37
votes
Accepted
Why does it take so long to restart a nuclear power plant?
When a reactor is shut down the core produces much less heat, but they do still produce heat through a mechanism known as decay heat. The fact that the core is producing less heat means that the ...
- 3,565
13
votes
Why does it take so long to restart a nuclear power plant?
Xenon is a result of the nuclear reaction and a neutron poison. If you don't wait for the xenon to decay, it eats up too many neutrons and you can't go critical. They always say "there are not ...
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8
votes
Why are Chinese aircraft carriers conventionally powered?
Carriers are ships intended to project power. The USA sits on a continent without any nearby enemies. So, American military doctrine is expeditionary in nature. The assumption is that if America ...
7
votes
Why does it take so long to restart a nuclear power plant?
The answer really boils down to two factors: safety and testing. I'm going to give a generic summary of these two things below, but the real answer is quite complicated.
The crux of nuclear plant ...
- 3,587
5
votes
Accepted
What is the *typical* quantity (in kg) of uranium-235 present at a given moment in a nuclear plant?
Atomic Weapons
The critical mass of metallic U-235 is about 50 kg[1] and the only U-235-based fission weapon deployed in combat--the Little Boy weapon--had about 64 kg of U-235[2]; there's more U-235 ...
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5
votes
Why did they build a sarcophagus over Chernobyl instead of pouring concrete over the building?
The likely reason is that simply pouring concrete over it would not have contained it.
The site is smoldering and emits gases of various types. It also has voids and shifts around, various areas ...
- 1,625
4
votes
Why did they build a sarcophagus over Chernobyl instead of pouring concrete over the building?
The original sarcophagus built around 1986 has some issues and it was estimated in 1988 that it would only last 20-30 years (here we are). Check out this link that explains some of the main issues ...
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3
votes
When backup cooling fails in reactors without passive safety, what is the risk of radioactive contamination?
I just thought that I would clarify something that Fred said. In an emergency shutting down the nuclear chain reaction is the easy part. The main issue is the decay heat. The decay heat comes from the ...
3
votes
How is the energy production of solar and wind compared with the prospect of nuclear fusion?
The reality of generating electricity from nuclear fusion on an industrial scale is still a very long ways off. It is speculative high cost, high risk venture, with a potential high payoff far off ...
2
votes
Critical mass in a molten salt reactor
Thorium is a non-issue, it can't go supercritical. The issue here is that we're talking about neutron-induced fission, and a Thorium nucleus that fissions will only release a single neutron. Since the ...
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2
votes
Accepted
How is the energy production of solar and wind compared with the prospect of nuclear fusion?
Fusion is widely extolled by advocates as being safe (but is that collective opinion justified)?
I would prefer to begin my discussion comparing fusion with renewable energy systems with an ...
2
votes
Accepted
How does a nuclear powered rocket engine work?
In Nuclear Thermal Rockets (NTRs)
the heat from a nuclear reaction replaces the chemical energy of the propellants in a chemical rocket. In an NTR, a working fluid, usually liquid hydrogen, is ...
- 9,667
2
votes
Which Gen IV reactor types use nuclear waste as fuel?
The claim to "use nuclear waste as fuel" is often misleading. In theory, almost all reactors can reuse the waste, but it requires reprocessing.
For example, in current LWR reactors, natural ...
- 161
2
votes
Why are Chinese aircraft carriers conventionally powered?
I'm not an expert on this so this is an "educated guess".
It boils down to what the advantage of nuclear power is. To laypeople it sounds cool, but for the military you need a tangible ...
- 133
2
votes
What are the design differences between a hydrogen bomb and a neutron bomb?
Fusion bombs are typically boosted by encasing them in a fissionable (uranium) housing. The gigantic neutron flux produced by the fusion reactions then fissions the housing and boosts the yield ...
- 14.7k
2
votes
Accepted
Half-life Unit Notations
The half life of Radium 214 is 2.46[s]. You can check half times at the following wikipedia article.
I am not sure what the 3 stands for, but I suspect that this is some sort of annotation/footnote ...
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1
vote
Transportation and storage of atomic weapons
Here are some general points:
Nuclear weapons cannot set each other off by virtue of the radioactive decay of their fissile components. So, for example, the warheads carried by ballistic missiles ...
- 14.7k
1
vote
Is there any technical bar from restarting the nuclear power plants of Germany?
Nothing is technically keeping nuclear plants from re-starting. Clearly technology exists to rebuild even partially dismantled plants. What does not exist in the wake of Fukushima is the political ...
- 6,891
1
vote
Accepted
Why are fission fragment reactors not used?
Several Reasons, but the biggest is that this technology isn't available yet.
Neither the fission beam tech is ready for commercialization, nor is the magnetohydrodynamic generator. The simplest ...
- 6,891
1
vote
Can be used a lab on a chip device as a nuclear fusion device?
The energies (expressed as temperature) required to get elements to fuse is far above the melting point of all engineering materials. For this reason, all fusion reactors must confine the plasma with ...
- 14.7k
1
vote
What are the key technical challenges to development of traveling wave reactors?
I am not aware of any technological challenges. There have been several sodium fast reactors that have operated, the latest being the Experimental Breeder Reactor II (EBR-II) in Idaho and the Fast ...
- 161
1
vote
How is the neutron capture cross-section increased in thermal breeder reactors?
You are correct that the average cross sections are much higher in a thermal reactor than in a fast reactor. However, it is not the magnitude of the cross sections that matter, but instead the ratio ...
- 161
1
vote
Nuclear wastegate thermal dissipation systems?
One way is to use massive pond systems for evaporate cooling.
Turkey Point nuclear plant. Closed loop system explained here - https://youtu.be/qt9dtYC7RDE
- 4,755
1
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Why does it take so long to restart a nuclear power plant?
They are many reasons for the time it takes to startup or return to full power operation in commercial nuclear power plants. In the US there are two main types of plants, Boiling Water Reactors(BWRs) ...
- 11
1
vote
Smallest possible controlled chain reaction-based nuclear fission reactor?
An almost-critical sphere of fissionable material would do. Add some neutron reflecting material that can be rotated to increase or decrease the neutron reflection. Or you could have two halves of a ...
- 254
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