Orion drive and related physics

[Nothalogh]

20 minutes ago, sevenperforce said:

They didn't name it after Sakharaov. Sakharaov proposed First Idea, Second Idea, and Third Idea. First Idea, nicknamed sloika, was a layer-cake design which was fusion-boosted fission. Second Idea involved the use of lithium deuteride as the fusion booster. Third Idea, developed by Sakharaov, Zeldovich, and Davidenko, separated the primary and secondary and use x-rays from the primary to compress the secondary; this was equivalent of the Teller-Ullam design. Third Idea was first tested in the RDS-37 shot.

Teller-Ullam is technically still classified, and although the basic principle is fairly clear, there seem to be critical details enabling the actual process which remain secret. The US didn't share any of the details with the UK until after UK's Grapple X test demonstrated that they had unlocked the secret.

Third Idea, eh?

Leave it to the Soviets to make a monumental piece of engineering sound clinical, bland, and like something found in a presentation by middle management.

[sevenperforce]

Of course the US was lightyears ahead of the Soviets when it came to thermonuclear weapons design. The Soviets derided Ivy Mike, the cryogenic hydrogen version of the H-bomb, as a "thermonuclear installation". But they didn't even come up with third idea until after Castle Bravo. In fact, if they had been a little more careful about taking atmospheric samples after Castle Bravo, they would have figured it out sooner. 

I wonder just how much of the thermal nuclear weapon design remains classified. The United States has a weapon design with some intermediate material that requires extremely careful and precise properties. Obviously there are details like timing and ratios. But I can't help thinking there are some other design elements which have remained secret all this time.

Building a gun fission weapon is easy enough. Building a spherical implosion  weapon is a little tougher, but still doable. Two-point implosion requires some insanely smart scientists. Fusion boosting isn't much of a challenge at all. Thermonuclear weapons are the really hard part. 

And, of course, miniaturizing thermonuclear weapons is flat-out impossible unless you happen to be the United States.

 

[Buster Charlie]

everyone interested should read this here:

http://www.projectrho.com/public_html/rocket/enginelist.php#id--Pulse--Orion

 

Yes I know this has some 'sci-fi stuff' but the whole page is written as a resource (I think) for people creating more scientifically sound sci-fi, so they have a lot of hard data and real resources. (I THINK)

 

It covers some of the issues of radiation and fallout, it's worth a read and it answers a lot of the questions and concerns being asked here.

 

edit: @Bill Phil beat me to it.

Edited February 20, 2016 by Buster Charlie

[Nothalogh]

48 minutes ago, sevenperforce said:

And, of course, miniaturizing thermonuclear weapons is flat-out impossible unless you happen to be the United States.

The upside of the Soviets being slow on the uptake for miniaturization, was that they had direct motive for building big honkin rockets

[Buster Charlie]

19 hours ago, fredinno said:

You would never do that anyways- Orion is limited in that you need it to be kept out of the magneosphere so that radiation doesn't hit Earth.

Orion Environmental Impact

Naturally, some people freak out when you tell them about a rocket that rises into orbit by detonating Two! Hundred! Atom! Bombs!. But it actually isn't quite as bad as it sounds.

First off, these are teeny-tiny atom bombs, honest. The nuclear pulse units used in space will be about one kiloton each, while the Nagasaki device was more like 20 kt. And in any event, the nuclear pulse units used in the atmosphere are only 0.15 kt ( about 1/130th the size of the Nagasaki device). This is because the atmosphere converts the explosion x-rays into "blast", increasing the effectiveness of the pulse unit so you can lower the kilotonnage.

So we are not talking about zillions of 25 megaton city-killer nukes scorching the planet and causing nuclear winter.

---

Some environmentalists howl that Orion should never be used for surface-to-orbit boosts, due to the danger of DUNT-dunt-Dunnnnnnnn Deadly Radioactive Fallout. However, there is a recent report that suggests ways of minimizing the fallout from an ORION doing a ground lift-off (or a, wait for it, "blast-off" {rimshot}). Apparently if the launch pad is a large piece of armor plate with a coating of graphite there is little or no fallout.

By which they mean, little or no ground dirt irradiated by neutrons and transformed into deadly fallout and spread the the four winds.

There is another problem, though, ironically because the pulse units use small low-yield nuclear devices.

