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Why the Tubes in the Steam Generator at St. Lucie Are Safe and Reliable

St. Luice Nuclear Plant
Last Saturday, the Tampa Bay Times published a story by Ivan Penn concerning wear in the steam generator tubes at FPL's St. Lucie Nuclear Power Plant. Earlier today, the paper published a letter to the editor from FPL's Joseph Jensen taking issue with the story's conclusions.

Steam generators are safe

The steam generators at the St. Lucie nuclear plant are safe. Since their replacement in 2007, our team of experienced engineers, with validation from independent experts and oversight from federal regulators, has inspected 100 percent of the tubes every 18 months during planned refueling outages. These inspections have shown that there are no tube integrity issues that would cause failure.

Steam generator tube wear is not a new issue in the nuclear industry. In fact, there is significant data and operating experience detailing how to safely monitor and manage this issue. Like belts in a car engine, a certain amount of wear is expected over time. But, with regular monitoring and inspection, the belt will be removed well before it causes any mechanical issue. The same is true for steam generator tubes.

While engineering analyses have shown that steam generator tubes can function with over 60 percent wear, no U.S. nuclear plant would ever come close to that level. The U.S. Nuclear Regulatory Commission requires that tubes with 40 percent wear be removed from service. Florida Power & Light's threshold, however, is even lower and more conservative than federal requirements.

The Times article also pays considerable attention to the number of wear "indications" on the St. Lucie generator tubes. In reality, there is a significant difference between an indication of wear, which could be anything from a scratch to a rub mark, and the potential for failure. Again using the car analogy, it's like having a dent in your car door — you can see it, but it does not make the vehicle unsafe.

With respect to how these components would perform given the plant's power uprate, the safety performance of the steam generators was both verified and validated by independent experts and then again by the Advisory Committee on Reactor Safeguards and the Nuclear Regulatory Commission — all of whom have detailed specific experience with the systems at St. Lucie. Given this fact, it is highly disturbing that the reporter chose to all but bury the perspective of our federal regulator, the NRC, while giving significant attention to the comments of two antinuclear activists.

Finally, some have implied that St. Lucie is similar to the now-closed San Onofre plant in California. Nothing could be further from the truth. The steam generators at San Onofre were a different design, made by a different manufacturer and operated at a higher power level. In fact, the type of wear evident at San Onofre is not present at St. Lucie.

Joseph Jensen
Site Vice President
St. Lucie Nuclear Power Plant
Juno Beach
For more on the St. Lucie plant, consult the FPL website.


Atomikrabbit said…
"it is highly disturbing that the reporter chose to all but bury the perspective of our federal regulator, the NRC, while giving significant attention to the comments of two antinuclear activists"

This kind of behavior in the press is all too ubiquitous and needs to be called out at every opportunity. FPL did a good job here - if they are also running PSAs on TV and radio, even better.
CaptD said…
They the same thing about San Onofre!

San Onofre's almost new replacement steam generators had more damage that all the rest of the entire nuclear fleet (to date) when they were inspected after a Unit 3 steam generator tube started leaking on 01/31/12, since which time both Units were never restarted and are now being decommissioned. Several investigations by the NRC and the State of CA regulators (CPUC) are currently underway in this multi-billion dollar debacle.

The truth of the matter is that until steam generators are idled and their tubes inspected the operating utility has no idea what is happening inside! In the above example, a single tube in Unit 2 (which was being refueled when Unit 3 started leaking) was later found to have wear (of its wall thickness) of 90% when the NRC safety limitation is 35% and the Utility had no idea that it was worn!

Until the tubes are inspected and there are many different techniques that can be used, nobody knows what condition they are in PLUS these tube must also be inspected for internal fatigue cracks which most Utilities do not do, using external older bobbin-coil testing instead....

Read the NRC AIT report about San Onofre and find out the facts about San Onofre:

The NRC confirmed that 8 tubs failed in-situ pressure testing in Unit 3 and one tube in Unit 3 had over 90% wear when its safety limitation was 35% and the Utility did not even have a clue that there were any problems.

