Chimgu nuclear accident
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 Satellite image of the Chimgu Nuclear Power Plant before the accident. From left to right: Reactors 1, 2, 3, and 4 (under construction). | |
| Date | 4 April 2003 |
|---|---|
| Location | Chimgu County, Chimchŏn Prefecture, Gangwŏn Province, Menghe |
| Outcome | INES Level 6 (serious accident) |
| Deaths | 364 |
The Chimgu nuclear accident, also known as the Chimgu disaster, was a nuclear accident that occurred at the Chimgu Nuclear Power Plant, located in Chimgu County, a part of Chimchŏn Prefecture (today Yŏng'an Municipality) in Gangwŏn Province, Menghe on April 3rd, 2003. It consisted of a partial nuclear meltdown in the Number 3 reactor building, brought on by a loss-of-coolant accident which resulted from a broken relief valve and several faulty pressure sensors. It is classified as a "serious accident," with a score of 6 on the International Nuclear Event Scale.
Subsequent investigations concluded that many of the problems leading up to the accident could be traced back to cost-cutting measures imposed during the construction of the Chimgu Nuclear Plant, including the installation of outdated electronic equipment and the omission of redundant safety systems. Workers at the plant were given insufficient training on how to handle a loss-of-coolant accident, and poor decisions in the first two hours after the accident intensified the problem. Human error also compounded the initial recovery effort, as the Gangwŏn Provincial Government, and later the Menghean central government, attempted to conceal the severity of the accident from the general public.
The accident resulted in three separate releases of radioactive material beyond the containment chamber. The first was a venting of contaminated coolant steam into the atmosphere as the incident was in progress. The second was a hydrogen explosion inside the Number 3 containment unit, which released radioactive gases but did not expose the core. The third was a continuous dumping of coolant water from the reactor facility into the Chim river, which empties into the Meng river and from there runs through several major population centers. On April 10th, the authorities imposed a 10-kilometer exclusion zone around the nuclear plant, and ordered that crops and livestock in the downwind area be destroyed.
Estimates of the death toll vary. Official state sources report that two plant workers and one emergency worker died of radiation exposure, with no statistically significant increase in cancer or birth defects downstream or downwind. Unofficial estimates place the number of radiation-related deaths as high as 200,000, though there is extensive debate over how to distinguish Chimgu-related cancers from cancers due to industrial pollution, also high in the area.
Background
Construction
Construction work on the Chimgu Nuclear Power Plant (침구 원자 력발 전소 / 沈溝原子力發展所, Chimgu Wŏnja Ryŏkbal Jŏnso) began on September 9th, 1994, as part of the Second New Five-Year Plan. The plant was commissioned on February 3rd, 1999, close to a year ahead of schedule. It was Menghe's sixth nuclear power plant built for the purpose of generating electricity for civilian needs, and the third to be opened after the Decembrist Revolution. Five more plants were still under construction at the time of the accident, part of a broad state-led campaign to expand the country's nuclear power sector.
As the province's cadre promotion system placed a strong emphasis on economic growth and infrastructure expansion, officials overseeing the plant's construction had strong incentives to complete the project below budget and ahead of schedule. This led to a number of cost-cutting measures which would prove disastrous in the future. Many parts were sourced from the lowest bidder, leading to a heavy reliance on small private enterprises with unscrupulous records. Economic growth targets also led officials to favor bidders from Gangwŏn province or from Chimgu county itself, even where better-quality foreign equipment was available. Migrant laborers hired for construction had little experience in reactor engineering, and worked exhausting 12-hour shifts with minimal breaks.
There were also ample opportunities for corruption. Ri U-hyŏn, the Party Secretary of Chimchŏn Prefecture and future Party Secretary of Gangwŏn Province, awarded the contract for the site to the state-owned Yŏng'an Oho Construction Company, which was run by his cousin. The company had no prior experience designing and building nuclear power plants. Oho Construction also bribed inspectors from the national Nuclear Regulatory Commission, offering them large sums of money to expedite the approval process. Similarly, many staff positions at the plant were filled through family and school-network channels, and in a few cases qualification documents were forged or altered in order to ensure that the employees held the necessary qualifications.
In a final effort to bring the plant online ahead of schedule, the facility manager, Yun Jae-sŏng, ordered that some of the pre-activation safety tests and employee drills be replaced by a series of on-paper exercises simulating equipment failure scenarios. Ironically, the engineer leading these exercises, Bae Chang-min, realized that the lack of redundancy in coolant systems could trigger a loss-of-coolant accident and meltdown, but Yun sealed his report in a file drawer and declared the facility safe for operation.
