For the first time in a long while, nuclear power plants are being built in the United States (Watts Bar Unit 2 really doesn’t count because it was “under construction” when I was in college back in the disco daze of the late 1970s). It would be solid and groovy if as many problems as possible experienced during construction back then are avoided now, like the problem experienced at the Zion nuclear plant in Illinois.
More than a year after the Atomic Energy Commission (NRC’s predecessor) issued operating licenses for the two reactors at Zion, workers discovered that sensors installed to detect low pressure in the steam pipes were wired according to the blueprints, but that the blueprints were wrong. These sensors had been put in place, tested, and accepted to be properly installed years earlier. Other workers launched an investigation into how this mistake was made and overlooked for so long.
The sensors were located in the pipes carrying steam from the steam generators to the turbine. If a pipe breaks, the pressure in that pipe drops. The sensors monitor pressure and initiate automatic plant responses, like shutting down the turbine and reactor, when appropriate. The mis-wired sensors meant that the plant would not respond to events as assumed in the safety studies.
During construction, workers noticed that the wiring in the plant did not match the blueprints. They communicated this situation back to Westinghouse, the reactor vendor. Westinghouse misunderstood the information they received. They thought that the sensors had been tested and that wiring changes had been made to correct deficiencies identified during the testing – a plausible scenario because functional testing often yields such outcomes. But no such testing had been conducted of these sensors. They had merely not been installed as specified on the blueprints.
Based on its mistaken perception, Westinghouse revised the blueprints to match how the sensors had been wired at the plant. In other words, Westinghouse “corrected” the blueprints to match the errors at the plant. When Westinghouse issued the revised blueprints, Sargent & Lundy (the architect/engineer for Zion) accepted the blueprints without any verification and included them among their “as-built” drawings for the plant. While the blueprints truly reflected the plant as it was built, it had been built wrongly.
Our Takeaway
The NRC’s regulations, particularly the quality assurance criteria in 10 CFR 50 Appendix B require plant owners to have effective programs to find and fix safety problems. Here, they scored 50% for having found safety problems but failing to fix them.
This event involved an error trap. Westinghouse received lots of reports from Zion about changes made to wiring arrangements as the result of functional testing results. As happened in this case, it was easy to mistake another report about blueprints not matching wiring configurations in the field as a request for another blueprint revision instead of a request to re-wire the sensors.
Over the past decade, the nuclear industry has emphasized three-way communications among operators. For example, a supervisor will instruct an operator to “start the alpha pump.” The operator will confirm understanding of the direction by responding something like “understood I am to start the alpha pump” and the supervisor will confirm correct understanding with something like “correct, you are to start the alpha pump.” The two verification steps avoid errors due to miscommunication.
Three-way communications can also avoid problems like those experienced by Westinghouse at Zion. Workers at Zion could have sent a message to Westinghouse about the difference between the actual wiring configuration and the blueprints. Westinghouse could have responded with its understanding of the difference as well as its expected resolution. Workers at Zion could have responded with confirmation that the situation and its solution were properly understood.
It’s literally as easy as 1-2-3.
“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.