You are the man. :)
You need to consider the time frame for the exposure and whether or not it was an acute or chronic dose. 10 rads over a lifetime isn't that big a deal. 10 rads in 10 minutes is a big deal. What you can look for is observable somatic effects like changes in the blood. If you can see somatic effects, you are probably talking about an acute dose. Otherwise you are likely going to be looking at stochastic effects that occur randomly and are independent of the amount of exposure and the received dose. Cancers are stochastic effects which is unfortunate since in most cases, cancers cannot be definitively linked to the agent the person was exposed to. There is a lot of anecdotal evidence, but you being a numbers guy can appreciate the limitations there.
On to curies. There is no straight line conversion from curies to rem/hour. A curie is a unit used to quantify the number of radioactive disintegrations per second in a specific type of radioactive material (not type of radiation, type of material, i.e., polonium, uranium, plutonium, cobalt-60). Here is a great discussion that succinctly summarizes the curie-REM relationship. (Link here: http://www.physlink.com/education/askexperts/ae553.cfm)
"Curies (Ci) and Roentgens (R) are both related to radiation, but they describe different properties.
A Curie is a unit associated with the number of radioactive disintegrations per second in a particular sample of radioactive material. The Curie describes the activity of a radioactive source. One Ci of radioactive material produces 37 billion disintegrations per second. A disintegration per second is also known as a Becquerel (Bq).
A Roentgen, on the other hand, is a measure of the amount of charge produced in a particular sample of air from ionizing radiation (i.e. - a type of radiation that has enough energy to remove an electron from an atom, producing ions). The technical definition is the amount of X or gamma radiation that produces one electrostatic unit of ionic charge in one cubic centimeter of dry air at standard temperature and pressure. The Roentgen describes the exposure of air from a radioactive source.
Radioactive decay produces various types of radiation in the form of particles (alpha, beta, neutron) and photons (x-rays, gamma rays). A radioactive source will emit these radiations at various frequencies, depending on its activity and its decay mode. Each type of radiation, depending on its energy, produces a different amount of ionization of air, and hence a different exposure. Alpha particles, for example, will produce substantially different amounts of ionization than highly penetrating gamma photons. The total exposure produced from a radioactive source is therefore related to the total number and type of radiation emissions from that source; the total number of emissions is related to the activity of that source.
Hence, there is no general equivalence between Curies and Roentgens, but a certain number of Curies of a particular radioactive material with a known size and shape will produce a certain number of Roentgens at a specified distance."
In your example of an accident releasing 100 curies - the first question is "Of what" Surveys and sampling will need to be done and a half life plot will need to be clculated to determine the specific isotope released. Let's say isotopic analysis confirmed that the material was Cobalt-60. Cobalt is a component of the steel used in the manufacture of reactor plant systems because of its excellent corrosion resistance properties. Cobalt gets activated in a flux and becomes radioactive cobalt-60. I'm going to use Cobalt-60 thumbrules because I no longer remember the conversion factors between Cobalt-60 and other isotopes. Suffice it to say, conversion factors exist to relate the different energy levels of the decay particles from Cesium, Cobalt, uranium, plutonium, etc. As my Fluid Dynamics and Het Transfer instructor used to say "The proof is left to the interested students…"
To find out the number of curies, you use the Curie-Meter-Rem rule. A 1 Curie point source emitter of Co-60, measured at 1 meter will give a dose rate of 1 Rem/hour. The dose rate falls off as a 1/r squared function. To determine the curie content of the source, you measure the radiation readings at 1 meter. Now, a little prudence and common sense is in order. If your radiacs are reading 10 Rem/hour and you are 10 meters away, it would be really stupid to walk in to measure the level at 1 meter when you can simply calculate it as follows.
DR1 = DR2 x (X2^2/X1^2) where DR is the dose rate measured at distances 1 and 2 and X is the distance at point 1 and 2.
In my example, 10 Rem is DR2, X2 is 10 meters. We want to calculate the dose rate at 1 meter so we can estimate the curie content. Plugging and chugging…
DR1 = 10 Rem/hour x 10^2/1^2.
DR1 = 10 Rem/hr x 100 = 1000 Rem/hr measured at 1 meter.
The dose rate at 1 meter is 1,000 Rem/hour, so we can estimate that there was 1,000 curies of cobalt 60 released.
You can also work it backwards if you somehow you knew the curie content of the material released, but this is a rare occurrence. In your example you had 100 curies of Co-60 released. We know that it will read 100 Rem/hour at 1 meter. Applying the formula above we can calculate the dose rate at 4 meters:
DR2 = DR1 x (X1^2/X2^2)
DR2 = 100 Rem/hr x (1 meter^2/4 meters^2) = 100 x (1/16)
DR2 = 6.25 Rem/hour dose rate. That's still pretty high so I would slap the guy who picked 4 meters and go with 10 meters next time.