Layout of the plant
The Chimgu Nuclear Power Plant used a conventional pressurized water reactor design, the most popular design for civilian nuclear plants. A "primary loop" of water circulates directly through the reactor core, where it acts as a neutron moderator and coolant. Hot, pressurized water is drawn from the core into a steam generator, where it transfers its heat to water flowing in a "secondary loop." This water, heated into pressurized steam, powers a turbine, which generates electricity. Steam from the turbine flows through a condenser, where it is cooled through heat transfer to water in the "tertiary loop." This water does not enter the reactor chamber itself, and may be safely vented from cooling towers as part of the plant's regular operation.
An important consideration in such a design is that the water in the primary loop must be kept circulating and under pressure at all times. If pressure falls, or if circulation stops, the water may boil, creating corrosive steam bubbles inside the reactor core itself. The narrow pipes inside the heat exchanges must also be kept free from blockage and corrosion, which could interrupt the regular flow of water. In the case of Chimgu, the plant's main water source was the mineral-rich Chim river, which flows southwest from the Chŏnsan mountains before joining the Meng river in southern Gyŏngnam province. As such, the purification of the water depended on a set of condensate polishers, thin polymer-mesh filters designed to keep the water in the secondary loop at a high level of purity.
At the time of the accident, the Chimgu Nuclear Plant had a total of four reactors. Reactor 1 began operation in 1999, Reactor 2 in 2001, and Reactor 3 in 2003. The fourth reactor had been completed, but it was not yet operational, and was scheduled to come online within 18 months. All reactors used the same fundamental design, and each was hooked up to two turbines, numbered 1 through 6.
Technical problems at Number 3 Reactor
The Number 3 Reactor came online on February 14th, 2003, and had been fully operational for less than two months at the time of the accident. During this time, the engineering team had already become aware of a few problems. The Number 5 turbine hooked up to the reactor was observed to exhibit unusually high levels of shaking and knocking during operation, particularly when running at close to full capacity. This was most likely the result of poor tolerance levels between parts, though the exact cause remains unknown.
Full replacement of the turbine was expensive, and would force the plant to run at reduced capacity until reconstruction was finished. It would also place a negative mark on the construction team's performance assessment. As such, Yun Jae-sŏng ordered the work teams at Reactor 3 to keep the Number 5 turbine running at reduced capacity until their on-site engineers could determine the source of the problem.
Accident
The secondary loop shuts down
On April 3rd, 2003, at around 10:00 AM, knocking in the Number 5 turbine abruptly increased, possibly as a result of a loose part coming detached. Vibrations from the turbine traveled up and down the secondary coolant loop, setting off an emergency safety valve which tripped the turbine at 10:04. Under normal circumstances, a turbine trip should re-route the turbine steam feed directly into the condenser, continuing circulation in the secondary loop but cutting off the flow through the turbine itself. In this case, however, the pipe linking the turbine to the condenser violently ruptured, possibly due to faulty components, a valve left open, or prior damage from the vibration surge nearby. Compressed steam and boiling water surged into the turbine room, damaging pressure sensors and short-circuiting electrical lines. This caused the main pump and condenser pump shut off.
In the control room, the reactor operators received an alert that pressure in the return side of the secondary loop was falling rapidly, and noticed that the main pumps were not operational. Yun Jae-sŏng, who was present at the time, ordered them to turn on the backup pumps to keep the secondary loop flowing. The wiring to the backup pumps, however, had also been damaged in the turbine trip, and electronic commands failed to activate them. Yun dispatched an engineer to turn the valves by hand.
The relief valve fails
Because secondary-loop water was no longer flowing into the steam generator, the primary loop of reactor coolant no longer had a way of transferring heat out of the system. The control team responded by putting the Number 3 reactor into emergency shutdown, inserting all control rods to stop the reaction. Even with all control rods inserted, however, the fuel rods still generated a large amount of decay heat. Pressure and temperature in the primary loop continued to climb as a result.
At 10:08, the pilot-operated relief valve attached to the primary loop pressurizer automatically blew open to relieve the buildup of pressure. Radioactive steam from the primary loop was vented into the reactor building, though it did not escape outside into the environment. The pilot-operated relief valve should have closed automatically after pressure fell back within acceptable levels, but due to a mechanical failure, it remained stuck in the open position. Because the solenoid used to pull open the valve was set to the "off" position, the workers in the control room mistakenly believed that the valve was closed.
Shortly after this time, the engineer sent to open the valves to the emergency pumps returned to the control room, where he reported that the valves were inaccessible because a ruptured pipe was venting high-pressure steam. At this point, the reactor engineers became fixated on the question of how to access the emergency pumps in the secondary loop. Complicating any response, any new water pumped into the system would have to pass through either the turbines or the ruptured diverter pipe. None of the workers present at the time had trained for this particular scenario, and there was heated disagreement over how to proceed. In the midst of this debate, one of the workers noticed that pressure in the primary loop was falling, and brought this to Yun's attention; Yun attributed this report to faulty equipment, noting that the relief valve was shut and the temperature was still high.
