55,060 --> 00:06:00,060 enough electricity to cover the gap for an estimated 45 seconds in the event that the 72 00:06:00,060 --> 00:06:04,040 steam cut out when there was no grid power available. 73 00:06:04,040 --> 00:06:08,440 The test that led to the incident itself had actually been carried out previously on several 74 00:06:08,440 --> 00:06:13,960 occasions. The first time was 4 years earlier in a different reactor with the same design, 75 00:06:13,960 --> 00:06:19,160 but the engineers found the output voltage produced under momentum rotation, was insufficient 76 00:06:19,160 --> 00:06:24,720 to drive the cooling pumps. It was attempted again 2 years after the first attempt and 77 00:06:24,720 --> 00:06:30,960 again a year after that, each time the test failed to achieve the desired goal. 78 00:06:30,960 --> 00:06:35,400 The fourth test was the one that led to the incident in 1986. 79 00:06:35,400 --> 00:06:40,300 Interestingly, the test focused more on electrical switching and electrical performance with 80 00:06:40,300 --> 00:06:43,840 minimal detail surrounding the reactor control. 81 00:06:43,840 --> 00:06:48,220 As a result, the test procedure had been heavily reviewed by the electrical engineering personnel 82 00:06:48,220 --> 00:06:53,600 and approved by the plant director however, the chief scientist and chief reactor designer 83 00:06:53,600 --> 00:06:57,960 were not involved in the co-ordination of the test itself. 84 00:06:57,960 --> 00:07:02,300 It seems at first glance that after 3 failed attempts they should have accepted 85 00:07:02,300 --> 00:07:07,420 the end result and investigated other options perhaps like redesigning including flywheels 86 00:07:07,420 --> 00:07:09,620 or including a UPS system. 87 00:07:09,620 --> 00:07:13,940 However with financial restrictions and a strong perception that this "gap" was a 88 00:07:13,940 --> 00:07:18,540 significant and unaddressed safety issue in the reactor's design, they pushed ahead with 89 00:07:18,540 --> 00:07:22,100 the test with the hope that they could prove it could work with the equipment that they 90 00:07:22,100 --> 00:07:26,180 had already installed. 91 00:07:26,180 --> 00:07:30,020 And now about the incident itself. 92 00:07:30,020 --> 00:07:35,220 This test had been planned for some time and the conditions required to execute the test 93 00:07:35,220 --> 00:07:38,540 required a power reduction for the unit overall. 94 00:07:38,540 --> 00:07:44,260 Under normal operational conditions the full 3.2GW of thermal power drove 2 turbines 95 00:07:44,260 --> 00:07:49,660 and in order to test low power operation they first needed to drop off one turbine and at 96 00:07:49,660 --> 00:07:57,380 on Friday, the 25th of April, plant operators began the 12-hour process of power reduction, 97 00:07:57,380 --> 00:08:03,900 reaching a target of 50% at 1.05pm that same day. At that time, turbine number 2 was switched 98 00:08:03,900 --> 00:08:08,580 off. Around 2pm, another power plant on the electrical 99 00:08:08,580 --> 00:08:14,500 grid had tripped, and the Kyiv electrical grid controller advised that the power should 100 00:08:14,500 --> 00:08:21,400 not be dropped further at Reactor 4 until the evening peak period had passed. Hence 101 00:08:21,400 --> 00:08:28,260 power at Chernobyl was maintained at 50% in Reactor 4, all the way through until 11pm 102 00:08:28,260 --> 00:08:34,700 that evening. Despite the original test plan requiring a drop to 30% prior to shutting 103 00:08:34,700 --> 00:08:40,060 off the Emergency Core Cooling System (the ECCS), was shut off anyway shortly after 2:00pm. 104 00:08:40,060 --> 00:08:48,600 At 4pm, the evening shift began. In the lead-up to the test, both day and evening 105 00:08:48,600 --> 00:08:52,920 shifts were run through the details of the test procedure at length, with the intention 106 00:08:52,920 --> 00:08:58,120 that the test be completed during the late day or early evening shifts of the Friday. 107 00:08:58,120 --> 00:09:03,160 However, with the 10-hour delay due to an unrelated power station trip elsewhere on 108 00:09:03,160 --> 00:09:08,280 the grid had meant that whilst most of the preconditions for the test had been achieved, 109 00:09:08,280 --> 00:09:12,080 When the night shift arrived for handover, the critical execution of the test itself 110 00:09:12,080 --> 00:09:17,520 was handed to the night shift to perform instead. 111 00:09:17,520 --> 00:09:21,800 Yuri Tregub was one of the two operators from the evening shift that was intended to run 112 00:09:21,800 --> 00:09:26,380 the test and he opted to stay around for the night shift to assist the night shift operators 113 00:09:26,380 --> 00:09:27,960 with the test. 114 00:09:27,960 --> 00:09:32,160 The night shift consisted of minimal staffing, with less experienced operators regularly 115 00:09:32,160 --> 00:09:36,100 given the night shift as a right of progression through the ranks, a standard practice in 116 00:09:36,100 --> 00:09:41,940 many companies the world over. Following references to reactor power in MegaWatts refer to MegaWatt 117 00:09:41,940 --> 00:09:47,860 thermal, meaning reactor power measurement specifically not the electrical output of 118 00:09:47,860 --> 00:09:55,220 the generator. Between 11pm and midnight the core was reduced from 50% to 30% and further to 700 119 00:09:55,220 --> 00:10:01,380 MegaWatt thermal (MWt) at 5 minutes past midnight now on Saturday the 26th of April as this was the 120 00:10:01,380 --> 00:10:07,220 targeted safe level for the test. The reactor power change was made significantly faster 121 00:10:07,220 --> 00:10:12,780 than during the previous night and day shift adjustments had been made. Reactors need to 122 00:10:12,780 --> 00:10:18,500 have their power levels increased and reduced gradually, otherwise instability can occur 123 00:10:18,500 --> 00:10:24,660 when the reactor goes out of equilibrium. So why do reactors go out of equilibrium? 