In all of this discussion I have assumed that the material was a pont source emitter. Depending on how the material was distributed, it may not always be a point source. You may have highy radioactive material in a run of piping that is 22 feet long - what is known as a line source. In this case you would use a slightly different calculation to determine dose rates.
DR1 x X1 = DR2 x X2
In this case let's say we measured general area radiation from the pipe at 6 meters and it was 5 Rem/hr. The dose rate at 1 meter would be calculated as follows:
DR1 x 1 meter = DR2 (5 Rem/hr) x 6 meters
DR1 = DR2 (5 Rem/hr) x (6 meters/1 meter)
DR1 = 30 Rem/hour
Note that at a distance of half the length of the pipe run and greater, you can use the point source formula.
Moving on…
I think you have confused dose and dose rate in the second part of your first question. Reading back through my response, I have used dose and exposure and dose rate and exposure rate interchangeably. Rather than change what I wrote, I took the easy way out with this disclaimer - they are interchangeable.
A dose rate is measured in millirem or Rem per unit time, usually an hour. Now that you know the curie meter rem rule for a point source emitter, 10 microcuries of Cobalt-60 scattered in in a 1 meter square area will result in a general area dose rate of 10 micro rem per hour measured at 1 meter. This converts to a dose rate of .01 millirem/hour. If you stay in that spot for 10 hours you will receive a total dose or exposure of 0.1 millrem. To put that inperspective, you receive anywhere from 10-60 millirem of exposure on a 5 hour flight from New York to San Francisco and can probably a few more millirem if the guy in the seat next to you is fat.
The short, easy answer is "It depends" On my first submarine, we went 10 years between nuclear refuelings. There are cores today that will never need to be refueld over the 20+ year service life of the submarine.
Commercial power plants aren't typically designed with the same robust, long lived fuel cells. Commercial fuel cells are "burned up" faster than that of a Navy warship. A little poking around the internet yielded service lives of anywhere from 2 to 10 years for commercial fuel cells.
No. They are spent and can no longer sustain a critical fission reaction. They won't interact with each other to cause fission events. They won't look "spent", and there isn't a dipstick or a gauge on the cell to indicate how many fuel particles are left, but the fuel has for the most part, been burned out of the fuel cell matrix. What's left behind are fission product poisons, that in many cases, absorb neutrons and would actually prevent fission from occurring.
That said, there is interaction from the standpoint that radioactive decay of activated structural components and decay of radioactive fission products and fission product poisons is going to generate some heat. Stacking a bunch of spent cells together just means you have a bunch of warm spent fuel cells stacked together. The heat generation is not additive and other than conductive heat transfer, with a small amount of radiative heat transfer if some of the surface radioactive meaterial decays and the decay particle hits an adjacent spent fuel cell it may add heat to the adjacent cells, but this is at a very low level.
Well the smart ass in me says it looks pretty much the same only drier…
Seriously, again, it depends. What type of decay, what isotope and how much water? I am assuming you mean that the fuel cell measured 100 Rem/hr on contact BEFORE it was place in the pool? If it was at the bottom of the pool covered by 16 feet of water, you would hve to account for both the impact of 4 tenth thickness of water shielding, plus the distance of 16 feet and the drop in dose rate with distance. For arguments sake, let's say the cell measured 100 Rem/hr 1 foot away. Using the formula above and assuming a point source you have DR2 = 100Rem/hr x (1 ft ^2/16 ft^2) = .39 Rem/hour or 390 millirem/hour due to the distance to the top of the pool. Now you have to add the shielding effect of the water - 16 feet is 4 tenth thicknesses, so the 390 millirem drops off even further to .039 millirem/hour. Such a dose rate is well within reason and stay times for working in spaces with those dose rates are easily managed. Back in the day, I had to conduct closeout inspections of portions of the primary side coolant system on the submarine I was the refueling Engineer for. Some of the general are radiation levels (dose rates) were 9 Rem/hour and my stay times were on the order of 90 seconds to manage my lifetime accumulated allowable exposure.
While the spent cells will get warmer with no water covering them to remove decay heat through natural circulation and convective heat transfer they won't heat up to 1800 degrees. In extreme cases, you may get some blistering in the fuel cell if there are fission product gasses trapped within the zirc matrix of the fuel cell assembly, but the probabiity of them getting hot enough to melt or burn is extremely low and in any event would take time - time enough to get water back into the pool or the fuel cells moved to a pool with water.
Going back to the earlier discussion about curies and dose rates, I think your real question is what the radiation levels would be coming from a dry spent fuel pool…
As discussed before, they won't be "interacting" with other fuel cells to produce sustained fission and criticality.
