Influence of time duration of FAs in spent fuel pool on VVER‐440 N‐Ph characteristics after reloading
26th Symposium of AER on VVER Reactor Physics and Reactor Safety (2016, Helsinki, Finland)
Fuel management issues
Abstract
INFLUENCE OF TIME DURATION OF FAS IN SPENT FUEL POOL ON VVER-440 N-PH CHARACTERISTICS AFTER RELOADINGVáclav Krýsl, Pavel Mikoláš, Karel Vlachovský E-mail: pavel.mikolas@skoda-js.cz, Tel: +420 378042828 ŠKODA JS a.s., Orlík 266/15, 316 00 Plzeň, Czech RepublicABSTRACTPraxis (not only) at Dukovany NPP shows that some fuel assemblies can be loaded into core after some time duration in spent fuel pool. This is connected with a reload strategy – also with the fact that central FA is individual and if one assembly from six pieces has been used, the remaining five pieces cannot be reused simply on other positions in the core preserving usually requested core symmetry. But not only the central assembly is a question – sometimes it seems to be suitable to reload also more FAs from spent fuel pool, which were put off earlier (not only several weeks ago).The principle lies in the fact that quality (reactivity) of a (partially spent) FA being changed in time – this depends on measure of burn-up (also fuel enrichment) and time of placement in spent fuel pool. The reason is that concentrations of some isotopes (actinides and fission products) are being changed in time.Some isotope‘s changes (at least Xe135 and Sm149) must be considered in any case, but the others not so necessarily – in case of time of some weeks. But in case of longer time – they should be taken into account.Possible solution: To follow changes of concentrations of sufficiently big amount of isotopes (actinides and fission product) in producing code (so called “micro-depletion”). This approach was introduced on AER Symposium last year (DYN3D code). This is in any case a correct approach, but it is not easy to realize it (especially together with the pin-by-pin approach).The other possibility is to apply a suitable correction on FAs properties – change of reactivity (keff) due to time duration in spent fuel pool.Such approach has been applied in MOBY-DICK code and it is shortly described in the paper. Numerical results are also provided.26th Symposium of AER on VVER Reactor Physics and Reactor Safety 24 10 – 14 October 2016, Helsinki, Finland