124 00:10:24,660 --> 00:10:31,980 The Iodine-135 conversion by decay to Xenon-135 becomes a Neutron absorbing fission by-product 125 00:10:31,980 --> 00:10:34,980 acting similarly to a control rod. 126 00:10:34,980 --> 00:10:41,060 Under normal reactor operation, a common uranium fission by-product is Tellurium-135 which 127 00:10:41,060 --> 00:10:47,380 has a very brief half-life of only 19 seconds, which then beta decays into Iodine-135 with 128 00:10:47,380 --> 00:10:54,980 a half-life of 6.6 hours which then subsequently also beta decays into Xenon-135. 129 00:10:54,980 --> 00:11:01,260 Xenon-135 has a half-life of 9.2 hours, however the bigger problem is its cross-section for 130 00:11:01,260 --> 00:11:09,040 Neutron absorption which is measured in units called "Barns,"" where 1 Barn is 10^-24cm2. 131 00:11:09,040 --> 00:11:13,160 The probability of fission occurring relates on two characteristics relating to the Neutron, 132 00:11:13,160 --> 00:11:18,880 speed of the Neutron first. Under a fission event or a decay event, Neutrons are released 133 00:11:18,880 --> 00:11:24,640 at high speed, imaginatively called "Fast Neutrons". In order to increase the probability 134 00:11:24,640 --> 00:11:29,580 that the nucleus will retain an additional Neutron when it hits it, we try to slow the 135 00:11:29,580 --> 00:11:35,900 Neutron down first, to a so-called "Thermal Neutron". The cross-sectional area in Barns 136 00:11:35,900 --> 00:11:41,020 of the nucleus the Neutron is fired at means that the larger that value, the larger the 137 00:11:41,020 --> 00:11:45,600 target area, the more likely the Neutron will hit that target. The larger the 138 00:11:45,600 --> 00:11:48,100 Barns, meaning the higher the probability the nucleus will 139 00:11:48,100 --> 00:11:52,940 ultimately capture the Neutron as well. Since there are two Neutron speeds there 140 00:11:52,940 --> 00:11:57,860 are two cross sections: Thermal and Fast. Carbon in the form of Graphite is 141 00:11:57,860 --> 00:12:01,620 commonly used in rods to slow down fast Neutrons turning them into Thermal 142 00:12:01,620 --> 00:12:05,640 Neutrons and interestingly Carbon does not tend to capture Neutrons in this 143 00:12:05,640 --> 00:12:12,040 process. Control rods on the other hand are typically made of Boron-Cadmium or 144 00:12:12,040 --> 00:12:17,160 Indium as these have higher Thermal and Tast Cross-Sections and capture the 145 00:12:17,160 --> 00:12:22,840 Neutrons very readily. At Chernobyl the reactor used Boron-Carbide control rods 146 00:12:22,840 --> 00:12:28,000 and Graphite Carbon moderator rods. Boron's Thermal Cross-Section is 200 147 00:12:28,000 --> 00:12:32,960 Barns and Fast Cross-Section is 0.4 Barns. Circling back to Xenon-135 which 148 00:12:32,960 --> 00:12:38,300 is why we're going down this discussion and why all this matters is its Thermal Cross-Section 149 00:12:38,300 --> 00:12:49,360 is a whopping 2M Barns and its Fast Cross-Section is 0.0008 or 1/1250th of a Barn. 150 00:12:49,360 --> 00:12:55,520 In addition, Xenon-135 captures its Neutrons like a control rod is designed to, which actually 151 00:12:55,520 --> 00:13:02,200 is a problem. Hence, it doesn't take very much Xenon-135 to start absorbing a lot of 152 00:13:02,200 --> 00:13:06,760 Neutrons and to slow your reaction rate down significantly. Under normal 153 00:13:06,760 --> 00:13:10,560 operation the ramp up and ramp down of the reactor power ensures that there are 154 00:13:10,560 --> 00:13:15,160 sufficient Neutrons in the reactor in its Neutron flux such that the Iodine 155 00:13:15,160 --> 00:13:19,840 and Xenon-135 balance leads to the Xenon absorbing excess Neutrons and 156 00:13:19,840 --> 00:13:24,200 converting it to other isotopes: an effect referred to as "burning-off" the 157 00:13:24,200 --> 00:13:29,600 Xenon. If the Xenon isn't being burned off at the same or a similar rate as 158 00:13:29,600 --> 00:13:33,960 it's being created then this leads to an effect referred to as "Reactor Poisoning". 159 00:13:33,960 --> 00:13:38,880 When poisoning occurs too many Neutrons are absorbed by the Xenon-135 and 160 00:13:38,880 --> 00:13:43,400 unlike a control rod whose position inside the reactor core can be precisely 161 00:13:43,400 --> 00:13:48,560 controlled (hence its name) the Xenon concentration isn't directly 162 00:13:48,560 --> 00:13:55,080 controllable by an operator and that's a problem. It becomes a somewhat random 163 00:13:55,080 --> 00:13:58,360 element impacting the reactors controllability and thus leading to 164 00:13:58,360 --> 00:14:04,840 instability in the core. One more detail, the control rod insertion and removal mechanism 165 00:14:04,840 --> 00:14:12,520 operated at 0.4 m/sec at Chernobyl, that's about 16 in/sec, and each rod 166 00:14:12,520 --> 00:14:21,080 extended at maximum to the full height of the core, which was 7m. Hence it would take between 18 167 00:14:21,080 --> 00:14:27,640 to 20 seconds to fully extend into or retract out of the core. Now that we've established that, 168 00:14:27,640 --> 00:14:34,280 back to the incident. At 12:05am, Aleksandr Akimov, the Unit Shift 169 00:14:34,280 --> 00:14:40,040 Chief in charge of the test, took over from Tugrub, though despite being weary after back-to-back shifts, 170 00:14:40,040 --> 00:14:45,560 Tugrub stayed to advise if needed. The reactor power dropped even further, despite the fact 171 00:14:45,560 --> 00:14:49,720 that the shift operator, Leonid Toptunov, hadn't moved the control rod positions. 172 00:14:49,720 --> 00:14:56,440 The core further dropped to approximately 500MWt by 12:28am, 173 00:14:57,000 --> 00:15:03,160 due to reactor poisoning. At this time, Toptunov transferred control of the control rod positioning 174 00:15:03,160 --> 00:15:09,080 from local to automatic regulation without first selecting the option to "hold power at required 175 00:15:09,080 --> 00:15:14,680 level." This resulted in the control rods being inserted far deeper into the reactor core than 176 00:15:14,680 --> 00:15:22,600 intended, dropping even further the power output to only 30MWt, effectively performing 177 00:15:22,600 --> 00:15:25,700 an unintended shutdown of the core. 178 00:15:25,700 --> 00:15:29,000 The operators and engineers involved in the control room debated whether they should continue 179 00:15:29,000 --> 00:15:33,000 the test or to just completely abort it at that point. 