15.11. Passive systems based on light-water core designs benefit from the considerable design and operating experience of existing reactors and therefore are attractive to utilities. A PWR design, designated as AP600, has been developed by Westinghouse Electric Corp. in cooperation with the U. S. Department of Energy (DOE) and EPRI. Similarly, a 600-MW(el) BWR, known as the SBWR, has been developed by the General Electric Co., with DOE and EPRI cooperation. In this case, the smaller size permits natural recirculation of the coolant, a significant design simplification.

15.12. Gas-cooled reactors of various types have been used to generate electricity since the earliest days of the nuclear power industry, particularly in the United Kingdom. During more recent years, prototypes of the high — temperature, gas-cooled reactor (HTGR) concept have operated in the United States and in Germany. This type of helium-cooled, graphite­moderated system features fuel embedded in small spherical particles that retain fission products. The modular high-temperature gas-cooled reactor (MHTGR) is a passive, inherently safe concept which builds upon HTGR experience.

15.13. Sodium-cooled fast reactors have also received development at­tention for many years. Most notable among experimental reactors is EBR — II, which has been operating very satisfactorily since 1961 at a rated elec­trical output of 20 MW. Demonstrations of passive, inherent safety char­acteristics led to the development of the integral fast reactor (IFR) concept at Argonne National Laboratory. Subsequently, a team led by the General Electric Co. developed a modular reactor concept PRISM (Power Reactor, Innovative Small Module), which appears promising for future energy requirements.

15.14. The advanced passive PWR and BWR are likely to receive early favor by electrical utilities seeking a 600-MW(el)-size unit, particularly since they utilize technology familiar to them. The other candidates for commercialization are the MHTGR and PRISM concepts, which, should they receive utility support, are likely to come somewhat later. Finally, we will mention examples of other interesting concepts which have potential. One is the process inherent ultimate safety (PIUS), developed in Sweden, and the safe integral reactor (SIR), developed by a team led by Combustion Engineering based on earlier PWR designs intended for maritime use.

THE AP600 [2]

Introduction

15.15. The AP600 (“advanced, passive”) reactor design features a two — loop Westinghouse PWR arrangement modified to have conservative safety margins and permit simplification of many supporting subsystems. The coolant loop arrangement and some of these features are shown in Fig.

15.1. In each loop, circulation is provided by two closely coupled canned motor pumps. As in the Combustion Engineering evolutionary PWR (§13.24), the steam generator has been enlarged to improve operating margins.

15.16. Some preliminary design specifications are summarized in Table

15.1. The core contains 145 fuel assemblies of the 17 x 17 lattice type with an active length of 3.66 m (12 ft), but similar to that described for the larger PWR in Table 13.1. However, the power density has been

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Close coupied pumps eliminate Hot-leg pipe small LOCA core

(31 in. ID) uncovery

reduced by about 30 percent to improve safety margins. Consistent with this reduction, a number of other specifications are less challenging than those listed in Table 13.1.