Modernization of Existing VVER-1000 Surveillance Programs

Abstract

According to generally accepted world practice, evaluation of the reactor pressure vessel (RPV) material behavior during operation is carried out using tests of surveillance specimens. The main objective of the surveillance program consists in insurance of safe RPV operation during the design lifetime and lifetime-extension period. At present, the approaches of pressure vessels residual life validation based on the test results of their surveillance specimens have been developed and introduced in Russia and are under consideration in other countries where vodo-vodyanoi energetichesky reactors- (VVER-) 1000 are in operation. In this case, it is necessary to ensure leading irradiation of surveillance specimens (as compared to the pressure vessel wall) and to provide uniformly irradiated specimen groups for mechanical testing. Standard surveillance program of VVER-1000 has several significant shortcomings and does not meet these requirements. Taking into account program of lifetime extension of VVER-1000 operating in Russia, it is necessary to carry out upgrading of the VVER-1000 surveillance program. This paper studies the conditions of a surveillance specimen’s irradiation and upgrading of existing sets to provide monitoring and prognosis of RPV material properties for extension of the reactor’s lifetime up to 60 years or more.

Changes to Irradiation Conditions of VVER-1000 Surveillance Specimens Resulting from Fuel Assemblies with Greater Fuel Height

“…It should be noted that these factors were left out on the modernization of the VVER-1000 surveillance program [3] and the results obtained in this study led to its revision. Some activities, such as the installation of metrological assemblies with extended neutron dosimeter sets and regular monitoring of the neutron flux at the outer surface of the reactor vessel, must be included in the modernization program to control the Lead Factor.…”

“…Schemes of container assemblies of different types. The irradiation conditions of specimens in CA with cylindrical containers in VVER-1000 with standard fuel assemblies and with low leakage core loadings were studied in detail earlier in [2][3][4]. The design of this type of CA leads to very inhomogeneous irradiation of specimens.…”

“…LF distribution in CA with cylindrical containers in VVER-1000 with standard fuel assemblies were estimated on the basis of surveillance dosimetry data and RPV neutron calculations validated by ex-vessel measurements in papers [2,3]. Lead Factors for assemblies with rectangular containers in the reactor with standard fuel assemblies has also been evaluated in the present paper.…”

“…Conditions of surveillance specimens irradiation in VVER-1000 with standard fuel assemblies are fairly well characterized [2,3]. But there are no experimental data on irradiation conditions of specimens irradiated in a reactor with fuel assemblies of the new type.…”