“High neutron flux” causes shutdown at New York nuke plant — “Neutrons are not equally spread around reactor core”

Published: July 18th, 2012 at 2:51 pm ET


Title: Nine Mile Point Unit 1 shuts down
Source: The Post-Standard
Author: Debra J. Groom
Date: July 17, 2012

Officials with Constellation Energy Nuclear Group, the plant’s owner, originally thought the turbine that spins to make electricity had tripped. But the Nuclear Regulatory Commission said late Tuesday the shutdown was due to a high neutron flux in the plant’s reactor. 

The cause of the condition is still under review.


Title: Four U.S. power reactors shut & NYC sweats during heat wave
Source: Reuters
Date: July 18, 2012

Constellation Nuclear Energy Group’s 630-megawatt Nine Mile Point 1 nuclear reactor in New York automatically shut on Tuesday due to high neutron flux — meaning neutrons are not equally spread around the reactor core. 

Title: NRC: Event Notification Report for July 18, 2012
Source: Nuclear Regulatory Commission
Date: July 18, 2012

Region: 1 State: NY
Event Date: 07/17/2012
Event Time: 11:18 [EDT] 



“On July 17 2012, at 1118 [EDT], Nine Mile Point Unit 1 experienced an automatic reactor scram due to high neutron flux as measured by the Average Power Range Monitoring system. The cause is currently under investigation.


Published: July 18th, 2012 at 2:51 pm ET


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56 comments to “High neutron flux” causes shutdown at New York nuke plant — “Neutrons are not equally spread around reactor core”

  • durando durando

    I'm wondering if anyone in the nuclear industry can comment on this situation possibly causing radiation leaks or meltdown.

    • MQ

      There have been more and more instances of radiation leaks/spills/problems all across the US nuclear powerplants lately. I would suggest to look into this US company that developed anti-radiation water filtration systems, also remove fluoride for those of you who know fluoride isn't exactly for the "teeth" 😉 Their site is: http://www.PureEffectFilters.com

  • aigeezer aigeezer

    I had the same questions, durando. As a non-nuke person, I rushed see what the opaque term "high neutron flux" actually means. About all I've seen so far is:

    "Within a nuclear fission reactor the neutron flux is primarily the form of measurement used to control the reaction inside. The flux shape is the term applied to the density or relative strength of the flux as it moves around the reactor. Typically the strongest neutron flux occurs in the middle of the reactor core, becoming lower toward the edges. The higher the neutron flux the greater the chance of a nuclear reaction occurring as there are more neutrons going through an area."


    Any experts to shed more light on the implications? Does it "happen all the time"? Is it a big deal?

  • Don't understand that second headline: "Four U.S. power reactors shut & NYC sweats during heat wave," as the number of power reactors shut doesn't appear in the article.

    Along with this unit [Limerick 1] that is now shut, here's the list of other non-operational plants and low-power stats per NRC current reactor status report – http://www.nrc.gov/reading-rm/doc-collections/event-status/reactor-status/ps.html

    Nine Mile Point 1
    Crystal River 3
    Oconee 1
    Turkey Point 3
    Fermi 2
    Ft. Calhoun
    San Onofre 2
    San Onofre 3

    Calvert Cliffs 1 @ 10%
    Nine Mile Point 2 @ 60%
    Byron 1 & 2 @ 85% & 83%
    St. Lucie 2 @ 81%
    Seabrook 1 @ 85%
    Millstone 2 @ 85%

    That's 9 plants down and 7 at 85% or less.

  • To the questions…

    A flux anomaly means that one portion of the core is fissioning more than others, hence getting hotter. If that portion isn't at core central, it initiates an automatic scram just in case there's an issue with the fuel or coolant circulation in that high flux area of the core. Once it's scrammed and the initial heat transient settles down, they can test and/or observe the core for what may be wrong.

    An emergency scram causes burps, but not really big ones. Anything exiting through the stacks should be first run through the filters, so it'd be mostly nobles (that the filters don't bind). Nine Mile Point 1 is a GE Mark-2 BWR, so there wouldn't be the kind of massive exterior steam dumping we saw at North Anna after the earthquake.

    But depending on what happens in the generator/turbine area per pressure relief, some less-than nobles could get out. It shouldn't be a that contaminated, but that depends on what's going on in the core. So long as all the control rods have fallen properly and there's juice to run the pumps, there's no chance of meltdown.

    • aigeezer aigeezer

      Thanks, JoyB.


      Wow, thanks Joy B – your knowledge on these matters is greatly appreciated.