At around 10:15, the pressurizer relief tank hooked up to the stuck-open relief valve overflowed, dumping radioactive primary loop water onto the floor of the containment building. From there, it flowed into a sump pit on the floor of the containment building, setting off an alarm at 10:16. Despite indications of rising temperature and pressure in the containment building, Yun remained adamant that the pilot-operated relief valve was closed, and attributed the alarms to an overflow out of the flooded turbine room. Automatic sump pumps began pumping water from both buildings into a holding tank outside the containment building, transferring radioactive coolant into the open.
Depressurization and partial meltdown
Meanwhile, the constant leakage of coolant worsened conditions inside the already overheated reactor. As pressure fell and temperature rose, the primary loop water began to boil, creating steam bubbles inside the reactor and the coolant pipes near it. Steam bubbles also interfered in the flow of coolant into the reactor itself, causing a backlog of water inside the pressurizer. Yun Jae-sŏng and the reactor engineer team interpreted the rising coolant levels in the pressurizer as further evidence that the relief valve was closed, even as alarms linked to the sump pump continued to sound. At this point, Yun was more concerned that coolant levels in the pressurizer were too high, and he ordered that the backup heat exchange be shut off to create more steam in the system. In reality, the growing steam voids inside the reactor had already left large sections of the fuel rods exposed.
The temperature of the primary coolant steadily increased over the course of the next hour, until the main reactor coolant pumps were pumping a steam-water mixture rather than pressurized water alone. This caused dangerous levels of cavitation, sending all four pumps into emergency shutdown between 11:24 and 11:28. Yun again dismissed the seriousness of the issue, confident that natural convection would continue to circulate the coolant until the pumps could be restored.
In fact, the steam voids inside the reactor quickly brought primary coolant circulation to a halt. This accelerated the boiling process, as fresh water was no longer being drawn into the reactor. Large sections of the fuel rods were now exposed, and their zircalloy cladding began to react with the high-pressure steam, in a chemical reaction that produced additional heat. Once the cladding melted off, the fuel pellets inside the rods were exposed, releasing particles of radioactive material into the coolant water leaving the reactor chamber. The melting reaction also produced large quantities of flammable hydrogen gas, which along with the radioactive material was channeled into the primary loop and vented out of the stuck-open relief valve into the containment building.
It took another hour for the vented primary coolant water to reach radiation detectors in the containment building, setting off an alarm at 12:41. Distrusting the sensors, Yun sent an engineer to the containment building to manually check the radiation levels. The engineer returned ten minutes later reporting that coolant water was pooled on the floor, and radiation levels in the spilled coolant were 400 times greater than normal. This was the first clear evidence that the cladding inside the reactor had degraded catastrophically.
Realizing that the high temperature readings in the tailpipe of the pilot-operated relief valve were not in fact the result of faulty equipment, the reactor operators activated a backup valve to cut the flow of coolant out of the system. By this time, the relief valve had been open for two hours and 47 minutes, and 150,000 liters of radioactive coolant had been released from the primary loop. The containment building was highly contaminated, and the sump pumps had drawn contaminated water into a holding tank which lacked proper radiation shielding. Pressure inside the containment building itself had also reached dangerous levels, as a result of the venting of steam and hydrogen gas into the reinforced space. Fearing a rupture or explosion, Yun ordered the venting of gases from the containment building into the atmosphere - the first release of radioactive material to result from the accident.
Response
Plant management alerts state authorities
Once the scale of the problems within the plant became clear, Yun Jae-sŏng contacted Ri U-hyŏn, the Party Secretary of Gangwŏn Province, and requested that he come to the plant immediately. The provincial government building in central Yŏng'an was a mere 30-minute drive away, and Ri arrived at 1:24. Inside a sealed room in the administration building, Yun explained the full scope of the accident as he knew it so far, including the unauthorized venting of coolant gases at 12:58. Ri had observed this during his drive in, as a white plume of steam issuing upward from the Number 3 reactor building.
Both Ri and Yun were firmly aware that the consequences of a severe accident under their watch could mean expulsion from the Party, or possibly execution. As part of the ongoing Disciplined Society Campaign, a number of other high-level officials had been sentenced to death for corruption and negligence which resulted in loss of life, and the chain of errors leading up to Reactor 3's partial meltdown could only be attributed to human error and poor quality control during construction. Yun decided to reach out to the national leadership directly, hoping that he could convince his superiors to keep the accident a secret and thus avoid a high-publicity trial and dismissal.
