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Three Mile Island: How bad UX led to a partial nuclear meltdown
The Three Mile Island accident of 1979 was a partial nuclear meltdown in Pennsylvania. The event spread fear and panic, sending many people to escape the area (Perrow, 1999, p.15). Three Mile Island remained a radioactive site indefinitely and the reactor had to be permanently shut down.
The Role of User Experience (UX)
This partial nuclear meltdown stemmed from a seemingly straightforward issue: a coolant valve failed to close after releasing pressure, resulting in the continuous leakage of over a thousand pounds of nuclear waste per minute. While this problem should have been relatively easy to address, its resolution was complicated by the control room’s interface design. This interface design, rather than the issue itself, was a key factor that perplexed operators and pushed the situation dangerously close to a full-blown nuclear catastrophe.
An Unclear System Status
The confusion arose when the valve light turned off, creating the misleading belief that the valve had successfully closed. However, this only indicated that the command had been sent, not necessarily obeyed. This situation underscores the significance of Nielsen’s usability heuristic (1994) — the visibility of the system status, which emphasises the need for appropriate feedback to keep users informed of the current status and to allow them to act accordingly. This discrepancy was a critical flaw, as it led the operators to mistakenly assume that the valve was successfully closed when, in fact, it was not.
On top of this, there were over two thousand instruments in the control room, but not one showed how much coolant was in the reactor. Instead, workers had to calculate this manually by measuring the pressure inside the reactor, despite the technology having the intelligence to calculate it. This added unnecessary complexity and cognitive load. Incorporating well-designed affordances, such as a clear coolant level indicator, could have enhanced the usability of the control room by allowing the operators to quickly and…
