On April 26, 1986 around 1:23 in the morning, the Chernobyl Power Plant experienced what is now considered the worst nuclear disaster in history. Reactor #4 exploded, releasing massive amounts of radioactive contamination that would ultimately spread to several countries. While there is much debate about the impacts, the magnitude of the effects, and the causes, there is no denying the valuable lessons that can be extracted from the incident.
The incident occurred as the plant was conducting a test to ensure the backup generators could provide sufficient power and maintain cooling water circulation should electrical power be lost. As power to the reactor was reduced, the circulating pump power was reduced, decreasing the water flow rate. This created steam voids in the coolant. Since the reactor had a positive void coefficient (by design), fewer neutrons were being absorbed. The rate of the nuclear chain reaction increased, increasing the energy in the reactor. In response, an emergency shutdown was initiated and the control rods were inserted. This caused an instantaneous power surge as it displaced the moderator (coolant) without adding the intended neutron absorption (due to the steam voids) that likely caused a superheated steam explosion.
The explosion likely damaged fuel channels and the reactor’s cooling equipment, leading to another increase in energy within the reactor and another explosion. This explosion likely caused the catastrophic damage to the reactor, resulting in widespread radioactive fallout and contamination affecting hundreds of thousands. The explosion killed two workers (perhaps three) and more than 100 were hospitalized. Within the first three months, it’s estimated that 28 emergency responders died of acute radiation sickness. And it was only the beginning. It’s estimated that anywhere between 50 to 250 million curies of radioactivity were released into the environment as a result of the incident. Ultimately, thousands of people were exposed to radiation and hundreds of thousands of residents were displaced from their homes. The total financial impact is estimated to be in the hundreds of billions of dollars.
Adapting to a Change in Work Scope (Or in This Case, Not Adapting)
HBO® released the miniseries “Chernobyl” earlier this year, which captured the incident and the response. The following insights are based on the documentary series and the reenactments, so it may not be entirely accurate or thorough, but it does provide insights with broader applications.
So often when we are facilitating incidents, we see that a part of the incident relates to a change in the scope of the work. The change(s) may occur in the environment, tools or even the people involved. Alternatively, there may be a discovery during the job that was unexpected that changes how the job should proceed. When a job is planned a specific way, but a change occurs to the task and the associated plan is not updated, there can be nuclear consequences, as seen at Chernobyl.
For instance, the changes to work scope that stood out to me included: the emergency response, the delay in the test, shift change and the reactor output dropping below 700 thermal megawatts (MWt).
In preparation for the test, the facility realized they were unable to reduce the reactor power to the required test output during the day shift of April 25 because of the power demand, delaying the turbine rundown test several hours. The site had been trying to successfully execute the required test for more than a year so the ~10-hour delay likely did not seem like a significant change or difference. Perhaps the schedule change was not flagged as a concern because this type of change occurs frequently—normalizing the work process deviation. This normalization may create a culture that adapts to change, but to the extent that workers don’t stop to question or consider the consequences of changes.
Unbeknownst to the decision makers, this delay had drastic effects. It pushed the test to the night shift, where one of the operators (in the series) states he had never performed the task before. Furthermore, the test wasn’t communicated to the entire plant, so the unexpected change of plant conditions was not fully understood by all employees. The control room operators were unfamiliar with the turbine rundown test and were provided inadequate, unclear instructions that even had sections crossed out. (These interactions are captured in pages 24 and 25 of the Episode 5 script, which you can see here.) In one scene, Akimov, the shift supervisor, and Toptunov, the senior reactor control chief engineer, try to clarify the instructions:
Akimov: “He says to follow the crossed out instructions.”
Toptunov: “Then why were they crossed out?”
Then Dyatlov, the deputy chief engineer, walked in and insisted the test commence. In the show, Dyatlov doesn’t allow much (if any) opportunity for the employees to ask questions or receive clarifications regarding the test. Dyatlov asks if the employees are ready, when one begins to explain, “I haven’t reviewed—we only just found out we…” and Dyatlov grabs the instructions and throws them toward the employee saying, “There. Review it. Or just do what I tell you. I think even you, as stupid as you are, can manage that.”
After demanding they follow his instructions, the critical test began within five minutes of the shift change.
The Importance of Communicating Concerns
The employees appeared to continue with the task because they were pressured and/or intimidated to get the job done. Realizing this situation is dramatized and may be extreme, we often experience similar situations in our investigations. When talking to employees, it is clear they put pressure on themselves and/or there is perceived pressure from their peers, management or clients. The perception may or may not be valid, however, it’s imperative that the culture in our work environments is such that everyone feels comfortable speaking up when a concern is identified. It’s equally important these concerns are heard. If the risks (consequence x probability) are properly identified, communicated and understood by all, an updated job plan or approach may be developed.
Stopping work to provide and ensure adequate instructions, and checking that the appropriate personnel and equipment functionality were in place to safely conduct the rundown test seem like extremely simple remedies with the benefit of hindsight. Unfortunately, many organizations don’t see the process deviations until they’re too late. Using a case study like Chernobyl can teach us to confront problems before they occur and not rely on hindsight after an incident happens. It shouldn’t take a catastrophic event to adapt work processes. We can often glean this insight from near-miss incidents or effective audits of our work process(es).
With a more thorough understanding and communication of risks associated with specific tasks, especially as change occurs, mitigation strategies may be implemented. As job plans are created, it is vital to talk to those who will be performing and involved in the work, so that clear instruction, effective tools and other task-critical items are developed. In addition, as changes occur in a job or unexpected results are experienced, stop work authority should be comfortably executed by anyone who recognizes a potential concern.
(This is the first in a series of "Avoiding Nuclear Meltdowns" blogs about Chernobyl.)