Large devices can be made very efficient, pretty much 100% of the uranium or plutonium is consumed in the nuclear reaction. It is much more difficult with low-yield devices, especially sub-kiloton devices. Some of the plutonium is not consumed, it is merely vaporized and sprayed into the atmosphere. Fallout, in other words. You will need to develop low-yield devices with 100% plutonium burn-up, or use fusion devices (with 100% burn-up fission triggers or with laser inertial confinement fusion triggers).

The alternative is boosting the Orion about 90 kilometers up using a non-fallout chemical rocket. Which more or less defeats the purpose of using an Orion engine in the first place. Remember that Orions are best at boosting massive payloads into orbit.

Most of the fallout will fall within 80 kilometers of the launch site. You can also reduce the fallout by a factor of 10 if you launch from near the Magnetic Pole.

---

When fissionables like plutonium undergo fission, their atoms are split which produces atomic energy. The split atoms are called fission fragments.

The good news is that they have very short half-lives, e.g., in 50 days pretty much all of the Strontium 94 has decayed away (because 50 days is 58,000 St94 half-lives).

The bad news is that they have very short half-lives, this means they are hideously radioactive. Radioactive elements decay by emitting radiation, shorter half-life means more decays per second means a higher dose of radiation per second.

The fragments that come screaming out of the detonation aimed at the sky are no problem. They are moving several times faster than Terra's escape velocity, you will never see them again (Terra's escape velocity is 11.2 km/s, the fragments are travelling like a bat out of hell at 2,000 km/s). The ones aimed towards Terra are a problem. The fragments can be reduced by using fusion instead of fission pulse units. The fragments can also be reduced by designing the pulse units to trade thrust in favor of directing more of the fragments skyward.

---

A more sophisticated objection to using Orion inside an atmosphere is the sci-fi horror of EMP melting all our computers, making our smart phones explode, and otherwise ruining anything using electricity. But that actually is not much of a problem. EMP is not a concern unless the detonation is larger than one megaton or so, Orion propulsion charges are only a few kilotons (one one-thousandth of a megaton). Ben Pearson did an analysis and concluded that Orion charges would only have EMP effects within a radius of 276 kilometers (the International Space Station has an orbital height of about 370 kilometers). So just be sure your launch site is in a remote location, which you probably would have done anyway.

 

[PB666]

2 hours ago, Buster Charlie said:

Orion Environmental Impact

Naturally, some people freak out when you tell them about a rocket that rises into orbit by detonating Two! Hundred! Atom! Bombs!. But it actually isn't quite as bad as it sounds.

First off, these are teeny-tiny atom bombs, honest. The nuclear pulse units used in space will be about one kiloton each, while the Nagasaki device was more like 20 kt. And in any event, the nuclear pulse units used in the atmosphere are only 0.15 kt ( about 1/130th the size of the Nagasaki device). This is because the atmosphere converts the explosion x-rays into "blast", increasing the effectiveness of the pulse unit so you can lower the kilotonnage.

So we are not talking about zillions of 25 megaton city-killer nukes scorching the planet and causing nuclear winter.

---

Some environmentalists howl that Orion should never be used for surface-to-orbit boosts, due to the danger of DUNT-dunt-Dunnnnnnnn Deadly Radioactive Fallout. However, there is a recent report that suggests ways of minimizing the fallout from an ORION doing a ground lift-off (or a, wait for it, "blast-off" {rimshot}). Apparently if the launch pad is a large piece of armor plate with a coating of graphite there is little or no fallout.

By which they mean, little or no ground dirt irradiated by neutrons and transformed into deadly fallout and spread the the four winds.

There is another problem, though, ironically because the pulse units use small low-yield nuclear devices.

Large devices can be made very efficient, pretty much 100% of the uranium or plutonium is consumed in the nuclear reaction. It is much more difficult with low-yield devices, especially sub-kiloton devices. Some of the plutonium is not consumed, it is merely vaporized and sprayed into the atmosphere. Fallout, in other words. You will need to develop low-yield devices with 100% plutonium burn-up, or use fusion devices (with 100% burn-up fission triggers or with laser inertial confinement fusion triggers).

The alternative is boosting the Orion about 90 kilometers up using a non-fallout chemical rocket. Which more or less defeats the purpose of using an Orion engine in the first place. Remember that Orions are best at boosting massive payloads into orbit.

