Tuesday, July 31, 2012

The intractable problem of spent nuclear fuel


Dear Readers,

Here's the link to a pdf slide show on spent nuclear fuel fires, their consequences, and how to reduce the risk as much as possible:


The presentation was created for an IEER Technical Training Workshop held in Takoma Park, Maryland last week (July 25-29, 2012). The title of the full workshop was: "Exploring the End of Nuclear Power and its Proliferation and Health Problems ".

My thanks to Arjun Makhijani (Director of IEER), the staff of IEER, and the other participants of the workshop (who saw me present this slide show in draft form).

The views expressed are my own.

Please share this presentation with your elected officials. Ask them to stop making ever-larger quantities of nuclear waste.

We'll never have any GOOD solutions to the "intractable" problem of what to do with nuclear waste, but we CAN stop making the problem bigger.


Ace Hoffman
Carlsbad, CA


Friday, July 20, 2012

Southern California Edison's extremely weak case for restarting SanO Unit II...


Dear Readers,

The Nuclear Regulatory Commission has determined that (in their opinion) Southern California Edison did NOT mislead the NRC about design changes to their failed replacement steam generators for San Onofre Nuclear (Waste) Generating Station.

The billion-dollar mistake was done according to the rules. They admit that the rules might need to be changed, but the rules were followed, according to the NRC.

Actually, though, SCE arrogantly described their efforts to avoid a proper "10CFR50.59 review process" which would have entailed not just heightened NRC scrutiny, but even some citizens' public scrutiny as well! But the NRC doesn't care what SCE said in those industry publications, where SCE bragged specifically about circumventing 10CFR50.59, which requires an open regulatory review process for significant design changes at a nuclear power plant.

It should be noted that the following string of changes actually occurred, all without need for a "10CFR50.59" review: The tube material was changed to a newer, more durable, but significantly less thermally conductive alloy, requiring 10% more surface area for the same thermal output. Hence more tubes, and hence they eliminated the stay cylinder in the center (to pack in even more tubes), and hence ALL the tubes were packed in a bit tighter than before. The tighter-packed tubes were too tight around the U-bends, near where the anti-vibration bar goes along for the ride (it's not connected to anything but the tubes themselves). (See section 8.b.1)

The whole thing was basically redesigned to flutter! And yet it passed 10CFR50.59 after-the-fact "scrutiny"! It feels like a foregone conclusion.

So much for finding the real "root cause" of why San Onofre has been inoperable since January. One key phrase turned up: "The replacement steam generators were designed and fabricated in accordance with quality assurance requirements, and 10CFR50.59 does not require the licensee to presume deficiencies in the design or fabrication." (p. 36)

Rushing to make a shipping schedule probably isn't considered a deficiency the licensee needed to presume might occur, either. But in fact a decision was made: "not to control the positive pressure, the dew point of nitrogen, and the oxygen content on the primary and secondary side of the Unit 3 replacement steam generators [during transport from Japan] to accelerate delivery schedule." (p. 45) The NRC is still reviewing whether "corrective action" will be taken on that and several other issues.

Also presumed not germane to 10CFR50.59 was whether shipping the entire steam generator in other than a "gravity-neutral position" (in fact 45 degrees OFF from that position) would have any impact. It seems the lifting points made rotation to a gravity-neutral shipping position difficult.

One of Unit 3's SGs was apparently damaged in handling: "Unit 3 replacement steam generator 3E0-88 accelerometers indicated up to a 1.23 g spike with a simultaneous recording on all three of the attached accelerometers. Mitsubishi provided an evaluation of the forces which showed loads were within allowable stress limits but exceeded stress for an operating basis earthquake. The team was not able to determine if this was properly considered." (p. 46) A steam generator weighs well over a million pounds. Don't drop it. Don't bump it.

Additional fabrication problems required extensive rewelding, nearly doubling the number of rotations of the Unit 3 SGs during fabrication. (p. 63)

As for computer modeling, they have a nice phrase for an error: "nonconservative results". Such "nonconservative results" (p. 47) from one computer program which calculates flow rates were diligently fed into another computer program to determine resultant vibrations, which, of course, were way below what actually happened. Garbage In, Garbage Out.

