-PhD in nuclear engineering from the University of Michigan.

-I work at a US national laboratory and my research involves understanding how uncertainty in nuclear data affects nuclear reactor design calculations.

-I have worked at a nuclear weapons laboratory before (I worked on unclassified stuff and do not have a security clearance).

-My work focuses on nuclear reactors. I know a couple of people who work on CERN, but am not involved with it myself.

-Newton or Einstein? I prefer, Euler, Gauss, and Feynman.

Ask me anything!

EDIT - Wow, I wasn't expecting such an awesome response! Thanks everyone, I'm excited to see that people have so many questions about nuclear. Everything is getting fuzzy in my brain, so I'm going to call it a night. I'll log on tomorrow night and answer some more questions if I can.

Update 9/24 8PM EST - Gonna answer more questions for a few hours. Ask away!

Update 9/25 1AM EST - Thanks for participating everyone, I hope you enjoyed reading my responses as much as I enjoyed writing them. I might answer a few more questions later this week if I can find the time.

Stay rad,


Comments: 1837 • Responses: 17  • Date: 

Cromiell1065 karma

Hi there, I'm currently 16 years old and am considering this field. Please do your best to answer some of my questions. :)

  • How many years of study did it take you to get your PhD?

  • What does your day-to-day routine consist of?

  • Would you recommend this job to young people? Why or why not?

  • How long did it take to get a job after your PhD?

  • What kind of work did you do for experience prior to your PhD?

  • In your field, which Canadian university is usually recognized as a good school? (I'm trying not to make this question sound generic, but I really do want to know your opinion on some of the universities in Canada. I've so far looked at U of T and Waterloo, so I don't have much to go on.)

  • What knowledge made up the core/basis of your education in university?

  • How has this job affected you as a person?

  • How long have you wanted to be a nuclear scientist?

There are about a million more questions I want to ask you, but I can't seem to put them into words just yet.

Thank you very much for doing this AMA. :)

Edit: Wow, never expected this to be at the top. Thanks for the answers, guys, they've been very helpful. Hopefully I'll get one from OP as well.

IGottaWearShades30 karma

How many years of study did it take you to get your PhD?

It took me 8 years from when I started college to get my PhD. 8-11 years is the normal range for a PhD.

What does your day-to-day routine consist of?

I wake up, feed my fish, and go to work. We have flexible hours (which is nice, especially when you're doing research-type work), and I usually show up between 9-10am and leave around 5-7pm. I spend most of my day in front of a computer writing code or research articles/reports, but my days are sprinkled with meetings, brainstorming sessions, and hitting the books when I need to remember/learn/discover something.

Would you recommend this job to young people? Why or why not?

I definitely recommend this job (and a career in nuclear in general) to young people. We're only going to need more and more energy and nuclear is the only way to get baseload (ie constant and reliable) power without directly emitting greenhouse gases.

How long did it take to get a job after your PhD?

I actually got my job 6 months to a year before I got my PhD. I finished all of my classes at UM and started a postmasters at the lab while I finished my dissertation work. There was 100% overlap between my dissertation work and my lab work, so my boss was happy to employ me while I finished up at school (he was on my dissertation committee too). Finishing up your dissertation work while working a full-time job is actually pretty common in nuclear. Hiring a postmasters/postdocs is way cheaper than having a salaried employee do the work, so managers are very open to the idea. It also opens a path for them to hire the employee later on if they want to keep them.

What kind of work did you do for experience prior to your PhD?

Before my PhD I did a couple of summer internships at national labs and one or two summers of research for professors. I also worked one summer as a telemarketer, which sucked.

In your field, which Canadian university is usually recognized as a good school?

I'm not very familiar with the Canadian universities, so I can't answer this question. It looks like some of my fellow Redditeers have answered this question below.

What knowledge made up the core/basis of your education in university?

This is a tough question, it's like trying to describe a painting in one sentence. The core of my education consists of methods (especially Monte Carlo methods) for solving the Boltzmann transport equation and knowledge of how radiation interacts with matter.

How has this job affected you as a person?

