4 START-UP CONDITIONS USING MCNP5, G.Farkas1, J.Lüley1, B.Vrban1, J.Haščík1, M.Petriska1, R.Hinca1, V.Slugeň1, J.Šimko2, Slovakia

22nd Symposium of AER on VVER Reactor Physics and Reactor Safety (2012, Průhonice, Czech Republic)


In general a reactor is initially started up from a precondition stage (200?C) by
withdrawing control rods or by changing the boron acid concentration in primary circuit
coolant until the reactor is slightly supercritical, thus producing an exponentially increasing
neutron population on a very long period. As the neutron population increases, the fission
heating and thus the reactor temperature increases. This increase in temperature produces a
decrease in reactivity. That would lead to the slowdown of increasing the neutron population
and the reactor power should saturate at certain higher level. Generally, core loading patterns
are designed in such way that isothermal reactivity coefficient should already be negative at
the Cold Zero Power (CZP). For VVER 440 reactors CZP is equal to 200 ?C. To meet this
requirement could be problematic, particularly for the first core loading, when all fuel
assemblies are fresh. Due to the first criticality start-up of the Nuclear Power Plant (NPP)
Mochovce units 3 and 4 in the near future, detailed analyses of core parameters are required
by the Slovak Regulatory Authority to support safe operation of the nuclear facility. The
article introduces determination of the thermal reactivity coefficients, especially summary
(isothermal) and moderator (density) reactivity coefficients between 200?C and 260?C with
step of 2 ?C. The work presents calculated critical parameters, especially critical boron acid
concentrations at given coolant temperatures and position of the 6 th control assembly group.
Numerical iteration procedure was applied to calculate the critical parameters as a substitute
for a critical experiment. Geometrical and material models were created in compliance with
the reactor design and the first fuel loading of the NPP Mochovce 3 and 4. All mentioned
calculations were performed by computational code MCNP5 1.60 supported by NJOY99.364
microscopic sections processing system and our control scripts.

Presentation / full paper

Only registered users from member companies are allowed to view and download presentations and full papers.

Please log in or sign up.