That's why it's good to use real-world modeling, not just computer modeling. Or, as the Augmented Inspection Team put it: "The accuracy of calculating fluid-elastic instability is limited based on inputs that are best determined by design-specific mockup test data. Mitsubishi did not perform design-specific mockup tests." (p. 49)

In one attempt to use "conservatisms" in their vibration analysis, a multiplier of 1.5 was inserted... but the multiplier was actually required to match real-world testing results! (p. 50)

It should be noted that in trying to isolate which software model failed, it was admitted (p. 56) that the models only predict "bulk fluid behavior based on first principles and empirical correlations". So the models don't actually handle fabrication differences between steam generators, or structural differences, etc.. In fact, someone with a slide rule did some calculations to check on these wonderful "computer programs". They're that basic.

Back in the real world, here's what happens:

"If operating velocities reach [a] critical value, vibration amplitudes can increase rapidly and fluid-elastic instability forces can lead to rapid pulsation and damaging of tubes." (p. 49)

The U-bend region of the tubes is most susceptible, but the industry believed everything would hold together -- until San Onofre proved otherwise: "This event at SONGS is the first US operating fleet experience of in-plane fluid-elastic instability, sufficient to cause tube-to-tube contact and wear in the U-bend region."

Shocked, are we? Well, then I should add that there is no standard for what margin of safety should actually be designed into steam generators to avoid fluid-elastic instability. Each manufacturer has a different value.

So, what about restarting San Onofre?

The AIT report indicates the only way SCE might be able to restart the reactors is by changing the operational parameters, because: "SONGS replacement steam generators were not designed with adequate margin to preclude the onset of fluid-elastic instability" which can cause "tube leakage and/or tube rupture." (p 56)

Replacing the steam generators will take several years and cost about a billion dollars. And what design would they use? And who would fabricate them? The old SGs weren't much better:

"The original steam generators installed throughout the domestic fleet of pressurized water reactors, including SONGS, experienced widespread corrosion of the tubes and tube support plates, stress corrosion cracking of the tubes, and wear at tube supports. These problems led to the replacement of nearly all of the original steam generators, in most cases well before the end of their design lifetime." (p. 41) And they can't simply make the old design out of the new alloy, because the heat transfer characteristics are so different.

They've already plugged well over a thousand tubes, many because they were already severely worn, others in the hope of reducing the amount of steam compared to water in certain areas of the steam generators.

Restarting Unit III seems out of the question at this point, and to restart Unit II, SCE has already determined that it would have to be at a lower power setting. (p. 56)

But the only way to know for sure that a lower power setting will work is to try it. And that might result in a tube rupture, possibly even followed by a cascading failure of one tube after another, resulting in a massive radiological release.

Zirconium cladding, hot fuel, loss of coolant... these are a dangerous combination! Add in a multitude of companies and agencies each laying blame anywhere but on themselves, confusing and inadequate regulations and regulatory oversight, language barriers, proprietary manufacturing operations, whistleblower intimidation here (and undoubtedly in Japan too) and you have a recipe for ... exactly what happened.

Or worse. Let's not restart San Onofre. Ever.


Ace Hoffman


Ace Hoffman
Author, The Code Killers:
An Expose of the Nuclear Industry
Free download: acehoffman.org
Blog: acehoffman.blogspot.com
YouTube: youtube.com/user/AceHoffman
Carlsbad, CA
Email: ace [at] acehoffman.org


Friday, July 13, 2012

San Onofre's steam generators are not SanO's biggest problem... spent fuel is.


Dear Readers,

If you look at the inspection results of nearly 10,000 U-shaped tubes inside one of San Onofre's four steam generators (two steam generators per reactor) you can clearly see where their current problem is.

There's a large circle representing a cutaway slice of the steam generator, and within that large circle is a smaller circle, about a quarter the diameter of the larger circle and offset to one side. Within the smaller circle is a dot.

That's the area where there was a rupture of one of the tubes last January (2012). The innermost dot represents where a single tube failed while the reactor was running, and where seven more tubes failed subsequent pressure testing.

The inner circle that surrounds the dot shows that the wear is less and less severe as you get further and further away from where the tube ruptured.