180 00:15:33,000 --> 00:15:38,980 Anatoly Dyatlov, the deputy chief engineer, was supervising the test, and despite Akimov 181 00:15:38,980 --> 00:15:43,520 and Toptunov's objections, he threatened to hand control of the reactor to Tegrub from 182 00:15:43,520 --> 00:15:48,320 the previous shift if they did not comply and continue to push ahead with the test as 183 00:15:48,320 --> 00:15:54,840 planned. In order to increase the power from the reactor, the operator on shift switched 184 00:15:54,840 --> 00:15:59,440 to full manual control of rod positioning and removed more control rods from the core 185 00:15:59,440 --> 00:16:06,500 to try and accelerate the reaction. And at 12:32am local time, only 26 control rods remained 186 00:16:06,500 --> 00:16:11,580 in the core, noting that there are 211 in total. 187 00:16:11,580 --> 00:16:16,000 In preparation for the test, several of the automatic SCRAM initiator triggers had been 188 00:16:16,000 --> 00:16:20,720 disabled as the test conditions would have triggered a core shutdown automatically had 189 00:16:20,720 --> 00:16:27,360 they been left enabled, although the manual SCRAM button (labelled AZ-5) was available 190 00:16:27,360 --> 00:16:33,160 if it was needed. The reactor gradually responded to the removal of the control rods and appeared 191 00:16:33,160 --> 00:16:42,240 to stabilise at about 200MWt at 1:00am. At 1:03am, a standby cooling circulation pump 192 00:16:42,240 --> 00:16:45,880 was switched into the left cooling loop in accordance with the test procedure to increase 193 00:16:45,880 --> 00:16:52,160 water flow to the core. At 1:07am an additional cooling pump was connected to the right cooling 194 00:16:52,160 --> 00:16:57,580 loop in accordance with the test procedure. Since water acts as a Neutron absorber as 195 00:16:57,580 --> 00:17:04,580 well as a coolant, this began to affect the core which was already unstable due to poisoning. 196 00:17:04,580 --> 00:17:10,080 At 1:15am, with the reactor power now dropping once again as a result of the increased cooling 197 00:17:10,080 --> 00:17:20,040 water flow, 20 more rods were removed from the core, leaving only 6 control rods in place. 198 00:17:20,040 --> 00:17:25,700 The steam drum that separated the liquid water from the steam at 1:19am hit the emergency 199 00:17:25,700 --> 00:17:31,720 low level shutdown height, however the operator blocked this because this would have rendered 200 00:17:31,720 --> 00:17:37,460 the test invalid, effectively aborting it before the test could really begin. 201 00:17:37,460 --> 00:17:44,380 At 1:21am, the reactor section foreman was on the open platform above the reactor core 202 00:17:44,380 --> 00:17:51,780 and observed that the fuel channel blocks, each weighing 350kg or 770lbs, were jumping 203 00:17:51,780 --> 00:17:56,920 up and down and felt shockwaves rippling through the floor. 204 00:17:56,920 --> 00:18:03,160 At 1:21.50, the pressure in the steam separator drums fell sharply and the 205 00:18:03,160 --> 00:18:07,640 operator attempted to manually control the water flow rate to keep the water level in 206 00:18:07,640 --> 00:18:12,920 the drum at an acceptable level so they could begin the test. 207 00:18:12,920 --> 00:18:16,640 Now believing that they had achieved this and the conditions were acceptable to begin 208 00:18:16,640 --> 00:18:26,680 the test, at 1:23am the instruction to manually shut the steam lines was given and at 1:23:04am 209 00:18:26,680 --> 00:18:31,420 the valves were all closed and the test officially began. 210 00:18:31,420 --> 00:18:36,680 As the flow rate into the core slowed down, the boiling rate accelerated at the bottom 211 00:18:36,680 --> 00:18:43,240 of the core, creating an increasing number of steam voids in the coolant. 212 00:18:43,240 --> 00:18:49,480 These voids reduced the Neutron absorption and drove the reactivity of the core up higher. 213 00:18:49,480 --> 00:18:54,800 The pressure in the pressure tubes increased and within 20 seconds of the steam shut off, 214 00:18:54,800 --> 00:19:03,060 temperature spiked and the reactor power increased past 530MWt. It is believed 215 00:19:03,060 --> 00:19:08,800 that the operator realised the reactor power was surging and at that point they initiated 216 00:19:08,800 --> 00:19:18,380 a manual SCRAM event and pushed the AZ-5 button at 1:23:40am. Whether this was the reason 217 00:19:18,380 --> 00:19:24,180 a SCRAM was initiated or not, it cannot be determined for certain. 218 00:19:24,180 --> 00:19:30,000 As the control rods were reinserted into the core, in only 4 seconds the reactor power 219 00:19:30,000 --> 00:19:38,340 shot up to an estimated 100 times maximum design value, rupturing several fuel channels 220 00:19:38,340 --> 00:19:45,320 and the 1,000T reactor support plate detached, warping the control rod mechanisms, jamming 221 00:19:45,320 --> 00:19:49,920 them in their position at only half inserted. 222 00:19:49,920 --> 00:19:55,000 The fracturing allowed steam and water to enter back into the reactor completely uncontrolled, 223 00:19:55,000 --> 00:20:01,880 which at 1:23:45am, only 41 seconds after the test began, the core was open to air from 224 00:20:01,880 --> 00:20:04,120 the outside. 225 00:20:04,120 --> 00:20:08,360 There is some debate about the conditions in the core at this point, given the limited 226 00:20:08,360 --> 00:20:12,960 instrumentation available that was still functional at that point and the inaccessibility following 227 00:20:12,960 --> 00:20:18,360 the explosion, however the more commonly postulated source was a Graphite fire at high temperature 228 00:20:18,360 --> 00:20:21,760 leading to hydrogen production and subsequent explosion. 229 00:20:21,760 --> 00:20:27,480 The second explosion at approximately 1:24am was significantly larger, blowing the reactor 230 00:20:27,480 --> 00:20:33,080 lid off completely and ejecting large quantities of fuel, moderator and control rod material 231 00:20:33,080 --> 00:20:39,560 as well as concrete, steel and radioactive byproducts as high as 1km (6/10th of a mile) 232 00:20:39,560 --> 00:20:41,280 into the air. 233 00:20:41,280 --> 00:20:46,020 The force of the second explosion killed the main circulating pump plant operator Valery 234 00:20:46,020 --> 00:20:51,920 Khodemchuk instantly, with a second dying from injuries sustained in the explosion a 235 00:20:51,920 --> 00:20:54,380 few hours later. 