Criticality Definition and 19 Threads

https://www.georgiapower.com/company/news-center/2023-articles/vogtle-unit-3-reaches-initial-criticality.html#:~:text=Vogtle%20Unit%203%20reaches%20initial%20criticality%20March%206%2C,safely%20started%20the%20nuclear%20reaction%20inside%20the%20reactor. "March 6, 2023 Georgia Power today...

How does U235 reach criticality via neutron capture when its natural decay process is via alpha emission. I know that U235 will reach criticality in a suitably shaped container after a specific concentration has been reached. In addition, I've read that the original U235 bomb (little boy) was...

Hi, Is there any tutorial or pdfs that can help me with the MCNP output data? I'm working on the criticality of the SCWR, and I designed the fuel assembly and run it on the MCNP, but I have no idea about data extraction.

Dear Community, I am having a question. I have developed a simple code to perform iteration power algorithm and find the keff value of a system. However, it is not still totally clear in my mind if I have to normalize all my scores by the eigenvalue, i.e. multiply by the keff (fluxes, power...

As a way of explanation I have to say I've been reffing RPG's since the mid seventies, some four months after D&D first came out, as it took that long back then for game ideas to move from the Great Lakes region to the West Coast. (I was Class of '78) So in the upcoming post vaccine era I'm...

Usually, critical phenomena can be categorized in some kind of universality class which determines the critical exponent. A typical example is the class of the Ising model; adding a next-nearest-neighbour hopping term does not change the critical behavior. The typical explanation is that the...

The Tokaimura Criticality Incident involved the improper mixture of 18.8% enriched uranium and nitric acid in a 100 liter precipitation tank that was 450 mm in diameter and 650 mm high. The tank was surrounded by a water filled cooling jacket. When enough of the mixture was in the tank a...

At critical points, when correlation lengths diverge near a phase transition, people often say that the spectral gap closes, which is to my understanding just the energy difference between the ground state and the first excited state (the first two eigenvalues of the hamiltonian). How should we...

I'm assessing criticality safety of a waste removal plan for a (theoretical) abandoned russian laboratory. In the laboratory plutonium was recovered from fuel rods. The room is mainly empty except for a dissolver, a sump below the dissolver and spilled metal chips on the floor. The dissolver...

In 1958, chemical operator Cecil Kelley was killed by a nuclear excursion in a mixing tank. A tank intended to reprocess trace amounts of dissolved plutonium-239 accidentally had dramatically more radioactive material dumped into it. The plutonium, being dissolved in a lower-density fluid than...

Please,I am working on the criticality calculation of an homogeneous finite cylindrical reactor core using four-group diffusion equations. I have been able to discretize the multigroup diffusion equations using the finite difference method(FED). But I am stocked on the iterative method to...

I usually do not ask for this kind of stuff, but this time I really have no way to verify if this is correct(and it has to be). So here it goes: On a subcritical nuclear reactor with 100 fuel elements we read the signal of 10e-9 A. When we add 10 more fuel elements, signal jumps to 10e-8 A. How...

I'm looking at the diagram (Figure 1) at http://en.wikipedia.org/wiki/Supercritical_fluid I get that the region in which both the temperature & pressure are higher than the critical point is called a supercritical fluid, which really means it is both a gas & a liquid, thermodynamically...

According to wikipedia: "In physics, self-organized criticality (SOC) is a property of (classes of) dynamical systems which have a critical point as an attractor. Their macroscopic behaviour thus displays the spatial and/or temporal scale-invariance characteristic of the critical point of a...

The Volume of the reactor and its criticality! What will happen to the "Keff" or to the criticality if the volume of the reactor was compressed to one-half its original volume and why ? if the reactor was operating at critical steady-state before changing the volume.

What programs model nuclear reactors and can determine if the reactor goes critical or not? It would be a big advantage if the given programs are open source as well, since the ones that cost money evidently cost a lot. I might be able to get hold of SCALE 6.1, but that program/code would be...

Hi All. I have been reading up about criticality this weekend and I have come across some terms that I could do with some help on. I think I understand Keff which describes the 'amplification' of reaction and includes the physical nature of the reactor, i.e. mass, shape, spacing...

Hi, I'm new to the entire neutronics field. I've learned about adjoints as a physics student in undergrad and I'm doing nuclear engineering for my graduate studies. I understand how to derive the adjoint operator for the diffusion equation, but I'm a bit confused as to how to calculate the...

please help me in understanding the following scenarios: 1. how could one approach first criticality in practice? 2. what would happen if we start-up with full power conditions from first criticality? 3. what would the shutdown requirement be in comparison to an equilibrium core? thank...