Most of the fallout will fall within 80 kilometers of the launch site. You can also reduce the fallout by a factor of 10 if you launch from near the Magnetic Pole.

---

When fissionables like plutonium undergo fission, their atoms are split which produces atomic energy. The split atoms are called fission fragments.

The good news is that they have very short half-lives, e.g., in 50 days pretty much all of the Strontium 94 has decayed away (because 50 days is 58,000 St94 half-lives).

The bad news is that they have very short half-lives, this means they are hideously radioactive. Radioactive elements decay by emitting radiation, shorter half-life means more decays per second means a higher dose of radiation per second.

The fragments that come screaming out of the detonation aimed at the sky are no problem. They are moving several times faster than Terra's escape velocity, you will never see them again (Terra's escape velocity is 11.2 km/s, the fragments are travelling like a bat out of hell at 2,000 km/s). The ones aimed towards Terra are a problem. The fragments can be reduced by using fusion instead of fission pulse units. The fragments can also be reduced by designing the pulse units to trade thrust in favor of directing more of the fragments skyward.

---

A more sophisticated objection to using Orion inside an atmosphere is the sci-fi horror of EMP melting all our computers, making our smart phones explode, and otherwise ruining anything using electricity. But that actually is not much of a problem. EMP is not a concern unless the detonation is larger than one megaton or so, Orion propulsion charges are only a few kilotons (one one-thousandth of a megaton). Ben Pearson did an analysis and concluded that Orion charges would only have EMP effects within a radius of 276 kilometers (the International Space Station has an orbital height of about 370 kilometers). So just be sure your launch site is in a remote location, which you probably would have done anyway.

 

Archaeologist aren't happy with the atomic bomb testing, it almost doubled atmospheric C-14 made dating in the 20th century complicated. C14 has a half life of 4000 years. Abombs used for a launch are just bad news and alot of unintended (but reasonably expected) consequences.

[Bill Phil]

1 minute ago, PB666 said:

Archaeologist aren't happy with the atomic bomb testing, it almost doubled atmospheric C-14 made dating in the 20th century complicated. C14 has a half life of 4000 years. Abombs used for a launch are just bad news and alot of unintended (but reasonably expected) consequences.

That's not quite a problem. Especially now.

The natural concentrations of C-14, and pretty much everything, are usually close to uniform. Plus we're using more accurate archaeological equipment.

[Nothalogh]

1 hour ago, PB666 said:

Archaeologist aren't happy with the atomic bomb testing

No problem, these wouldn't be tests. 

[Elukka]

Regarding the efficiency of Orion drives, I did some back-of-the-envelope math. You should take this with a grain of salt.

Basically I took the stated pulse unit yield of one Orion design and compared that with the effective jet power required for the given performance (thrust and isp). As near as I can reason the difference between bomb power and jet power must be the portion of energy lost to all the various inefficiencies in the system.

The result was that ~38% of the bomb's total yield is harnessed for useful thrust. That's actually pretty nice and more than I expected. It's also a very rough number, but assuming my math is right it should be in the ballpark.

[PB666]

11 hours ago, Bill Phil said:

That's not quite a problem. Especially now.

The natural concentrations of C-14, and pretty much everything, are usually close to uniform. Plus we're using more accurate archaeological equipment.

The C14 issue is about detecting frauds, notably frauds produced just after WWII when there was an attempt to cash in on American wealth in some European countries. Some of those paintings are still out there, haven't hit the market yet.

[PB666]

15 hours ago, sevenperforce said:

They didn't name it after Sakharaov. Sakharaov proposed First Idea, Second Idea, and Third Idea. First Idea, nicknamed sloika, was a layer-cake design which was fusion-boosted fission. Second Idea involved the use of lithium deuteride as the fusion booster. Third Idea, developed by Sakharaov, Zeldovich, and Davidenko, separated the primary and secondary and use x-rays from the primary to compress the secondary; this was equivalent of the Teller-Ullam design. Third Idea was first tested in the RDS-37 shot.

Teller-Ullam is technically still classified, and although the basic principle is fairly clear, there seem to be critical details enabling the actual process which remain secret. The US didn't share any of the details with the UK until after UK's Grapple X test demonstrated that they had unlocked the secret.