236 00:20:54,380 --> 00:20:57,820 Power went out through the facility with only battery backed up lighting remaining, 237 00:20:57,820 --> 00:21:02,740 though the large amount of radioactive dust made visibility difficult in this early morning 238 00:21:02,740 --> 00:21:04,840 hours. 239 00:21:04,840 --> 00:21:10,680 At 1:26:03am, the fire alarm was activated by Akimov. 240 00:21:10,680 --> 00:21:17,120 At 1:28am, 14 firemen stationed on site arrived at the Reactor 4 building and began fighting 241 00:21:17,120 --> 00:21:22,260 the numerous fires that had broken out in and surrounding Reactor 4. 242 00:21:22,260 --> 00:21:25,420 In the following 30 minutes, the operators received mixed messages about whether the 243 00:21:25,420 --> 00:21:30,620 reactor had been breached and tried a multitude of things to re-establish core cooling with 244 00:21:30,620 --> 00:21:33,620 no success. 245 00:21:33,620 --> 00:21:42,500 Aleksandr Kudryavtsev and Viktor Proskuryakov were the trainees from other shifts, sent 246 00:21:42,500 --> 00:21:48,020 to observe and learn from Tuptunov during the test execution. 247 00:21:48,020 --> 00:21:52,260 They were sent by the shift lead to turn the manual control rod positioners to ensure a 248 00:21:52,260 --> 00:21:56,860 full core shutdown, still believing that they were operable. 249 00:21:56,860 --> 00:22:01,460 Upon reaching the reactor hall, with the upper biological shield in the reactor no longer 250 00:22:01,460 --> 00:22:07,660 containing radiation, in the 1min they observed the blue-red fire in the core of 251 00:22:07,660 --> 00:22:14,540 Reactor 4, their skin was darkened with a so-called "Nuclear Tan," also known as a Radiation 252 00:22:14,540 --> 00:22:21,800 Burn, as they absorbed a fatal dose of radiation. They returned to report the state of the reactor 253 00:22:21,800 --> 00:22:26,940 core to the control room, however when they arrived and told the story, they were not 254 00:22:26,940 --> 00:22:34,580 believed. By 2:00am a group of 100 firefighters from Pripyat converged on the largest fires 255 00:22:34,580 --> 00:22:39,860 on the roof of Reactor 4 and by 5:00am in the morning the majority of the fires had been 256 00:22:39,860 --> 00:22:44,960 extinguished. Following the explosion in the early hours a group of people from the town 257 00:22:44,960 --> 00:22:51,420 of Pripyat gathered on a nearby bridge to watch the fire from a distance. The flames 258 00:22:51,420 --> 00:22:54,920 were of many different colors reaching into the sky. 259 00:22:54,920 --> 00:22:59,720 However, the prevailing wind direction was blowing the fallout from the explosion 260 00:22:59,720 --> 00:23:02,760 directly across where they were standing 261 00:23:02,760 --> 00:23:04,640 in that part of town 262 00:23:04,640 --> 00:23:08,240 and none of the people on that bridge survived. 263 00:23:08,240 --> 00:23:09,500 At 6:00am 264 00:23:09,500 --> 00:23:13,320 Akimov was relieved by the unit chief, although he stayed on site fighting 265 00:23:13,320 --> 00:23:15,320 extreme nausea. 266 00:23:15,320 --> 00:23:18,800 By 6:35am all the fires had been extinguished by a contingent of now 267 00:23:18,800 --> 00:23:25,200 186 firefighters on the scene, with the sole exception of the Graphite fire in the remains 268 00:23:25,200 --> 00:23:34,200 of the core of Reactor 4. At 8:00am the day shift began, including the construction crews of 269 00:23:34,200 --> 00:23:42,600 286 people building Reactors 5 and 6 continued on site. No instruction was given to evacuate 270 00:23:42,600 --> 00:23:48,420 at that point. As the day went on in the town of Pripyat nearby, dozens of people became 271 00:23:48,420 --> 00:23:53,980 increasingly unwell, reporting severe headaches, metallic tastes in their mouths accompanied 272 00:23:53,980 --> 00:23:58,940 by uncontrolled fits of coughing and vomiting. Later in the evening on Saturday, the order 273 00:23:58,940 --> 00:24:04,000 was given to assemble transportation for a mass evacuation of Pripyat, and at midnight 274 00:24:04,000 --> 00:24:10,620 on Sunday the 27th of April, buses arrived in town ready for the evacuation order to be given. 275 00:24:10,620 --> 00:24:17,740 At 1:13am on Sunday, Reactor 1 was shut down, followed by Reactor 2 the next hour. At 7:00am 276 00:24:17,740 --> 00:24:22,240 Monday morning it was finally confirmed that the Graphite in the core was not only still 277 00:24:22,240 --> 00:24:27,840 burning but it was emitting extremely large amounts of radiation. 278 00:24:27,840 --> 00:24:32,600 The order was given to begin sky drops of a mixture of sand, boron and lead into the 279 00:24:32,600 --> 00:24:36,820 open reactor core from above via helicopters. 280 00:24:36,820 --> 00:24:42,600 From approximately 10:00am that morning helicopter dumps began and between the 27th of April 281 00:24:42,600 --> 00:24:50,320 on the 1st of May, 1,800 flights dropped over 5,000T of material into the reactor 282 00:24:50,320 --> 00:24:55,680 core. Following the incident it was confirmed that very little of this material ever actually 283 00:24:55,680 --> 00:25:00,360 reached the core because at that time the core had melted through deeper into the building 284 00:25:00,360 --> 00:25:10,000 structure. At 2:00pm Sunday Pripyat was evacuated with 43,000 residents leaving in a space of 285 00:25:10,000 --> 00:25:18,320 only 3-1/2hrs on a contingent of 1,200 buses. It was orderly and efficient, 286 00:25:18,320 --> 00:25:22,560 although somewhat belated. 287 00:25:22,560 --> 00:25:29,280 The fallout from this incident was far-reaching, with radioactive material in the upper atmosphere 288 00:25:29,280 --> 00:25:34,500 carried by the jet stream to the United States and Asia, though the largest concentrations 289 00:25:34,500 --> 00:25:38,500 of radioactive material fell over Europe. 