On New Year’s Day 1986, a worker using a 4-watt walkie-talkie at the River Bend nuclear plant in St. Francisville, LA generated a spurious signal in a nearby transmitter. The false signal tripped, or de-energized, two of the four transformers that connected the plan to offsite power. About an hour later, another worker with a 5-watt walkie-talkie caused a false signal which tripped the other two transformers. When the second set of transformers tripped, the plant was disconnected from all sources of offsite power. Luckily, the reactor was shut down at the time, having automatically shut down about six hours earlier due to causes unrelated to walkie-talkie usage.
On July 25, 1983, a worker in the upper cable-spreading room at the Grand Gulf nuclear plant near Port Gibson, MS used a walkie-talkie. The signal emitted by the radio transmitter interfered with a nearby solid state device, causing a false indication of high temperature in the residual heat removal (RHR) equipment area. This false signal initiated an isolation of the RHR system. As a result, the plant, which was shut down at the time, lost one of its two RHR shutdown cooling loops. The other RHR shutdown cooling loop was unavailable due to maintenance and testing. This left the plant without its normal means of cooling the reactor core while shut down. Operators restored one of the RHR shutdown cooling loops about 30 minutes later after verifying that the high temperature signal did not result from an actual pipe break or leak.
On May 31, 1979, a health physics technician in the in-core instrument room at Sequoyah Unit 1 in Tennessee attempted to communicate with the control room operators using a walkie-talkie. Keying his walkie-talkie resulted in a false signal of improper pressure in the pressurizer and the unnecessary actuation of emergency systems to inject makeup water to the reactor vessel.
“Command and control” is vital. Walkie-talkies gave those in command the communication tools to control the activities of workers throughout the plant. But that enhanced command and control came with strings attached, since in some areas of the plant, the walkie-talkies interfered with control circuits with undesired outcomes.
These examples occurred many years ago. They and unexpected outcomes like them caused the processes used to vet proposed activities to be both broadened and deepened. As a result, many potential interferences and unintended consequences have been weeded out pre-emptively rather than post-hoc.
It’s easy to cite the cases like these that slip through, but it’s important to recognize the many more cases that are prevented by the safety checks and reviews. These efforts cost money, but their cost is small compared to the cost of not doing them and relying on trial and error to flush out problems.
“Fission Stories” is a weekly feature by Dave Lochbaum. For more information on nuclear power safety, see the nuclear safety section of UCS’s website and our interactive map, the Nuclear Power Information Tracker.