On January 31, 2012, in SONGS Unit 3, one tube started leaking radioactive coolant in one of brand new replacement steam generators (RSG’s) E-088 that was reverse-engineered by SCE and manufactured by a complacent Mitsubishi Heavy Industries (MHI). The leak started small, but increased enough in a very short period of time to warrant the emergency shutdown of the reactor. When tested later (in March 2012), eight (8) steam generator tubes (wear range 72-100%, length of wear 23-34 inches) in the newly replaced San Onofre Unit 3 RSG E-088 failed “in-situ” main steam line break pressure testing and therefore were plugged, after only after 11 months of operation, something that had never happened before in the history of the US Nuclear fleet. Additionally, several hundred of the Alloy 690 Thermally Treated tubes were also plugged due to tube-to-tube wear. SONGS RSG’s now have more damaged and/or plugged tubes than all the rest of the US reactor fleet combined. Southern Californians were very lucky, because a potentially serious nuclear accident in Unit 3 was narrowly avoided. This accident could have potentially caused a nuclear meltdown and threatened the health and safety, economy and environment of Southern California. NRC website also states, “The severity of one of the wear indications at a Unit 2 (steam generator tube to*) retainer bar was significant enough (90 percent thru-wall) to warrant in-situ pressure testing. This pressure test confirmed the structural integrity of this tube (there was no leakage).” This means that Southern Californians lucked out again, because Unit 2 just happened to be shutdown for refueling, otherwise, this tube could have also leaked radiation due to any design bases accident or unanticipated transients. Finally, the NRC AIT Team displayed poor judgment in their review of SCE’s 10 CFR 50.59 Evaluation and the NRR Specialists wisely questioned the inadequacy SCE’s 10 CFR 50.59 Evaluation. The NRR now needs to review the NRC AIT Teams’ failure to enforce NRC Regulations and find out what exactly happened to ensure the Public Safety. * Wording added for clarification
Engineer-Poet said…
Oh, wow, the anti-nuke FUD machine is in full swing!
CaptD said…

If the NEI sponsored blog is truly professionally run (as they wish their readers to believe) why are they reluctant to allow discussions about the technical issues of how San Onofre and St. Lucie are related?

By approving name calling and other bullying (like labeling someone as an "anti-nuke") comments to be posted on their moderated blog the NEI is "shooting itself in the foot", instead of hosting a meaningful discussion about reactor safety! Just because I have posted technical information that is counter to what the NEI is saying is no excuse to be ridiculed on this blog; I call upon the NEI moderators to step up and require that all posted comments be technically relevant to the discussion to which they are posted. Where are the technical replies that are counter to my statements?

If the above is not acceptable to the NEI, then they should in all fairness, notify readers that they only post comments that are in agreement to their own articles.
CaptD said…
I agree with this statement which was submitted to the NRC:

Scott Burnell, an NRC spokesman, said Monday February 27th, 2014 said that St. Lucie does not have a tube wear problem. The problems that led to the permanent closure of the two California reactors, he said, resulted from tubes rubbing against each other. At the St. Lucie plant, the tubes are rubbing against antivibration bars."The St. Lucie steam generator wear comes from existing, well-understood causes," Burnell said. "There is no steam generator safety issue, nor tube integrity safety concern at St. Lucie."

NRC is wrong again. Yes, there is steam generator safety issue and tube integrity safety concern at St. Lucie due to tubes rubbing against anti-vibration bars. Majority of the steam generator tube leaks in the world except San Onofre have been caused by tubes hitting the anti-vibration bars due to flow-induced random vibrations, when the fluid velocities start exceeding the threshold of 20 feet/second. Tubes rubbing against anti-vibration bars not only get thin, but develop internal cracks due to high cycle fatigue.

Between 2004 and 2006, three primary-to-secondary leaks occurred at the Cruas NPP: Unit 1 in February 2004 and unit 4 in November 2005 and February 2006. The three leaks were all the result of a circumferential crack in the tube at the location where the tube passes through the uppermost tube support plate (TSP #8). Analyses carried out by EDF, further to the last two events, resulted in them being attributed to high cycle fatigue of steam generator tubes due to flow-induced vibration. The results of in situ examination initiated by the Cruas NPP operator showed that the flow holes of the uppermost Tube Support Plates (TSPs) were partially or completely blocked by corrosion products. This phenomenon is referred to in this paper as TSP “clogging-up” and it was considered potentially generic for EDF NPP fleet. For the Cruas leakages, it was established that the association of TSP clogging-up and the specificity of the Cruas steam generator (central area in the tube bundle where no tubes are installed) were responsible for a significant increase in the velocity of the secondary fluid in the tube bundle central area. The high velocity of the fluid in this region increases the risk of fluid elastic instability for the tubes. Based on this preliminary analysis, EDF has implemented preventive measures (stabilizing and plugging of tubes in the central area of the tube bundle deemed sensitive to high cycle fatigue risk).

