Sunday, October 14, 2012

Guest Post on San Onofre by Nuclear Engineer Ken Schultz. Steam generators not a safety issue

Combustion Engineering steam generators
are similar to this Westinghouse version

I recently blogged about how I "told you so" about the San Onofre Steam Generators: Steam Generator Thoughts and Future. I told you so. I noted that the new steam generators have problems, and I referenced my previous predictions that the SONGS plants will be restarted with lower water speeds and lower power output.

On October 9, the NRC held a public meeting near the plant.  (Here's the L A Times report.) At the NRC meeting, a set of panelists expressed their views on the steam generator issues, followed by questions from the audience.  One of the panelists was Ken Schultz, who is a nuclear engineer and a registered professional engineer in the state of California. Dr. Schultz has graciously allowed me to use his opening statement as a guest post.  A summary of his statement might be: "Steam generator tube ruptures at San Onofre will not be a safety issue."

Remarks to NRC Pubic Meeting, Tuesday 9 October 2012 on San Onofre Steam Generator Tube Leakage

Dr. Kenneth R Schultz, Ph.D., P.E.
Hi, I’m Ken Schultz and I live in Leucadia about 25 miles downwind of San Onofre.  I am a Registered Professional Nuclear Engineer and retired a year ago after a 40 year career at General Atomics, working on a variety of nuclear projects.  I have never worked for Southern California Edison nor for San Onofre Nuclear Generating Station.  I have no financial ties to either of them and am not being paid to attend this meeting, something I’m get used to being retired.  My knowledge about SONGS comes from my general training as a nuclear engineer and from the press.  I am the chair of the local Section of the American Nuclear Society, which is the professional technical association for people working in all aspects of nuclear energy.  Our members include people throughout Southern California, including people working at SONGS.  My remarks today are my personal opinions and do not necessarily represent positions of the ANS

We are here to discuss the NRC’s current regulatory oversight status of SONGS.  I have interacted with members of the NRC during my career and have always found them to be technically skilled, extremely conscientious and critical of all data and conclusions given to them.  In my interactions with them on advanced nuclear reactor designs, they were always interested in new designs with improved safety characteristics, and encouraged their investigation.  I have no doubt that the NRC staff are applying the same skills and dedication to their oversight of San Onofre.

I am concerned that the press is saying the NRC thinks this may be a long investigation.  I think it’s important to keep perspective that the size of the investigation is consistent with the size of the risk.  A case in point is the SONGS steam generators situation.  These are clearly important pieces of equipment and cost a great deal.  They appear to have been incorrectly designed and to be wearing out prematurely.

Now, everything in a nuclear power plant must be investigated from a safety perspective, but the steam generators appear to not be a serious safety issue.  Based on the tiny radiation dose that resulted from the failure of the Unit 3 steam generator tube, I estimate that even if all the 515 steam generator tubes that are affected by the premature wear problem were to fail simultaneously, the radiation released to a person standing at the worst place on the site boundary for the full duration of the accident would result in a dose of less than 1 µSv.  Let’s put that in perspective. Low doses of radiation are a natural part of our environment.  Life on earth evolved in the constant presence of low level radiation.  Every year each of us living in Southern California receives about 3,000 µSv of radiation from cosmic rays, radioactive minerals in the earth and our food, and from medical and dental x-rays.  If we live at higher elevation, like Denver, we’d receive about 6,000 µSv/year.  If we fly a lot we’ll get an extra 2,000 µSv/year.

So that extra µSv from a steam generator accident would be like spending less than a day in the mountains, or taking less than one airline flight.  I don’t see this as a safety issue.  Further, there is growing scientific evidence that low level doses of radiation are not only not harmful, but may be beneficial in stimulating the body’s cellular repair systems. Again, I don’t see the steam generator problem as a safety issue and urge the NRC to proceed with their investigation.


Mike Mulligan said...

That is why a lot of people think engineers and especially nuclear engineers are nothing but professional gunslingers...

Bill Rodgers said...


Then the same logic could be used for those that have earned engineering degrees who support anti-nuclear positions.

Those anti-nuke engineers are paid gunslingers for those who would have us increase the use of natural gas.

See, just a few change of words and your comment can be used to make equally incorrect generalizations about engineers who favor non-nuclear power generation.

curious said...

Please explain how the analysis of 515 failed tubes shows a 1 micro-sievert dose while the licensing analysis for one failed tube - shown in the UFSAR (Table 15.6-7) - indicates a thyroid dose at the exclusion area boundary of 3.9E-4 rem (equals 3.9 micro-sievert)using "realistic assumptions."

Howard Shaffer said...

1 or 3.9 microsievert so what? The difference is in the assumptions. 3.9 microsievert is 0.39 millirem, as "curious" calculated. Less than one dental x-ray. Less than an hour on a jet flight.

The dose is not significant.

For those who cling to the half century old idea that any amount of radiation is dangerous, it means something. For those up to date on the science it means no effect.

An example is a sun tan. This is a skin burn from the suns radiation. Mild tans fade in few weeks (heal) but more severe ones can produce scars and third degree burns. Too many over years can cause cancer. Same with the radiation we can't see and feel.

Bill Rodgers said...


Without looking at the source documents you are pulling those numbers from since no links were provided, I am going to hazard a guess that the difference lies in how the analysis was performed for the USFAR.

The USFAR usually assumes complete and total instantaneous failure of critical components. That is a physical impossibility with most systems but is required for licensing purposes.