IIRC, I read the report back in 1982 just after the big report was released. There are two areas. 1 was the timing of the nuetron injection and the detonation of the cells on the outside (rumours are that this gave the a-bomb developers trouble). 2nd was the lithium deuteride matrix (as I understand it the matrix is enriched with tritium). Obviously reports after the fact have the matrix embedded in some type of heavily compressible media (styrofoam), this was done IMO to give the lithium deuteride momentum which increased pressure when the stuff converged at the center of the apparatus. The matrix itself might be heavily responsive to the compressive xrays. There is a considerable amount of sophistication in the H-bomb, its not something someone can walk off the street can do, I suspect that you would need a crew of dozens of people working out the kinks in the electronics, electronic testing, of course you need a radioactive neutron generator that can be turned-on, deuterium, lithium hydride is extremely reactive, the plutonium used in the outer shell is very dangerous. Thus there are many technical aspects of building the bomb that are not common knowledge simply because of the training involved.

BTW, do you think any government, US, Soviet, god only knows what the Chinese developed . . .  would disclose the working details of an H-bomb for orion or even allow a third party country in the US to make H-bombs for private space craft ventures. This in an of itself kills Orion, the second tech entity X developes a mini-H bomb DHS is all over them like flies on a honeypot in  the middle of a feed lot.

 

[Nothalogh]

2 hours ago, PB666 said:

BTW, do you think any government, US, Soviet, god only knows what the Chinese developed . . .  would disclose the working details of an H-bomb for orion or even allow a third party country in the US to make H-bombs for private space craft ventures. This in an of itself kills Orion, the second tech entity X developes a mini-H bomb DHS is all over them like flies on a honeypot in  the middle of a feed lot. 

That's why the sooner we have an operating Mars colony, the better 

Edited February 20, 2016 by Nothalogh

[sevenperforce]

If there is fissile mass on Mars, then building nukes for illegal Orion drives suddenly becomes VERY lucrative. 

[HebaruSan]

4 hours ago, PB666 said:

BTW, do you think any government, US, Soviet, god only knows what the Chinese developed . . .  would disclose the working details of an H-bomb for orion or even allow a third party country in the US to make H-bombs for private space craft ventures. This in an of itself kills Orion, the second tech entity X developes a mini-H bomb DHS is all over them like flies on a honeypot in  the middle of a feed lot.

US national security projects often have integral private contractor involvement. ICBMs are built by Lockheed and Boeing. Nuclear power plants are operated by electric utility companies. Union Carbide and Bechtel have run or co-run the national laboratories that research nuclear weapons. None of these companies show signs so far of building their own weapons to hold the world hostage (unless you stretch the definitions and consider the "military industrial complex" to already be doing this collectively).

If there was suddenly a huge market for 4-week trips to Mars, I'm thinking a compromise would be worked out in which you, whoever you are, can build an Orion drive, but you have to rely on the Air Force to operate it and provide the fuel, and they'll send (armed) crewmembers to each ship to act as its caretakers. The nuclear weapons industries would ramp back up on the ground, and the military would still take custody of each bomb and retain control through detonation, in cooperation with their "private sector partners". The ship's captain would control operation of the snack bar, the passenger compartment's rotation, day to day life support, etc., but when he wanted to do a burn, he would put in a request to the USAF staff on board, who would coordinate with command back on Earth and turn their keys when all the proper checklists were completed.

[Nothalogh]

8 minutes ago, HebaruSan said:

If there was suddenly a huge market for 4-week trips to Mars, I'm thinking a compromise would be worked out in which you, whoever you are, can build an Orion drive, but you have to rely on the Air Force to operate it and provide the fuel, and they'll send (armed) crewmembers to each ship to act as its caretakers. The nuclear weapons industries would ramp back up on the ground, and the military would still take custody of each bomb and retain control through detonation, in cooperation with their "private sector partners". The ship's captain would control operation of the snack bar, the passenger compartment's rotation, day to day life support, etc., but when he wanted to do a burn, he would put in a request to the USAF staff on board, who would coordinate with command back on Earth and turn their keys when all the proper checklists were completed.

What an utterly horrifying concept.

As ludicrous as a biometric interlock on a fire alarm or an ejection seat. 

[HebaruSan]

3 minutes ago, Nothalogh said:

What an utterly horrifying concept.

As ludicrous as a biometric interlock on a fire alarm or an ejection seat. 

What concerns do you have? Are you worried about hijackers?

