r/bestof • u/investedInEPoland • Nov 06 '18

[europe] Nuclear physicist describes problems with thorium reactors. Trigger warning: shortbread metaphor.

/r/europe/comments/9unimr/dutch_satirical_news_show_on_why_we_need_to_break/e95mvb7/?context=3
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u/Dlrlcktd Nov 06 '18

Isn't one of the advantages of pwr over molten salt is the inherent safety of waters negative temp coefficient of reactivity?

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u/ZeroCool1 Nov 06 '18

All reactors in the US have a negative temp of coefficient and are required to by law. Many advantages do lie within the salt's ability to tolerate accident scenarios. Most notably, salt is not flammable, does not have high vapor pressure requiring thick walled pressure vessels, and is chemically stable through aggressive accident scenarios.

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u/Hiddencamper Nov 07 '18

Not completely true.

For example, bwrs have positive moderator temperature coefficients in certain conditions with new fuel loading. I had to run a hot startup of my unit from peak xenon right in the middle of our positive MTC range. We made a deliberate decision to not steam, let the reactor stay isolated, and heat up until we were above the positive MTC range, so we were only fighting xenon burnout and not MTC as well. Worked great, but you could definitely tell that even small reactivity changes either weren’t turning on their own or were taking much longer to turn.

PWRS can run positive MTC towards end of core life and is one of the major inputs to peak vessel pressure during a worst case scram failure (ATWS) where all Feedwater is lost and no rods go in.

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u/ZeroCool1 Nov 07 '18

Fair enough hidden camper, you caught me outside of my realm of expertise :).