SAFETY STRUCTURES, SYSTEMS, AND COMPONENTS

DOE O 420.1, Facility Safety, (DOE 1996) Paragraph 4.1.1.2 specifies that safety structures, systems, and components be designed in accordance with a quality assurance program that satisfies 10 CFR 830.120. 

The basic description of the faciUty/activity and its operations, including safety structures, systems, and components. 

The SFs are intended as a basis for determining whether a structure, system or component performs or contributes to one or more SFs. They are also intended to provide a basis for assigning an appropriate gradation of importance to safety structures, systems and components that contribute to the various SFs. This means that the SFs are mostly related to the structures, systems or components. In the present report, the SFs are used in a more general sense, not necessarily related only to plant equipment but also to human factors such as personnel actions. In particular, there is no plant equipment directly considered at Level 5 of the defence in depth. Therefore, one more special SF has been added to the hst in the framework of this report ... 

A-4. This list of safety functions may be used as a basis for determining whether a structure, system or component performs or contributes to one or more safely functions and to provide a basis for assigning an appropriate gradation of importance to the safety structures, systems and components that contribute to the various safety functions. 

Forsberg, C. W., D. L. Moses, E. B. Lewis, R. Gibson, R. Pearson, W. J. Reich, G. A. Murphy, R. H. Staunton, and W. E. Kohn (1989). Proposed and Existing Passive and Inherent Safety-Related Structures, Systems, and Components (Building Blocks) for Advanced Light Water Reactors. Oak Ridge, TN Oak Ridge National Laboratory. 

The Seismic Safety Margins Research Program developed a computer code called SMACS (Seismic Methodology Analysis Chain with Statistics) for calculating the seismic responses of structures, systems, and components. This code links the seismic input as ensembles of acceleration time histories with the calculations of the soil-structure interactions, the responses of major structures, and the responses of subsystems. Since uses a multi-support approach to perform the time-history response calculations for piping subsystems, the correlations between component responses can be handled explicitly. SMACS is an example of the codes that are available for calculating seismic response for PSA purposes. 

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... 

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 final element of the Standard MHTGR licensing bases is the classification of plant equipment. In concert with development of the lOCFRlOO Design Criteria, this classification of equipment is done to focus attention on the minimum set of structures, systems, and components (SSCs) capable of performing all of the radionuclide control functions required to limit releases from DBFs to those allowed by lOCFRlOO, and, therefore, capable of fulfilling the design commitments made in the criteria. To draw this focus, these SSCs are designated as "safety-related."... 

Table 3,2-4 lists the structures, systems, and major components of the plant and indicates the classification and, if "safety-related", the radionuclide control function of each. This correlation of equipment classified as "safety-related" to the radionuclide control function performed by each is also illustrated on Figure 3.2-2. The specific application of the classification process resulting in the indicated "safety-related" designations is discussed in Safety-Related Structures, Systems, and Components for the Standard MHTGR. (Ref. 6)... 

GA Technologies, Inc. (GA). Safety-Related Structures, Systems, and Components for the Standard MHTGR. DOE-HTGR-87-003, Rev. 0. GA, San Diego, CA, January 1987. 

Effective maintenance, surveillance and in-service inspection (MS I) are essential for the safe operation of a nuclear power plant. They ensure not only that the levels of reliability and availability of all plant structures, systems and components (SSCs) that have a bearing on safety remain in accordance with the assumptions and intent of the design, but also that the safety of the plant is not adversely affected after the commencement of operation. 

Structures, systems and components important to safety vhich are installed as redundant items, or are called upon when normal operating conditions are threatened or lost, are normally kept in standby or off-line states. Examples of such SSCs are reactor containment vessels, emergency electric power sources, isolation valves and safety valves. Some of these SSCs cannot be monitored in situ for their operating reliability. Testing and surveillance for the actual conditions under which they are expected to operate, and which are generally difficult or impossible to reproduce, are usually undertaken under simulated conditions. These simulated conditions should be carefully planned, and the results should be interpreted prudently. 

Structures, systems and components important to safety should be included in the preventive maintenance programme. The operating organization should review the programme as appropriate in order to ensure that items important to safety have been properly identified and classified, and that the applicable requirements of the... 

The design of safety class structures, systems and components (SSCs) shall provide defense-in-depth features against the uncontrolled release of radioactive materials to the environment under normal conditions, AOEs, and DBA conditions. 

Quality Standards. Safety class structures, systems, and components shall be designed, fabricated, erected, and tested to quality standards commensurate with the importance of the safety functions to be performed. 

Fire Protection. The probability and effect of fires, explosions, and related perils at DOE facilities shall be minimized. Safety class structures, systems, and components shall be designed and located to minimize, consistent with other safety requirements, the probability and effect of fires and exp I os i ons. Noncombust i bIe and heat res i stant mater i a Is sha11 be used whenever practical throughout the unit, particularly in areas vital to the control of hazardous materials and maintenance of safety functions. Eire detection and fighting systems shall be designed and provided with sufficient capacity and capability to minimize the adverse effects of fires and explosion on safety class structures, systems, and components. 

Sharing of Structures. Systems, and Components. Safety class structures, systems, and components shall not be shared among nuclear facilities unless it can be shown that such sharing will not impair their ability to perform their safety functions, including, in the event of an accident in one nuclear facility, an orderly shutdown and cooldown of the remaining nuclear reactor fac i I i t i es. 

Support Systems. Support systems (e.g., electrical power, cooling) required to ensure that safety class structures, systems and components can provide their required safety function shall also be considered safety class systems. 

Safety class structures, systems, and components should be designed to withstand the effects of natural phenomena, without loss of capability to perform their safety functions. 

A system to provide heat removal capability for all safety class structures, systems, and components. This system should have the capability to remove the total heat-load during all normal conditions and AOEs and transfer this heat to the ultimate heat sink (described be Iow). 

Forsberg, C.W., et al. (1989) Proposed and existing passive and inherent safety-related structures, systems and components (building blocks) for advanced light water reactors , ORNL-6554, Oak Ridge National Laboratory. 

Adequate quality assuranee measures, proportionate to the safety classifieation of structures, systems and components. 

The probabilistic safety analyses should confirm that the structures, systems and components which ensure that the risk connected to the plant is low, be classified at the appropriate level. 

Pursuant to the provisions of 50.34, an application for a construction permit must include the principal design criteria for a proposed facility. The principal design criteria establish the necessary design, fabrication, construction, testing, and performance requirements for structures, systems, and components important to safety that is, structures, systems, and components that provide reasonable assurance that the facility can be operated without undue risk to the health and safety of the public. 

The development of these General Design Criteria is not yet complete. For example, some of the definitions need further amplification. Also, some of the specific design requirements for structures, systems, and components important to safety have not as yet been suitably defined. Their omission does not relieve any applicant from considering these matters in the design of a specific facility and satisfying the necessary safety requirements. These matters include ... 

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