The US Nuclear Regulator Commission (NRC) recently posted a blog written by Kenneth Karwoski, Senior Advisor for Steam Generators that attempts to help people understand a little more about steam generators. The blog post was titled Where There’s Steam, There’s … a Steam Generator.
Aside: Many of my colleagues would immediately point to the title as misleading. Their professional experience includes plants that produce a large quantity of steam without using steam generators. End Aside.
Since Mr. Karwoski’s job is to be a senior advisor for steam generators at the NRC, I understand why he would make the following parochial statement:
Steam generators provide vital technical and safety functions at many U.S. nuclear power plants.
My direct experience with nuclear power plants is limited to those that include steam generators, but I am aware that my experience in the specialized application of using nuclear energy inside sealed submarines full of people breathing in the same limited air space where the reactor operates is not representative of the whole range of design options.
In the mid 1950s, a series of experimental reactors called BORAX-1, BORAX-II and BORAX-III were built at a facility in Idaho then known as the National Reactor Testing Station. Those reactors proved that the radioactivity that was introduced into the water used to cool light water reactors was low enough to allow the water to boil in direct contact with nuclear fuel rods, producing steam to turn turbines without the need for expensive heat exchangers.
GE followed up on those experiments with the Vallecitos Boiling Water Reactor and then developed a series of boiling water reactors that use primary coolant to directly drive steam turbines.
Boiling water reactors continue to be a safe and cost-effective design choice. They have the potential to be far more cost competitive than pressurized water reactors under regulatory regimes that impose radiation dose and dose rate rules that are based on actual, vice imaginary health effects.
It is in the full knowledge of the existence of boiling water reactors that I assert that classifying steam generator u-tubes as performing a “vital safety function” is an exaggeration. All heat exchangers should be built carefully. They are worth maintaining in order to keep the system functioning as designed. They are worth repairing if any of the heat exchange surfaces begins leaking and allowing mixing of fluids that the designers prefer to keep separate.
However, steam generators in light water reactors do not require perfection. Minor failures should be accepted and fixed; they should not result in a decision to destroy multibillion dollar assets under the false assertion that the failure is a “safety issue.” The decision to permanently shut down units 2 and 3 at San Onofre was roughly equivalent in scale to deciding to decommission an aircraft carrier due to a single tube leak in a steam condenser.
The first person to post a comment on the NRC blog about steam generators was CaptD, someone I have encountered in other forums. He tried to make the case that people should be terribly concerned about the leaking steam generators and should blame the decision makers at SCE for selecting an “unproven and radical design” instead of replacing steam generators that had proven to be less durable than desired (San Onofre’s original equipment stead generators lasted only 30 years) with identical pieces of equipment.
He called San Onofre a “nuclear near miss” and claimed that it should enter technological history as an “engineering debacle of epic proportions like the Tacoma Narrows Bridge.”
I had to respond to that false characterization, even though I believe that San Onofre’s closure was an economic debacle of epic proportions.
I completely disagree with CaptD.
What people really should be told is that the operators at San Onofre correctly shut down Unit 3 when they received an indication that there was a tiny leak in one of the tubes of the generator that turned out to be just 1/2 of the “very strict limits” that the NRC imposes to require a unit shut down.
The action was correct because tube leaks tend to grow rather rapidly, but they do not tend to spread to other tubes. The small diameter of each tube prevents leakage from ever getting very large, even in the case of a complete rupture. The nature of primary coolant in a reactor where fuel rod cladding is intact makes primary to secondary leakage more of a nuisance than a safety issue – after all, the coolant is almost pure water containing tiny quantities of radioactive material with half lives longer than a few seconds.
The most exposed person would have received a radiation dose of about 5.2E-5 millirem (5.2E-7 mSv) in a world where the average annual dose is about 300 millirem (3 mSv) from background radiation.
After inspecting and plugging damaged tubes, both units 2 and 3 should have been restarted, probably no later than March or April 2012. Everyone should remember that steam generators are only a design choice – 1/3 of all of the reactors in the US don’t even bother to try to separate primary from secondary water. Pressurized water reactors with isolated primary systems were the right choice for their initial application – producing power inside sealed submarines full of people.
I lay the blame for the destruction of 1500 jobs and the capacity to produce about 14 billion kilowatt-hours of emission free electricity every year solidly on overly conservative decision-making and political action designed to force California to burn more natural gas.
PS – I have been privy to communications from an intervenor with an unusual position. He has determined that it is worth his time to file legal paperwork to advocate for the interests of SCE rate payers and California air breathers to force SCE to publicly disclose the basis for its decision to destroy an asset paid for by consumers under traditional rate of return regulation. My intervenor friend is a lawyer with a rock solid case. This will be an interesting story to continue covering.