Nuclear Island Structures

The nuclear island structure is designed and constructed in accordance with seismic class... 

The barriers between the Nuclear Island structures and non-Nuclear Island structures are rated to withstand fires outside the Nuclear Island to a sufiicient degree that safety significant SSCs within the Nuclear Island will not fail. 

The nuclear island structures include the containment (the steel containment vessel and the containment internal structure) and the shield and auxiliary buildings. The containment, shield and auxiliary buildings are structurally integrated on a common basemat, which is embedded below the finished plant grade level. 

The nuclear island structures, consisting of the containment building, shield building and auxiliary building are founded on a common reinforced concrete basemat foundation as discussed in Section 3.8.5 of the EDCD (Reference 11.3). 

Adjoining buildings, such as the radwaste building, turbine building and armex building are structurally separated from the nuclear island structures. This provides space to prevent interaction between the nuclear island structures and the adjacent structures during a seismic... 

The nuclear island structures consist of vertical shear / bearing walls and horizontal floor slabs. The walls carry the vertical loads from the structure to the basemat. Lateral loads are transferred to the walls by the roof and floor slabs and the walls then transmit the loads to the basemat. The walls also provide stififiiess to the basemat and distribute the foundation loads between them. 

During normal operations, the nuclear island structures will be operated within Ihe design parameters (Section 13.5 of the EDCD, Reference 7.3 gives details of normal operations). This ensures the safety of plant persoimel and persons outside of the site boimdary. The following design requirement is identified ... 

The nuclear island structures will withstand a seismic event with 0.3g peak ground acceleration. 

The non-nuclear island stmctures comprise the annex building, diesel generator building, radwaste building and turbine building. The non-nuclear island structures contain no safety elass 1 equipment. 

That part of the annex building adjacent to the nuclear island is analysed and designed to prevent adverse interaction with the nuclear island structures for a 0.3g level earthquake. 

The design description is focused on the Nuclear Island portion of the plant with the interfaces with the remainder of the plant (hereafter referred to as the Energy Conversion Area) and a standard site identified. The Nuclear Island is considered to be that portion of the plant that has within its boundaries the standard reactor modules and "safety-related" (as defined in Section 3.2) buildings, structures, systems and components dedicated to assuring reactor... 

Another modification to the guidance provided by Regulatory Guide 1.70 is the clear distinction given to structures, systems and components within the Nuclear Island as opposed to those in the Energy Conversion Area (see Section 1.6). The discussion of the latter systems, which have no radionuclide control functions, is limited to a functional description and an identification of interfaces with the Nuclear Island. 

Within the Nuclear Island, each reactor module is housed in adjacent, but separate, reinforced concrete structures located below grade enclosed by a common maintenance hall. This configuration provides significant design... 

The Standard MHTGR, which is the subject of this PSID, consists of all the systems, subsystems and buildings and structures identified in the first column of Tables 1.6-1 and 1.6-2, i.e., the Nuclear Island. In addition, those portions of the interfacing systems and subsystems (second column of Table 1.6-1) that are physically contained within the Nuclear Island boundary are also part of the Standard MHTGR. The interfacing systems identified with an asterisk in Table 1.6-1 are presented in detail to emphasize the particular importance to radionuclide control of their interfaces with the Nuclear Island. 

The Standard MHTGR plant is broken up into two major areas a Nuclear Island containing the four reactor modules and the Energy Conversion Area containing the two turbine generators. All "safety-related" structures, systems, and components are contained within the Nuclear Island portion of the plant. 

The probability of a turbine missile strike on any given area of the Nuclear Island is a function of the energy and direction of an ejected missile and the orientation of the turbine with respect to that area. The turbine-generator is arranged so that the planes of rotation of the turbine disks do not intersect any structures, systems, or components required to function to meet lOCFRlOO limits, thus minimizing the probability of adverse effects from a turbine missile. The orientation of the turbine is shown on the plot plan, Figure 1.3-1. 

This section covers the building arrangements and discusses the provision for accident localization. It also discusses the containment structure, the ultimate barrier for defence-in-depth. The section also covers the accessibility of plant equipment and gives an overview on radiation exposures. The seismic protection of the nuclear island is briefly discussed. 

The internal structures of the containment and other buildings of the nuclear island are conventional reinforced concrete structures. 

Figure 9 also gives the neutron wall loadings pw and for NUWMAK the value of the power per unit weight p i of the nuclear islands. The reference value taken for the power density is that prevailing in the pressure vessel of pressurized water reactors (PWR). The structure of a PWR is less complex than that of a DT tokamak reactor would be and the materials required for its construction will, with all probability, entail lower specific energy costs than tokamak materials. In addition, the reference volumes chosen here for the tokamak reactors do not include essential subsystems of the nuclear island (e.g., start-up heating, fuel injection, selective vacuum pumps) because too little is as yet known about these. Power density comparisons made on this basis should therefore hardly lead to a pessimistic assessment of the economic chances of the tokamak as a power reactor principle. 

The mean volumetric net eletric power density in nuclear islands of recent conceptual tokamak power plant designs would be 2.5 to 4% of the value common today in the less complex structures of light water reactor nuclear islands (Fig. 14). Such tokamak reactors would require about 2 kg of construction material per kWei to be built or a factor of 17 more than for the PWR. 

A containment and a structural unit of the nuclear island provided to protect the reactor against external impacts and also limiting the radioactive release under design basis and beyond design basis accidents. 

The nuclear island footprint was maintained by increasing the height of the reactor vessel and of the containment structure, while maintaining their diameters, thereby avoiding the need to repeat most of the structural and seismic analysis already completed. 

These building structures are set out such that the turbine building and the other principal buildings are adjacent to the nuclear island so as to meet their functional purpose. 

API000 structures within the Nuclear Island do not collapse such that safety significant SSCs could be prevented from delivering the KSFs. 

Nuclear Island building structures have been designed such that precipitation cannot cause structural failure, access safety significant SSCs or otherwise compromise the capability of safety-significant SSCs to deliver safety functions. 

The effects of damage to SSCs within non-Nuclear Island buildings and the structures of these buildings on safety-significant plant located elsewhere are bounded by the consideration of seismic hazards. 

Nuclear Island building structures will withstand extreme wind such that KSFs are not compromised. 

Nuclear Island building structures and equipment will protect against smoke entering the building such that KSFs and MCR operator actions are not compromised. 

This chapter has provided an overview of the buildings and civil structures of the APIOOO. In particular, it describes the key nuclear island facilities that support the passive cooling features and also the design requirements imposed on them. Read in conjunction with Chapter 6 of this PC SR, this chapter provides a good overview of the functionality of the APIOOO. 

The CAREM nuclear island is located inside a pressure suppression containment system. The building surrounding the containment is in a single reinforced concrete foundation mat. It supports all structures with the same seismic classification in one block, allowing the integration of the RPV, the safety and reactor auxiliary systems, the fuel elements pool and other related systems. This building acts as a secondary containment. 

Figure 10 Model calculation for specular reflection and off-specular scattering reflecting the Island structure on top of the polymer multilayer for the system In Figure 9(c) with an average diameter of the islands of d=900nm. Experiment performed by the authors on the reflectometer SPN at the Joint Institute of Nuclear Research, Dubna, Russia.

---