At 2:07, Ri U-hyŏn made a direct call to Choe Sŭng-min on the secure phone line from his office in Yŏng'an. He explained that the primary and secondary coolant loops at the Chimgu Nucelar Plant had failed, and that the reactor was unstable. He did not, however, mention the fact that the reactor was undergoing a meltdown, and in testimony he claimed that he was still uncertain whether a meltdown was in progress. He also left out the release of radioactive material, instead assuring the Chairman that all contamination was limited to the reactor containment building. Choe, still in Donggyŏng, called an emergency meeting of the Standing Committee of the Supreme Council, to brief his peers on the situation. Ri attended the meeting remotely. As Ri predicted, Choe ordered that the events at the Chimgu Nuclear Plant be kept tightly classified, as news of an ongoing nuclear accident could trigger panic and chaos in the nearby city of Yŏng'an. Choe also feared that news of the accident could damage Menghe's emerging nuclear industry and its international prestige on the world stage. As such, there was no public announcement that an accident had taken place, and no effort to evacuate the area.
Stabilization of the reactor
Immediately after concluding its special session, the Supreme Council dispatched an emergency response team of military construction workers to Chimgu county to restore the flow of coolant and maintain order. The general public was told that the movement of vehicles to the site was part of a safety drill to demonstrate the country's emergency readiness. The soldiers, too, were briefed on a need-to-know basis, and none were told that the reactor core was partially melted.
The main priority of the emergency response team was to replenish the primary and secondary loops with water and restore the flow of coolant through the overheating reactor core. Manual readings from the reactor thermocouples and a timeline check of the open valve had by now confirmed the occurrence of a loss-of-coolant accident. Yet because the secondary loop was still ruptured, this meant that until it could be restored, steam from the primary loop would have to be periodically drawn out of the system and replaced with cold water. This procedure helped stabilize the system, preventing the fuel from melting through the base of the reactor pressure vessel, but it also created a large buildup of wastewater contaminated with particles of nuclear fuel.
By the time the afternoon shift rotated out at 10:00 PM, the temperature in the core had already started to decline, but the engineering team was making little progress in repairing the damaged section of the secondary loop. Given the severity of the damage to the reinforced piping, and the extent of the damage to the pumping systems, it would take several days to fully restore the secondary loop to normal operation. During that time, the plant would continue to accumulate radioactive wastewater from the primary loop.
Hydrogen explosion
Although the temperature in the Number 3 reactor was no longer rising, it was still far above normal levels, and continued to produce steam bubbles in the coolant water. And as at the time of the accident, the chemical reaction between the steam bubbles and the degraded cladding produced a buildup of hydrogen gas inside the reactor pressure vessel. Because there was no oxygen inside the reactor pressure vessel, the engineering team initially allowed the buildup to continue, hoping to draw it down with a catalytic recombiner once the right equipment arrived.
The hydrogen bubble exploded at 3:52 AM on April 6th, two days after the accident began. Fifteen repair workers were injured in the blast, two of them fatally. The explosion produced a crack in the reactor pressure vessel, and spread to a second hydrogen bubble which had formed in the containment building, collapsing a portion of the roof. This began a second release of radioactive material into the atmosphere, as steam mixed with reactor debris was expelled upward through the containment vessel and into the nighttime sky. When the sun rose over the plant, a plume of smoke was clearly visible in the predawn light.
Monitoring of radiation levels
Shortly after the hydrogen explosion, plant staff contacted Yun and Ri, who made another confidential call to Choe Sŭng-min. Once again, Ri U-hyŏn reassured Choe that radiation levels were probably too low to have any lasting health effects, and Choe responded by agreeing that the main priority should be to prevent a general panic. As such, there was no general announcement that a disaster was underway, and no move to evacuate areas around the plant.
When Choe presented this decision at a special meeting of the Supreme Council later in the morning, the Minister of Public Health, Yŏm Gi-ha, objected, saying that if the hydrogen explosion had indeed fractured the core, an evacuation was urgently necessary. Prevailing winds over Chimgu at this time of year were blowing to the southwest, and could carry radioactive material from the nuclear plant to Yŏng'an, a city of 1.2 million people. Additionally, the planting season was about to begin, and farmers throughout the area were plowing their fields in preparation. If radioactive isotopes settled on the ground, they could contaminate crops and accumulate in livestock, widening the impact beyond the area. Once again, Choe responded with skepticism, confident in Ri's report that the radiation release was minimal. His response stressed the possibility that overly cautious farmers would destroy their crops or kill off their livestock, setting off another economic crisis or another famine. Finally, the Supreme Council reached a compromise, under which personnel from the military construction team would measure radiation levels outside the Chimgu Nuclear Power Plant in order to determine whether there was a risk to the public, and only evacuate if radiation levels were substantially above acceptable limits.
It took two days for the radiation-monitoring teams to complete a full survey of radiation levels around the plant. The results, presented to the Supreme Council on the evening of April 8th, revealed sharply elevated levels of reactor by-product isotopes in the area downwind of the plant, contradicting Ri's and Yun's reports that the release had been minimal. During this time, the wind had carried small concentrations of released gases to Maverica, where they were picked up at stations originally set up to monitor Menghe's nuclear weapons program. International news media were questioning whether Menghe had experienced a nuclear accident, and some of these reports were starting to break through the country's internet censorship. The new radiation findings, paired with pressure from foreign diplomats, pushed Choe Sŭng-min to change course on the question of publicity.