      • Thanks, y'all. But I had to laugh at myself for the description right above, precisely backwards because BWRs (like this and Fukushima) aren't all that much like PWRs (like TMI2). The control rods in these beasts don't 'fall' (now with New and Improved Control Rod Drives!) into the core from above, they lift up through the bottom of the vessel by means of hydraulics. A little more reliable mechanism than the original PWR gravity-feeds, for whatever that's worth…

        I gets cornfuzed sometimes. §;o)

        • PhilipUpNorth philipupnorth

          Many thanks Joy, for the clarification. I was just going to post the following:

          Nuke engineers, way to go on another great BWR Nuke Plant Design Flaw:

          Nuke engineer: We need to put the heat exchanger on TOP of the core, so we get a maximum of steam for the turbine loop. So where to put the control rods? Let's see…there isn't room to have the control rods drop into the core from above…So, let's have the control rods come UP FROM UNDERNEATH THE CORE!

          Nuke critic: Except, what happens if there is a meltdown of the fuel core? Won't the control rod holes in the bottom of the reactor function as pathways to allow the melted corium to exit the reactor?

          Nuke engineer: There are so many redundant safety systems that a meltdown simply could not occur.

          Nuke critic: Let's just ask the people of Japan what happens when three nukes melt down, and the cores exit the reactors through those control rod holes?

          Fatal Design Flaw!

          • To tell the truth, there are holes in the bottom of PWR vessels too, just a bit smaller (for instrumentation). So if a reactor decides to do a total melt-down, the corium's going to get out. The pertinent question is what happens THEN?

            And that's where the biggest design flaw of BWRs rears its ugly head – the containment is guaranteed to breach if the core melts through. Too small, not well or easily pressure-regulated, pretty darned vulnerable. As is the accompanying torus, which at Daiichi unit 2 exploded and 'collapsed' on Day-2.

            The big dome containments at PWRs are far sturdier and designed to contain much more gnarl in the event of accident/explosion. Of course, they've more equipment, thus more that can go wrong. They keep these containments at a negative atmospheric pressure to contain steam explosions, though I don't know of any of those that have actually happened outside TMI2. When the restoration of feedwater to hot, boiled-dry steam generators blew the guts out of gen-B and damaged gen-A.

            The meltdown-associated hydrogen explosions of containment atmosphere were hefty – the biggest pegged the gage at 32+ psig. It held, which is more than we can say about any of the affected reactors at Daiichi.

            • nedlifromvermont

              Actually the containment at TMI was breached …

              Nuclear engineer and industry whistleblower Paul Blanche showed the data he discovered on radiation monitors he had access to, which confirmed a breach and large radioactive release, to officials at the NRC, and they responded, "You're right, it was breached … we missed it."

              Fool me once, shame on you (Big Nuclear Unnecessary Sham)

              Fool me many times, shame on me, and planetary doom!

              peace …

              • Arnie surmised the same thing, for the same reason – that large amounts of meltdown-produced radioactive isotopes "got out." But the truth is that releases have nothing to do with the integrity of the containment building, because the RCS is not and never was isolated to the containment building.

                I was frankly surprised it held – 32+ psig is a HUGE explosion in that really very large space, more than twice design basis. Hatches to containment have been known to blow out for no apparent reason, making them NOT blowing in this case sincerely amazing. Yet they didn't blow.

                The makeup and letdown lines to the auxiliary building were operating when the accident occurred, and remained open throughout the course of the accident. The header on the vent gas storage tank was wide open, and remained wide open until June of 1979 when it was "discovered" and closed. And when the guts of steam generator B were blown by cool water suddenly flushed onto red hot and dry heat exchange tubes, the emergency steam dump valves outside containment opened and THAT is what set off the exterior radiation alarms.

                The reactor and steam generators and associated pumps/piping were enclosed by containment. The coolant load of fission products and failed fuel was never contained at any point, and had several avenues of escape straight to atmosphere.

              • Also consider that a million gallons of reactor coolant that had flooded the containment floor was pumped by the sumps into tanks in the aux building basement. The rupture diaphram failed, the water got loose (and it took 10 years to filter it enough to allow release to the river). The aux building filter banks (on the way to the vent stack) were totally saturated by iodine-131 within mere minutes and remained totally saturated for a month – keeping exactly NOTHING from going right on out.

                One of our team was designated ST – Surveillance Technician – whose task was to change the sample filters on the release stack twice a day or more. Those little bitty pieces of paper were themselves so radioactive they had to be immediately put into a lead box. Even worse, particulates were going out in large amounts as well. The sample system had lines for both gas and particulates, even though there was no actual particulate filtration at TMI-2. Because particulates are 'not allowed' by regulatory law.