CaptD said…
Cont. 2

Mitsubishi Root Cause states, "Tube wear patterns similar to those observed at SONGS were reported at the Plant-A (St. Lucie) large U-bend steam generators that were replacements for CE manufactured OSGs. The Plant-A (St. Lucie) steam generators were designed by another vendor (AREVA). They are slightly smaller than the SONGS steam generators but have U-bend tubes, flat bar AVBs, and BEC type TSPs, that are similar to the SONGS RSGs, except SONGS features a 12 AVB design and Plant-A has an 8 AVB design. The Plant-A (St. Lucie) inspection results show a wear pattern with many tubes in the center of the U-bend that have tube-to-AVB wear similar to that found in the SONGS steam generators. The total number of indications and average wear depth at Plant-A are comparable to that at SONGS. The tube-to-AVB wear depths at Plant-A have reached a plateau. The reason for such a plateau is unclear. It may be indicative of the type of tube vibration mechanism or an effect of the support condition. But it is clear that the number of tubes with tube-to-AVB wear at Plant-A is growing."

A power uprate can increase the random vibrations and fluid velocities and could intensify the damage, shorten the life of the steam generators and increase the risk of tube leak as we saw in San Onofre. Despite this, the US Nuclear Regulatory Commission (NRC) has approved a power uprate for unit 2 in 2012 at the St. Lucie nuclear station that increased power output of the unit by 17 percent. Now if the flow holes get partially blocked at uppermost tube support plate due to corrosion products, then the steam generators can experience in-plane fluid elastic instability and Film Boiling in the U-tube bundle hot-leg side with high heat flux due to increased power at normal power operations and design basis accident conditions. That is almost saying that SG can potentially experience multiple tube ruptures, a reactor meltdown and cause a Florida Fukushima.

The problem with CE steam generators is that only CE Engineers knew how to build replacement steam generators with increased power output. AREVA and MHI have failed in rebuilding CE replacement steam generators with high thermal output. FPL is advised to reduce the power so the fluid velocities are less than 20 feet/second. That is the advise of Dr. Pettigrew. Do not trust the AREVA computer models, but learn how to calculate the velocity manually. I am sure that FPL does not want to go down the path of San Onofre. Less and safe nuclear power is better than no power and the increased risk of a Florida Fukushima. FPL is also advised to contact Combustion Engineering (Now owned by Westinghouse) for Technical help.
jimwg said…
Sure be nice to list similar equipment incidents and irregularities that occur in oil and gas generating plants and see where the numbers game goes there. And I never saw any non-Green literature stating that these tubes could lead to any meltdowns or widespread contamination. Talk about FUD-spreading in spades. Too bad one can't sue fearmongers with nuclear beefs and hang-ups standing in way of progress and delivering power to others who badly need it!

James Greenidge
Queens NY

CaptD said…

To prove my point, I'll repost this NRC documentation since it speaks to many of the points pro-nuclear people are denying about San Onofre:

This entire document is great reading but especially Pages 20 & 21:

If you respond without first studying this document closely then I will not respect your opinions !

As I used to tell my students, " At some point, you just have to learn the material and stop guessing, it makes you look ridiculous".
Anonymous said…
A "Florida Fukushima" eh? You just blew whatever credibility you might have been trying to build to smithereens with that FUD statement. You're into FUD, nothing more, and that "Florida Fukushima" proves it. NEI doesn't need purveyors of FUD on their blog. If I were the owner of the blog, this would about do it for the FUDmeisters.

Mitch said…

What's even worst and scarier is CaptD has _students!_ We REALLY gotta get out there with some straight unbiased nuclear education!!!
CaptD said…
To those that say, "It can't happen here," did you know that Turkey Point suffered a "Water Hammer" event that created a sonic boom, which made communication inside their control room impossible?

Just because something has not happened to you, does not mean it will not happen to you in the future. This is why people have insurance, so they don't end up with bills they cannot afford to pay.

