This is probably a decent representation of the ratio of the boron part of the rod to the graphite "tips".

https://i.stack.imgur.com/Ai7Yp.jpg

You're welcome. The Mo-99 at Darlington is specifically in Unit 2, which was just completely refurbished and can operate now for another 30 years. There is also lots of exciting work happening in Chalk River, just not with a research reactor. If medical isotopes interest you, check out the work with Ac-225 in Chalk River as a targeted alpha therapy for cancer treatment.

https://www.cnl.ca/health-science-2/actinium-225/

You can calculate decay by Nt=No(1/2)^(t/t1/2), where Nt is the number of atoms at time t, No is the original number of atoms, and t1/2 is the half-life. So 1 h later for a 6 h half-life means 89% of the dose is still there.

You would need to ask one of the pharmacists what they do if someone is late. I'm assuming there is a cutoff time.

Hello fellow Canadian! Mo-99 is NOT made from nuclear weapons waste. It is deliberately made in reactors or accelerators specifically as a medical product. Canada used to be one of the largest suppliers of Mo-99 in the world, making it in the NRU research reactor in Chalk River. That reactor shutdown in 2018. The Darlington CANDU plant is now equipped to make Mo-99, in addition to lots of carbon free power.

https://world-nuclear-news.org/Articles/Darlington-ready-to-produce-medical-radioisotope

As others have said, it's not "stocked" on a shelf like many medications. It is custom made to order and patients are scheduled.

The boiler side of reactors is not my area of expertise, but I'll try to answer your question. My understanding is the water that is used to make steam for the turbine is a closed loop because the water chemistry and steam quality is very important to safely operating the fast spinning turbines with many blades. For that reason, the water needs to be fresh water.

For desalination, my understanding is there is still enough heat in the steam after it has run through the turbines that it can still boil water, but is not useful for generating further electricity. It is a way to use this waste heat. I believe such systems completely separate the turbine loop water from the desalination water. Essentially, it is seawater sprayed on hot piping to create fresh water steam. The turbine water (downstream of the turbines) flows through the piping in a closed loop to keep it hot.

As for desalination at nuclear plants, there is experience in Kazakhstan and Japan in doing so. I don't know why it hasn't seen more widespread use. I am guessing the need is not that great as lots of reactors are located near large bodies of fresh water by design. The nuclear physics in a reactor can also be complicated by changing temperature, so complicating the heat removal system is probably avoided unless it is a specific requirement.

It depends what you mean by coming out of the plant. In most nuclear reactor designs, the fuel is cooled by water under pressure being pumped over it. By the time the water exits the core, it is typically something over 300C and 15 MPa, but under the critical point of water at that given pressure.

This water is not used to drive the steam turbine directly. It goes through a heat exchanger to heat a secondary loop of water to create steam for the turbine. The steam needs to be condensed back to water in order to be reused. Some reactors use bodies of water, some use cooling towers. The steam coming out of cooling towers is considerably colder at less than 50C and at atmospheric pressure.