Public announcement and evacuation
On the morning of April 9th, 2003, the MCTV News Network formally announced that the Chimgu Nuclear Power Plant had experienced a leak in one of its coolant systems, resulting in a release of radioactive material into the air. The reporters described the situation within the reactor as stable, and made no mention of the partial meltdown. This was the first public admission that an accident had taken place, and already five days had passed since the rupture of the secondary coolant loop.
As part of the same announcement, the Menghean government ordered a mandatory evacuation of all residents living within a 10-kilometer radius of the Chimgu Nuclear Power Plant. This area contained roughly 40,000 people. A column of express buses and military trucks, gathered together during the night of the 8th-9th, assisted in the evacuation, bringing people to temporary relief camps stationed outside the perimeter. Residents were told that the evacuation was only temporary, and that they could return to their homes once the situation was fully stable. This would prove overly optimistic.
Within the Supreme Council, Minister of Public Health Yŏm Gi-ha again criticized the evacuation, arguing that the 10-kilometer limit was too conservative. Elevated levels of radioactive isotopes had been detected at much greater distances, particularly to the west, where the prevailing winds had carried them. Many of the temporary refugee centers, which lacked the necessary facilities for long-term residence, were still located within this moderate-exposure zone. Worse still, the status of the Number 3 reactor was still not entirely clear, and if its contents were to melt through the base of the reactor pressure vessel and into the groundwater, the catastrophic explosion and contamination would affect a much wider area.
On April 10th, as new data on radiation levels flowed in, the central government announced the creation of a new "Advisory Evacuation Area" extending 50 kilometers away from the Chimgu Nuclear Power Plant, but only across a southwestern arc. Pregnant women, children below preschool age, and adults in poor health were advised to leave this area if possible, and remain outside it until the reactor was fully stabilized. This time, there was no coordinated evacuation effort, and the movement of buses through the area unfolded over a longer period of time. This zone had an estimated population of 262,000 people, far more than what the relief agencies were equipped to resettle. The government also declared that residents in this area should not plant crops, and should exclusively feed livestock from covered feed stores, until survey teams confirmed that each farm individually was below acceptable radiation levels. As this was a predominantly poor and rural area of the country, still mainly dependent on agriculture, the ban on planting hit the local economy hard. Many households ignored it and planted crops anyway, especially as months dragged by and the radiation-survey effort remained incomplete.
The mandatory evacuation area was extended again on April 15th, after studies of wind patterns and particle dispersal confirmed initial predictions that the plume of contaminated air would drift southwest. The new mandatory evacuation zone had a 10-kilometer radius to the northeast, northwest, and southeast, but in the broad southwest quadrant it extended out 20 to kilometers. The new area contained some 20,000 residents, and covered much of neighboring Rogŭp county. As in the original mandatory evacuation zone, the government requisitioned buses and Army trucks to bring residents to camps outside the perimeter, stating that they would be allowed to return when radiation levels returned to normal.
Release of contaminated water
In addition to the releases of contaminated steam, several releases of contaminated water took place during the accident and in its immediate aftermath. The first was the rapid release of water from a ruptured pipe in the secondary loop. This water pooled in the basement of the turbine building, where the backup pumps and generators were located. In order to bring the backup pumps on line, emergency workers pumped this water from the basement on the first day of the emergency, dumping it directly into the Chim river. The secondary-loop water was only slightly radioactive, as it did not come into direct contact with the primary loop water but only flowed past it on the other side of a heat exchanger; even so, under normal conditions it would not be released without prior treatment.
The more heavily contaminated water was initially contained on site. During the loss-of-coolant accident, highly contaminated primary loop water was collected in a holding pool after being drawn out of the drainage sump in the containment chamber. This pool was not intended to hold contaminated water, only freshwater leaks and rainwater intrusions. It had a limited capacity and it was not properly shielded. Subsequently, emergency workers pumped large volumes of unfiltered river water through the core of the Number 3 reactor in an effort to cool it to safe levels. As the filtration and heat exchange systems were still offline, much of this water was either vented as steam or collected in other on-site containment pools. As the cooling continued, these pools began to fill beyond their normal capacity.
On April 16th, at about 3:00 PM, part of a retaining wall around a drainage water holding pool collapsed, sending the contents of the pool spilling directly into the Chim river. From there, the contaminated river would flow southeast through Yŏng'an, then into the Meng river, the largest river in Menghe. Its course there would bring it through Hwasŏng, Menghe's third-largest city at the time, followed by Sangha, Chŏnjin, Onju, Myŏng'an, and Chanam at the river mouth. This time, the government issued an immediate alert to the affected areas, advising residents to adopt the same measures recommended during an industrial waste spill. Residents were forbidden from drinking, bathing, fishing, or swimming in the water, and were not to use it for irrigation. Any canals linking the Meng river to irrigated farmland were to be closed, and any fish farms in the river's course would be destroyed. Fresh bottled water was imported from other parts of the country in a massive, organized relief effort, until the water filtration plants confirmed that there were no longer radioactive isotopes in the water.
