Extention of Pool at the Reactor Analyses in Slovakia after Fukushima, VUJE
26th Symposium of AER on VVER Reactor Physics and Reactor Safety (2016, Helsinki, Finland)
Intermediate storage of spent fuel decommissioning and radwaste / Spent fuel disposal and actinide transmutation
Abstract
EXTENSION OF POOL AT THE REACTOR ANALYSES IN SLOVAKIA AFTER FUKUSHIMARadoslav ZAJAC, Vladimír CHRAPČIAK VUJE Inc., Okruzna 5, SK 918 64 Trnava, Slovakia Radoslav.Zajac@vuje.skABSTRACTSlovak nuclear industry consists of four VVER-440 units in operation, interim spent fuel storage facility, two VVER-440 units and one A1 unit under decommissioning.Neutron Physical characteristics for routine operation are evaluated for each unit in routine operation. One of the neutron physical characteristics component is the chapter focused on support solutions of the emergencies states for safety state recovery or functional recovery of selected parameters.Chapter of design extension conditions analyses has been gradually integrated into the document of neutron physical characteristics after Fukushima accident according to Slovak NPPs and Slovak Nuclear Regulatory Authority requirements.Operator of the reactor unit is usually provided with data in tabular form, graphical dependences of core parameters and also for downtime period of reactor.The operator can read parameters when necessary:1. Decay heat of the core after reactor shutdown from the full power in the case of BOC and EOC. The history of decay heat is divided into four time ranges. The first one is set from 0 s to 120 s, the second range takes from 1 min to 60 min, the third from 1 hour to 24 hours and the last one from 1 day to 30 days.2. Decay heat of the core during the downtime period between previous and following cycle. The history of decay heat is divided into four time ranges. The first one is set from 0 s to 120 s, the second range takes from 1 min to 60 min, the third from 1 hour to 24 hours and the last interval depends on the length of reactor downtime.3. Minimum water flow through the core necessary to remove decay heat during the full power period and also during downtime period. The history of minimum flow is again divided into four time ranges. The first one is set from 0 s to 120 s, the second range takes from 1 min to 60 min, the third from 1 hour to 24 hours and the last interval is different and depends on the case of full power period or downtime period.26th Symposium of AER on VVER Reactor Physics and Reactor Safety 63 10 – 14 October 2016, Helsinki, Finland 4. Decay heat in pool at the reactor dependence on the time. The graph represents actual sum of decay heat assemblies in the pool during the reactor period. The number of spent fuel assemblies varies from period to period. The time axis (x axis) is divided into months and the specific dates are written in axis.5. Time to achieve the limit parameters. This part follows three parameters dependant on time during the period. The first parameters present the time values to achieve limit coolant temperature 100 °C; the second parameter is the time to fuel uncovering and the third shows the time values to reach limit fuel temperature 1200 °C. The time axis (x axis) is divided into months and the specific dates are written in axis.6. The next part is focused on dependences of time to achieve the temperature of water saturation 100 °C in the pool at the reactor at the BOC and EOC, time of the lowering water to the level of fuel in the pool at the BOC and EOC, time to achieve fuel limit temperature 1200 °C at the BOC and EOC in the pool.7. The last point of neutron physical characteristics document is formed by two tables which define the point of boiling time in the reactor and in the pool.Before the Fukushima accident the document of neutron physical characteristics included time dependence of decay heat in the reactor at the BOC and EOC only. In the area of design extension conditions was defined a large series of analyses which became a serious part of neutron physical characteristics for VVER-440 reactors in Slovakia.26th Symposium of AER on VVER Reactor Physics and Reactor Safety 64 10 – 14 October 2016, Helsinki, Finland