Calculation of differential and integral rod worths

ulriksvensson

Hi forum members. I need some guidance in the following question.

In the Studsvik code Simulate-3 you can calculate differnetial and integral rod worths with the input card CRD.OCB. Further, you can specify if you want to lock hydraulics and fission products to some predefined state via the SAV.LOK card.

While this being a highly un-physical calculation in the first place, what would be the most apropriate in your opinion, to use SAV.LOK or not to use SAV.LOK? If you would use SAV.LOK what would you lock? Arguments?

I suppose the answer depends on what the result would be used for so let's say it's for a stone-age reactivity balance calculation.

Thanks in advance.

QuantumPion

SAV.LOK is used for holding temperatures and/or fission product concentrations constant during a fast transient such as rod ejection. This is physically real as these transients occur faster than the temperature or fission products change. With the CRD.OCB function, you use SAV.LOK so that the worth of each rod step is compared to the initial condition. Without the SAV.LOK card, each rod step worth will be compared to the equilibrium conditions of the previous rod step. Either way is physically valid, how you utilize this function depends on what you are trying to analyze.

ulriksvensson

Thanks for your reply. What I meant by unphysical is that for instance you cannot calculate total reactivity by summing up contributions from power defect and rod worths because in reality the problem is non-linear and therefore these calculations are not additive.

QuantumPion

Sure you can, it's just not as accurate without counting for secondary effects. But it's accurate enough in the context of operations. How do you think plant operators controlled the reactor back in the days before the advent of the PC?

ulriksvensson

I know they used to do this but the difference between these type of calculations and an on-line core follow system can be 50 ppm. That's a lot.

QuantumPion

It's a lot by today's standards but typical tech spec limits for ECC's are in the range of 500-1000 pcm.