Pressure vessel calculations for VVER-440 reactors.

Area of Science:

• Nuclear Engineering
• Radiation Physics
• Computational Physics

Background:

• Accurate assessment of fast neutron load is critical for reactor pressure vessel (RPV) integrity.
• Existing methods may require refinement for precise neutron transport calculations outside the reactor core.

Purpose of the Study:

• To develop and validate a mixed calculational procedure for determining the fast neutron load on the reactor pressure vessel.
• To apply the developed procedure to a specific nuclear power plant unit for practical assessment.

Main Methods:

• A mixed calculational procedure combining a core design code and the Monte Carlo code MCNP was developed.
• Neutron source determination on outer surfaces using a core design code.
• Neutron transport calculations outside the core performed with MCNP.
• Reaction rates in activation detectors at surveillance positions and cavity were calculated.

Main Results:

• The developed procedure was successfully applied to Unit II of the Paks Nuclear Power Plant (NPP) in Hungary.
• Calculated reaction rates in activation detectors showed fairly good agreement with experimental measurements.
• Validation confirmed the reliability of the mixed calculational approach for fast neutron load assessment.

Conclusions:

• The mixed calculational procedure provides a reliable method for determining fast neutron load on RPVs.
• The validated method enhances the accuracy of safety assessments for nuclear reactors.
• Application to Paks NPP Unit II demonstrates the practical utility of the developed technique.