The answer to your question is yet another "It depends" It depends on how long the spent fuel has been in the pool, what the power history was prior to shutdown, time elapsed from shutdown to when the fuel cells were removed from the core and placed in the pool, the specific isotopes that are decaying - fission products, activated corrosion particles and oxides, activated structural materials in the fuel cell assmebly, etc.
A Higgs-Boson walked into Saint Peters. The priest looked up and came running down the aisle and stopped in front of the Higgs-Boson and said "You can't come in here, we don't allow Higgs-Boson particles in Saint Peters."
The Higgs-Boson replied, "But Father, how can you have Mass without me?"
I told that to our priest this morning and he laughed out loud…
Captain Robert Nicholas Miller, Commanding Officer, USS TICONDEROGA (CV 14) from May 1965 - June 1966. Back then, a typical command tour was one year so it doesn't look like it impacted his career. Couldn't find anything about whether or not he made Flag officer.
http://www.navsource.org/archives/02/people/miller_robert_n.jpg
Dogs -
Thanks again! This is all really helpful. I'm slowly getting it.
I like the curie-meter-rem rule. Distance is good - and more distance is a whole lot better. I read it over several times to make sure it sank in. And it makes sense that different materials decay with different effects. I guess all disintegrations are not created equal?
Something I don't understand from the formula though. What happens at range=0?
Let's say your damnfool dog ate a 1-curie pellet of that cobalt-60 "just because". He poops it out 10 hours later (assuming he's still with us). How many rem has he received? [Yes, I really do love these problems!]
It is most heartening to know that a bunch of spent fuel units cannot get together and start a chain reaction, even if all the water is gone. Although I get the sense if they were removed from the reactor relatively recently, didn't sit for long, and weren't operated at full power during their lifespan, things might be a little dicey if the water in the pool were to escape through a crack in the floor…
I'd like to understand just a little more about general levels of radioactivity of the components we're talking about here though. Precision doesn't matter - I'm looking for orders of magnitude. I humbly request that whenever you feel that (apparently irrepressible) urge to say "it depends", to instead make a simplifying assumption or fill in a value you feel is reasonable, and then just let me know what that assumption was along with the answer. :)
rem/hour measurement, taken at 1 meter in air for a:
- new fuel unit about to be installed into a reactor
- running fuel core undergoing a chain reaction at full power
- spent fuel core (completely used up) immediately prior to being placed in spent fuel pool
- spent fuel core, in air, after 10 years in the spent fuel pool
I enjoy reading these posts, especially when they are filled with data and empty of name calling!
BTW: I'd still like to see some links that say that it is NOT possible for SFR's to burn and or cause a meltdown if they are left without cooling water…
davefairtexHere is a great site filled with factual info that you might enjoy!
http://is.gd/s61jRU
Thanks for being interested enough to ask questions…
The wiki is incorrectly titled. It should read "List of military nuclear accidents and incidents"
A spill of radioactive liquid is not a nuclear accident. It is a nuclear incident and there is a big difference.
Even then, the article takes a lot of literary license in calling the loss of USS THRESHER and USS SCORPION as nuclear accidents.
Note that the vast majority of the naval accidents/incidents are Soviet.
CaptD -"I enjoy reading these posts, especially when they are filled with data and empty of name calling!"
It usually takes two to tango. Our friend Dogs is being very patient in explaining these things. His responses take real work to come up with. It seems clear if you approach him asking for help in really understanding his field, he's more than willing to do so. And he's actually pretty gentle about it too. Many engineers I know are not so kind or patient.
What's an SFR? Google tells me its a French mobile telephone company.
One thing I'm slowly beginning to understand is just how powerful this stuff really is. Imagine running a massive submarine for 20 years using 100 pounds of metal. Its almost magical. Same thing with a power plant. You can generate 800 mw of power for 2-5 years with maybe 1000 pounds of material. A coal plant will consume at least 6 million metric TONS of coal to do the same thing. What's that, a factor of 12 million difference?
With this much power lying around, there are bound to be issues. When Dogs talks about "activation" it means normal things like steel get turned radioactive (cobalt-60) just by being nearby.
I think we all hope for a day when our home solar panels hooked up to the PEM stacks in the basement create enough power for our homes and our cars. But even then, anytime you store energy, its dangerous simply by definition. The power to do a lot of work can usually get released in a dangerous and unpleasant way when things go wrong.
I cannot control what Wiki does…That said I would agree a spill is not in the same "universe" as a reactor meltdown!
Spent Fuel Rods are not all alike some of them in Fukushima are of the MOX type and are much more dangerous because they have Pu in them… Think more highly reactive…Storing energy can be dangerous but nothing is like NUCLEAR because of the radioactive No Go Zone it can create for generations!