It's hard to say how this career has affected me as a person - I've only ever been me, so it's hard to tell how I've changed. College definitely made me smarter and taught me how to focus, and coding tends to sharpen your mind too. I find myself constantly thinking about different problems and puzzles, and not just related to all things nuclear, and I find myself asking a lot of "what if" and "why" questions.

How long have you wanted to be a nuclear scientist?

I've wanted to be a nuclear scientist since my high school physics class. I had a great teacher and she inspired me to make a career in helping to provide the world with clean, plentiful energy.

Frajer503 karma

How safe is nuclear energy?

IGottaWearShades1445 karma

Nuclear power is one of the safest (if not the safest) form of generating electricity. Nuclear gets a bad rap because most people don’t understand how it works and because fear of the unknown is a very real thing. Most nuclear reactors (Chernobyl excluded) are designed so that they become less reactive as they heat up, meaning that the “runaway” accident that you always hear about (where the reactor cannot be shut down and burns a hole through the concrete containment) could never happen - the reactor would shut itself down before anything reached an unsafe temperature. Chernobyl was not designed this way because it was made principally to produce plutonium for the Soviet weapons program. I live about 200 miles downwind from a nuclear power plant in the US, and I don’t worry about it at all.

Reactor designs are getting safer and safer, and there’s an emphasis today on designing reactors that are passively safe (meaning that no reactor operator action or external power is required to shutdown the reactor safely during an accident scenario). Even without this focus on passive safety the track record of nuclear is pretty good when compared to other forms of generating energy. Nobody died from Three-Mile Island, and I doubt anyone is going to die from Fukushima. Estimates on the death toll from Chernobyl vary greatly - some people say it was around 50 deaths, and some say it was on the order of 1000.

It’s also important to keep risks in perspective. 1000 people die every year from falling down stairs - is that an unreasonable risk? Absolutely not. ~30,000 people die every year from the particulates that are released from coal power plants. (See link below). The chances of a major radiation release from a US nuclear plant within the next year is on the order of 0.1% based on NRC estimates. Nuclear power has killed zero people in the US and no more than thousands internationally (from Chernobyl) over the past 30 years, which makes it one of the safest viable sources of base-load power. A comparison of the risk associated with each form of generating electricity is available at:


Resonance1584214 karma

What about nuclear waste?

IGottaWearShades5 karma

First, there really isn't that much waste. One nuclear fission releases 50 million times as much energy as a coal combustion reaction, which means nuclear power plants don't use very much fuel (this is why submarines and aircraft carriers use nuclear reactors, because you don't need to refuel them very often - they can go on month- or year-long missions without needing to refuel). All of the nuclear waste (we call it spent nuclear fuel) from 30 years of reactor operation in the US can fit on one football field (stacked 10 feet high). This is REALLY impressive when you consider that nuclear power generated about 20% of the US's electricity during that 30 year period. In fact, Yucca mountain, the proposed nuclear waste repository, is only about the size of a football field (field, NOT stadium).

Second, you can recycle most of that waste. Only 5-6% of the uranium atoms in nuclear waste have fissioned, but the products from these fissions "poison" the fuel (they gobble up neutrons) to the point where the fuel cannot support a self-sustaining chain reaction. You can remove that 5-6% of bad actors using chemical reprocessing and put the other 94-95% of the fuel back into fast breeder reactors* until it's essentially entirely consumed. We don't reprocess fuel today because it's cheaper to just mine more uranium and make more "fresh" (non-recycled) fuel, but this won't always be the case.

Most of the long-lived radioactivity in nuclear waste comes from that 94% of recyclable fuel, so reprocessing can DRAMATICALLY reduce the long-term heat load of nuclear waste. There's also a lot of useful isotopes in nuclear waste, such as Pu-238 (which was used for the nuclear batteries in the Voyager space probes) and Moly-99 (which is used in medical procedures). After you reprocess the fuel and take this useful stuff out, the remainder of the fuel (which is less that 1% of its original volume and mostly Cesium and Strontium) is not extremely radioactive. In fact, this stuff will be harmless in only 300-500 years. 500 years may seem like a long time for you and me, it's not very long in the grand scheme of things. There are houses and even TREES that have been standing for more than 500 years, so I'm confident we can keep this stuff safe in the Nevada desert for 500 years.

