,Yalta,17-th Symposium of AER1 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”

,Yalta,17-th Symposium of AER2 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

,Yalta,17-th Symposium of AER3 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

,Yalta,17-th Symposium of AER4 BARRIERS fuel matrix (barrier 1) fuel pin cladding (barrier 2) boundary of the primary coolant system (barrier 3) containment system (barrier 4)

,Yalta,17-th Symposium of AER5 BARRIER 1 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 makes approximately 99% (for fuel burnups MWd/kgU)

,Yalta,17-th Symposium of AER6 BARRIER 2 The adopted fabrication processes and proven pin operation practices allow to ensure the level of pin failure probability (leakage) not exceeding several units per /reactor-year

,Yalta,17-th Symposium of AER7 BARRIER 3 integrity of the equipment retaining the controllable and uncontrollable leakages at reasonably low level effective primary coolant purification system

,Yalta,17-th Symposium of AER8 BARRIER 4 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

,Yalta,17-th Symposium of AER9 FIRST BARRIER PENETRABILITY initial fuel structure irradiation parameters physical and chemical properties of radionuclides

,Yalta,17-th Symposium of AER10 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.

,Yalta,17-th Symposium of AER11 UNIT SYSTEM CHARACTERISTICS BY 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 10 6 Bq/kg (10-4 Ci/kg).

,Yalta,17-th Symposium of AER12 THIRD BARRIER EFFICIENCY depends on controllable (defined by design technology) uncontrollable (defined by abnormal operation of the equipment) coolant leakages 1. Value of permissible uncontrollable coolant leakage into VVER-1000 (model B-320) containment rooms amounts to 100 kg/h 2. Operational limit on the leakage of the primary circuit into the secondary one is equal to 4 kg/h.

,Yalta,17-th Symposium of AER13 EFFICIENCY OF THE FOURTH BARRIER DEPENDS UPON: containment space containment integrity efficiency of ventystem effectiveness of purification system liquid waste management system storage system efficiency

,Yalta,17-th Symposium of AER14 BASIC PROBLEMS  existing calculation methods are certified for the burnups of MWday/kgU. For high burnup are used empirical correlations  investigation of influence of iodine isotopes spiking at high burnups on operational limit

,Yalta,17-th Symposium of AER15 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

,Yalta,17-th Symposium of AER16 BARRIERS STATUS MONITORING SHOULD BE REALIZED IN 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)

,Yalta,17-th Symposium of AER17 CLM at Operating Reactor make 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

,Yalta,17-th Symposium of AER18 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

,Yalta,17-th Symposium of AER19 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

,Yalta,17-th Symposium of AER20