Bad dog…sit Ubu, sit.
I can tell you are a software engineer because you want to multiply by zero and get something other than zero…
For arguments sake to put you in the ballpark, apply the Curie-Meter-Rem rule and run it in to 1 inch (assume the particle was trapped mid-poop )
The formula is slightly different:
D1 x X1 = D2 x X2
D1 x 1" = 1 Rem/hr x 39"
D1 = 1 Rem/hr x (39/1) = 39 Rem/hr dose rate
Multiply by 10 hours and Fido has just zorched his GI tract with 390 Rem. It may not kill him, but he will most likely exhibit signs of radiation poisoning and have a lot of vomiting and diarrhea. Just what everyone needs…a vomiting dog with radioactive diarrhea.
390 Rem over 10 hours is probably not a Lethal Dose, but it is close.
In humans, the dose of radiation expected to cause death to 50 percent of an exposed population within 30 days is known as LD 50/30 and is in the range from 400 to 450 rem received over a very short period. 10 hours isn't an acute dose, but it isn't chronic either.
There are studies of sample mice populations being exposed to between 600-700 Rem. It takes a few days for symptoms to show up and a few more days for deaths to occur. After 30 days it is almost impossible to discern between healthy and irradiated mice.
http://www.informatics.jax.org/greenbook/chapters/chapter22.shtml
There's always the possibility for "dicey", but understand that as a matter of procedure, spent fuel cells are not removed from the core until decay heat generation rates are manageable within a spent fuel pool. They also are not removed until they are spent. Cores are rated for a certain number of hours of operation, typically denominated to 100%. For example, a core may be rated for 20,000 hours of full power operation. Cores are rarely operated at 100% of the time - it takes time to start-up and shut down cores, so there will be periods of time where the plant is operated at less than 100%. You can still calculate the "burn rate". 2 hours at 50% power is accounted for as 1 hour of 100% operation against the 20,000 hour total. Likewise, operation at 20% would take 5 hours of operation to add another hour to the 20,000 hour rating total. Operating power levels over time are meticulously tracked and recorded so this total can be tracked to the hundredth of an hour.
Refueling operations are expensive and plant downtime means customers aren't getting electricity, which means the power company isn't making any money. Rightfully so, there is a good business practice to use up all of the fuel in a fuel cell before shutting down a plant for a refueling operation. Unless a fuel cell were to start exhibiting problems (uneven power flux, larger impact of fission product poisons, physical integrity compromise) it isn't going to be removed until it is "empty".
It will read whatever the background radiation levels are. A fuel cell doesn't accumulate fission product poisons until after it has undergone criticality. New fuel has never been exposed to a moderator and doesn't emit any radiation except for stocahstic, random, spontaneous fission events that likely won't be detectable since the particle won't even leave the fuel matrix, much less be capable of causing another fission event. I had to personally inspect every single new fuel cell that was going into my boat's new core. It was an underwhelming event and I spent more time getting into and out of the cleanliness suits (like the suits egg heads wear at chip manufacturing facilities to run the software that egg head software engineers write )
Depending on the plant's specific core type, thousands to tens of thousands of Rem/hour. A human being in the reactor compartment of an operating plant would receive LD 50/30 almost immediately and would likely receive an immediately incapacitating dose.
Tens to hundreds of Rem/hour. Some due to fission product poison decay, some due to activated materials, oxides, etc. From my personal experience, the highest I saw was around 30 Rem/hr.
There will be a little variability from cell to cell since both fuel particles and burnable poisons are deliberately placed within the fuel matrix to help "shape" the flux of an operating plant.
Since the half life of the predominant oxides and isotopes of structural materials, you are still going to see pretty significant readings. Not quite as high as a spent fuel cell that had just been removed, but high enough to be a concern. Complete wag here, but I'd estimate levels at about half of what you'd measure on a recently removed spent fuel cell.
[quote=CaptD]Spent Fuel Rods are not all alike some of them in Fukushima are of the MOX type and are much more dangerous because they have Pu in them… Think more highly reactive…
Storing energy can be dangerous but nothing is like NUCLEAR because of the radioactive No Go Zone it can create for generations!
[/quote]
NO, NO, NO!!! Your statement is 100% incorrect.
One core at Fukushima Daiichi had MOX fuel. It IS NOT more highly reactive, it is "differently" reactive. Plutonium fuel particles are no more inherently dangerous than uranium oxide fuel particles.
Because plutonium is more toxic than uranium, cleanup - if a core containing MOX fuel were to be damaged, breached and fuel particles disperesed - would be necessarily more complex, but not prohibitively so.