This announcement, however, came too late for the areas immediately downstream of the plant, as news first had to be approved by the central government before it was made public. Large numbers of rice farms, already flooded for the growing season, were contaminated, and emergency response workers were sent in to check radiation levels and occupy the land for decontamination.
The drinking water shutoffs in Hwasŏng and Chŏnjin also proved contentious, as relief water took time to arrive and was not sufficient for bathing and cleaning. Further unrest emerged from rumors that trace levels of radioactive isotopes were still detected in the tapwater after it was approved for use again. A number of foreign governments advised nationals living in the lower Meng river basin to move elsewhere until the area was confirmed as clean by independent experts, spurring an outflow of foreign businesspeople and striking another blow to the local economy.
Aftermath
Death toll
The exact death toll from the Chimgu nuclear accident is still heavily disputed, and much of this dispute is political. The General-Directorate for Energy, under the Ministry of Economic Development, has a strong incentive to expand the country's nuclear power sector, and its detractors have accused it of covering up the true death toll in favor of its own less severe statistics. Government officials contend that the higher death figures are the product of biased science and anti-nuclear alarmism, and have refused to allow any independent studies of radiation levels and their health effects.
Other issues stem from the question of how to set the baseline for the number of deaths. Apart from the handful of high-exposure cases around the plant itself, which were well-documented and acknowledged by the Menghean government, most radiation exposure would have occurred in moderate doses, through the consumption of air, food, and water contaminated by radioactive material. Cancer from these sources could take several years to be diagnosed, and even then might not cause death until several years later. Adding to measurement difficulties, the Chim river also experiences high water pollution from non-radioactive industrial waste, which in combination with air pollution has contributed to an elevated baseline rate of cancer in southeast Gangwŏn Province. Many working-age adults from Chimgu county also migrated to Menghe's coastal cities to seek work, often in workplaces with lax safety standards. Finally, news of the radiation leak led individuals in the Chimgu area to consult oncologists and report suspicious symptoms at above-average rates, resulting in a rise in the share of cancer cases which are officially diagnosed. All of these problems have contributed to an elevated background level of reported cancer and illness, making it hard to distinguish how much of that increase stems from the radiation releases themselves.
Fifteen people are known to have died as a direct result of the accident, including non-radiation-related injuries. These figures are not disputed, though sources differ on the number of subsequent deaths in the military construction units.
- 1 plant worker died prematurely (in 2007) due to exposure to irradiated coolant
- 2 construction-battalion workers died from injuries sustained during the hydrogen explosion
- 12 construction-battalion workers died prematurely (up to 2010) due to exposure during cleanup work
Estimates of the indirect death toll vary widely, depending on the methodology used. The Menghean Ministry of Public Health estimates that by 2018, a total of 350 civilians (apart from plant workers and emergency workers) had died from medical conditions which could clearly be traced to the radiation release. Independent estimates tend to run higher. A Septentrion Health Organization study using a linear no-threshold model projected that a total of 12,000 people would die prematurely as a result of the radiation release, but other experts have challenged the validity of the linear no-threshold model in assessing the effects of low-rate, long-term exposure. The highest estimate, from the League of Scientists Against Nuclear Power, placed the number of deaths at 200,000, including premature deaths which had not yet taken place but would take place before the end of the century. Critics contend that the League deliberately inflated this estimated through a number of questionable statistical practices, and that the figure includes a large number of deaths which cannot be attributed to radiation exposure.
Economic and psychological effects
By some estimates, the greatest harm from the Chimgu nuclear accident stemmed from its economic and psychological fallout. Gangwŏn Province was already a marginalized part of Menghe, which had not benefited as much from the Menghean economic miracle due to its distance from the trade-linked coastline. The nuclear accident and recovery effort further impoverished this area of the country.
During the mandatory evacuation of the 10-kilometer zone, residents were not given time to gather their belongings, and most escaped with only a suitcase or bag. The initial announcement stated that the evacuation would only be temporary, but in 2005 the emergency response team clarified that the exclusion zones would not be approved for full-time residence and agriculture until 2023 or later. The goods and property left behind thus represent an annual net loss to the economy, and a one-time loss of wealth for families already living at the margin of dollar-a-day poverty.
Some 70% of households in the mandatory and advisory evacuation zones depended on agriculture as their main source of livelihood, and the rate was higher in some of the areas further downwind. As a result of the temporary ban on farming downwind of the gas releases, and the order that irrigated farms be decontaminated downstream of the water releases, many non-evacuated households missed the spring planting season and could not produce a harvest that year. Because the central government organized a major food shipment operation, there was no famine in the area, but the short-term damage to agriculture drove up food prices and undercut incomes.
