WWER safety analysis in case of simultaneous positive reactivity introduction by control rods withdrawal and pure condensate injection
21st Symposium of AER on VVER Reactor Physics and Reactor Safety (2011, Dresden, Germany)
Reactor dynamics and safety analysis
Abstract
Results of calculation assessment of positive reactivity insertion rate are presented
under condition of simultaneous effect on reactivity of two provided by WWER project
reactivity operation systems – extract of regulation group and decrease of boron acid
concentration. Showed that maximal positive reactivity insertion rate is achieved at hot zero
power and it?s too less than limit value 0.07?eff/sec defined by normative document ?Nuclear
safety regulation of NPP with pressurized water reactors?. For given reasons concluded that
necessity of application of the extended protection PZ-2 actuation time is absent on interval of
pure condensate transportation for full exclusion of possibility of positive reactivity insertion
simultaneously by two different operation systems.
The work was performed in framework of orders BMU SR 2511 and BMU R0801504
(SR2611). The report describes the opinion and view of the contractor ? SSTC N&RS – and
does not necessarily represent the opinion of the ordering party – BMU-BfS/GRS and T?V
S?D.
INTRODUCTION
According to the Ukrainian regulation ?Rules of Nuclear Safety for Nuclear Power
Plants with Pressurized Water Reactors? 1 an introduction of positive reactivity
simultaneously by two or more means of impact on reactivity isn?t permitted. Preventive
protection PP-2 upon valve opening on the feed and bleed line is provided for realization of
this requirement on Ukrainian NPPs with WWER reactors. It forbids extraction of regulating
group CR under pure condensate feed is injected in reactor core. The given action really
excludes simultaneous carrying-out by personnel of operations on introduction of positive
reactivity by two or more means of impact on reactivity. However possibility of introduction
of positive reactivity by two means of impact on reactivity after realization of this action
remains, because upon valve closing on a feed and bleed line action of protection PP-2 stops,
but transportation of a pure condensate in reactor core proceeds. Transportation time can
amount to 15 minutes depending on the flow of the feed and bleed line. Therefore during this
time interval the situation is possible when positive reactivity can be introduced