This was exactly what Chris and Gunderson started hollering about early in the Fukushima Daiichi accident that made me realize that neither knew what they were talking about. Arguing over the presence of MOX fuel in a reactor core while there is an accident in progress is like the fire department standing in front of your garage with pressurized, but idle hoses, while your house is burning down debating over whether the gas in your gas can for your lawnmower is 87 or 93 octane.
Storing energy from any generation source is not in and of itself dangerous provided proper operating procedures are followed in normal and casualty scenarios. However there is a lot of difference in the relative safety between different types of power generation. Coal is by far and away the worst in terms of lives lost. For every 1 person killed in the nuclear power industry, 4000 are killed in the coal industry.
I don't like using comparative metrics, because anyone can squish numbers around to develop a metric that supports their position, but this one is pretty good.
http://www-958.ibm.com/software/data/cognos/manyeyes/visualizations/2e5d4dcc4fb511e0ae0c000255111976/comments/2e70ae944fb511e0ae0c000255111976
Deaths per terawatt hour produced
Coal: 161
Oil: 36
Natural Gas: 4
Biofuel/Biomass: 12
Peat: 12
Hydroelectric: 1.4
Nuclear: 0.04
Now can we discuss the No Go Zone that is being created on our planet by the burning of fossil fuels compared to nuclear power and put things in perspective?
[quote=Dogs_In_A_Pile]Now can we discuss the NO Go Zone that is being created on our planet by the burning of fossil fuels compared to nuclear power and put things in perspective?
[/quote]
Jason Heppenstall mentioned a sobering statistic I was not aware of in his last blog entry How Not to Eat a Planet.
There are many things about nuclear power that are abhorrent, but the one statistic that suffices is that there is, on average, one serious accident for every 3,000 years of reactor use. Thus, with the approximately 11,000 extra reactors that would be needed to phase out coal, we could expect around four Chernobyls or Fukushimas per year, and also lack the money or resources needed to deal with these disasters.Just one nuclear accident is too many, leaving an uninhabitable zone for the rest of time.
Biggest surprise of the day: new fuel has no radioactivity. Uh, so…how do you start the plant? In other words, what thing fires off all the neutrons to start the chain reaction?Its good to get a sense of just how radioactive all that stuff is; if you have 10 of those spent fuel units sitting in the pool in water, its probably ok (now we could calculate the rem/hour from the source under 8 feet of water and adding another 10 meters of air), but if the water leaks away things get more unpleasant, especially up close. They won't be exploding but they'll be emitting heat and radioactivity and it is a place to keep great distance from to keep that dosage level down. Seems like a problem for our lucky plant workers rather than a problem for the public.
The moral of our dog story is, avoid touching the radioactive material. What is survivable on your desk at 1 meter is almost fatal when placed in your pocket for a day. Which brings me to contamination. If you manage to ingest iodine or cesium it will be like Fido's Unfortunate Meal Experience, except it won't get pooped out. 10 microcuries ingested over the course of a year means .00039 x 24 x 365 = 3.15 rems per year for the rest of your life to tissue within an inch…oh now that's a problem. That was for a point source, but this is a whole bunch of particles diffused throughout your body. That equation would seem to get really evil when 1 inch decreases to 1 mm. Is there a new equation? Or do we just multiply by 25 and your lucky liver gets blasted with 75 rems per year?
When the radioactive dust comes to town, I guess the answer is, stop breathing. :) Seems to me I'd much rather have large chunks of highly radioactive stuff that I can keep a healthy distance from, than a whole lot of much less radioactive individual particles that I end up breathing in or eating that stays with me for life. I tried researching studies on implications of ingested contamination, but it doesn't seem like there really are any large conclusive studies about it. Except the one about thyroid cancers in Russia after Chernobyl. Factor of 10 increase in younger people. Seems like best bet is to hide and not breathe for the first 6 half-lives of I-131 (48 days?) once the criticality stops happening. And the 10 microcuries of cesium would seem to be a pretty unpleasant experience too, if you manage to ingest it all. Outside the body, its a big ho-hum. Inside, not so good.
One thing I did find amusing is that there is a lower level of mortality from cancer (and indeed all causes of death) in nuclear industry workers than in the public of that same country. Another surprising result for me. Perhaps the attention paid by them to cancer from radiation makes them avoid all the other easy to avoid cancer-causing substances? (If you're going to work a a nuke plant, best not to smoke…duh)
http://www.nap.edu/openbook.php?record_id=11340&page=194
So how might a member of the public measure particulate contamination? A member of the public seems far more at risk from lots of tiny airborne molecules of radioactivity than some large chunk of an intense radiation source. Because I just love gadgets like this, I bought this keychain radiation detector that starts chirping at 100mrem/hour. After looking at the numbers, I'm concerned this thing is never going to be useful unless a chunk of a spent fuel assembly happens to land in my backyard.