290 00:25:38,500 --> 00:25:44,060 The first signs of this were detected by the Forsmark Nuclear Power Plant in Sweden at 291 00:25:44,060 --> 00:25:52,940 9:30am on Monday 28 April, only two days after the incident and some 1,100km or 680mi 292 00:25:52,940 --> 00:25:54,140 away. 293 00:25:54,140 --> 00:25:58,060 An American spy satellite provided detailed evidence to the world outside of the Soviet 294 00:25:58,060 --> 00:26:04,460 Union on Tuesday the 29th of April that showed the scale and severity of the incident at Chernobyl. 295 00:26:04,460 --> 00:26:13,220 In the weeks following the incident a tunnel was bored from underneath Reactor 3 to under Reactor 4 and a large slab of concrete was put in position 296 00:26:13,220 --> 00:26:18,900 under Reactor 4 to prevent the still molten core from entering the water table beneath. 297 00:26:18,900 --> 00:26:27,740 A month later, despite radiation levels dropping on site, the idea of a concrete sarcophagus was proposed to contain any further releases of radiation. 298 00:26:27,740 --> 00:26:29,740 More about that in a moment. 299 00:26:29,740 --> 00:26:36,100 31 people died as a direct result of the incident in the first 3 months alone, though the 300 00:26:36,100 --> 00:26:39,740 following years would be much worse. 301 00:26:39,740 --> 00:26:44,020 Akimov died on the 10th of May, 14 days after the incident. 302 00:26:44,020 --> 00:26:51,500 Toptunov died four days later, on the 14th of May, along with Aleksandr Kudryavtsev and 303 00:26:51,500 --> 00:26:59,100 Viktor Proskuryakov, the other trainee, dying on the 17th. 304 00:26:59,100 --> 00:27:02,940 Many of the operators involved couldn't provide critical details of the incident in 305 00:27:02,940 --> 00:27:08,460 the days following due to their medical condition after the incident. 306 00:27:08,460 --> 00:27:12,940 The town of Pripyat has been abandoned since the incident occurred, although interestingly 307 00:27:12,940 --> 00:27:18,500 tourists have more recently been allowed with controlled visits to the town. 308 00:27:18,500 --> 00:27:24,580 Both Caesium and Strontium radioisotopes are the primary fallout materials that are preventing 309 00:27:24,580 --> 00:27:31,140 rehabitation of impacted areas in the fallout zone. The half-life of Caesium-137, for example, 310 00:27:31,140 --> 00:27:36,660 is 30 years, hence safe habitable levels may be hundreds of years away depending upon the 311 00:27:36,660 --> 00:27:43,460 concentration in any given area. A forest area of about 4sqkm downwind of the plant 312 00:27:43,460 --> 00:27:49,860 turned reddish brown following the incident and completely died. The losses of livestock were huge 313 00:27:49,860 --> 00:27:54,480 across many parts of Europe, specifically looking at the United Kingdom though, it restricted 314 00:27:54,480 --> 00:28:00,060 the movement of sheep from upland areas when Caesium-137 fell across parts of Northern 315 00:28:00,060 --> 00:28:06,940 Ireland, Wales, Scotland and Northern England. Immediately following the disaster in 1986, 316 00:28:06,940 --> 00:28:15,860 a total of 4,225,000 sheep had their movement restricted across 9,700 farms to prevent contaminated 317 00:28:15,860 --> 00:28:21,780 meat from entering the human food chain, and that was just the United Kingdom. 318 00:28:21,780 --> 00:28:28,500 Longer term, 237 people suffered from acute radiation sickness and it's estimated that 319 00:28:28,500 --> 00:28:35,060 about 4,000 people will die prematurely in total due to cancers caused by the radioactive 320 00:28:35,060 --> 00:28:38,300 fallout from Chernobyl. 321 00:28:38,300 --> 00:28:41,340 So what went wrong? 322 00:28:41,340 --> 00:28:45,700 As I said before, there are two formal groups that debate the true cause of the incident 323 00:28:45,700 --> 00:28:50,160 – design flaw or people factors. 324 00:28:50,160 --> 00:28:56,860 One of them was the INSAG-1 report International Nuclear Safety Advisory Group in 1986 and 325 00:28:56,860 --> 00:29:02,580 their second report, INSAG-7, in 1992 followed the declassification of documents from the 326 00:29:02,580 --> 00:29:08,460 former Soviet Union, which argued the primary cause was human factors. 327 00:29:08,460 --> 00:29:16,300 The other was the IAEA, International Atomic Energy Agency's 1993 revised report that 328 00:29:16,300 --> 00:29:22,600 also took detail from the declassified documents and their conclusion focused on the RBMK design 329 00:29:22,600 --> 00:29:25,180 as the primary cause. 330 00:29:25,180 --> 00:29:28,200 Let's consider design flaw first. 331 00:29:28,200 --> 00:29:33,300 The RBMK design lacked several key features that contributed to the outcome at Chernobyl. 332 00:29:33,300 --> 00:29:37,340 The first, a positive steam void co-efficient. 333 00:29:37,340 --> 00:29:40,000 It's a measure of how a reactor responds 334 00:29:40,000 --> 00:29:43,220 to increasing steam formation in the cooling water 335 00:29:43,220 --> 00:29:45,220 surrounding the fuel rods. 336 00:29:45,220 --> 00:29:47,460 Reactors cooled by boiling water 337 00:29:47,460 --> 00:29:50,240 contain a proportion of steam in their core. 338 00:29:50,240 --> 00:29:52,940 Since liquid water is more efficient as a coolant 339 00:29:52,940 --> 00:29:55,920 and more effective at absorbing Neutrons than steam is, 340 00:29:55,920 --> 00:29:58,660 if there's a change in the proportion of steam bubbles 341 00:29:58,660 --> 00:30:00,700 or voids in the coolant, 342 00:30:00,700 --> 00:30:02,380 there will be a corresponding change in 343 00:30:02,380 --> 00:30:08,380 core reaction rate as a result. The ratio of these changes is termed the void co-efficient 344 00:30:08,380 --> 00:30:14,280 of reactivity. If the void co-efficient is negative, an increase in steam will lead to 345 00:30:14,280 --> 00:30:21,220 a decrease in reactivity. When the void co-efficient is positive, an increase in steam will lead 346 00:30:21,220 --> 00:30:26,480 to an increase in reactivity which will in turn lead to more heat being generated which 347 00:30:26,480 --> 00:30:31,640 will in turn further increase the reactivity. Hence positive void co-efficients are considered 348 00:30:31,640 --> 00:30:35,640 to be fundamentally bad design for nuclear reactors. 