Off to one side is a smaller area of concentrated wear, and a few other locations also show some isolated damage.

This is very bad for San Onofre. But perhaps very good for humanity.

Prior to failure, the tubes evidently vibrated for some time (minutes? hours? months?): Since the plant was shut down in January, hundreds of tubes in that one steam generator have been plugged due to damage. Within those tubes there were thousands of locations with damage, such as where the tubes pass through restraining plates that were supposed to limit their vibration to tolerable amounts.

Southern California Edison has determined that the "root cause" of the steam generator failure in January was probably "fluid elastic instability", a synchronized, uncontrolled vibration that sometimes occurs when a fluid rapidly traverses large bunches of parallel tubes. The tubes wore down until one ruptured, radiation was released, and the reactor was shut down.

Hundreds of tubes in the other three (virtually identical) steam generators also have significant wear, indicating the problem is not unique to that one steam generator.

A report by Fairewinds Associates, commissioned by Friends of the Earth (and linked to below) shows that the amount of wear is unprecedented in the nuclear power industry.  Here is a relevant quote from the Fairewinds' report, quoting Edison's own Condition Report:

"'The location of the tube-to-tube wear in the Unit 2 SG was in the same region of the tube bundle as in the Unit 3 SGs. This indicates the existence of causal factors similar to those resulting in tube-to-tube wear in the Unit 3 SGs.' This quote from Edison's Condition Report is just one example indicating that the failure modes between Unit 2 and Unit 3 are identical."

But here's the thing: Southern California Edison wants to claim they can operate reactor Unit 2 at reduced power and thus avoid the problem entirely. But even if they run at 50% power, there's always the possibility they will end up pushing a steam generator beyond its capacity: For example, if one steam generator fails, they would have to immediately start removing 100% of the heat from the reactor with the only remaining steam generator (this is a "fatal flaw" of having only two steam generators, where most pressurized water reactors have three or four). Because there are only two steam generators to remove the heat, 50% power (the minimum power output SCE said they would try) seems to this author to be well above whatever maximum would ensure adequate heat removal with the other steam generator in the event of the total loss of one steam generator.

But far more frightening even than having to rely on one faulty steam generator is the possibility of a nuclear reactor runaway power surge. Such an event could cause the reactor operators to have little choice but to try to run the steam generators at full capacity (and even that might not be adequate). Such power surges were described in detail (and carefully modeled on a computer) by the late Dr. A. Stanley Thompson a decade ago.

But even that isn't San Onofre's biggest problem. In a letter to this and other activists (shown below), Dr. Thompson explained what San Onofre's biggest problem really is: The spent fuel.

If they restart the reactors, they'll begin again to produce 500 pounds per day (250 pounds per reactor) of the deadliest, most difficult-to-contain hazardous waste on the planet: Spent fuel. Spent fuel is approximately 10,000,000 times more lethal than "fresh" unused nuclear reactor fuel and contains plutonium, cesium, strontium and other radioactive poisons. Mere millionths of a gram are lethal, and they'll be making 250 pounds per day per reactor.

The taxpayers, ratepayers, local citizens, and future generations will all have to shoulder this burden forever.

So there's no reason to restart San Onofre. Don't do it.


Ace Hoffman
Carlsbad, CA

(1) Letter from Friends of the Earth (2012)
(2) Letter from A. Stanley Thompson, (2003)
(3) Southern California Edison press release (added just after this newsletter was first circulated and posted)
(4) Contact information for the author of this newsletter

(1) Letter from Friends of the Earth (June 12th, 2012)

Dear All,

Friends of the Earth was leaked an internal Edison document regarding the tube wear in the San Onofre steam generators. It revealed that the steam generators are by far the worst in the nation. Attached you'll find our press release, the Edison document, and the recent Fairewinds report. We also just received word that the NRC just released the most comprehensive data yet on the San Onofre steam generators.




Friends of the Earth
Washington, DC

FOE press release:
or: http://goo.gl/JPvQn

Fairewinds report:
or: http://goo.gl/I7N0R

Edison document:
or: http://goo.gl/ghCef

(2) 2003 letter from the late Dr. A Stanley Thompson (with some of his cv):

Dear [Ace] Hoffman and others:

I've been wondering about our future as anti-nuclear activists.
I want to thank you, my anti-nuclear friends, and wish us every success.