I think Yucca mountain would be an acceptable place to store the fuel even without reprocessing, but I think reprocessing is really the way to go. Nuclear waste is really a political problem, not a scientific problem, and Harry Reid has fought so hard to block Yucca mountain because he's afraid it will hurt the tourist industry in Vegas. As it stands, nuclear waste isn't an immediate problem that we have to solve today. After a few years, the radioactivity in spent nuclear fuel has decayed away enough that the fuel can be placed in dry cask storage (big concrete casks, see http://en.wikipedia.org/wiki/Dry_cask_storage). We'll have to do something with that fuel eventually, but it can stay in dry cask storage almost indefinitely.

*-There was a question about Terrapower and traveling wave reactors below that I'll answer here. Terrapower is an experimental nuclear design company founded by Bill Gates and Intellectual Ventures. Fast breeder reactors are capable of creating more fissile fuel than they consume (this is known as "breeding" fuel). How is this possible? In a reactor, non-fissile U-238 can absorb a neutron and turn into fissile Pu-239. The average fission reaction releases more than 2 neutrons, so it's possible to use one of those neutrons to continue the fission chain reaction and the other to create Pu-239. Ergo, you make more fuel than you use. I think fast reactors will be big sometime in the not-too-distant future, but they won't get big for awhile - we have so much more experience building light water reactors that any other reactor design won't be economically competitive for many years.

[deleted]3 karma


IGottaWearShades279 karma

Nuclear power really doesn't make that much waste. Here's a picture of all of the waste (it's inside of those big concrete casks) that was generated by the Maine Yankee Nuclear Plant during its 25 year lifetime. During this time the plant produced the majority of Maine's electricity (source: Wikipedia). For 25 years of energy, that's not much waste. http://www.scientificamerican.com/media/inline/presidential-commission-seeks-volunteers-to-store-nuclear-waste_1.jpg

Nuclear power doesn't make very much waste because the fission reaction is so energy dense. One fission reaction releases ~200 million eV of energy and one coal combustion reaction releases ~4 eV of energy, which means that you need 50 MILLION combustion reactions to release as much energy as one fission reaction. Nuclear power plants are only refueled once every 18 months (and even then they only replace 1/3rd of the core). There's a coal plant not far from my parents' house and it needs to be refueled almost every day, and I've had the pleasure of being stuck at the railroad tracks while the 93-car train delivered the daily supply of coal to the plant.

Opponents to nuclear like to propagate the image that nuclear plants make gobs of waste, but that simply isn't true. The Yucca mountain repository (which is designed to hold 30 years of USA nuclear waste (and nuclear power generated 20% of the USA's electricity during that 30 year period) ) is only about the size of a football field.

Furthermore, you can reduce the volume of nuclear waste by 90+% if you reprocess the fuel, which I'll discuss in another post...

seodoth23 karma

What if someone flies an airplane into a nuclear plant?

ephphatha284 karma

How many rads per second do you gain at work?

IGottaWearShades292 karma

Zero above background - I work in an office. The background dose in America is usually around 300 millirem/year, although it can vary by a factor of 2 or 3 depending on where you live.

DanTheRip188 karma

Could you submit some kind of prof?

Also have you ever done something like this(http://www.youtube.com/watch?v=THNPmhBl-8I) at a party?

IGottaWearShades201 karma

I sent a message to the mods, I'm hoping they'll respond and then vouch for me.

An no, I've never done something like that at a party - I only order hard drinks.

Lichloathe159 karma

How far are we away from nuclear fusion do you think we are? Where it is stable and efficient.

IGottaWearShades260 karma

Very far away. There are fundamental materials limitations that make the future of fusion power a dismal one. The typical fusion reaction (also the easiest one to get to happen) involves fusing deuterium and tritium into helium and a 14.1 MeV neutron. From a reactor materials perspective, 14.1 MeV neutrons are going insanely fast, and they do a lot of damage to fusion reactor materials.