[Nothalogh]

30 minutes ago, HebaruSan said:

What concerns do you have? Are you worried about hijackers?

Well, you have described a hijacking of sorts, by the planetside governments

[fredinno]

20 hours ago, Buster Charlie said:

Orion Environmental Impact

Naturally, some people freak out when you tell them about a rocket that rises into orbit by detonating Two! Hundred! Atom! Bombs!. But it actually isn't quite as bad as it sounds.

First off, these are teeny-tiny atom bombs, honest. The nuclear pulse units used in space will be about one kiloton each, while the Nagasaki device was more like 20 kt. And in any event, the nuclear pulse units used in the atmosphere are only 0.15 kt ( about 1/130th the size of the Nagasaki device). This is because the atmosphere converts the explosion x-rays into "blast", increasing the effectiveness of the pulse unit so you can lower the kilotonnage.

So we are not talking about zillions of 25 megaton city-killer nukes scorching the planet and causing nuclear winter.

---

Some environmentalists howl that Orion should never be used for surface-to-orbit boosts, due to the danger of DUNT-dunt-Dunnnnnnnn Deadly Radioactive Fallout. However, there is a recent report that suggests ways of minimizing the fallout from an ORION doing a ground lift-off (or a, wait for it, "blast-off" {rimshot}). Apparently if the launch pad is a large piece of armor plate with a coating of graphite there is little or no fallout.

By which they mean, little or no ground dirt irradiated by neutrons and transformed into deadly fallout and spread the the four winds.

There is another problem, though, ironically because the pulse units use small low-yield nuclear devices.

Large devices can be made very efficient, pretty much 100% of the uranium or plutonium is consumed in the nuclear reaction. It is much more difficult with low-yield devices, especially sub-kiloton devices. Some of the plutonium is not consumed, it is merely vaporized and sprayed into the atmosphere. Fallout, in other words. You will need to develop low-yield devices with 100% plutonium burn-up, or use fusion devices (with 100% burn-up fission triggers or with laser inertial confinement fusion triggers).

The alternative is boosting the Orion about 90 kilometers up using a non-fallout chemical rocket. Which more or less defeats the purpose of using an Orion engine in the first place. Remember that Orions are best at boosting massive payloads into orbit.

Most of the fallout will fall within 80 kilometers of the launch site. You can also reduce the fallout by a factor of 10 if you launch from near the Magnetic Pole.

---

When fissionables like plutonium undergo fission, their atoms are split which produces atomic energy. The split atoms are called fission fragments.

The good news is that they have very short half-lives, e.g., in 50 days pretty much all of the Strontium 94 has decayed away (because 50 days is 58,000 St94 half-lives).

The bad news is that they have very short half-lives, this means they are hideously radioactive. Radioactive elements decay by emitting radiation, shorter half-life means more decays per second means a higher dose of radiation per second.

The fragments that come screaming out of the detonation aimed at the sky are no problem. They are moving several times faster than Terra's escape velocity, you will never see them again (Terra's escape velocity is 11.2 km/s, the fragments are travelling like a bat out of hell at 2,000 km/s). The ones aimed towards Terra are a problem. The fragments can be reduced by using fusion instead of fission pulse units. The fragments can also be reduced by designing the pulse units to trade thrust in favor of directing more of the fragments skyward.

---

A more sophisticated objection to using Orion inside an atmosphere is the sci-fi horror of EMP melting all our computers, making our smart phones explode, and otherwise ruining anything using electricity. But that actually is not much of a problem. EMP is not a concern unless the detonation is larger than one megaton or so, Orion propulsion charges are only a few kilotons (one one-thousandth of a megaton). Ben Pearson did an analysis and concluded that Orion charges would only have EMP effects within a radius of 276 kilometers (the International Space Station has an orbital height of about 370 kilometers). So just be sure your launch site is in a remote location, which you probably would have done anyway.

 

Good luck convincing people.

[sevenperforce]

On the subject of pure fusion propulsion....

Assuming, for the sake of argument, that you can use a ground-based laser array to initally ignite a tritium-deuterium pellet into fusion, would it be possible to build an exhaust/recoil bell which was also a parabolic reflector to focus the visible-light portion of the fusing pellet's radiation to ignite the next pellet? 

