This could be a remanence of some old interface, but if it was intentional, why?
There are use cases for "high supply" alerts on this building, namely to tell if a fixed-speed nuclear reactor is overproducing or underproducing steam if the steam is routed into a variable-speed consumer - such as an oil refinery or desalination for settlement/farms/industry.
It can also be used to alert me to manually adjust the reactor's power level depending on the storage's charge, performing a kind of oscillation that functions as as a crappy form of Automatic Power Regulation, which allows me to save Uranium.
It's possible to argue that this is a form of cheesing the game to get APR without unlocking the MOX Reactor, but I would argue this definitely falls under skillful gameplay instead of cheese, and the player (me 😄) should be rewarded. It requires an deep understanding of turbines/shafts/fixed vs variable loads to even realize that there is benefit to doing this, and careful design of builds to maximize the benefit while keeping out problems. COI is an awesome game precisely because it usually rewards these things.
Also, balance-wise, it does not deprecate or otherwise threaten APR. Any steam that goes through the Thermal Storage still suffers the 10% energy loss, and manually oscillating the reactor's settings is micro-intensive, which calls for the need to design whatever is consuming the steam to be more consistent, especially the turbine shafts.
