THE PRACTICE OF CONSIDERING REACTIVITY SPATIAL EFFECTS WHEN MEASURING EMERGRNCY PROTECTION EFFICIENCY IN VVER REACTORS
24th Symposium of AER on VVER Reactor Physics and Reactor Safety (2014, Sochi, Russia)
Core surveillance and monitoring
Abstract
THE PRACTICE OF CONSIDERING REACTIVITY SPATIAL EFFECTS WHEN MEASURING EMERGRNCY PROTECTION EFFICIENCY IN VVER REACTORS
Afanasiev D.V., Pinegin A.A. NRC “Kurchatov Institute”, Moscow, Russia Orlov V.I., Tolmasova E.V. VNIIAES, Moscow, Russia
ABSTRACT
The paper discusses the problem related to comparison of experimental and calculated values of emergency protection efficiency for VVER reactors. According to Regulations requirements measurements of emergency protection efficiency without of the one most effective control rod are carried out at the start of a fuel cycle. Search values of reactivity are turned out from indications of regular reactivity meters or using of personal computers by processing of currents of the ionization chambers (IC), located in biological shield channels, and further are compared to calculation results of the emergency protection efficiency made under the BIPR-7A program.
Drop of emergency protection into the reactor core is accompanied by sharp reduction of a neutron flux and by reduction of appearance speed of new generations of delayed neutrons emitters. As a result a new asymptotic (asymptotical) distribution of a neutron flux in the core isn’t established. In these conditions results of measurements depend on disposition IC and on local character of IC current formation. It leads to systematic methodical errors at determination of the emergency protection efficiency by reactivity meters indications, which are based on the turned solution of the dot kinetics equation (ORUK method). As a result we have considerable systematic differences between calculated and experimental values of reactivity because spatial effects are not taken into account.
For elimination of this systematic methodical error the modified ORUK (MOD ORUK) method was offered. This method, allowing account spatial reactivity effects, is implemented within the NOSTRA program. Under the offered method the value of emergency protection efficiency is accounted on the basis of measured IC currents by the ORUK method with use of special settlement amendments.
This paper presents results of processing by the MOD ORUK method of measurements of emergency protection efficiency for some of serial VVER-1000 reactors fuel charge and their comparison with settlement values. The analysis of the presented results shows that divergences between calculated and experimental values don’t exceed 15%.