After the bombs were dropped on Japan in 1945 I accepted an invitation
into what I thought was to be my lifetime engineering occupation: to help
develop for peacetime use this limitless and safe source of energy "too
cheap to meter." I studied reactors and how to design the best possible
nuclear power plant. Based on a design course I taught to engineers at Oak
Ridge National Laboratory, I wrote the book, "Thermal Power from Nuclear
Reactors" (John Wiley, 1956).

In my study I discovered many reasons why no one should build nuclear
devices of any kind. I became unpopular with Congressional committees.
Professors in nuclear departments would not let me talk with their
students. No one would publish what I wrote. Members of the public
questioned why I was trying to spoil the gift of nuclear energy to human
society? I felt alone in my effort.

As many of you have stated, nuclear reactors have demonstrated that they
are neither cheap nor safe. They are of necessity designed, built and
operated by fallible human beings, some of whom may be vindictive. The
failure of Chernobyl demonstrated failure and some of its results,
including the death of thousands of Ukrainians, of birds in the Pt. Reyes
sanctuary in California, and the discard of polluted milk in Italy and of
reindeer meat in Lapland. The most intolerable reactor of all may be one
which comes successfully to the end of its planned life having produced
mountains of radioactive waste for which there is no disposal safe from
earthquake damage or sabotage.

Who still wants to build nuclear reactors? The military establishment in
any country can use a nuclear reactor to produce Pu-239 for nuclear bombs,
a symbol of status. With a nuclear reactor NASA can produce even more
dangerously radioactive Pu-238 for super batteries in its space projects.
With a nuclear reactor available, a university professor can head a
prestigious Department of Nuclear Engineering. With the promised
construction of nuclear reactors, his students can look forward to
prestigious employment. There is now an immense effort by vested military
and civilian groups to continue various expensive and expansive nuclear

I have self-published a pamphlet, "Comments on Nuclear Power" (100 pages).
I no longer feel alone in the fight against nuclear proliferation, thanks
to all of you. Each of us approaches the battle against military and
civilian nuclear reactors from a different life experience. Let us not be
torn asunder by our differences in viewpoint. Let us not weaken each
other's credibility with bickering and slander. Our differences of
viewpoint should be a source of strength. I hope we can use that strength
to advantage against our entrenched "paid" opposition.

A, Stanley Thompson, Eugene, Oregon, USA 13 May, 2003


The author of this newsletter (see below) has a copy of Dr. Thompson's pamphlet, which discusses runaway nuclear reactor power surges, and hopes the Nuclear Regulatory Commission considers Dr. Thompson's remarks carefully before relicensing San Onofre or any other reactor, anywhere. They are all deathtraps.

Southern California Edison press release (seen just after this newsletter was first posted and circulated):


July 13, 2012

Media contact:
Media Relations, (626) 302-2255
Investor relations contact: Scott Cunningham, (626) 302-2540

ROSEMEAD, Calif., July 13, 2012  Southern California Edison (SCE) has released steam generator tube wear data associated with the San Onofre Nuclear Generating Station (SONGS) to the Nuclear Regulatory Commission. The data show that most of the wear, or tube wall thinning, was less than 20 percent. This is far below the 35 percent wall-thinning limit, which would require that the tube be plugged. The majority of this wear is related to support structures. The nature of the support structure wear is not unusual in new steam generators and is part of the equipment settling in.

"We're using this information and additional detailed data collected through testing to develop our repair plans according to best practices and industry standards, particularly the data on the unexpected tube-to-tube wear," said Senior Vice President and Chief Nuclear Officer Pete Dietrich. "Safety continues to be the guiding principle behind all the work we are doing."

The data include the various types of wear on the tubes and the number of tubes affected.

There were three major categories of wear: anti-vibration bar wear, tube support plate wear and tube-to-tube wear. Two minor categories of wear were also included: retainer bar wear and wear due to a foreign object. The foreign object wear, also not unusual in new steam generators, was only found in Unit 2 and was caused by a piece of welding material about the size of a quarter rubbing against two tubes.