[quote=davefairtex]Biggest surprise of the day: new fuel has no radioactivity. Uh, so…how do you start the plant? In other words, what thing fires off all the neutrons to start the chain reaction?
Its good to get a sense of just how radioactive all that stuff is; if you have 10 of those spent fuel units sitting in the pool in water, its probably ok (now we could calculate the rem/hour from the source under 8 feet of water and adding another 10 meters of air), but if the water leaks away things get more unpleasant, especially up close. They won't be exploding but they'll be emitting heat and radioactivity and it is a place to keep great distance from to keep that dosage level down. Seems like a problem for our lucky plant workers rather than a problem for the public.
The moral of our dog story is, avoid touching the radioactive material. What is survivable on your desk at 1 meter is almost fatal when placed in your pocket for a day. Which brings me to contamination. If you manage to ingest iodine or cesium it will be like Fido's Unfortunate Meal Experience, except it won't get pooped out. 10 microcuries ingested over the course of a year means .00039 x 24 x 365 = 3.15 rems per year for the rest of your life to tissue within an inch…oh now that's a problem. That was for a point source, but this is a whole bunch of particles diffused throughout your body. That equation would seem to get really evil when 1 inch decreases to 1 mm. Is there a new equation? Or do we just multiply by 25 and your lucky liver gets blasted with 75 rems per year?
When the radioactive dust comes to town, I guess the answer is, stop breathing. :) Seems to me I'd much rather have large chunks of highly radioactive stuff that I can keep a healthy distance from, than a whole lot of much less radioactive individual particles that I end up breathing in or eating that stays with me for life. I tried researching studies on implications of ingested contamination, but it doesn't seem like there really are any large conclusive studies about it. Except the one about thyroid cancers in Russia after Chernobyl. Factor of 10 increase in younger people. Seems like best bet is to hide and not breathe for the first 6 half-lives of I-131 (48 days?) once the criticality stops happening. And the 10 microcuries of cesium would seem to be a pretty unpleasant experience too, if you manage to ingest it all. Outside the body, its a big ho-hum. Inside, not so good.
One thing I did find amusing is that there is a lower level of mortality from cancer (and indeed all causes of death) in nuclear industry workers than in the public of that same country. Another surprising result for me. Perhaps the attention paid by them to cancer from radiation makes them avoid all the other easy to avoid cancer-causing substances? (If you're going to work a a nuke plant, best not to smoke…duh)
http://www.nap.edu/openbook.php?record_id=11340&page=194
So how might a member of the public measure particulate contamination? A member of the public seems far more at risk from lots of tiny airborne molecules of radioactivity than some large chunk of an intense radiation source. Because I just love gadgets like this, I bought this keychain radiation detector that starts chirping at 100mrem/hour. After looking at the numbers, I'm concerned this thing is never going to be useful unless a chunk of a spent fuel assembly happens to land in my backyard.
[/quote]
dave -
You have given me more homework. You're batting around .300 with the latest post - if you played second base you'd be in Cooperstown.
I am off for a 6 mile run, will tackle your latest upon my return.
I hope I didn't get marked down for buying that radiation detector…it was practically crying at me to buy it!
Absolutely No Not Never. Toys and gadgets are cool. You actually get marked up…
Just ask Rob Hare - he had a flashlight app on his iPhone which came in very handy. We were at the Martenson Lowesville seminar a few years ago in the Shenandoah Mountains of south central Virginia. There is a circuit trail near the seminar site that runs up to a couple of rock face overlooks at about 3700 feet. For some odd reason that had nothing to do with scotch, a bunch of us decided to take a hike in the middle of the night and go sit on the rock ledge. After an hour or so we headed back and of course the flashlights we brought did not work.
Enter Rob Hare - aka Inspector Gadget - with his flashlight app to save the day (or at least prevent a sprained ankle or two)
No kidding…there's an app for that.
This has been a very productive thread and I thank you for your time.
Lakhota!!! You are more than welcome - Pilamaya yelo (I googled it )
We haven't heard from you in ages. Cat and I sincerely hope you have been well. Please send me a PM and let us know how you have been.
[quote=davefairtex]Biggest surprise of the day: new fuel has no radioactivity. Uh, so…how do you start the plant? In other words, what thing fires off all the neutrons to start the chain reaction?
[/quote]
New fuel is like mayonnaise. Until you open it, you don't have to put it in the refrigerator.
Okay, maybe not the best analogy. There are a couple of dynamics for new fuel and achieving criticality. First, the fuel has to be arranged in a very specific geometry with relation to other fuel cells and second, you must have a moderator surrounding the fuel. Most plants have control rods - made of a material that readily absorbs neutrons that move within channels in the fuel cell matrix. As the control rods are withdrawn, the neutrons from the fuel can travel into other fuel cells, strike the nuclei of other fuel particles and trigger the release of other neutrons. When rods are inserted, the absorb neutrons and "turn off" the fission process.
