Worry about annual output a few of kg neutrons in nuclear power station?

An isotope U235 fuel atom will averagely release 200MeV heat energy, 2.5 neutrons and 2 smaller nuclei in random species, during nucleus fission induced by thermal neutron tender hit or say massage in rhetoric.

In other words, if 200/2.5 = 80MeV heat is generated, then 1 neutron will pop up as one of many fission crumbs.

Given 1MeV = 1.6*10^-13J, neutron mass = 1.67*10^-27kg, and to make engineering sense, it’s better to convert it to heat/weight ratio 7.66*10^15J/kg, or approximately 8 petajoules per kilogram neutrons.

Let me take a sample nuclear power station to calculate neutron productivity.

Japan Fukushima Daiichi nuclear power plant: 6 reactors, total power 4546MW.

As a reasonable estimation, the efficiency of heat to electricity is about 35%, so the thermal power must be larger than 4546/35% = 12989MW.

Theoretical max yearly heat energy = 365*24*12989*1000 = 114*10^9kwh.

Because night energy consumption is far less than day time, and equipment also need maintenance time, thus above data should be discounted by a factor of duty cycle.

As per statistics, duty cycle 0.6 is reasonable, so the yearly real heat output = 68*10^9kwh.

Given 1kwh = 3.6MJ, therefore heat yield = 245*10^15J/year.

By afore calculated 7.66*10^15J/kg, now I get result of neutrons total mass = 245/7.66 = 32kg/year.

To facilitate calculation on other nuclear power stations, I define the Neutron’s Co-Productivity NCP as total mass of fissional neutrons per megawatt electrical power per year.

Calculated from this Japan sample, NCP is about 32/4546 = 0.007kg/MW/Year = 7g/MW/Year, or 7mol/MW/Year in favor of chemists, as 1mol = 1g for neutrons counts = Avogadro constant.

Provided no significant change of efficiency 35% of heat engine, the value of NCP should be almost constant.

For a typical 300MW reactor, it will produce 2.1kg neutrons per year.  

Yes, a few of kilograms neutrons per year, no big deal, that's it!

Sometimes it's concerned that how many electric energy can be generated if 1kg neutrons are fissioned out, and it can be easily deduced via multiplying prior 7.66*10^15J/kg by 35% heat engine efficiency, then convert unit to get result = 7.4*10^8 kwh/kg.

In neutron economy, assuming 1kwh electricity sold for $0.05, then ratio of market value to neutrons mass is about 3.7*10^7 $/kg, or say 18.5g neutrons will make some mess to environment per million US dollar sales of electricity.

All above indicative data are deduced from inter-parameter stoichiometry on system pool, so beware of correct understanding, e.g. 80MeV/neutron cannot be interpreted as "one neutron carries 80MeV kinetic energy", and in fact, a newborn neutron usually carry circa 2MeV, and most likely will be cooled to about 0.025eV by protons in water molecules or by graphite.

Neutron’s density is extremely high, even a spoon of neutrons may have more weight than the Himalaya Mountain.

Imagining these 32kg neutrons tightly packed together, it’s still so tiny, that you have to see it with help of a microscope.

There are many possibilities for neutrons destiny:

1. Hit a hydrogen nucleus in water molecule, fused to deuterium;

2. Hit a generated deuterium, fased to tritium;

3. Absorbed by power adjusting control bar, which is made of cadmium;

4. Absorbed by U238, the major component of fuel-escorting material, then decayed to Np239 after 23 minutes, then decayed to Pu239 after 2.4 days (by the way, Pu or plutonium is excellent igniter for nuke hydrogen bomb);

5. Absorbed by whatever miscellaneous atoms in structure or containers;

6. Beta decay to a hydrogen atom, if no other destiny after about 15 minutes;

Supposedly, scientific community should produce a pie chart to depict percentages of all possible destinies, so public can be well informed and have a good judge about risks, but unfortunately there is no such chart.

The tritium has 12 years half-life beta decay to helium, with a radioactive energy release up to 18KeV, and usually renders average 5.7KeV electron projectile, because the ghost particle neutrino takes away quite a portion of energy.

Its energetic electron projectile can destroy some cells if inside human body, though short fly distance down to a few of centimeters, nevertheless tritium is still harmful to human if too much exposure.

In contrast, medical X-ray render far higher energy and deeper penetration radiation, up to 150KeV; however, accurate comparison must depend on dose condition.

As nuclear wastewater may contain significant tritium, of course, public is worry about its discharge.

Although no reliable data of neutrons destinies, we can assume all neutrons go for tritium, so a water H2O can consume 2 neutrons, or say, 1 kg neutrons can make up 10kg or 10 liters water, then the said power plant, at max, it could produce 320kg pure tritium-water per year.

I believe above estimation is super exaggerated, and the real tritium productivity may be just a very small fraction,because the published cross section curve of neutron absorption is very low:

In contrast, the probability of absorption by proton is far bigger by almost 3 orders of magnitude, therefore the major component of heavy water must be harmless and safe deuterium water. Following figure can prove it by cross section curve:

Still clueless about the data contrast? look at the principle cross section data of fuel element uranium U235 isotope:

The data imply that the possibility of tritium creation is less than a tiny millionth of fuel nuclei fission.

Now the plant said it accumulated 1 million tons of waste water, if the imagined one year product of pure tritium-water is mixed, then the dilution ratio is about 1:3,125,000.

Japan government approved the discharge in sea on a long span of 30 years.

How is the risk to our health and ecology? Judge it by yourself with common sense and herein scientific analysis data.

Nobody worry about tritium when they enjoy luxury watch with luminous convenience, even many users never know it made of radioactive tritium.

Thinking nuclear power is dirty? No, don't be scared or frustrated by some rare nuclear disasters, believe me, it is even cleaner than most other energy sources.

*** Outlook for future evolution of potential new nuclear fuels ***

Anyway, roaming neutron is nasty,but why leave me alone and not fund me to explore next generation of clean nuclear fuel?

My research is focusing on the isotope Lutetium 176, and my revolutionary invention can drive it to release cleanest yet huge beta decay power by catalysis of artificial extreme tiny "neutron star" weighed under 1 gram.

Lutetium 176 is deemed as the only half-baked element in the long time process of star nucleosynthesis, with 1.2MeV potential beta decay energy or 180MWh/kg latent heat locked in high spin nucleus, so I believe humankind can continue "bake" the left half to unleash it.

No conventional way to speed beta decay unless applying bizarre means, e.g. mimick pulsar influential, and if speeding half life to 1 day, its power can boom to 1.3MW/kg.

The abundance of Lu176 amongst all lutetium isotopes is 2.6%, obviously far larger than 0.72% of U235 amongst uranium, thus purification Lu176 by centrifuges is far cheaper than U235 extraction.

Following figure presents the energy level of isomer Lu176:

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