  • In Unit 2, 1,595 tubes showed wear of some type and 510 tubes were ultimately plugged; six tubes for showing wear of more than 35 percent and the rest for preventative measures.
  • In Unit 3, 1,806 tubes showed wear of some type and 807 tubes were ultimately plugged; 381 tubes for wear of more than 35 percent and the rest for preventative measures.

The complete data for both units is available on the commission website for SONGS information: www.nrc.gov/info-finder/reactor/songs/tube-degradation.html.

Both units of the plant are currently safely shut down for inspections, analysis and tests. Unit 2 was taken out of service Jan. 9 for a planned outage. Unit 3 was safely taken offline Jan. 31 after station operators detected a leak in a steam generator tube. The units will remain shut down until SCE and the commission are satisfied that the units are safe to operate.

About Southern California Edison
An Edison International (NYSE:EIX) company, Southern California Edison is one of the nation's largest electric utilities, serving a population of nearly 14 million via 4.9 million customer accounts in a 50,000-square-mile service area within Central, Coastal and Southern California.

(4) Contact information for the author of this newsletter:


Ace Hoffman
Author, The Code Killers:
An Expose of the Nuclear Industry
Free download: acehoffman.org
Blog: acehoffman.blogspot.com
YouTube: youtube.com/user/AceHoffman
Carlsbad, CA
Email: ace [at] acehoffman.org


Monday, July 9, 2012

At San Onofre, "fluid elastic instability" is a fancy term for "busted"


Dear Readers,

San Onofre Nuclear (Waste) Generating Station has been shut down for nearly six months, ever since one of the heat transfer tubes inside their new steam generators in Reactor Unit 3 ruptured suddenly and unexpectedly.

The normal pressure difference from one side of the tube to the other is enormous: About 1,000 pounds per square inch, so even a tiny leak spews many gallons of "primary coolant" (which is highly radioactive) into the "secondary coolant loop" (which, ideally, is not radioactive at all). When a leak occurs, the primary coolant flashes to steam as it exits the broken tube, and the steam is so hot it can cut through the tube like a welder's torch, eventually cutting a complete circle around the tube, releasing it to fling around and damage other tubes.

There are nearly 10,000 U-shaped heat transfer tubes inside each steam generator. They are about the thickness of a credit card and the diameter of your thumb.

Reactor Unit 2 was already shut down for massive repairs and refueling when Unit 3 sprang a leak. Neither unit has operated since then (and the lights have remained on. We do not need San Onofre). An older reactor, Reactor Unit 1, was retired 20 years ago for basically the same reason, and has since been dismantled. It's time to dismantle Units 2 and 3, too.

SanO's majority owner and operator, Southern California Edison, recently claimed to have identified the cause of Unit 3's current problem as "fluid elastic instability". And although Unit 2 is of identical design and also has two new steam generators which are also experiencing excessive wear, SCE claims Unit 2 will not suffer the same problem if they restart it at reduced power. SCE wants to do that next month, probably at half power, which does NOT mean the pressure differences and flow rates are half as much, because efficiency drops off substantially when the plant is not run at its maximum practical output (and so do profits for SCE!).

If Unit 2 runs without problems, they'll bump the power up to 60%, then 70% and then 80%. (So far that's as high as they've said they'll dare to go.) Then they'll start talking about restarting Unit 3 at reduced power as well.

If nothing ruptures, they'll shut the reactor down periodically to check for wear, since they can't tell what's happening inside the steam generators while the reactor is operating. The extra shutdowns are costly and hold additional dangers. (The Nuclear Regulatory Commission keeps careful track of how many times a reactor is cycled on and off.)

Restarting either SanO unit should be opposed by everyone in Southern California. It's not worth the risk.

Fluid elastic instability was first identified around 1970 and occurs when a fluid -- usually a steam/water mixture (in this case mostly steam) flows across a bundle of tubes. In the case of San Onofre, the steam/water mixture traverses the tubes at the U-portion of the tubes at their top.

A cascade of tube failures is substantially more likely under fluid elastic instability conditions than most other tube-rupture scenarios. If a cascading tube failure occurs, the fact that SanO's design has only two steam generators (whereas most Pressurized Water Reactors (PWRs) have three or four) becomes an additional serious liability: The second (only remaining) steam generator has to remove ALL the heat from the reactor. Debris from the first steam generator failure may further complicate matters.

