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Fast reactors
Published in Kenneth Jay, Nuclear Power, 2019
It is desirable that the coolant should be liquid at ordinary temperatures or else the reactor will have to be heated, to melt the coolant, before it can be brought into operation. Anyone who has chased a globule of mercury around on the floor knows that this metal would meet the requirement, but it is not good in other respects. The most promising of the possible metals seem to be sodium or certain alloys of sodium and potassium. Sodium is not too good on the score of melting—it has to be heated nearly to the boiling point of water before it becomes liquid—and some warming is necessary; some of the sodium-potassium alloys have much lower melting points but they are not such good heat-transfer materials and they cost more. Sodium is quite good for heat transfer and is not too expensive. It does not attack most of the materials of construction provided that it is kept free from oxygen, though reducing the oxygen content to an acceptably low level is not always an easy matter. Sodium also has the drawback that it becomes radioactive when exposed to neutrons, owing to the formation of the gamma-emitting isotope sodium-24; therefore all parts of a coolant circuit containing sodium that has been through the reactor core—pumps, pipes, heat-exchangers, valves—have to be shielded with thick concrete shields.
Shielding Systems and Radiation Shields
Published in Robert E. Masterson, Nuclear Engineering Fundamentals, 2017
Here again, d is the depth of penetration into the shield. Sometimes, boron is added to these radiation shields because it produces lower-energy gamma rays than iron and water do. For example, adding Boron-11 to a shield produces a relatively low-energy gamma ray having an average energy of 0.5 MeV. Hence, Boron-11 is sometimes used in shielding systems because it can reduce the thickness of the shield. Boron is relatively plentiful and inexpensive as well. Liquid metal–cooled fast reactors may also need some additional shielding systems that are not present in thermal water reactors. This is because the liquid sodium coolant can become far more radioactive than ordinary water. Sodium-24 is a radioactive beta emitter with a half-life of about 15 hours. However, unlike ordinary water, it can absorb even fast neutrons, and the sodium that flows through the reactor core becomes radioactive very quickly. The beta rays generate a lot of heat and they can also be very penetrating, especially if their energy is high. Hence, thin sheets of metal are often used to surround the piping system in these types of reactors. In other words, in a fast reactor, reactor operators must be shielded from high-energy neutrons, as well as the effects of both beta rays and gamma rays.
Residence time distribution studies using radiotracers in chemical industry—A review
Published in Chemical Engineering Communications, 2018
Meenakshi Sheoran, Avinash Chandra, Haripada Bhunia, Pramod K. Bajpai, Harish J. Pant
Radioactive properties of radiotracers are used to follow the process fluid for online RTD diagnosis. Several radiotracers are available depending on their half-life, activity, activation energy, cost, availability, physical, or chemical properties, etc. Tracers are mainly intrinsic and extrinsic. Intrinsic tracers should be chemically identical with the process material. Also, the sample of the process material can be activated and used as an intrinsic tracer (IAEA, 2008). The intrinsic tracers can be used where the process is dominated by atomic or molecular diffusion like reaction kinetics or solubility which has to be studied. For example, sodium (24Na) is used as an intrinsic tracer to trace the NaOH phase. Tritium is also an intrinsic radiotracer (IAEA-TECDOC-291, 1982; Pant et al., 2009c). In the case of extrinsic tracer, the detectable constituents are outside the molecular structure and have identical dynamic properties that of the material to be traced (IAEA, 2008; Plummer, 2005). The chemically identical radiotracer is not required in the case of extrinsic tracer, e.g., to follow the water, Na131I can be used as an extrinsic radiotracer. The only requirement in the case of extrinsic radiotracer is that they should behave as that of flowing phase.
La mesure de débit par dilution – Quel avenir pour cette technique ?
Published in LHB, 2022
Christian Lallement, Arnaud Belleville, Alexandre Hauet, Christian Perret
Les traceurs utilisés sont préférentiellement les sodium 24, brome 82, iode 131, indium 113, qui permettent une analyse directe sur le terrain par un compteur Geiger et donc l’accès rapide au résultat du jaugeage (Figure 5), et le tritium, dont l’analyse est plus longue et ne peut se faire qu’en laboratoire.