Since neutrons have no charge, there's nothing we can do to prevent fusion neutrons from colliding with and damaging the inner wall of fusion reactors. Any operating fusion reactor would have to shut down once every 1-2 years to completely replace the inner wall of the reactor (which could in itself take 1-2 years). I doubt that any fusion reactor could be economical because of this. The fact that we also haven't hit breakeven yet (the point where you get as much energy out of a fusion reactor as you put into it), makes me very skeptical about the future of fusion power.

There are aneutronic fusion reactions that don't emit any neutrons, and I think any viable fusion reactor will run on these reactions. Unfortunately these reactions are much more difficult to achieve than D-T fusion, which makes them even farther away than D-T fusion.

Also, it should be noted that fusion isn't a magic bullet that produces energy without making any radioactivity. That 14.1 MeV neutron activates (makes radioactive) the structural materials in a fusion reactor. In fact, fusion reactors would actually be more radioactive than fission reactors; however, this radioactivity is not as long-lived as that from a fission reactor, and decays away more rapidly. Again, since aneutronic fusion reactions don't make any neutrons, they should not create any radioactivity and would not have this problem.

EDIT - I discuss cold fusion in another post farther down.

IGottaWearShades141 karma

Hey everyone, thanks for participating in this AMA. I definitely was not expecting such an overwhelming response! I'm done answering questions for the night, but I'll try and answer a few more tomorrow night - I definitely think the nuclear waste question deserves a better response than the few snippets I've given.

Stay rad,


20c8e4399c98 karma

What made you want to be a scientist and go into this field?

What do you do in your spare time?

What advice would you give students or young scientists going into the field of nuclear energy/materials research?

What research are you watching (besides your own)?

IGottaWearShades197 karma

1-I was always good at math and science, but I had a really good high school physics teacher who inspired me to get serious about it and go into nuclear engineering. I originally wanted to work on nuclear fusion research so that I could help provide mankind with a limitless source of energy, but after a few undergrad courses in nuclear I started to realize that fusion would probably never be a practical source of electricity, and that nuclear fission reactors can (more-or-less) provide us with that limitless source of clean energy.

2-I enjoy running, rock climbing, playing the piano, and hiking. Yes, I have played Dungeons and Dragons before.

3-Take some computer science classes. Programming is a HUGE part of nuclear (at least at the research/academia level) and it's very hard to find bright students who are good coders. Learn C++ or Fortran; MATLAB is useless. Learning some parallel programming would be great too, nuclear codes are heading in that direction in the future. The job outlook for nuclear energy and materials research is great, so stick to it!

4-I'm really interested in what's going on with next-generation reactors and small modular reactors. These reactor designs can be used to do more than just generate electricity. There are reactor designs that can produce high temperature heat to desalinate water, can produce hydrogen, etc. There are also lots of exotic reactor designs, like high-temperature gas-cooled reactors that physically cannot melt down (they can remain at a safe temperature after any accident just by transferring heat to the air around the reactor vessel) and molten salt reactors, where the fuel is in a liquid form to begin with. We only have light water reactors in the United States (which are great for generating electricity), but it will be interesting to see what kind of new uses we discover for nuclear power once we start building the next-generation of reactors.

ase891348 karma

Do you think you could build a nuclear bomb given the resources to do so?

IGottaWearShades115 karma

Anyone holding a Secret or higher clearance cannot speculate on classified subjects. Fortunately I do not have a clearance, so I’m free to speculate wildly.

Given a significant quantity of HEU or plutonium, high-precision machining tools, and LOTS of spare time...maybe within my lifetime. The Manhattan Project involved a some of the brightest human minds ever to exist and a blank check from the US government, and is one of the most impressive feats in human history. A lot of the engineering tricks that made the Manhattan Project successful are highly classified, and I’d have no idea whether anything I came up with could be successful without testing it - which I don’t plan to do.

kighl35 karma

Its pronounced nucular. SHENANIGANS!

IGottaWearShades93 karma

It is not, President Bush.

thetebe31 karma

As the chosen profession seems to often be portraited as goverment run in the movies or tv series we get over here (Sweden), is it any truth to this, or are there good amounts of research being done outside that theatre for private companies?

When working for nuclear weapons, what where your feelings about the work you did having such terrible possible future?

Could you elaborate a bit on the uncertainties and the design problem?