                Bottom line – the PWR containment building is designed to contain explosions and other breaches of the primary components of the systems. It is not and never was designed to contain the RCS [Reactor Coolant System] or the turbine/generator steam loop, condensers, demineralizers and feedwater tanks. Thus any radioactive gas and/or particulates that get loose INTO THE WATER of either loop will NOT be contained. Releases are inescapable.


          agree with the others JoyB. You're posts are awesome!

          Now, I'd like to ask why neutrons are used for baseline measurements and not some other particle. And can you shed some light on what type technology's used to detect this 'flux'…

          • Aw, thanks!

            Neutrons are the particle assessed because neutrons are what initiates and sustains the fission reaction. You don't want too many of 'em flying around (in moderation) because they'll split fuel atoms and release even more neutrons to do the same thing.

            Because BWRs have only one primary loop (reactor coolant and steam), they don't use boron added to the water to control excess neutrons. The flux is 'shaped' using control rods, inserting (less neutrons) or withdrawing (more neutrons). The control rods are made of 'poisons' like silver, cadmium, boron, halfnium, etc., which absorb neutrons and slow or stop the reaction.

            There are neutron detectors at various stations of the core to tell the operators the flux conditions. Here's some info I found on the technology current, though I'd guess many of these antique plants are still using dino-systems –



        • richard richard

          you get confused 😉 sheesh.

          wind turbines and solar cells are a lot easier to explain.

    • MaidenHeaven MaidenHeaven

      Thank You Joy for sharing your expertise & explaining it in laymen s terms.

  • PhilipUpNorth philipupnorth

    As I understand this (non-nuke expert), the fuel assemblies are placed in a reactor so as to create a balance in the neutron flux, positioning the center of flux in the middle of the reactor. As fuel assemblies become spent, they may be moved from the middle of the reactor and replaced by assemblies from the periphery in order to increase neutron flux in the center of the reactor core. This lengthens the useful life of a fuel load. (Don't spend a lot of time learning about such things, since nuke power is about to go away).

    See the status for US nukes here:

    See event reports for nuke industry f***ups here:

    Bookmark these two pages for future reference for a nuke disaster coming soon to a town near you!

  • Shammalammadingdong

    Out of spec SCADA systems are rampant lately. I wonder if they regret releasing STUXNET into the wild.


      and if they hadn't, would that have made nuclear power safe for use within the biosphere?

      • Shammalammadingdong

        When I was in training they seemed like the safest most controlled thing in the world.

        Reality, not so much.

        • Radio VicFromOregon

          Hmmm…i'd like to hear more about that, Shammalammadingdong. Please share stories of training and feeling it was so safe?

          • Shammalammadingdong

            When it's just the math and theory and equations, it all seems to make sense. Wonder if there is a way to include the earthquake/tsunami/random act of god variables in the math?

            All that stuff was classified, they'd put me in Longbeard if I started posting notes.

  • dosdos dosdos

    The danger in a flux is that the concentration of neutron flow escapes the reactor and containment vessels of a fission reactor. The reason water is favored as a medium is that it slows the free neutrons in the reaction, keeping the exchange inside the core, making a stable criticality possible. If the flux leaves the center, the number of neutrons to further excite the core drops, and the neutrons escape the core.

    Now when the neutrons escape the core in sufficient and focused quantity, you get the equivalent of a neutron bomb, frying everything electrical around, including nervous systems (including brains) and bones. Now not every flux is that dangerous, but the potential is certainly there, and as heavy as neutrons are among atomic particles, they can do considerable damage to a nervous system in the space of a heart beat.

  • eatliesndie eatliesndie

    one cause of high neutron flux can be damaged or displaced fuel rod/s or assemblies – I guess there could be many causes. Nuclear power is way stupid and dangerous, now and for ever.

  • TheBigPicture TheBigPicture

    All too dangerous. Three Mile Island, Chernobyl, Fukushima, (do the math).

    • Shammalammadingdong

      The math is perfect. It's the variables not included in the math that seem to cause problems. Since those can't be safely predicted at this point….

      It follows that every single equation and mathematical thought process involved in the nuclear industry….


      They're invalid. Nothing more than kids scribbling on the sidewalk in chalk.

  • pjrsullivan

    Is it now 26 or 27 nuclear power plants that have unexpectedly gone off line in the last 8 or 9 months or so?

    Anybody else keeping count?

