Cool welcome to DB. I am a new guy as well there. I am in Operations and hope to complete my education by learning the real deal about nuke power. I learned alot in school but know almost nothing when it comes to nuke power plant operations. The one thing I do feel comfortable disscussing is neutronics.
My best bud works at Wstinghouse and he told me about a reactor where they shove Li-6 in it to make tons of tritium. Not sure what for but tritium can be used for not so nice purposes. I have also seen them used in watches.
If one "knows" neutronics, then some of the uses of H-3 that should come to mind include: radioisotope tracers for medical research, D-T fuel for fusion reactors (my favorite disposable fusion reactor being the W88), boresight illuminators, exit signs and of course, wristwatches. Due to H-3s relatively short half-life, constant production is a necessity. Why fear the gentle glow?

I am sure the computer code is much nicer to model just one nuclide that is being made in the burn and being put in the reactor at startup.
That is an assumption, and an incorrect one at that.
Reactors are nothing more than a complex balancing act of neutrons. You have to make the reactor prompt sub-critical and makeup with the difference with delayed neutrons. Otherwise the reactor period would be fractions of a micro second long and how in the hell can you control that? Neutrons are born in die in a matter of nanoseconds. They either will leak from the reactor or will get absorbed somewhere in the reactor. The key is to get the geometric and material buckling just right to support a chain reaction and have reactivity mechanisms in place that make the reactror stable. Temperature coeffcients, 1/v cross sections for fission, and the 6 groups of delayed neutrons allow us to control this reactor.
6 groups is a statistical model, and one hears the term and sees that table often, but http://public.lanl.gov/jomc/PNE/spriggs2.pdf on page 8 shows some analyses of an 8 group model and why it is useful. As far as neutrons dying in nanoseconds, I'll bet you a can of pop that isn't true , a little Google search shows you could eat a sandwich and still have the stable free neutron exist.
When you can get a steady state system going you will have to start fighting poison buildup. Xenon and Sumarian are nasty poisons that can prevent some reactors from starting up after a shut down if you can't get enough positive reactivity in it. Not only that, you will breed in Pu-239 and this makes the balancing act even more difficult. Pu-239 is a bigger neutron maker in fission events than U-235. I am constantly thinking in aww about the amount of engineering work that just goes into designing a core to last 24 months.
Sumarian, isn't that the people that discovered bronze, or like Conan the Sumarian ? oh, Samarium. Well, considering that the fission yield of Sm is nearly zero http://www.tpub.com/content/doe/h1019v2/css/h1019v2_69.htm I wouldnt worry about a samarium-precluded startup. Xenon is usually mitigated by waiting until it has reached equilibrium to restart, changing the moderator temperature to gain positive reactivity, or deborate. Here we find ourselves back at Boron.
As far as 24 month fuel cycles......there are places in this world where one can operate 20 years on a core (no hints from the bubbleheads

) without the use of boron. It all depends on the fuel loading and which burnable poisons are used.
So in short boron is used to be a fine tuneing tool to control the reactor by modifying the material buckling of the reactor and it is used to make Li-7 to try and make the reactor coolant less acidic.
So, boron is there for neutron flux control?(yes) or chemistry control?(hmmm)
I'll bet there is something called "volatile chemistry control" that a chem tech can use for that, even in a plant without boron!
a new post just as I posted mine. Here is a dig at the french.
They like to use Na as a reactor coolant. Na becomes a very nasty gamma emmiter when activated by a neutron. Imagine trying to fight a Na fire due to a LOCA and on top of that is is s**t hot with gammas. That is one good thing about light water. Even when you activate H-1, it will not become radioactive. H-2, or deuterium is a stable nuclide.
well, even H-2 has a capture cross-section of 0.0253 eV = 550.0 micro barn , and then we once again have the beautiful soft beta glow of H-3.
Also, sodium coolant is used because of the excellent heat transfer qualities. Not exactly a French idea. Unless you want to tell GE and Argonne to dump the PRIZM design.
Russians like to have graphite moderated and water cooled reactors. Yuck... That is why Chernobyl got in trouble.
No one has burned down or blown up a CANDU, which also fits your description. What DID get Chernobyl in trouble is doing a complex set of experiements with a large reactor, and violating their own testing safety parameters. 10CFR50.59 keeps us from being tempted to do the same here. An excellent description is found at
http://www.chernobyl.co.uk In summary, boron is used because it is the most-cost effective means of soluble neutron absorption (the cost of soluble hafnium compounds would be staggering!) first and foremost. It does have drawbacks, as the often seen pictures of DB's head testify. It doesnt respect mechanical seals, and it is a wonderful transport agent for CRUD. You can count on spending quality time with the RP techs if you get enough on ya...