Do the field talk about the growing danger of a collapse inside the Sarcophagus and the possible new release of radioactive particles once again getting airborne?

This might be one of the most interesting AMAs I've seen in a while, sir.

IGottaWearShades84 karma

Although governments are responsible for the birth of nuclear power and they still have a STRONG role in nuclear science research and development, there is a significant amount of nuclear research that is being done by private companies. Mostly this research is being performed by the reactor vendor companies (Westinghouse, GE, Areva, etc.), who design nuclear reactors. They develop radiation-resistant materials, improve the performance of the nuclear fuel, develop core loading patterns, etc. This research is extremely proprietary, so the different vendors don't correspond much. You don't see much of this side of nuclear research at a national lab, but you see it more if you're in academia (because they do more consulting).

I did work at a weapons lab, but the work I did had little, if any, application to the weapons program. I think the science and extreme conditions you have to deal with when designing weapons makes for a very interesting problem, and I know that some will argue that the nuclear weapons are an effective deterrent and might even promote world peace. However, I'm not comfortable knowing that my work could be used to kill someone (even if it's for the greater good), so I'm happy that I don't work on weapons stuff.

Nuclear data, such as the probability that a uranium-235 atom will fission when hit by a 1 eV neutron, is determined experimentally in a laboratory, and everything that is calculated experimentally has an uncertainty associated with it. Other sources of uncertainty include dimensional uncertainties (Are the uranium pellets perfectly cylindrical? Do we exactly know the spacing between the fuel rods?), fuel composition uncertainties (Do we know exactly how much U-235 versus U-238 is in a fuel pellet?), fuel burnup uncertainties (when uranium and plutonium fission there is a probabilistic distribution of fission products and daughter nuclides that can be formed), and coolant temperature uncertainties (nuclear physics and materials effects are temperature-dependent). Nuclear scientists build benchmark experiments and observe how these systems behave in order to estimate the impact of these uncertainties. Reactor designers incorporate safety margins in reactor designs to account for the effect of these uncertainties. The better that we understand the sources and effect of these uncertainties, the safer we can make reactors and the more we can shave off these safety margins. Increasing the power of a reactor by 0.5% may not seem like much, but it's actually very significant when that reactor is producing 3000 MW of power.

Unfortunately I haven't really been following the status of the Chernobyl Sarcophagus, so I don't think I'm qualified to address this. I CAN say, that one of the good things about radioactive contamination is that things don't stay radioactive forever. The extremely long-lived stuff (with half-lives on the order of 100,000 years) is not very harmful because it decays too slowly to hurt you. The extremely short-lived stuff (with half-lives on the order of seconds) isn't that troublesome because it decays so quickly. The really bad stuff is somewhere in the middle: the Strontium-90, Cesium-137, and Iodine-131 (with half-lives of about 30 years, 30 years, and 8 minutes, respectively). Essentially all of the Iodine-131 from Chernobyl has decayed away and about half of the strontium and cesium is gone, which makes things a little better.

People in the nuclear field don't talk about Chernobyl very much. The attitude towards Chernobyl is less "we should be ashamed of our industry because of this disaster" and more "what were they thinking!?" Asking a nuclear engineer about Chernobyl is kind of like asking a medical doctor about using leeches to cure disease - it's more of a legacy from a more ignorant age than a practical concern.

stuffineedtoremember26 karma

How many years of schooling did it take / how much did that cost

Did you ever sleep during school or was there too much work

IGottaWearShades67 karma

I did my undergrad and PhD in a total of 8 years, which was a little fast. The norm is 4-5 years for an undergrad degree in nuclear engineering, and 5-6 years for the Master's + PhD.

I was lucky enough to do this without accruing any debt. I got a scholarship for my undergrad and a fellowship for grad school. There are lots of good fellowships out there for engineering grad school, and most grad engineers finish without taking on much/any debt. Even without a fellowship, most professors will only accept students if they have enough money to fund them (ie pay their tuition and give them a living stipend).

I managed to actually get some sleep while in school, but I also didn't have to work a job and I didn't date much in undergrad.

cherryrae18 karma

I'm not asking this in a condescending tone at all, (but with genuine curiousness if there is a loop hole to student loans...) trust fund/family money?

