SOLUTE colaborates in the project of AP1000®

SOLUTE is working with Westinghouse Spain (WES) in developing various projects in the field of civil engineering in recent years. WES is part of the Westinghouse Electric Company group (WEC). WEC is the pioneer and global leader in desing and construction of nuclear plants.

WES is on charge of designing several key structures on the AP1000® project. The AP1000® is the safest and most economical nuclear power plant available in the worldwide commercial marketplace (see Reference 1), and it is the only Generation III + reactor to receive Design Certification from the U.S. Nuclear Regulatory Commission (NRC).

The AP1000® (Advanced Pressure 1000 Mw) is a PWR reactor (Pressure Water Reactor) that uses pressure water as coolant and includes passive safety elements to keep the reactor refrigerated in case of emergency. This passive protection consists of reducing the dependence on electromechanical components to let reach the reactor to the coolant fluids. Instead of this, laws of physics as natural convection, condensation and gravity are entrusted of refrigerating the reactor (see Reference 1).

WES, and SOLUTE's engineers working for it, performs the design of several structural elements for two essential buildings of the plant:

  • the auxiliary building (see Figure 1).
  • the shield building (see Figure 1).

Many facilities are hosted in the auxiliary building, depending on the type of plant, as refrigeration system pumps, electrical penetrations, heating, ventilation and air conditioning components and many other.

From a structural point of view two decissions must be made prior to going deep in the design process. For one hand we have to decide the type of material to employ, and for the other hand the type of structural system.

Reinforced concrete will be usually found as main material. However, composite steel-concrete slabs become an alternative to build the floor structures.

The structure of the multistory auxiliary building is materialized through a columns and beams frame where one-way or two-way floor slabs may be built as well as shear walls or other structural elements tipically used in building contructions.

Both decissions must be made in order to minimize the volume and seismic mass as well as providing the highest ductility to face the ductility demand in case of earthquake.

Another aspect to consider is the design and calculation of module structural element, by means of development of precast enclosures (composite structures and precast concrete). In this way, improving quality and reliability of structural systems is intended, and also the constructive performance.

The containment building will host the containment vessel, it means, the place in which the reactor is located as well as other nuclear fuel facilities to handle it in its way to the reactor or from the reactor as nuclear waste this time.

The containment building is cylindrical and its main geometric features are as follows (see Reference 2): output diameter 50.0 m; wall thickness about 1.0 m; 75.0 m height from basemat to top of dome. The dome cover up the building and host one of the passive mechanism of refrigeration: a water tank that contains enough water for cooling the reactor during 72 hours in case of accident (See Reference 1).

Two objectives should be meet when designing the structure of the containment building:

  • to face the high forces transmitted to the structure in normal, abnormal or extreme conditions
  • to become an effective biological shield against radiation.

The compliance of the first objective results from a double additive calculation, on one hand a global calculation where there are several load combinations in which several single weighted hypotheses take part, like Dead Load (weight of structural elements, permanent loads), live load or operation load, difference of pressure inside and outside the containment, thermal load, wind load (from usual wind velocity to tornado), seismic load, etc. On the other hand, a local or detail calculation is performed, in which the margin planned for the structural components in the global calculation have to be large enough to withstand the pipe attachments, the supports of heating system, vent and air conditioner,  the platforms that surround containment vessel, etc

As a curiosity, recently The U.S.NRC (United States Nuclear Regulatory Comission) has granted Westhinghouse AP1000® a combined construction and operating license in U.S, after the structural revision of Shield Building has been performed since 2006, with the aim of providing this building the capacity of withstanding an aircraft impact.

The third prominent task in which SOLUTE is working, apart from the design of building component mentioned above, is the conception, design and calculation of structural connections between Auxiliary Building and Shield Building, so the integrity of the containment requirements are guaranteed in order to the emissions to the exterior are the stated by Regulatory Organization, even in accident conditions.

WES currently provides the  monitoring and technical assistance to the China Plants (Sanmen 1-2  y Haiyang 1-2) under construction, where the first worldwide AP1000® plant is expected to be started up by the end of 2013. Tasks involving Solute engineers include review of calculations and updating of design derived from the specific conditions of plants under construction.

All of these tasks are developed by mean of tools and procedures as the followings:

  • Westinghouse Quality Management System. A set of procedures developed for the compliance of US N.R.C. safety requirements to take part in the nuclear field.
  • Codes and standards of the property used to check structural elements. Some of these documents are ACI-349, ANSI/AISC N690, AWS codes, ASME Boiler and Pressure Vessel code and many others.
  • Advanced Finite Element Codes for designing structural elements.

References:

  1. http://www.ap1000.westinghousenuclear.com/ , main web of AP1000® project
  2. Ingeniería Civil de Centrales, José Manuel Goded, Notes of the subject given ETSICCP of Madrid.
  3. “Nuclear sí, pero lejos”, article published by the newspaper EL País, 26/12/2011.

Authors:

Lucas Rodríguez Velasco

Pedro Sánchez Hernández