Nature can destroy any land based nuclear reactor, any place anytime 24/7 and to think otherwise is illogical.

The American people cannot afford to pay for a Fukushima-type Trillion Dollar Eco-Disaster, yet they continue to allow reactors with questionable safety records to keep operating despite their owners poor safety track records while at the same time politicking for even less oversight from an already too cozy relationship with their regulators, the NRC.
Dan Williamson said…
And there it is! It took a while, but we finally got around to the Trillion Dollar Eco-disaster. That favorite catch-phrase usually gets laid on the table right up front. And what kind of "students" would a pajama-blogger have anyway?
Anonymous said…
"Too bad one can't sue fearmongers with nuclear beefs and hang-ups standing in way of progress and delivering power to others who badly need it!"

Too bad we have the First Amendment, you mean?

"I never saw any non-Green literature stating that these tubes could lead to any meltdowns or widespread contamination."

According to NRC staff:

"Main steam line break and steam generator tube rupture (SGTR) are both included as design basis accidents in Chapter 15 of most FSARs and the SRP and they are addressed as accident initiators in most plant-specific PRAs."

"The NRC has used estimates as low as 1E-3 as the probability of the failure to depressurize
and cool down the RCS in risk analyses of these containment bypass scenarios. The human
error contribution to the estimated increment to core damage frequencies per year in these
scenarios ranged from 29 percent to 93 percent. Operators have to identify the ruptured SG
in order to isolate it, while primary and secondary temperature and pressure changes mask
the diagnostic evidence they need to do so."
Anonymous said…
Oh my God, a water hammer! Oh my God, we're all gonna die! Nature is gonna destroy us all! Ahhhh!

Come on, guys. This is nothing but FUD, FUD, and more FUD. NEI's blog should not be a showcase for FUD like this. Members of NEI pay good money to belong to this organization, they should not have to put up with this crap on their website. There are plenty of whacked-out anti-nuclear sites out there who would be glad to host this kind of FUD, we don't need it here. And forget about this "First Amendment" canard. This isn't government censorship we're talking about, just keeping nonsensical crap out of a privately-owned blog. Sheesh.

Anonymous said…
My First Amendment question was a response to Mr. Greenige's lamentation that opponents could not be sued for criticizing nuclear power, not to what's posted on this blog.

NRC staff and agency licensing documents are now considered "FUD"?

It's a little distressing that some here would rather only hear cheerleading, not discussion of the issues. Even from a purely strategic viewpoint, it seems like you'd want to know what nuclear power's opponents are saying, rather than just holding an online rally.
Anonymous said…
I'm willing to discuss issues. I'm not willing to indulge the purveyors of FUD. Anyone who tries to link issues of steam generators with the damage at the Fukushima plant (which doesn't even have steam generators) caused by a natural disaster is pushing nothing but FUD. Anyone who tries to scare us with mentions of water hammers and nature wiping out reactors is more interested in FUD than anything else. FUD isn't going to cut it here.
Bluesteele25 said…
This entire thread is extremely interesting. I was a Shift Engineer and then a Control Room Supervisor at Arkansas Nuclear One Unit 2. This is a Combustion Engineering design that completed a power uprate to over 1000 MW coincident with the replacement of both original steam generators in the 2000-2011 timeframe. I was present for startup and the first post replacement run and we did not encounter any issues. To my knowledge, there have been no issues associated with the 'new' steam generators since that time.

I do know that our Design, Modifications, and Systems Engineering groups were heavily involved in the design, procurement, manufacturing, and certification processes prior to receipt. These steam generators were fabricated in Spain through a joint Westinghouse-Equipos Nucleares (ENSA) effort.

This record surely means that the above statement regarding the inability of manufacturing facilities (other than the original CE engineers) to replicate or improve upon the original CE designs for power uprates can not be correct. It shocks me that SONGS 2 and 3 would go through this hugely expensive evolution and subsequently be forced into early retirement. Does anyone really know what happened here?

I have heard anecdotally that Mitsubishi chose to eliminate a type of U-tube stabilizer somewhere in the 180 degree bend area as a cost savings measure and that all of the flow analysis submitted to the NRC backed up the elimination as a something that could be done without consequence. If true, that is such a hideously expensive blunder.

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