[SomeGuy123]

One thing that liquided me off is in the Neil Stephenson book Seveneves, they don't even discuss Orion.  They have 2 years and the obvious ability to remanufacture the existing nuclear stockpile into a hastily designed nuclear shape charge.  They could have built hundreds, maybe thousands of separate Orion drive ships in the remaining time, welding those things together out of aluminum plates and things basically.  Launch em from remote areas.  The coming armageddon would kill everyone before probably anyone actually got cancer from the fallout.

1 hour ago, sevenperforce said:

On the subject of pure fusion propulsion....

Assuming, for the sake of argument, that you can use a ground-based laser array to initally ignite a tritium-deuterium pellet into fusion, would it be possible to build an exhaust/recoil bell which was also a parabolic reflector to focus the visible-light portion of the fusing pellet's radiation to ignite the next pellet? 

Why bother?  As your vehicle picks up speed, even if it worked, you'd very rapidly leave the range of your laser.  It would be very short range because once the light intensity drops below the threshold for fusion you stop getting any thrust.

Another huge problem - I don't think this works in air.  I think air would soak up too much of the energy.

It would be a much better idea to beam electricity via microwaves and use the electricity to accelerate propellant.  High thrust, high ISP, and your thrust goes to zero much more slowly.  (farther away you get the microwave beam gets less intense but as long as you are receiving some power you can run the engine at lower power or in bursts or just 1 run ion engine in a bank of them)

Edited February 20, 2016 by SomeGuy123

[sevenperforce]

4 minutes ago, SomeGuy123 said:

Why bother?  As your vehicle picks up speed, even if it worked, you'd very rapidly leave the range of your laser.  It would be very short range because once the light intensity drops below the threshold for fusion you stop getting any thrust.

I think you missed the point. I suggested a laser ground array to initially ignite the first pellet, but after that, the light from the fusion of the first pellet is supposed to ignite the next one using a parabolic mirror which doubles as the exhaust bell.

[SomeGuy123]

1 minute ago, sevenperforce said:

I think you missed the point. I suggested a laser ground array to initially ignite the first pellet, but after that, the light from the fusion of the first pellet is supposed to ignite the next one using a parabolic mirror which doubles as the exhaust bell.

Won't work.  Wrong spectrum of light.  Mirror would melt because it can't be tuned for the broad spectrum light from fusion.

Better to use magnets and electric fields.  

As for the startup of your fusion engine, there are various discussions of this.  You might need microwaves beamed for a "jump start" or onboard fusion power reactors or solar panels or a fuel cell bank or capacitors or something.

Edited February 20, 2016 by SomeGuy123

[Buster Charlie]

2 hours ago, fredinno said:

Good luck convincing people.

Not to be rude, I thought this was "Science & Spaceflight > Orion drive and related physics" Not "Politics & Sociology > How to decrease fear of fission"

[SomeGuy123]

1 hour ago, Buster Charlie said:

Not to be rude, I thought this was "Science & Spaceflight > Orion drive and related physics" Not "Politics & Sociology > How to decrease fear of fission"

To be fair, they are strongly related.  Orion drive's best use case is for putting immense heavy payloads into orbit.  The heavier the better.  (heavier payloads, you can use bigger and more efficient nukes that cause less fallout)

If we as a society valued space exploration enough, we would have done this decades ago, and just accepted a few extra deaths from cancer.  

We could have orbiting towns by now or lunar cities.

Edited February 21, 2016 by SomeGuy123

[Buster Charlie]

2 minutes ago, SomeGuy123 said:

To be fair, they are strongly related.  Orion drive's best use case is for putting immense heavy payloads into orbit.  The heavier the better.  (heavier payloads, you can use bigger and more efficient nukes that cause less fallout)

If we as a society valued space exploration enough, we would have done this decades ago, and just accepted a few extra deaths from cancer.  

We could have orbiting towns by now or lunar cities.

That's my point. My Reply is simply that I don't have to 'convince' anyone about the Orion Drive, i'm not in a position to make a difference in this, i'm just chatting about the technical side.

 

What really liquided me off about lost potential is, not just the payload size, but the fact that it could put said huge payload into mars orbit in FOUR WEEKS, not you know, a year or two.

This alone is why I think we're not serious about space exploration unless we explore fission drives.

 

AS far as cancer, you'd probably get more cancer deaths from stone construction and burning coal (they release radioisotopes)