SCE was very reluctant to admit they've got a fluid elastic instability problem, and when they made a presentation to the Southern California Association of Governments (SCAG) last week, they didn't try to explain what fluid elastic instability is. They just said that it was apparently the problem.

However, the phenomenon is described in a 2001 ASME handbook on flow induced vibrations by M. K. Au-Yang: Upon crossing the "critical velocity" the tube vibrations "suddenly rapidly increase without bound, until tube-to-tube impacting or other non-linear effects limit the tube motions." The vibrations: "become correlated and bear definite phase relationship to one another..."

In other words, the tubes rock back and forth together like people doing "the wave" or some other motion in a stadium.

Fluid elastic instability is difficult to model using computer simulations and SCE did not do full-scale modeling of the new steam generator design. They also skipped full-scale hot testing after installing the new steam generators in 2010 and 2011.

When a tube started to leak in January 2012, the reactor operators did NOT suspect fluid elastic instability, and did NOT do the immediate prudent thing: Shut down the reactor.

Instead, they kept running at full power until it was determined that the leak was growing -- always a bad sign. Permitted leakage rates, and total amounts, would have both soon been exceeded. Normally, when the reactor is shut down for routine maintenance, faulty tubes are plugged. This process continues for the life of the plant or until so many tubes are plugged that the steam generators have to be replaced. When the plant was built, it was believed that the steam generators would last the full life expectancy of the plant. But throughout the nuclear industry, replacing steam generators has become a huge business.

Fluid elastic instability is relatively rare but is much more frightening than a typical steam generator tube leak. Some leaks are left to spew, because rather than grow, they clog up with crud and stop spreading. But growing leaks cannot be ignored.

Of the nearly 40,000 tubes inside the four new steam generators in the two operating reactors at San Onofre, more than 1,300 were found to have excessive wear to such a degree that they needed to be plugged. About 10% of those were pressure-tested before being plugged, and eight failed the pressure tests -- some failed at pressures BELOW standard operating pressure!

SCE officials are very reluctant to say how many tubes have failed in Unit 2, stressing that "only two" tubes indicated tube-to-tube wear, which, they feel, was probably caused by turbulence, not fluid elastic instability. They aren't certain, though, and just because fluid elastic instability hasn't been experienced in Unit 2 yet, doesn't mean it can't happen there, either under normal operating conditions or during an emergency.

SCE has no idea when fluid elastic instability might occur. Their computer models are known to have been off by 300 to 400 percent. Flow rates are known to be way too high, and there is way too much steam and not nearly enough water at the top of the tubes (a mixture with more water would have been much better at dampening vibration).

Maybe SCE is right that lowering the power output will ensure safe operation. But what if they're wrong? SCE wants to experiment with all our lives.

And let's say they succeed. Let's say they get the reactors operating again. Then, they will just go back to producing more spent fuel nuclear waste, a growing problem for which there is still no solution. It will mean the next time there is an earthquake or a tsunami, San Onofre will threaten our farmlands, our cities, and our lives once again. It will mean San Onofre will continue to threaten SoCal at least until the NRC relicenses the plant in 2022/2023, and then for 20 more years after that (and so on ad infinitum). The NRC has never denied a nuclear power plant a license renewal in its history, and is especially unlikely to do so in California where new nuclear power plants are forbidden by state law.

San Onofre is shut down today because it was poorly designed, poorly constructed, and poorly operated. Let's keep it shut down. It's not going to get any better.


Ace Hoffman
Carlsbad, CA

The author, an educational software developer, has been observing San Onofre's follies for more than 20 years, since moving to California from Connecticut. He has studied the nuclear industries' follies for about 40 years. His book, The Code Killers, written in 2008, is available for free download from his web site: www.acehoffman.org .


Ace Hoffman
Author, The Code Killers:
An Expose of the Nuclear Industry
Free download: acehoffman.org
Blog: acehoffman.blogspot.com
YouTube: youtube.com/user/AceHoffman
Carlsbad, CA
Email: ace [at] acehoffman.org