Usage of calculation codes in the overall safety analysis system is reduced to verifying compliance with the acceptance criteria limiting the effects of abnormal situations. The primary way of verifying compliance the acceptance criteria is the calculation of the reactor performance during an abnormal situation. Some calculation model parameters (design, operating and referring to mathematical models) are known with specific uncertainty. Variation of the values of these parameters makes certain impact on the calculation results. Evaluation of the uncertainty of calculated characteristics due to variation of calculation model parameters is the primary goal of applying the method of uncertainty and sensitivity analysis.
The issue is topical due to the fact that new reactor designs and operating VVER units are facing the requirement of unit energy extension, and to meet this objective it is necessary to evaluate (and ultimately reduce) the degree of conservatism in safety analyses.
The report outlines the problem as seen by the developers of the neutronic part of the code. It also describes an approach to selection of variable neutronic model parameters and their variation when using the uncertainty and sensitivity method, taking into account the peculiarities of typical design basis accidents whose analysis requires coupled neutronic and thermal hydraulic calculations. The experience of using the method of uncertainty and sensitivity analysis showed that feasibility of its findings essentially depends on the quality and volume of code verification. This is due to the fact that the uncertainty estimations of the calculated characteristics, obtained during the verification process, determine the parameter range of the calculation models, and, therefore, the range of calculation result uncertainty.
Through the example of modeling specific emergency conditions, the paper demonstrates the application procedure of the method of uncertainty and sensitivity analysis using a coupled neutronic and thermal hydraulic model of VVER-1000, prepared on the basis of KORSAR/GP and SAPFIR_95&RC_VVER codes. Uncertainties of calculation results are estimated at variation of model parameters, corresponding to the nominal uncertainties of the codes ORSAR/GP and SAPFIR_95&RC_VVER certificated in the Russian Federal Service for Ecological, Technical and Atomic Supervision.
1 Artemov V.G., Gusev V.I., Gudoshnikov A.N., Egorov A.P., Korotaev V.G., Kuvshinova O.V., Piskarev A.V. Razrabotka, testirovanie i verifikaciya vtoroj bazovoj versii raschetnogo koda KORSAR s prostranstvennoj nejtronnoj kinetikoj dlya raschetov v obosnovanie bezopasnosti reaktorov tipa VVER [Development, Testing and Validation of the Second Basic Version of the KORSAR Code with Spatial Neutron Kinetics for Safety Substantiation of VVER-type Reactors]. Trudy 4 mezhdunarodnoj nauchno-tekhnicheskoj konferencii «Obespechenie bezopasnosti AES s VVER» [Proc. 4th Int. sci. tech. conf "Safety Assurance of NPP with VVER"]. Podolsk, 2005, pp. 67-68.
2. Artemov V.G., Artemova L.M., Korotaev V.G., Mikheev P.A, Shemaev Yu.P. Analiz temperaturnogo sostoyaniya tvelov na osnove sopryazhennogo nejtronno-fizicheskogo i teplogidravlicheskogo rascheta [Analysis of fuel Thermal Condition Based on Coupled Neutronic and Thermal-Physical Calculations]. Trudy konf. "Nejtronika-XXIII" [Proc. conf "Neutronika-XXIII"]. Obninsk, 2013.
3. Vasilenko V.A., Migrov Yu.A., Volkova S.N., Yudov Yu.V., Danilov I.G., Korotaev V.G., Kut'in V.V., Bondarchik B.R., Benediktov D.V. Opyt sozdaniya i osnovnye kharakteristiki teplogidravlicheskogo raschetnogo koda novogo pokoleniya KORSAR [Experience of Creating and Main Characteristics of the New-generation Thermal Hydraulic Code KORSAR]. Teploenergetika - Thermal Engineering. 2002, no. 11, pp. 11-16.
4. Programma SAPFIR_95.1. [SAPFIR_95.1 Code]. Software attestation certificate No. 205. – Federal Environmental, Industrial and Nuclear Supervision service of Russia, 15.12.2005.
5. Programma SAPFIR_95&RC_VVER. [SAPFIR_95&RC_VVER Code] Software attestation certificate No. 206. – Federal Environmental, Industrial and Nuclear Supervision service of Russia, 15.12.2005.
6. Programma SAPFIR_95&RC_VVJeR.2 [SAPFIR_95&RC_VVER.2 Code]. Software attestation certificate No. 321. Federal Environmental, Industrial and Nuclear Supervision service of Russia, 18.04.2013.
7. Programmnyj kompleks KORSAR/GP [KORSAR/GP Software Package]. Software attestation certificate No. 263– Federal Environmental, Industrial and Nuclear Supervision service of Russia, 23.09.2009.
8. Gorokhov A.K., Dragunov Yu.G., Lunin G.L. et al. Obosnovanie nejtronno-fizicheskoj i radiacionnykh chastej proektov VVER [Assessment of Neutronics and Radiation Parts of VVER Designs]. Moscow, IKC «Akademkniga» Publ., 2004.
9. Spasskov V.P., Dragunov Yu.G., Ryzhov S.B. et al. Raschetnoe obosnovanie teplogidravlicheskikh harakteristik reaktorov i RU VVER [Computational Validation of the Thermohydraulic Characteristics of the VVER Reactor]. Moscow, IKC «Akademkniga» Publ., 2004.
10. Vladimirov A.V., Granovskiy V.S, Gudoshnikov A.N., Danilov I.G., Donchenko D.N., Korotaev V.G., Migrov Yu.A. Analiz neopredelennostej pri chislennom modelirovanii avarijnykh rezhimov VVER s pomoshh'yu PK PANDA/KORSAR [Analysis of Uncertainties at Numerical Modeling of VVER Emergency Modes Using PANDA/KORSAR Codes]. Trudy mezhvedomstvennogo seminara "Teplogidravlicheskie aspekty bezopasnosti aktivnykh zon, okhlazhdaemykh vodoj i zhidkimi metallami" TEPLOFIZIKA-2008 [Proc. Interagency Seminar "Thermohydraulic Aspects of the Safety of Water- and Liquid-metal-cooled Reactor Cores", THERMAL PHYSICS-2008]. Obninsk, 2008, pp. 160.
