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A.V. Zhurbenko, Y.M. Semchenkov, P.D. Slavyagin RRC “Kurchatov Institute”

IMPACT OF CHANGED FUEL PERFORMANCES ON SAFETY BARRIER EFFECTIVENESS AT NORMAL OPERATION OF NPP WITH VVER. A.V. Zhurbenko, Y.M. Semchenkov, P.D. Slavyagin RRC “Kurchatov Institute”. CONTENTS. 1. Defence-in-Depth Concept 2. System of Barriers as the Basis for Radiation Safety

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A.V. Zhurbenko, Y.M. Semchenkov, P.D. Slavyagin RRC “Kurchatov Institute”

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  1. IMPACT OF CHANGED FUEL PERFORMANCES ON SAFETY BARRIER EFFECTIVENESS AT NORMAL OPERATION OF NPP WITH VVER A.V. Zhurbenko, Y.M. Semchenkov, P.D. Slavyagin RRC “Kurchatov Institute” 24-28.09.2007,Yalta,17-th Symposium of AER

  2. CONTENTS 1. Defence-in-Depth Concept 2. System of Barriers as the Basis for Radiation Safety 3. Factors have influencing on the Barriers Efficiency 4. Barriers Status Monitoring 24-28.09.2007,Yalta,17-th Symposium of AER

  3. DEFENCE-IN-DEPTH CONCEPT • prevention of anticipated operational occurences • prevention of design accidents by means of normal operation systems • prevention of beyond design basis accidents by means of safety systems • management of beyond design basis accidents • emergency planning 24-28.09.2007,Yalta,17-th Symposium of AER

  4. BARRIERS • fuel matrix (barrier 1) • fuel pin cladding (barrier 2) • boundary of the primary coolant system(barrier 3) • containment system (barrier 4) 24-28.09.2007,Yalta,17-th Symposium of AER

  5. BARRIER1 • Has been substantiated: • for a 3-year fuel cycle of VVER-1000 • for a 4-year fuel cycle of VVER-440 • FP designed retention in fuel matrix makesapproximately99% (for fuel burnups 40-43 MWd/kgU) 24-28.09.2007,Yalta,17-th Symposium of AER

  6. BARRIER2 • The adopted fabrication processes and proven pin operation practices allow to ensure the level of pin failure probability (leakage)not exceeding several units per 10-5 1/reactor-year 24-28.09.2007,Yalta,17-th Symposium of AER

  7. BARRIER3 • integrity of the equipment • retaining the controllable and uncontrollable leakages at reasonably low level • effective primary coolant purification system 24-28.09.2007,Yalta,17-th Symposium of AER

  8. BARRIER4 • containment system equipped with systems of treatment and processing of volatile fission products and liquid drainages The integrated effectiveness of all the barriers is called to provide the satisfaction of radiation criteria for annual dose limits of public arising from gaseous discharges and liquid drainages to the environment with allowance made for climatic and hydrological conditions at plant site during every normal operation condition or reactor state 24-28.09.2007,Yalta,17-th Symposium of AER

  9. FIRST BARRIER PENETRABILITY • initial fuel structure • irradiation parameters • physical and chemical properties of radionuclides 24-28.09.2007,Yalta,17-th Symposium of AER

  10. OPERATIONAL LIMIT OF FUEL PIN LEAKAGE IS REGULATED BY THE FOLLOWING VALUES • 0.2 % of fuel pins (of the total number of fuel pins in the core) may have defects of “gas untightness”-type • 0.02 % fuel pins (of the total number of fuel pins in the core) may have serious defects of type “fuel - coolant direct intact” The second barrier effectiveness at normal operation is denominated by PBYa-RY-AS-89 as operational limit for fuel pin leakage. 24-28.09.2007,Yalta,17-th Symposium of AER

  11. UNIT SYSTEM CHARACTERISTICSBY DEFINED OPERATIONAL LIMIT • efficiency of primary purification system as 30 t/h • purification efficiency as 90% • reactor thermal power as 3000 MW For these performances of operating VVER-1000 plants the operational limit of specific activity according to iodine-131 in the primary coolant amounts to 3.7 x 106 Bq/kg (10-4 Ci/kg). 24-28.09.2007,Yalta,17-th Symposium of AER

  12. THIRD BARRIER EFFICIENCY • depends on controllable (defined by design technology) • uncontrollable (defined by abnormal operation of the equipment) coolant leakages • Value of permissible uncontrollable coolant leakage into VVER-1000 (model B-320) containment rooms amounts to 100 kg/h • Operational limit on the leakage of the primary circuit into the secondary one is equal to 4 kg/h. 24-28.09.2007,Yalta,17-th Symposium of AER

  13. EFFICIENCY OF THE FOURTH BARRIERDEPENDS UPON: • containment space • containment integrity • efficiency of ventystem • effectiveness of purification system • liquid waste management system • storage systemefficiency 24-28.09.2007,Yalta,17-th Symposium of AER

  14. BASIC PROBLEMS • existing calculation methods are certified for the burnups of 40-43 MWday/kgU.For high burnupare used empirical correlations • investigation of influence of iodine isotopes spiking at high burnups on operational limit 24-28.09.2007,Yalta,17-th Symposium of AER

  15. Status Monitoring of First and Second Barriers • avoiding abnormal operation conditions • timely detection of failed fuel assemblies (with abnormal cladding tightness) • avoiding prohibited radioactive effects of anticipated operation occurrences and design accidents by means of detecting and timely discharging of leaking fuel 24-28.09.2007,Yalta,17-th Symposium of AER

  16. BARRIERS STATUS MONITORINGSHOULD BE REALIZEDIN VVER REACTORS, INCLUDING: • rated power increase and at power operation prolongation • reduced periods of scheduled reactor trips for servicing and refueling • reaching the average design burnup in a 4 or 5-year equilibrium fuel cycle of VVER-1000 and 5 or 6-year equilibrium fuel cycle of VVER-440 • implementation of new types of fuel (for example, MOX-fuel and uranium regenerate based fuel) 24-28.09.2007,Yalta,17-th Symposium of AER

  17. CLM at Operating Reactormake it possible: • to separate the quantitative contribution to FP activity levels due to failed fuel pins from that of residual contamination of the primary circuit • to determine to which operation year the failed fuel assembly refers • to assess the number of leaking fuel pins in the core for the time moment of analysis completion • to determine fuel burnups in leaking pins 24-28.09.2007,Yalta,17-th Symposium of AER

  18. Selection of CLM methods for shutdown reactor depends upon the following factors: • adopted concept of handling leaking fuel • fuel assembly design • availability of equipment and technology for fuel assembly “repair” CLM at shutdown reactor is aimed at the elaboration of conclusion on the possibility of further reactor operation or that of resolution to pre-term fuel discharge. So the criteria being used differ from that for normal operation 24-28.09.2007,Yalta,17-th Symposium of AER

  19. TASKS TO EXTEND THE CAPABILITIES OF THE CASE METHOD • substantiation of availability to use the existing CLM case method for fuel assembly without the axial hole in fuel pellets • practicing the method of longtime hold-up as an additional CLM method to be used for the cases, where because of cladding defect location it becomes impossible to initiate FP release from leaking claddings by pressure changing • modernization of existing CLM facilities using up-to-date engineering solusions and pin database, which will enable reducing man-power and personnel exposure 24-28.09.2007,Yalta,17-th Symposium of AER

  20. THANK YOU FOR YOUR ATTENTION ! 24-28.09.2007,Yalta,17-th Symposium of AER

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