On to the moderator. The moderator (typically water) does several things. From a fission standpoint, the moderator acts as a buffer to slow down neutrons that are generated within the fuel cell matrix. Neutrons are born at high energies and travel into other fuel particles where they may cause more fission events. However, these high energy "fast" neutrons aren't very good at causing fission since they are moving so quickly and with higher energies. The water 'moderates' fast neutrons into slower speeds and lower energies - these neutrons are very effective at triggering further neutron release when they hit adjacent fuel target nuclei. The second and very important function a water moderator serves is to remove heat from the fuel power unit and transfer it to steam generators where it transfers its heat producing steam to drive either propulsion or electrical generation turbines or in the case of nuclear powered ships and submarines, both.
Once a new fuel cell has been installed in a core in the right geometry, and covered with moderator, the control rods are slowly and very, very meticulously withdrawn. This is typically done in intervals so instrumentation can measure the growing neutron population. At some point, criticality is achieved and for the existing temperature and pressure conditions, the reactor is critical and "self-sustaining" - in other words, it's making enough fast neutrons, that are being moderated to thermal neutrons to sustain fission. There are a lot of dynamics about pressure and temeperature effects on the fission process, but that is specific to each reactor core design. I cannot and won't elaborate on Naval Nuclear Propulsion core design as that is classified information.
Once a fuel cell has "gone critical" and been exposed to a flux, that's it. Fission product daughters and fission product poisons are "born" and are now within the physical boundary of each fuel cell matrix. They are radioactive and have their own specific decay mechanism and half-life. This decay is what contributes to decay heat generation following a shutdown. These fission product daughters and poisons accumulate in the fuel matrix over time and that's what leads to the rods becoming radioactive sources. Don't worry, a fuel cell isn't like a balloon. If operated properly - even at the extreme ends of operating parameters (and the design margins are very conservative) all of the fission product daughters and poisons are contained within the fuel cell matrix.
Again, the driver as to how severe this scenario might get is pre-shutdown power history and how long the spent fuel has been in the pool. As you recall from early discussion, fuel cells aren't transferred in spent fuel pools until decay heat generation rates are manageable. That said, "manageable" assumes water that will remove heat through convective heat transfer (sure there is a small amount of radiative heat transfer) and natural circulation of the water in the pools.
Not touching radioactive material is a pretty good rule always. Then again, we are bombarded daily with radioactive particles from multiple naturally occurring sources without even knowing it.
Not so fast on the "desk at one meter to back pocket for a day" scenario. It depends on what type of radiation it is. If it's alpha, who cares. Alpha particles are stopped by the layer of dead skin. If it's beta, clothing will shield the particles from entering soft tissue and ionizing and/or damaging the cell structure or DNA. Gammas are a different beast - they will penetrate and cause damage so you have to be careful. Neutrons are treated the same as gamma except they are much more damaging because they are a larger particle and tear the cell and DNA apart irreparably more so than gamma.
We used a following nice little anecdotal story when teaching new nuclear operators at Nuclear Power School and Prototype Training.
You are handed a plate with 4 cookies on it. One cookie is made with alpha particles, one is made with beta particles, one is made with gammas and one is made with neutrons. You are required to hold one in your hand, put one in your pocket, eat one and you may throw one away. Explain your choice of what to do with the cookies.
I'm not going to tell you - I figure you have given me enough homework over the last week so now it's my turn. You have one day to answer!!!
Moving on…if you ingest a particle of iodine or cesium, you will indeed pass it. Iodine is tricky since it is preferentially deposited in the thyroid. Let's say you were smart enough to take a KI tablet and your thyroid is full of non-radioactive iodine so you don't get any stuck. This also assumes that youtook the KI tablet when you were supposed to - not when the knuckleheads on the news said to following Fukushima. Anyone in the US who took KI tabs was foolish. Hawaii included. They had a higher risk of iodine poisoning than from any risk from airborne radioactivity from the accident. Fear sells and ignorance buys.
Anyway, in most cases, an ingested particulate is passed through the body and eliminated via urination or defecation. With the according dose to the exit pathway. So your 10 microcurie scenario isn't at all realistic as it will probably be passed from the body within 24 hours. Note however, that there are some isotopes you may run across that are nasty because they are preferentially deposited. Iodine is one of those. Strontium is another. Sr is known as a bone seeker because it is very chemically close to calcium and will be deposited in your bones. Radium is another. These are double edged sword - radiological oncologists have developed very effective techniques to "place" boneseekers and other preferentially deposited isotopes in the human body for up close and personal targeted radiation therapy in cancer patients. The size and activity of the particle are tightly controlled so as to control exposure.
