Validation of Advanced Computer Codes for VVER Technology: LB-LOCA Transient in PSB-VVER Facility

The OECD/NEA PSB-VVER project provided unique and useful experimental data for code validation from PSB-VVER test facility. This facility represents the scaled-down layout of the Russian-designed pressurized water reactor, namely, VVER-1000. Five experiments were executed, dealing with loss of coolant scenarios (small, intermediate, and large break loss of coolant accidents), a primary-to-secondary leak, and a parametric study (natural circulation test) aimed at characterizing the VVER system at reduced mass inventory conditions. The comparative analysis, presented in the paper, regards the large break loss of coolant accident experiment. Four participants from three different institutions were involved in the benchmark and applied their own models and set up for four different thermal-hydraulic system codes. The benchmark demonstrated the performances of such codes in predicting phenomena relevant for safety on the basis of fixed criteria. 1. Introductory Remarks VVER reactors have some unique and specific features (e.g., large primary and secondary side fluid inventory, horizontal steam generators, and core design), which require dedicated experimental and numerical analyses in order to assess the performance of safety systems and the effectiveness of eventual accident management strategies. The predictive capabilities of computer codes used in reactor safety analysis needs be validated against relevant experimental data, prior to their application to simulate the behavior of a nuclear power plant. To this purpose a “VVER code validation matrix” [1] was developed in the framework of the OECD/NEA activities, based on the experience of the validation matrices for light water reactor already developed in the 80 and then extended in the 90 [2–5]. 2. The PSB-VVER Project The OECD/NEA PSB-VVER project (2003–2008) has been set with the objective to obtain the required experimental data not covered by the VVER validation matrix [1]. A test matrix was defined considering the inputs received by the Russian Safety Authority Gosatomnadzor [6]. Five tests were executed in PSB-VVER integral test facility, operated at Electrogorsk Research and Engineering Centre, Elektrogorsk (EREC) [7], which are briefly outlined below and summarized in Table 1. The main objectives of the experiments were as follows:(i)to generate experimental data in order to validate computer codes for transient analysis of VVER reactors,(ii)to address the scaling issue,(iii)to contribute to the investigations of postulated accident scenario and actual phenomena occurring VVER-1000,(iv)to support