IGottaWearShades52 karma

A little bit of family money, but not much (my parents are a kindergarten teacher and an accountant). They definitely helped me get through school (they paid my rent and helped with living expenses at first). Summer internships pay very well in nuclear, and you can make summer money go a long way during the school year.

TKInstinct25 karma

Is there any room for Chemists in the Nuclear fields? That's what I'm doing, and I was interested in the use of Thorium in Power Plants.

IGottaWearShades39 karma

Nuclear engineering is actually a very diverse field, encompassing radiation physics, thermohydraulics, and material science. Chemists are valuable in at least two sub-specialties: materials for nuclear reactors and chemical separation of irradiated materials.

Regarding reactor materials: The materials used in reactors must be resistant to heat, radiation, corrosion, and mechanical fatigue. Research is constantly being done to assess the lifetime of current reactor materials and formulate new materials that can withstand reactor environments for longer periods of time.

Regarding chemical separation: Many useful isotopes (plutonium-238, technetium-99m, …) must be created in nuclear reactors and then isolated for medical applications, to be used in a radiation source, to be reused as fuel in a reactor, etc. The chemical processing steps include reduction and extraction steps. See, for example, http://en.wikipedia.org/wiki/PUREX.

As for thorium, the future looks less promising. Thorium tends to be attractive to countries like India that lack large uranium reserves. However, thorium is much more difficult to use than uranium because it must be irradiated by neutrons before it becomes useful fuel - a process called “breeding.” Most breeder-reactor concepts require spent-fuel processing, which isn’t currently economically viable in the US - it’s cheaper to mine and enrich natural uranium than to reuse the uranium and plutonium in spent fuel! Research on breeding fuel has taken new life in recent years, but most projects focus on breeding fuel from unenriched uranium, not thorium. I’m not saying that thorium isn’t a viable option, but most of the breeder-reactor research outside of India involves breeding fuel from uranium, and it’s unlikely that the US breeder designs will move past the drawing board in the next 20 years.

a_plan_so_cunning5 karma

How does a modern nuclear warhead actually work? I get the going boom part, but how does it actually work?

HerrGeneral91319 karma

Although I'm not the OP, I find nuclear weaponry immensely fascinating and so I'll try to answer the question.

The most important part of any nuclear weapon would be the fissile material- in almost all "normal" cases, plutonium. Not only does it have to be immensely pure, you also have to have enough in order to cause an uncontrolled nuclear chain reaction. This reaction is set off by basically compressing the plutonium together very quickly.

Around this core of plutonium is the explosive. This is just a normal high explosive, albeit highly refined and perfectly shaped in order to direct the explosive force inward, almost like a lens.

The bomb is set off by detonating the shell of high explosive all at once (timing is important in order to make sure the plutonium implodes perfectly). The shockwave from the detonating explosives compresses the plutonium enough that it reaches critical mass. At that point, the nuclear chain reaction starts, and that little sphere of plutonium turns into a little piece of the sun on earth- releasing ungodly amounts of energy.

Obviously, this is very oversimplified and I'm sure I got some things wrong- but that's the gist of it. Most of this information is freely available on the internet, such as Wikipedia.

IGottaWearShades15 karma

Adding to what you said:

I don’t work on nuclear weapons, but I’ll give you what I know. Frankly, http://en.wikipedia.org/wiki/Nuclear_weapon_design is just as good.

For any kind of bomb to be effective, it must release a lot of energy very quickly (before the energy shockwave blows the bomb apart). Fission weapons do that by reaching a prompt-critical configuration very quickly. (The “prompt critical” state of a warhead is very different from the “critical” state of a power reactor; see http://en.wikipedia.org/wiki/Prompt_critical#Critical_versus_prompt-critical ).

There are two typical designs to quickly make a weapon prompt-critical: gun-type configurations (which rapidly insert a small piece of uranium into a larger piece of uranium) and implosion configurations (which rapidly crush a sphere of uranium or plutonium into a smaller shape, which leaks fewer neutrons). Both types have a wikipedia page.

Fusion weapons derive most of their power from deuterium-tritium fusion. The explosion from a fission device is used to achieve the high temperatures and pressures required for fusion.