The rated power of current integral reactor designs is limited to 700 MWe due to manufacturing limitations in the size of the RPV. The maximum diameter of the RPV is limited to 7 m, based on present technological capabilities. The steam generators have to be of a special compact design with a high power density to enable their location inside the RPV.

In-service inspection(ISI), maintenance and replacement of equipment and components is recognized to be more difficult as a result of the compactness of the

integral reactor designs and therefore, these aspects have received special attention in the design stage itself Some unique solutions and special tools have been developed for this purpose

The design characteristics are chosen to enhance nuclear safety and thus enable siting close to population centers. Decommissioning is also facilitated due to the availability of a fairly large RPV which can be used to store all the active components for a few decades in a safe maimer

New concepts of integral designs are being developed in the Republic of Korea and the Russian Federation In other countries, some modifications to existing designs have been undertaken Other design areas receiving active attention include safety — related heat removal systems for integral reactors, design of compact steam generators and decommissioning aspects

From operational point of view, integral reactor designs do not differ in principle from loop type reactors The principal advantages of integral reactors over current generation loop type reactors include the following:

• Enhanced safety level due to the location of primary coolant circuit within the RPV, in particular, a reduction in the probability of accidents accompanied by core damage

• Use of natural convection principle in the design of the primary coolant circuit not only provides a passive system for emergency decay heat removal, but also permits design of natural circulation reactors operating at rated output

• Reduction of neutron fluence on the reactor vessel to a negligible level enhances RPV life substantially

• Significant increase in shop-fabrication of the reactor systems reduces the volume of assembly work at site, and improves conditions for implementation of quality control procedures.

• Stringent requirements of leak tightness for the outer containment shell are relaxed as a closely fitted steel containment vessel called guard vessel functions as the first containment barrier A reinforced concrete shell would be adequate as an outer containment for protection from external effects Consequently, requirements of special safety systems for primary coolant inventory control and decay heat removal are also substantially simplified

• Potential reduction in construction time improves the economics of integral reactors

• Simplification of decommissioning work enables an earlier reuse of the site

Aspects currently receiving greater attention from designers of integral reactors include the following’

• Significant increase in overall dimensions and weight of the RPV resulting in the need to employ special handling and transport facilities during construction/assembly work

• Restriction of maximum reactor power capacity to 700 MWe as a consequence of limitation in allowable overall dimensions due to constraints in production capability of the industry

• Special design characteristics of the steam generators such as compactness and high power density which have a critical impact on the RPV dimensions

• Designs to facilitate comprehensive planned maintenance for trouble-free operation and replacement of major components.

• Use of nitrogen gas for pressurization