Integrity of the reactor pressure vessel

Since the integrity of the reactor pressure vessel is an essential safety requirement, it is useful to summarize the fundamental recommendations for the certain prevention of accidents. These recommendations concern the materials, the design, the fabrication, the inspection and the operation of the vessel. 

Three safety relief valves protect the integrity of the reactor pressure vessel against overpressure, in case of strong unbalances between the generated and removed power. 

One of the main tasks of nuclear-reactor safety research is assessing the integrity of the reactor pressure vessel (RPV). The properties of RPV steels and the influences of thermal and neutron treatments on them are routinely investigated by macroscopic methods such as Charpy V-notch and tensile tests. It turns out that the embrittlement of steel is a very complex process that depends on many factors (thermal and radiation treatment, chemical compositions, conditions during preparation, ageing, etc.). A number of semi-empirical laws based on macroscopic data have been established, but unfortunately these laws are never completely consistent with all data and do not yield the required accuracy. Therefore, many additional test methods are needed to unravel the complex microscopic mechanisms responsible for RPV steel embrittlement. Our study is based on experimental data obtained when positron annihilation spectroscopy (PAS) and Mdssbauer spectroscopy (MS) were applied to different RPV steel specimens, which are supported by results from transmission electron microscopy (TEM) and appropriate computer simulations. 

One of the most important tasks of nuclear-reactor safety research is to check the integrity of the reactor pressure vessel. Based on the results obtained, it is possible to conclude that the test methods used here could permit substantial progress to be made in the microstructural study of RPV steels and in the optimisation of the temperaturetime regime for the regenerative post-irradiation thermal treatment of RPVs. 

COLLADO, J.M., Design of the reactor pressure vessel and internals of the IRIS integrated nuclear system. Advanced Nuclear Power Plants (Proc. Int. Congress Cordoba, Spain, 2003), ICAPP03- ISBN 0-89448-675-6 (2003). 

The primary cooling system is of integrated design the reactor pressure vessel (RPV) accommodates reactor core, steam generators, primary coolant, and absorber rod drive mechanisms. 

The report addresses the reactor pressure vessel internals in BWRs. Maintaining the structural integrity of these reactor pressure vessel internals throughout NPP service life, in spite of several ageing mechanisms, is essential for plant safety. 

Fracture toughness requirements for protection against pressurized thermal shock are defined in 10 CFR Part 50,61, These requirements should be reviewed for applicability if applicable, they provide the basis for ensuring the integrity of the reactor vessel for pressurized thermal shock conditions,... 

Criterion 32 - Inspection of reactor coolant pressure boundary. Components which are part of the reactor coolant pressure boundary shall be designed to permit (1) periodic inspection and testing of important areas and features to assess their structural and leaktight integrity, and (2) an appropriate material surveillance program for the reactor pressure vessel. 

This section discusses the measures employed to provide and maintain the integrity of the Reactor Coolant Pressure Boundary (RCPB) throughout the facility s design lifetime. The RCPB is defined in accordance with ANSI/ANS 51.1-1983. Included are all pressure containing components such as pressure vessels, piping, pumps, and valves which are ... 

The reactor plant (RP) is equipped with an integral, vessel-type PWR. The reactor cross-section is shown in Fig 7.7.1. The reactor pressure vessel (RPV) is of 16.75 m height, 5.34 m diameter and 230 m volume. 

Already the first measurements performed in the containment about one day after the onset of the accident showed that the major fraction of fission product iodine was plated out in the sump water, while only a very smaU fraction was airborne in the containment atmosphere. Taking the different voliunes of both phases into account, an integral iodine partition coefficient of about 2 1(F was calculated from these data (Pelletier, 1980). The pH of the siunp water was about 8.6 (due to sodium hydroxide solution which was automatically injected into the containment sump to improve iodine retention in the liquid phase) the value of the partition coefficient is consistent with the data obtained in the CSE experiments, when the lower pH of the sump water in these experiments is taken into account. This high value indicates that in the TMI-2 accident the bulk of the fission product iodine was released from the primary circuit to the containment in the form of an iodide compound and not as elemental I2. This assumption is consistent with the observation made later on that only about 1% of the iodine present in the sump water was in the form of iodate it is also consistent with the redox conditions in the reactor pressure vessel which were mentioned above For such an H2 H2O... 

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