Constant enthalpy is achieved by having just an insulated line, a valve and thermometer well. The entropy of the steam increased because it is a highly irreversible process. You know the pressure (ambient) and temperature at the exit. You trace back on a diagram or with steam table software to the same enthalpy and pressure in the line. The saturated steam tables will then have the quality, or you can calculate it from properties such as specific volume actual and the reference specific volumes of the saturated liquid and vapor phases.
[Editor's note: The following letter came to our sister site, SustainablePlant.com, which linked to Béla Lipták's "Lessons Learned" column for May 2011 on the Fukushima nuclear plant disaster.]
Fukushima: What Went Wrong?
Thank you for the coverage of the nuclear plants in Japan. Because I live in Hawaii, I've been watching the stories on TV and reading news coverage. As a chief engineer and thinking from an operations design perspective, it brings back some heated meetings in which we asked for items about which the design engineers fought us tooth and nail.
Their argument was that these things weren't necessary for normal operation, and we were asking for things that just cost more money and were not needed. I remember one event with GE, where they did not even come close to what we had asked for, and this came to a point where we wanted to drop them as non-compliant. It had nothing to do with anything but cost, and they were right that the design would work in normal operation, but it had almost none of the redundant designs that we'd asked for.
Béla Lipták, PE, wrote some of the best articles I've ever seen about the conditions and points that could have helped at Fukushima ("The Fukushima Nuclear Accident - Part 1".) As someone who lived through concept, design, construction, commissioning and operations, I can see exactly what he's saying. I too thought of many things that an outsider can see that would have prevented or controlled the events. I agree up to a point that no one could have envisioned all the events—or could they?
I have seen or read nothing of any meeting about preparing for such events, even though we know about earthquakes and tsunamis, and have known for years. Why wasn't a team of plant engineers, operators and designers of modern power plants put together to address the already known design questions? Even if there were, there should have been a report of design ideas made public, so people living around the plants could feel more comfortable that something like this would not happen. I know hindsight is always better, but here is a case where people like myself could provide input to help and be a part of a team. No one set of eyes can see it all, but most of the time, it just comes down to dollars.
What came to mind was our company's jumbo ferry project. Because it was for a passenger vessel, and a situation you never want is the ship in the dark or dead in the water, we named things that we wanted the ship run without—rather that just what the regulations said we had to do. Maybe it is time for a similar group for nuclear power plants.
Owner/President, CED Consulting LLC
In our May cover story, ("Distributed Safety Arrives"), the number of installed DeltaV SIS systems was misstated. The online version has been corrected. There are over 700 systems, of which 170 are distributed. We regret our lack of clarity.