349 00:30:35,640 --> 00:30:39,760 Although it's an over-simplification to say that the void co-efficients are the main contributor 350 00:30:39,760 --> 00:30:45,040 to overall power co-efficients of reactivity in a nuclear reactor, in the RBMK design it 351 00:30:45,040 --> 00:30:49,600 is the largest contributor and it is positive. 352 00:30:49,600 --> 00:30:55,400 Not only that, but with the RBMK design the void co-efficient depends on the reactor configuration 353 00:30:55,400 --> 00:31:01,240 and its stability which is dependent on other factors such as the reactor's ORM which 354 00:31:01,240 --> 00:31:07,320 leads to the next issue. The minimum number of rods to satisfy the ORM was 355 00:31:07,320 --> 00:31:13,740 far too low. The ORM stands for the Operational Reactivity Margin and it's a 356 00:31:13,740 --> 00:31:18,760 set of formulae that calculate the safe number of control rods to be inserted at 357 00:31:18,760 --> 00:31:24,540 any given time in the reactor. If there are too few control rods below the ORM 358 00:31:24,540 --> 00:31:30,000 the reactivity of the core will be unstable. In the technological 359 00:31:30,000 --> 00:31:34,960 regulations on operation of 3rd and 4th power units of the Chernobyl Nuclear Power 360 00:31:34,960 --> 00:31:42,880 Plant with RBMK-1000 reactors, dated 1983, the text translates from Russian approximately 361 00:31:42,880 --> 00:31:44,720 as follows. 362 00:31:44,720 --> 00:31:48,440 "Section 6.6.4: 363 00:31:48,440 --> 00:31:53,040 Minimum reactivity margin in the process of power lifting after a short-term stop should 364 00:31:53,040 --> 00:31:55,640 make not less than 15 rods. 365 00:31:55,640 --> 00:32:02,060 If at extraction of CPS (Control and Protection System) rods during reactor turn up to a critical 366 00:32:02,060 --> 00:32:08,080 condition the reactivity margin will decrease to 15 rods and will continue to fall. 367 00:32:08,080 --> 00:32:12,840 To dump all rods to bottom limit switches, rods to bring into the zone of their greatest 368 00:32:12,840 --> 00:32:14,640 efficiency. 369 00:32:14,640 --> 00:32:19,160 By the curves of poison out to define an idle time." 370 00:32:19,160 --> 00:32:25,960 That's not necessarily the best translation however we interpret that as meaning there 371 00:32:25,960 --> 00:32:32,480 should be 15 rods in the core in a situation the core was in immediately prior to the incident 372 00:32:32,480 --> 00:32:35,540 not 6. 373 00:32:35,540 --> 00:32:41,720 After the incident calculations were re-done estimating with the specific conditions at 374 00:32:41,720 --> 00:32:50,760 1:23:30am that the minimum equivalent number of rods for ORM was 8, which was still 375 00:32:50,760 --> 00:32:57,560 more than were inserted at the time. Clearly operators were either unfamiliar with the 376 00:32:57,560 --> 00:33:03,400 regulations or if they were under the duress of the test at the time they didn't recall them or 377 00:33:03,400 --> 00:33:11,240 they didn't appreciate the risk of ignoring them. How this is a bad design is such that operators 378 00:33:11,240 --> 00:33:17,240 didn't have a visual indication or a real-time calculation to estimate the ORM when they're 379 00:33:17,240 --> 00:33:24,440 operating the reactor. Thirdly, the reactor control and protection mechanism, the control rods 380 00:33:24,440 --> 00:33:32,040 themselves, were badly designed. The control rods each had a section of Graphite for 152mm 381 00:33:32,040 --> 00:33:37,560 (that's 6") at their furthest position. When the control rods were fully extracted 382 00:33:37,560 --> 00:33:43,800 as they were being inserted into the core, the first Graphite segment also displaced water in 383 00:33:43,800 --> 00:33:50,680 the rod channel and then the Boron-Carbide control rod material would follow after the Graphite. 384 00:33:50,680 --> 00:33:55,160 The rate of insertion and removal was such that when they were commanded to be inserted, 385 00:33:55,160 --> 00:34:01,400 the reactor had the top position of the fuel rods exposed to an unintended moderator. 386 00:34:01,960 --> 00:34:09,320 The Graphite displaced 150mm of absorbing water with 150mm of Graphite as a moderator, 387 00:34:09,320 --> 00:34:15,880 for half a second. As the rods were inserted into the core, the additional set of moderators 388 00:34:15,880 --> 00:34:20,520 continued to track through the core until they reached final insertion when they were taken out 389 00:34:20,520 --> 00:34:26,920 of play. This had the effect of slowing enough Fast Neutrons to become Thermal Neutrons, 390 00:34:26,920 --> 00:34:33,240 which ironically led to an acceleration of the reaction rate for a period of time before the 391 00:34:33,240 --> 00:34:39,240 Boron-Carbide could then absorb excess Neutrons and slow down the reaction rate as they were 392 00:34:39,240 --> 00:34:45,880 intended to. Hence, inserting the control rods created a "power blip" in the reactor core 393 00:34:45,880 --> 00:34:50,920 before the control rods began controlling as they should have. When a reactor is operating 394 00:34:50,920 --> 00:34:56,360 under stable operational conditions at moderate to full load, this isn't a problem, 395 00:34:56,360 --> 00:35:01,680 and at normal load it's barely measurable. However when the reactor is 396 00:35:01,680 --> 00:35:08,320 heavily poisoned and highly unstable already it was the spark that set off a 397 00:35:08,320 --> 00:35:14,360 rate of fission sky-rocketing out of control. Now let's consider the human 398 00:35:14,360 --> 00:35:19,640 factors. The training for the test was provided for the shifts when they were 399 00:35:19,640 --> 00:35:24,880 supposed to carry out the tests not the graveyard shift. Pressure to execute the 400 00:35:24,880 --> 00:35:30,040 tests to close a known safety design flaw at the early hours of the morning bypassed 401 00:35:30,040 --> 00:35:36,280 their rationale and caution. There's also the effect of "RBMKs have been operating 402 00:35:36,280 --> 00:35:41,320 all over Russia for a decade without incident therefore they must be safe" that serves 403 00:35:41,320 --> 00:35:47,040 to throw common sense out the window as well. There weren't incidents in RBMKs because 404 00:35:47,040 --> 00:35:52,600 of a combination of factors including: operators of the other plants followed the rules, they 405 00:35:52,600 --> 00:35:55,720 understood reactor poisoning and how it functioned, 406 00:35:55,720 --> 00:36:01,240 the government regularly covered up and kept incidents a secret (even small ones) meaning 407 00:36:01,240 --> 00:36:05,440 there were incidents in other RBMK reactors, it's just the other operators were never 408 00:36:05,440 --> 00:36:07,320 told about them. 409 00:36:07,320 --> 00:36:14,220 And any high risk testing at other plants, they'd been handled by more experienced operators. 