    • Not keeping track, but have been intrigued by the number of 'events' having to do with internal computer control for primary and secondary systems, as well as emergency systems and alarms. Sort of makes ya wonder whether STUXNET actually turned itself off on its embed date, or is still going and the patches haven't all yet been installed.

      • PhilipUpNorth philipupnorth

        As if Stuxnet isn't enough to worry about in a nuclear plant, Joy, I remember reading somewhere that the space people who look after we humans on Planet Earth (Anunnaki?) have been interfering with nuclear power plants to save the human race from destruction by our own technologies. Let's see, now. What website was that on?

      • Shammalammadingdong

        STUXNET was reported to have broken into the wild a handful of months ago.

  • dave14139

    Not burning a load of MOX now are they????

    • U.S. is increasing nuclear power through uprating. Los Angeles Times April 17, 2011By Alan Zarembo and Ben Welsh.http://articles.latimes.com/2011/apr/17/local/la-me-uprates-20110418

      [Excerpted] Turning up the power is a little-publicized way of getting more electricity from existing nuclear plants…

      The power boosts come from more potent fuel rods in the reactor core and, sometimes, more highly enriched uranium. As a result, the nuclear reactions generate more heat, which boils more water into steam to drive the turbines that make electricity…

      In an uprated reactor, more neutrons bombard the core, increasing stress on its steel shell. Core temperatures are higher, lengthening the time to cool it during a shutdown. Water and steam flow at higher pressures, increasing corrosion of pipes, valves and other parts.

      [end excerpt]

      • The article is deliberately vague about "more potent fuel"?

        I suppose it could mean more U-238?

        Joy can you please answer this question about what more potent fuel would be made of?

        Would it necessarily involve mox or could it contain a higher concentration of uranium?

        Wouldn't a higher concentration of uranium 238 mean more plutonium is created as the U-238 captures neutrons?

        • They can increase the U235 content in the fuel. And they can go with a MOX. Burning 'hotter' fuel changes the dynamics of the reactor – AND the flux – significantly. I have read that operators have not been re-certified per the new calculations necessary. For the purposes of control, that is.

          The configuration of 'enhanced' cores is different that what they may be used to. Not saying this particular flux problem is related to that, given that it was an 'automatic' scram. Could more likely have been a temp/pressure transient complicated by 'excess' neutron activity. There are redundant sensors for triggering a scram, and those include both temperature and pressure…

        • CAVEAT – Operators who are ex-Navy are fairly used to calculating the thermodynamics for 'hotter' fuels, as fuel for Naval reactors is more enriched than for civilian reactors.

          At the same time, Naval reactors are much smaller than civilian reactors. So there's that… §;o)

          • Thank you very much Joy

            Doesn't stuxnet have to be inserted through some external drive?

            How the heck would US plants get infected?

            Did some country pay "employees" to insert the virus in US plants in retaliation for the US/Israel making sure it was inserted in theirs?

            Cyber-war is insane.

            • I told my 15 year old science-minded son that US nuclear plants are running the fuel hotter than design specifications presumed and he said:

              "That's just a nuclear disaster waiting to happen"

              Even a 15 year old with some background in physics understands this is insane…

              • CB CB

                I see its in the genes.

                • No just a smart kid who has a huge appetite for knowledge…

                  • Shammalammadingdong

                    Whatever you do, make sure you tell them to never run any tests backwards.

                    I didn't know how to figure out the questions, so I worked them backwards from the answers provided.

                    Got me 1 ticket to Nuke Power School. Knowledge is dangerous. Knowing how to use your brain is even more so.

  • razzz razzz

    I'm pretty sure the company that made and sold the plans for a nuke plant are the same ones that are responsible for the arrangement of fuel assemblies in the core. Like Fukushima, GE sold them the plans and each reactor is assigned an onsite GE nuke engineer to oversee all the important decisions. Even the onsite GE engineers phone home to GE central stateside to get instructions and approvals.

    If the French were responsible for this nuke plant design, they should have final say for fuel assembly positioning and types of fuel being used.

  • AGreenRoad AGreenRoad

    Now where is that duct tape and baling wire? .. fix that durn neutron flux quick, or we may not get no mo moonshine out of this durn reactor…

    Dag nab it… somebody stole my duct tape.. Now how are we ever going to fix this neutron fluxing thing a jing?

  • AGreenRoad AGreenRoad

    12 reasons why all nuclear power plants must be shut down; via A Green Road http://agreenroad.blogspot.com/2012/03/12-reasons-why-all-nuclear-power-plants.html

    Nuclear Power; EXPENSIVE, Dirty, Dangerous And Toxic; via A Green Road