Part 2 of 3 Parts (Please read Part 1 first)
Some of the problems at the plant included two diesel leaks. The National Commission for Nuclear Safety and Safeguards (CNSNS) stated that the verification of the generator was found be satisfactory. During the first four months of 2020, Unit 2 was in the yellow danger category because this diesel generator was not available. One plant worker said, “Given the speed of contract delivery, contractors came in a hurry, because they were commissioned during refueling. The connection (to the generator) is likely loose.” A group of one hundred and fifty employees led by Hector Lopez Villarreal disagreed with decisions made by plant management.
During normal operation and fueling, the management of the nuclear power plant uses the color monitoring system to indicate the degree of risk anticipated in operating the reactors. This system has been adapted from the standards used by the U.S. Nuclear Regulatory Commission (NRC). The NRC characterized the safety significance of its findings using a green, white, yellow and red color-code with green representing findings having low safety significance and red assigned to findings with high safety significance.
In the second half of 2020, Laguna Verde recorded one orange warning that several systems could fail. In September of 2020, operators carried out work to change the reactor’s control rod mechanisms despite being forbidden to do so under the Administration Procedure for assessing and managing risks before performing any maintenance work on Unit 1 and Unit 2.
The nuclear power plant remained in an emergency condition on December 20 for over two hours due to a major power outage in Unit 2. The 2-13/20 Reportable Event Notification indicates that the power outage was caused by human error on the installation of electrical panels. The fatal fault caused the AT3 electrical autotransformer, which is one of the plant’s critical energy sources, to accelerate. About midnight there was an increase in operation of the auxiliary transformer T2T22. This was considered an ‘unusual event’ so the plant operators declared an emergency. The diesel generators were running as a precaution.
Unusual events are defined as an event that is unexpected. This includes earthquakes, roadblocks near the plant, fires and other unexpected occurrences. The building suffered a blackout as workers completed efforts to install a steam dryer which improves steam quality by reducing moisture in the vessel that surrounds the core and suspends the dry well drain. Unit 2 was left without the access control program and the air conditioning and ventilation system. This disrupted the checkpoints used to verify that workers had not been exposed to radiation.
This chain of events occurred when the standby transformer was not connected because it was undergoing maintenance. The declared state of emergency ended at around 2 AM on Monday, the 21st of December. The AT3 transformer had previously been reported as having problems. In the first four months of 2020, both Units at the plant were in the yellow risk category due to the problems emerging in this system according to a case report on the incident.
Please read Part 3 next