410 00:36:14,220 --> 00:36:19,360 More experienced operators would have known to abort the test, or at least let the reactor 411 00:36:19,360 --> 00:36:25,440 gradually stabilise, burn off the Xenon-135 and get rid of the reactor poisoning for several 412 00:36:25,440 --> 00:36:28,640 hours before they began the test. 413 00:36:28,640 --> 00:36:33,520 Had they done that, there wouldn't have been an incident. 414 00:36:33,520 --> 00:36:41,440 Like Challenger, the Space Shuttle, interestingly in the same year, the clear go/no-go criteria 415 00:36:41,440 --> 00:36:45,960 for the test to initiate had to be set. 416 00:36:45,960 --> 00:36:48,040 And at Chernobyl it had been. 417 00:36:48,040 --> 00:36:55,320 700MWt for the reactor with the correct ORM prescribed control rods in position. 418 00:36:55,320 --> 00:37:02,080 Not 200MWt and certainly not with only 6 control rods inserted. 419 00:37:02,080 --> 00:37:06,600 Clearly the operators didn't understand enough about the fission reaction and the 420 00:37:06,600 --> 00:37:12,940 reactor poisoning to appreciate why the test had been set the way it had been. 421 00:37:12,940 --> 00:37:20,340 They had made exceptions to the test to the go/no-go criteria on the fly without knowledge, 422 00:37:20,340 --> 00:37:26,000 experience or authorisation from those that should have been consulted first. 423 00:37:26,000 --> 00:37:31,200 The thing that amazes me is that it was so vital that the facility continued to generate 424 00:37:31,200 --> 00:37:36,860 electricity for the Soviet Union's power grid that despite the incident, the drawn-out 425 00:37:36,860 --> 00:37:42,000 clean-up and precautions taken, they pushed ahead anyway. 426 00:37:42,000 --> 00:37:45,580 Reactor 1 was restarted on the 29th of September that year. 427 00:37:45,580 --> 00:37:51,020 On the 10th of October, order was given to recommence construction of Reactors 5 and 428 00:37:51,020 --> 00:37:52,020 6. 429 00:37:52,020 --> 00:37:54,980 Reactor 2 came back online on the 9th of November. 430 00:37:54,980 --> 00:37:58,940 At that point the sarcophagus was still under construction over Reactor 4. 431 00:37:58,940 --> 00:38:04,600 It wasn't even completed until the 14th of December in 1986. 432 00:38:04,600 --> 00:38:11,500 The design life of the initial sarcophagus structure was 30 years, and it took some 300,000T 433 00:38:11,500 --> 00:38:19,420 of concrete and 6,000T of steel to construct, albeit hastily. Reactor 3 came back online on the 434 00:38:19,420 --> 00:38:25,180 21st of April 1987 and with this achieved, it was announced two days later, finally, 435 00:38:25,180 --> 00:38:29,900 Reactors 5 and 6 would no longer be completed and construction was finally stopped on them. 436 00:38:29,900 --> 00:38:38,060 In coming decades, Reactors 1, 2 and 3 continued to supply electricity until Reactor 3 was the 437 00:38:38,060 --> 00:38:43,540 last to be shut down on the 15th of December in the year 2000. 438 00:38:43,540 --> 00:38:50,840 Doing the math on the original sarcophagus for a moment, that design life ended in 2016. 439 00:38:50,840 --> 00:38:55,060 The Ukrainian government realised this was coming and the hastily built structure needed 440 00:38:55,060 --> 00:39:01,180 to be done properly and in 1992 launched an international competition to design and construct 441 00:39:01,180 --> 00:39:09,020 the NSC for New Safe Confinement Structure over the top of the entire existing sarcophagus. 442 00:39:09,020 --> 00:39:14,940 In 1997 the project formally began and after 2004 conceptual designs were completed. 443 00:39:14,940 --> 00:39:23,140 In 2007 it was awarded to Novarka: a consortium lent by French construction companies. 444 00:39:23,140 --> 00:39:29,420 Civil works began in 2010 with construction practical completion expected in mid 2018. 445 00:39:29,420 --> 00:39:34,780 The large arch structure is designed to stop particulates from escaping the enclosed space 446 00:39:34,780 --> 00:39:41,360 for the next 100 years, whilst allowing enough room inside to begin safely dismantling, removing 447 00:39:41,360 --> 00:39:47,280 and disposing of radioactive material both from the original sarcophagus as well as the 448 00:39:47,280 --> 00:39:52,440 reactor itself, gradually over that 100 years. 449 00:39:52,440 --> 00:39:56,680 The cost of the shelter implementation plan which includes the structure's costs is 450 00:39:56,680 --> 00:40:00,360 $2.3B USD. 451 00:40:00,360 --> 00:40:05,940 It's extremely difficult to confirm with absolute accuracy, however physics models 452 00:40:05,940 --> 00:40:11,640 and known measurements of radioactivity comparing airburst fused nuclear detonations, it's 453 00:40:11,640 --> 00:40:19,000 estimated that the Chernobyl incident released some 400 times more radioactive material than 454 00:40:19,000 --> 00:40:24,760 the bombing of both Hiroshima and Nagasaki at the end of the Second World War. 455 00:40:24,760 --> 00:40:30,360 100,000 square kilometers of land was significantly contaminated with fallout. 456 00:40:30,360 --> 00:40:31,880 The worst hit regions? 457 00:40:31,880 --> 00:40:35,000 Belarus, Ukraine and Russia. 458 00:40:35,000 --> 00:40:40,480 The Soviet Union claimed that they had spent $18B USD at the time in 1988 459 00:40:40,480 --> 00:40:45,440 on containment and decontamination as a result of the incident. 