However, the analysis of the 515 tubes (once again without the source documents to review) is probably based on real time data.

So if I am reading between the lines correctly, your question is one about real data aquired during an accident event versus computer models based on very, very conservative assumptions that have questionable engineering basis in the real world but are required by regulators to earn a reactor operting license.

However as Howard makes the case above, the difference between 1 mSv and 3.9mSv is not significant.

Curious said...

Howard, sorry if I was not clear. My question is, how does Dr Schultz come up with a nearly identical (if lower) dose for the rupture of 515 tubes? I guess he is considering tiny pinholes in lots of tubes, not actual tube breaks. To further speculate, maybe he took the release from the January pinhole and multiplied it by 515. But so what? The concern is (in my mind) not with pinholes themselves, rather that the fretting mechanism that causes pinholes may also cause multiple tube ruptures with leak rates far in excess of that analyzed for the single tube in the UFSAR. Multiple tube ruptures can have extreme consequences ( fuel melt combined with containment bypass, etc).

Howard Shaffer said...

Dear "curious." May I most respectfully suggest you reread the FSAR?

Multiple tube failure is considered in the design. The steam generator shell is the boundary that contains primary coolant. There are two isolation valves on the steam line leading to the turbine.

Multiple tube rupture won't lead to fuel melting. There is no way tube ruptures can disable the Emergency Core Cooling Systems.

Mike Mulligan said...

Most operators think the FSARs are the plant's grammar school comic books. You go in there looking for engineering foundation information is always a big laugh.

You are right, truth is truth no matter if the pro nukes or anti nukes say it. I have a lot of issue with the truth of the anti nukers.

I think the big story in this is nuclear plant engineering modeling needs to be strictly regulated.

curious said...

Thanks for being patient with me, and I’m sorry that I am using an anonymous name here.

Some of you may be interested in Generic Safety Issue 163, “Multiple Steam Generator Tube Leakage” (available at The concern here was that a main steam line break (outside containment and upstream of the steam isolation valves) can lead to primary to secondary leakage of tube rupture proportions sufficient to deplete the reactor water storage tank inventory via emergency core cooling system injection lost to the secondary side of the SGs (and therefore not available for recirculation from the containment sump) thereby leading to core damage with containment bypass.

The resolution of this GSI is based on the ability of the plant tube inspection program to detect degraded tubes, allowing them to be plugged before they degrade sufficiently to be a concern. It seems to me that the NRC will have to be satisfied that the SONGS SG inspection program will remain adequate in light of this new degradation mechanism.

Meredith Angwin said...


I am not sure I can answer your question, but I will try. According to this NRC document,
the leak estimated a dose of approximately 0.000452 mrem to a member of the public. The annual regulatory limit to a member of the public is 100 mrem per year.
Also, in section 10 of this NRC document,
the same estimate appears. I think that this release estimate was the basis for Schultz's estimate.


I tend to agree with you about regulating modeling. I know that humans make mistakes, hindsight is 20-20, and all that. However, computer models grow over time, they evolve, and you can usually check an "improved" model run against a slightly older model run to make sure you are in the right ballpark with your results. These models weren't in the right ballpark, and that surprises me.

Atomikrabbit said...

Without access to the San Onofre FSAR I can't be certain, but I am fairly sure based on my generic experience with the bases for FSARs, that the dose cited by Anonymous in that document is based on an instantaneous circumferential rupture of a S/G tube at maximum differential pressure, assuming RCS gross activity and iodine is at maximum Tech Spec limits.

It probably also assumes that the steam dumps to condenser are not available and contaminated secondary steam must be released to atmosphere.

The releases would still be within the already conservative 10CFR limits, and of no consequence physiologically, but fodder for whichever fear-mongering entities would seek to exploit them.

Mike Mulligan said...

(I don't think the first time went through.)

Well, I can see the future. The root cause of the San Onophre S/G problems are everyone is penny pitching on the design, manufacturing and testing. The bought the cheapest S/G possible. And everyone withdrew too much profits out of these components weakening the design, manufacturing and testing.

And remember for a lot less consequence accident...a tiny S/G LOCA driven by a penny pitching Ideology is marginally less worst than a meltdown. All your defenses are aligned against not exceeding off site doses of a accident...Jazcko agrees with me. You have zero defenses for certain accidents that can rip a plant and plants away permanently from the grid without a meltdown and off site released..

Talking about nuclear accidents you have no defenses against, it is our unmitigated nuclear catastrophe of unimaginable low electricity loads/ prices and low natural gas prices. The only thing keeping the price of our electricity up is the price of green electricity and their mandates. The new Kewaunee nuclear plant shutdown based on low natural gas prices is our New England Compounding Center shooting fugal contaminants into our spines to reduce pain because we can only survive though the gross profits at any cost and the austerity penny pinching ideology.

I think this is really serious for the large utilities who owns lots of nuclear plants....

Meredith Angwin said...


Let's see. I disagree with you about the cause being penny-pinching. They ordered steam generators and believed the generators would be more efficient than the former generators. That is not penny-pinching, it is good business practice.

However, their computer models said everything in the new generators would be A-OK, and it wasn't. As I have said before, I just don't get how that could happen. Computer models grow and evolve, and if these were giving very different results from previous models, it should have been some kind of red flag. However, I do not think that anyone was penny-pinching by trusting the models.

As far as natural gas prices go, I believe they are heading up, and in the near future. I have a post today that includes some links on gas prices. It is at ANS Nuclear Cafe.