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Tidal turbine

Scientific discovery and discussion
scotia
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Re: Tidal turbine

#161839

Postby scotia » August 24th, 2018, 3:40 pm

9873210 wrote:The Tc99 in the waste has a yield of about 6% and a half life of 200,000 years. Ignore every other isotope and the claim is still false.
The idea of background radiation level in thousands of year (with implications of safe after 50 years) is as far off as the idea of absolutely deadly forever.
For every complex problem there is an answer that is clear, simple, and wrong.

Are you sure about your figures? I understand that, resulting from the fission of U235, there is generated Tc99 with a yield of about 6%. Now this Tc99 is confined within the fuel rod, which is bombarded with an intense flux of neutrons. And there is a significant cross section (a few barns) for the capture of these neutrons by Tc99, so producing Tc100 which decays with a half-life of 16 seconds into stable (non-radioactive) Ru100. Now the fuel rods remain in a reactor for typically about a year. So when they are taken out for reprocessing, what is the Tc99 yield in the waste? I find it difficult to believe that it remains the 6% which you have quoted - but you may be correct. Can you clarify where you obtain this figure on which your pronouncements are based?

9873210
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Re: Tidal turbine

#161989

Postby 9873210 » August 25th, 2018, 6:37 am

scotia wrote:
9873210 wrote:The Tc99 in the waste has a yield of about 6% and a half life of 200,000 years. Ignore every other isotope and the claim is still false.
The idea of background radiation level in thousands of year (with implications of safe after 50 years) is as far off as the idea of absolutely deadly forever.
For every complex problem there is an answer that is clear, simple, and wrong.

Are you sure about your figures? I understand that, resulting from the fission of U235, there is generated Tc99 with a yield of about 6%. Now this Tc99 is confined within the fuel rod, which is bombarded with an intense flux of neutrons. And there is a significant cross section (a few barns) for the capture of these neutrons by Tc99, so producing Tc100 which decays with a half-life of 16 seconds into stable (non-radioactive) Ru100. Now the fuel rods remain in a reactor for typically about a year. So when they are taken out for reprocessing, what is the Tc99 yield in the waste? I find it difficult to believe that it remains the 6% which you have quoted - but you may be correct. Can you clarify where you obtain this figure on which your pronouncements are based?

Not entirely sure, but

The cross section of U235 is several hundred barns, so the Tc99 should be destroyed far slower than it is produced. This is supported by reports that destroying waste Tc99 by putting it back into a reactor would take several decades rather that the several years that it took to create it. So I expect most of the Tc99 makes it into the waste.

The only measurement I can find says Tc99 says it is 0.1% of the waste. Over 95% of both the fuel and the waste is U238, which does nothing except dilute my precision. With various assumption 0.1% of the waste is consistent with being a 1 to 6% of the original U235. In any case 0.1% Tc99 is more active than pure U235.

scotia
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Re: Tidal turbine

#162016

Postby scotia » August 25th, 2018, 11:11 am

9873210 wrote:
scotia wrote:
9873210 wrote:The Tc99 in the waste has a yield of about 6% and a half life of 200,000 years. Ignore every other isotope and the claim is still false.
The idea of background radiation level in thousands of year (with implications of safe after 50 years) is as far off as the idea of absolutely deadly forever.
For every complex problem there is an answer that is clear, simple, and wrong.

Are you sure about your figures? I understand that, resulting from the fission of U235, there is generated Tc99 with a yield of about 6%. Now this Tc99 is confined within the fuel rod, which is bombarded with an intense flux of neutrons. And there is a significant cross section (a few barns) for the capture of these neutrons by Tc99, so producing Tc100 which decays with a half-life of 16 seconds into stable (non-radioactive) Ru100. Now the fuel rods remain in a reactor for typically about a year. So when they are taken out for reprocessing, what is the Tc99 yield in the waste? I find it difficult to believe that it remains the 6% which you have quoted - but you may be correct. Can you clarify where you obtain this figure on which your pronouncements are based?

Not entirely sure, but

The cross section of U235 is several hundred barns, so the Tc99 should be destroyed far slower than it is produced. This is supported by reports that destroying waste Tc99 by putting it back into a reactor would take several decades rather that the several years that it took to create it. So I expect most of the Tc99 makes it into the waste.

The only measurement I can find says Tc99 says it is 0.1% of the waste. Over 95% of both the fuel and the waste is U238, which does nothing except dilute my precision. With various assumption 0.1% of the waste is consistent with being a 1 to 6% of the original U235. In any case 0.1% Tc99 is more active than pure U235.

Thanks - I had already come to the same conclusion. I made optimistic assumptions of 3 barns for Tc99 and 300 barns for U235, and got a 100 to 1 ratio - which stretches out further to 200 to 1 since the Tc99 has to be generated during the life of the fuel. And I also looked up the computations on "burning" Tc99 in a reactor which suggests that you can reduce its effective half life to a few decades. The paper also appears to suggest that more Tc99 could be "burned" than is produced. So maybe the Irish sea could become redundant as a repository. Not that any of the public would notice.
Again - thanks for wakening up the dormant brain cells of a septuagenarian.
And just in case there are any listeners who have undergone a medical examination which involved consuming Tc99 - don't worry, you will excrete most of it which should ultimately reach the nearest sea.


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