460 00:40:45,440 --> 00:40:52,920 In Belarus, the total cost between 1986 and 2005 was estimated all inclusively at a staggering 461 00:40:52,920 --> 00:41:01,120 $235B USD in total, factoring in loss of agriculture, compensation claims, 462 00:41:01,120 --> 00:41:04,760 containment, evacuation and much more. 463 00:41:04,760 --> 00:41:10,280 Interestingly, the incident forged a much closer tie between the United States and the 464 00:41:10,280 --> 00:41:17,000 Soviet Union and played a key role in the dissolution of the Soviet Union in 1991, five 465 00:41:17,000 --> 00:41:19,040 years later. 466 00:41:19,040 --> 00:41:21,600 So what do we conclude from this? 467 00:41:21,600 --> 00:41:28,760 Personally, when I was 9 years old at the time, I vividly remember watching the television 468 00:41:28,760 --> 00:41:36,080 news with a radiation/radioactivity symbol showing a cloud all over Europe. 469 00:41:36,080 --> 00:41:39,640 I was terrified it would spread through the world and we'd all become sick and die, 470 00:41:39,640 --> 00:41:43,360 the sort of thing that makes an impression on a child I suppose. 471 00:41:43,360 --> 00:41:48,840 There's several learnings about the RBMK reactor design that have since been addressed 472 00:41:48,840 --> 00:41:55,800 by significant retrofitting and the remaining operational RBMKs in Russia are better for that. 473 00:41:55,800 --> 00:42:02,760 But rather than explore those things, considering there's a dwindling number of active RBMKs 474 00:42:02,760 --> 00:42:08,360 using this design left in operation anymore, let's focus on two other points instead. 475 00:42:08,360 --> 00:42:13,480 An operator display that showed the operator the currently calculated ORM based on the 476 00:42:13,480 --> 00:42:17,960 reactor core configuration would have provided additional information to inform their decision. 477 00:42:17,960 --> 00:42:22,300 Without that key stability metric clear front and center for the operator they 478 00:42:22,300 --> 00:42:25,900 relied on their own mental map and understanding and training of what was 479 00:42:25,900 --> 00:42:31,860 likely to be stable versus what wasn't. If abnormal operational steps for any 480 00:42:31,860 --> 00:42:36,900 plant that you're operating are planned but not essential, if they slip in time 481 00:42:36,900 --> 00:42:46,220 due to unforeseen circumstances, stop. Just stop. You have to reassess if it's 482 00:42:46,220 --> 00:42:52,880 still safe to execute the job, because time changes risk. 483 00:42:52,880 --> 00:42:59,400 Be aware of your biases as well, knowing that just because nothing happened yesterday, and 484 00:42:59,400 --> 00:43:05,720 the day before, and the day before that, doesn't mean it can't happen today. 485 00:43:05,720 --> 00:43:13,920 That attitude, unchecked, leads to complacency, and complacency leads to incidents. 486 00:43:13,920 --> 00:43:19,360 But finally the problem lies with nuclear fission as an energy source. 487 00:43:19,360 --> 00:43:24,720 The RBMK design allowed for larger reactor cores for less money but at the expense of 488 00:43:24,720 --> 00:43:28,760 their stability and overall safety. 489 00:43:28,760 --> 00:43:35,640 Given the Chernobyl incident and its cost to both human life, plants, animals, agriculture 490 00:43:35,640 --> 00:43:42,720 and the staggering amounts of money to contain the radioactive fallout, can you really justify 491 00:43:42,720 --> 00:43:49,200 saving some money on your reactor design? If you're going to build yourself an atomic bomb 492 00:43:49,200 --> 00:43:55,200 in super slow motion, otherwise known as a nuclear fission reactor, you'd better design it 493 00:43:55,200 --> 00:44:01,440 to be as stable as possible with as many fail-safes as possible too. Train your people 494 00:44:01,440 --> 00:44:06,960 properly, share when incidents and learnings occur to prevent the next incident. 495 00:44:10,800 --> 00:44:17,840 As of the time of recording, there are about 450 nuclear power stations operating globally, 496 00:44:17,840 --> 00:44:21,280 with 50 new reactors currently under construction primarily in China. 497 00:44:21,280 --> 00:44:29,040 The estimated nuclear capacity growth is about 25% between 2015 and 2040, 498 00:44:29,040 --> 00:44:34,320 and it's driven by a fear of Carbon as well as simple economics. 499 00:44:34,320 --> 00:44:40,320 None of the new reactors being built are RBMKs, so I suppose that's something. 500 00:44:40,320 --> 00:44:48,600 But what worries me more though is that between Three Mile Island, Chernobyl and Fukushima, 501 00:44:48,600 --> 00:44:54,960 people are still betting that nuclear fission electricity generation is a better option 502 00:44:54,960 --> 00:45:01,360 than the alternatives despite these incidents and despite the risk. 503 00:45:01,360 --> 00:45:08,400 And with these incidents so far showing just how bad it can be when they go wrong, is that 504 00:45:08,400 --> 00:45:18,480 really the right decision? Is that the right way to go? Is it really worth it? I just don't 505 00:45:18,480 --> 00:45:22,200 get it. 506 00:45:22,200 --> 00:45:26,440 If you're enjoying Causality and want to support the show, you can. Like some of our backers, 507 00:45:26,440 --> 00:45:30,960 Carsten Hansen and John Whitlow. They, and many others, are patrons of the show via Patreon, 508 00:45:30,960 --> 00:45:36,360 and you can find it at https://patreon.com/johnchidgey (all one word). Patron rewards include a 509 00:45:36,360 --> 00:45:44,360 named thank you on the website, a named thank you at the end of episodes, access to pages of raw show notes, as well as ad-free, high-quality releases of every episode. 510 00:45:44,360 --> 00:45:50,360 So if you'd like to contribute something, anything at all, there's lots of great rewards, and beyond that, it's all very much appreciated. 511 00:45:50,360 --> 00:46:02,360 Causality is part of the Engineered Network, and you can find it at https://engineered.network/, and you can find me at Mastodon @chidgey@engineered.space, or the network on Twitter @Engineered_Net. 512 00:46:02,360 --> 00:46:04,360 This was Causality. 513 00:46:04,360 --> 00:46:11,360 I'm John Chidgey. Thanks so much for listening. 514 00:46:11,360 --> 00:47:05,880 [Music]