The evacuee camps themselves were only built to support a temporary population, and lacked adequate facilities for full-time residence. The provincial government shut down several of these camps following reports of crime and unsanitary conditions. Yet evacuees were not given an expedited option for changing their household registration, and still faced sub-standard treatment and services if they sought residence outside of Chimgu county or Rogŭp county. Some households were able to obtain new land in other parts of their registered counties; others joined Menghe's large "floating population" of migrant workers.
Those who left the area faced discrimination in other parts of the country. Many employers refused to hire workers from Chimgu and Rogŭp counties, based on unscientific rumors that their radiation exposure could spread to others through contact. Those who did find work were mainly given dirty, dangerous, low-paying jobs, contributing to the gap in mortality rates with the rest of the population.
A 2013 study by the Ministry of Public Health concluded that even with wide margins of error, the number of depression-related deaths - suicides, drug overdoses, and deaths due to smoking and alcoholism - far outweighed the number of radiation-related deaths among the population of Chimgu evacuees. Nuclear power advocates have cited this study as evidence that the mandatory evacuation was, in fact, more harmful than the radiation release, and that nuclear power more broadly is safer than the various fossil fuel alternatives.
Political consequences
An official investigation by the Menghean government found that Yun Jae-sŏng was guilty of running the reactor in an unsafe manner, ignoring signs that the coolant loop was ruptured, interfering in the reactor control staff's efforts to control the breach, and conspiring to conceal the incident from the central government. Ri U-hyŏn was charged with conspiring to conceal the incident from the central government and allowing gross violations of safety guidelines during the plant's construction. Ri Dong-ha, the chief executive officer of the Yŏng'an Oho Construction firm, was charged with safety violations in plant design. All three men were sentenced to death, but Ri U-hyŏn and Ri Dong-ha later had their sentences commuted to life in prison. Yun was executed in 2004, shortly after his trial.
The political aftershocks in the central government were less visible but more profound. Although the official narrative composed after the accident exculpated Choe Sŭng-min of any responsibility, instead blaming Yun and Ri for misleading him about the level of radiation released, the Chairman had in fact played a central role in the initial efforts to suppress public knowledge and delay an evacuation. In combination with the 1999 Menghean financial crisis and the excesses of the Disciplined Society Campaign, these errors tarnished Choe Sŭng-min's aura of good judgment, particularly in the upper levels of government.
Some anonymous insider accounts tell of a secret meeting on April 30th, 2003, in which twelve members of the Supreme Council confronted Choe in his office in the Donggwangsan palace and pressured him to end his centralization of power. Fearing an insider coup, Choe had no choice but to agree.
While this exact meeting is not officially documented, it is generally agreed that 2003 marked a turning point in Choe's centralization of power. Although he held on to his three official posts, he took a less active role in policymaking over the next few years, delegating more authority to the ministry heads and the Party apparatus. His personality cult also grew more subdued, and purges of subordinate party members became less frequent.
Consequences for nuclear power
Several days after the disaster became public, on April 11th, the General-Directorate for Energy under the Ministry of Economic Planning ordered all operational nuclear plants in the country to reduce their output and run checks of all systems. The other two working reactors at the Chimgu Nuclear Power Plant were temporarily shut down, and all ongoing reactor construction was frozen.
The General-Directorate for Energy then established a special fact-finding commission to review the chain of events leading up to the Chimgu accident and identify corrective measures. The preliminary report, issued in February 2020, contained a scathing indictment of the procurement and design process at Chimgu, and uncovered additional safety violations unrelated to the disaster, including vulnerability to earthquakes and floods. The report also found evidence of bribery and regulatory failure, beyond the levels cited in Yun Jae-sŏng's trial. Based on the contents of the report, the General-Directorate for Energy ordered a new, comprehensive round of inspections at all of Menghe's nuclear power plants, to identify and correct safety issues. When the other two reactors at Chimgu were brought back online in 2007, they had been modified with backup coolant pumps in a hardened building, triple-redundant piping routes for coolant, and new safety valves imported from Dayashina, and the entire structure was given improved structural support. Frozen construction projects were allowed to resume in 2006, under a reshuffled and greatly expanded inspection apparatus which applied higher reliability standards to critical parts.
Given the country's large and growing energy needs, Menghe continued to build new nuclear power plants, and by 2010 all of its reactors present in 2003 were again operational, save for the Number 3 Reactor at Chimgu. The inspection period and five-year new construction freeze did, however, delay the growth of nuclear energy in Menghe, bringing its share of overall energy production below the level that would have otherwise been achieved. Much of that gap was filled by coal. Repeated studies have concluded that the death toll from the Chimgu nuclear accident falls far short of the death toll from pollutants released by Menghean fossil-fuel power plants, which have also faced accusations of poor safety and regulatory capture.