For airborne particulate, 90% of the particulate that is inhaled is exhaled, so in the event of exposure to airborne particulate following an accident, you start with determining the amount of airborne activity, take 10% of that and assume it is still in the lungs, nose or throat. Follow up treatment is dependent on what the isotope is and how much activity is present. Just because you snorkel down some airborne particulate doesn't mean you will have short or long term problems. Airborne particulate is a layer of complexity beyond surface contamination because alpha and beta particles inside your body will cause a lot more biological damage to living tissue than they will if they had just been external skin contamination. That's why isotopic determination is critical (no pun intended) in the event of airborne contamination.
When any type of radioactivity comes to town, the mantra to follow to reduce exposure is Time-Distance-Shielding.
Minimize your time exposed to whatever the source is.
Maximize your distance from whatever the source is.
Utilize available shielding between you and whatever the source is.
Regarding half lives, you can do the math, but for emergency response and follow up accident response and recovery planning, we consider the radioactivity from a source to be zero when 5 half lives have elapsed. Yes, we all know that there is still something left, and if you always walk half the remaining distance to a wall you will never reach the wall, but after 5 half lives, what's left is considered to be zero. 6 half lives is more than 5 half lives so it's even 'zeroer.'
Little known fact about smoking…pack a day smokers will receive 2-5 Rem per year to their lungs from the naturally occurring radioactivity uptaken by the tobacco plant that they deliberately choose to ingest into their bodies along with other hot, toxic, combustion by-products. I have actually heard a smoker tell me he was getting an early start on his lung cancer radiation therapy. In his case, Darwin was clearly wrong.
There are any number of good radiac products out there that will measure radioactivity. In a price no object scenario you could get a detector specifically calibrated for alpha, beta, gamma and neutron separately. Although beta and gamma can be detected by the same instrument. You would want it to be sensitive enough that it could measure background radiation. Determining background levels is important because you have to know what you are starting with. The area near one of the facilities I trained at was subject to temperature inversions that would trap radon. We took portable air samples several times a day to establish background levels. If they were elevated, we would do an isotopic analysis to determine what it was. So if on one day background was 60 counts per minute we would set our alarms at 160 counts per minute. During days when a temperature inversion was in progress, it was not unheard of the have background readings of 44 counts per minute. You have to know where your baseline is, and you have to know that your baseline can vary from day to day. What you are looking for isn't the change from 30 to 50 counts per minute. You are looking for the change from 30 to 1100 counts per minute.
Without knowing the specifics of you detector, I'd say it's too limiting. If it doesn't start chirping until it's detecting 100 mrem/hour, that is way too insensitive. I'd be taking action if I was being exposed to a 10 mrem/hour dose rate and I would want my radiac to be sensitive enough to detect down to 0.1 mr/hour on up to 100mr/hr. If I started seeing levels approach 100 mrhour, I'd be clearing out as fast as possible.
I think I got to most of your questions and cleared up some of the misconceptions.
Don't forget your radioactive cookie homework. You have until 8:10 PM tomorrow evening.
It would seem to the untutored mind that you gave me all the information required in the paragraph immediately preceeding the question! I have two types of shielding - skin, and clothing. Once I use those two things best, the question boils down to, which cookie should I eat?* Hold the alpha cookie in my hand, since as you said earlier, its effects are stopped by my dead skin layer.
- Put the beta cookie in my pocket, since its effects will be stopped by the clothing.
- Throw the neutron cookie away, since its effects are more damaging than the gamma cookie, and it can't be stopped by any of the shielding (shirt, skin) I have at my disposal.
- Eat the gamma cookie, since it hurts less than the neutron cookie, and also can't be stopped by any shielding I have at my disposal.
I had no idea the nuclear world was so complicated! Or so tasty! Before today, I would never have considered eating a gamma cookie, and yet here I am wolfing one down…
Seriously though, the world you describe is wonderfully complex. Each radioactive source emits varying amounts of each of these cookies, and different radioactive molecules are absorbed (or rejected) by the body in different ways. Tricking your body into rejecting particles would seem to be a good idea - but without poisoning yourself by taking too much. I will think more deeply upon all you have said and respond later.
Thanks again for all your time, super helpful. As Don Rumsfeld said so often, there are the known knowns - the things we know that we know. And there are the known unknowns - the things we know that we do not know. And then there are the unknown unknowns…coming into this discussion, I had a lot of the last. So many things that I didn't know that I didn't know!
http://www.youtube.com/watch?v=GiPe1OiKQuk
[Not a fan of the Iraq war, but I have to say, I love this particular video clip, and the whole concept of unknown unknowns and why understanding that concept is so important]