I am sure that many reading these articles will remember the early days of Star Trek, where the story was much more important than the physics. Of course with Star Trek, they at least tried to have the distinction between matter and antimatter, unlike the less well known BBC TV series Dr. Who, which actually prided itself in having no basis in physics whatsoever. Well, you might not think it can happen, but sometimes in our power plants we lose that vital link between physics and phenomena and end up like Alice in Wonderland.
I was sitting in my office, trying to keep my fountain pen from dumping ink all over the thermal kit I was reviewing, when Richey Reynolds walked into my office and said, “I have Bohr’s International Generating (BIG) BWR Power Station on the line and they are looking for some help with an unstable steam system.”
I put my pen in a safe place and asked Richey to transfer the call.
Richey and I listened to the plant engineer describe his plant, which was a typical Nuclear Boiling Water Reactor (BWR). The most interesting thing about the problem was that it seemed to be connected to the time of year. In the summer, things got bad, but they always seemed to get a little better in the winter. Our first guess was based on the usual suspects for winter/summer changes; condensers or cooling towers. It also could have been a problem with the condenser pressure measurement. However, the real problem was more incredible. Looks like old Richey Reynolds and I were in for a turbulent time.
Richey and I were eager to get to the site and tear into the condenser, but that little engineer in my head said, “Hold on there, Buckwheat, better think this through before you make a fool of yourself.”
After many years of suffering the results of ignoring that warning, I decided to listen to that little engineer and asked the plant to send us some data to review. When we looked over the data, confusion immediately set in; we either had to redraw the Mollier diagram or something was rotten in Denmark. Looking at data collected during a long period of time, we noticed that not only were the expected parameters varying with the time of year, condenser pressure and condenser cooling water inlet temperature, but also many unexpected parameters were varying. An example of what we saw is displayed in Figure 1. This is a graph of two independent main steam pressure measurements on the same pipe. The difference between these measurements varies with respect to the time of year. This was our first hint that something was not quite on the up and up. We started looking at other plant parameters and noticed that they also followed this trend. Next we evaluated the temperature measurements when compared to the pressure measurements.
Theoretically, the temperature measurements should follow the pressure measurements in a saturated system. However, in this case they did not. The steam line temperature stayed at approximately 547°F, even when the pressure dropped to 1,000 psia (saturation temperature for 1,000 psia is 544.7). Figure 2 shows this disjunction between temperature and pressure with the normal pressure point. Once we identified a loss of physics accident (LOPA), we started looking to see if there were other instances. Unfortunately, many of the plant parameters were showing the intrusion of paranormal activity.
So what would be the impact of such a problem? Is this just a data issue and not an actual problem? We did see that the generation corrected for condenser pressure was drifting in a similar fashion. The generation is actually measured completely independently of the other parameters, so there was not a common failure that could affect the measurement of generation. But, there was a link between the problem and actual generation. To understand the problem, we need to understand the thermal power calculation at a BWR power plant.