The conflicting demands to balance safety with power generation have led the Menghean government to heavily promote research on safer reactor designs. Menghe is today one of the leading players in the development of Generation IV reactor concepts, particularly molten salt reactors, which offer strong passive nuclear safety protections. All Menghean reactors built after 2010 have used Generation III designs, increasing safety and efficiency compared to previous models, and there are plans to bring the pre-Chimgu Generation II reactors offline before 2030.
Despite a government consensus that the death toll was small and a repeat disaster unlikely, the nuclear accident at Chimgu stirred strong opposition to nuclear energy among the Menghean population. An independent survey conducted in 2005 found that 54% of Menghean citizens believed the country should permanently close its nuclear power plants within the next ten years, and only 29% supported increasing the number of nuclear plants. In the years since the accident, the balance of public opinion has shifted in the direction of favoring nuclear power, but the anti-nuclear movement remains relatively strong. Spontaneous demonstrations outside existing plants and new construction sites were common in the decade after the accident, spurring an increased focus on plant security.
The Menghean Socialist Party remains committed to expanding Menghe's nuclear energy sector, and shows no sign of giving in to public opposition on the issue. Yet much of the opposition is linked to distrust in the government following its handling of the Chimgu accident, including its delay in ordering an evacuation and its initial efforts to cover up the nature of the problem. When a chief researcher in the Menghean Council of Nuclear Scientists dismissed the anti-nuclear movement as driven by radiophobia and pseudoscience, online netizens fiercely criticized his statement as elitist and deceptive.
Critics have also pointed out that most of Menghe's nuclear plants, particularly those ordered after 2006, have been built in rural areas, far from the cities and industrial sites they are meant to serve. This zoning strategy places the burden of disaster risk on communities which are already poor and marginalized, while insulating party elites and wealthy business owners. Defenders of the system argue that the placement of nuclear power plants away from cities reduces the public exposure in the unlikely event of a radiation release.
Anti-nuclear sentiments in Menghe are also rooted in the memory of the Pan-Septentrion War, in which Menghe was subjected to two atomic bombings. Menghe and Dayashina are the only two countries in Septentrion whose civilian populations have suffered nuclear attacks.
Long-term contamination
In 2004, the emergency response team updated its cleanup timetable, stating that the 10-20km mandatory evacuation zone around the Chimgu Nuclear Power Plant would remain off-limits to civilian residents for a period of 20 years. As of 2019, completion of the cleanup effort is scheduled for 2023.
A survey of the evacuated area in 2016 determined that the average radiation exposure for a person living in the mandatory evacuation zone would be approximately 30 nanosieverts per hour above the natural baseline. The average human is exposed to 240 millisieverts per year, or 2.7 nSv/h, from natural background radiation of all types, and thus radiation levels within the exclusion zone are 10% above normal, comparable to the additional cosmic radiation exposure from living at an elevation of 800 meters. This average level will decline further once the cleanup effort is complete.
Radiation levels were highest inside the containment chamber around the Number 3 reactor, as the venting of contaminated steam and the rupture of the reactor pressure vessel both released large amounts of radioactive material. In 2015, it was reported that the containment chamber was still unsafe to enter for more than 30 minutes at a time, and once the reactor core was removed, the cleanup team concluded that it was safer to seal off the building permanently rather than attempting to restore it to regular operation. The water storage pools which stored contaminated water from the containment building sump are also radioactive to this day, and because some of the coolant water seeped into cracks in the concrete base, the cost of digging up the entire concrete basin and shipping it elsewhere for safe disposal was deemed prohibitive. Once the breach to the river Chim was sealed, the water was filtered to extract particles from the reactor core and cladding, and the holding pools were filled in with concrete.
Several studies have examined the lasting effects of radiation releases on food produced in the contaminated area. Sediment immediately downstream of the breach site is 1,000 times more radioactive than sediment 10 kilometers upstream, but the concentration level declines as one moves downriver. Fish caught in Hwasŏng municipality in 2010 had radiation levels 10 times above the normal level, though this is still within the acceptable health limit for seafood. As contaminants tend to accumulate as one moves up the food chain, predatory fish had higher levels of radioactive isotopes, as did bottom-feeders in Yŏng'an municipality. Fish in the Meng river system have been observed with deformities and mutations at substantially above-average rates, but these effects have been traced to the illegal dumping of non-radioactive hazardous waste, and are present in waterways not affected by the release of coolant from the Chimgu site.
Repeated audit studies have found that rice grown in the area downwind of the radiation release no longer has a statistically significant level of radioactive isotopes compared with rice grown in other parts of the country, and the Ministry of Public Health does not regulate crops from Chimgu and Rogŭp counties differently from rice in other parts of the country. Nevertheless, radiophobia and popular superstition remain obstacles to normalization, and crops from southwest Gangwŏn province typically sell at much lower prices.