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ahaanomegas
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Which substance is the best moderator for fission reactors, if there is even a definition for "best"? My current physics book says heavy water. Do you agree? Please explain.
Astronuc said:Protons are the best at slowing down neutrons, however they can also absorb neutrons (and form deuterons) in competition with the fuel. Heavy water or D2O slows down neutrons but does not readily absorb thermal neutrons, there it is considered a better moderator for thermal fission reactors.
Moderating ratio is a figure of merit for moderators.
http://www.tpub.com/content/doe/h1019v1/css/h1019v1_131.htm
But that wouldn't work for a hot reactor. D2 doesn't compress to a liquid but for pressures well beyond what we normally achieve terrestrially.law&theorem said:It's not "the best".
Definition of "the best" is moderating ratio, so liquid D2 maybe "the best". D2 is gaseous state in environmental temperature. When D2 is compressed into liquid state, it would be "the best".
Astronuc said:But that wouldn't work for a hot reactor. D2 doesn't compress to a liquid but for pressures well beyond what we normally achieve terrestrially.
Supercritical fluid would seem more appropriate. The moderator needs a certain density.nikkkom said:Above critical temp (IIRC close to 40K) D2 has no liquid state per se.
Since you brought up the idea of solid hydrides, which is being considered in some high temperature concepts, e.g., SCWR, the other complication of high pressure deuterium would be the propensity for the hydrogen to diffuse into the structural metals and forming hydrides. This would be bad news for steels or Inconels as it would undermine their structural integrity, especially when it comes to shutdowns. Probably the primary system would have to be cladding in Al or Cu or some other element that does not readily allow diffusion of hydrogen into the metal or formation of hydrides. However at the pressure required to maintain a supercritical deuterium fluid, I'm not sure there is a metal that could handle it.QuantumPion said:A dense solid compound of deuterium would be good, i.e. "heavy paraffin" or perhaps ZrD2. Remember that the moderator can be outside the reactor and doesn't have to also be the coolant (e.g. CANDU, RBMK, MAGNOX, etc).
A moderator in a scientific study is responsible for overseeing and managing the research process. This includes selecting and managing participants, collecting and analyzing data, and ensuring the study is conducted ethically and accurately.
A good moderator should have strong communication and interpersonal skills, as well as attention to detail and the ability to remain unbiased. They should also be knowledgeable about the subject matter and have good problem-solving abilities.
The best moderator for a specific study will depend on the research question, methodology, and target population. It is important to consider factors such as experience, expertise, and availability when selecting a moderator.
Some common mistakes that moderators make include bias in participant selection or data collection, failure to follow ethical guidelines, and misinterpretation of data. It is important for moderators to be aware of these potential pitfalls and take steps to avoid them.
To ensure the accuracy and validity of a study, a moderator should carefully plan and design the research, use reliable and valid measures, and follow ethical guidelines. They should also regularly review and analyze the data to identify any potential errors or biases.