Design of SSC

For non-ideal mixtures, particularly in azeotropic mixtures, a simple method cannot be used to design an SSC in a shortcut manner. A common approach is to use repeated simulations, for example, by estimating the side stream location and flow rate, and then attempting to converge on a solution (Rooks et al, 1996). This method, however, is time-consuming and provides few insights. To overcome these drawbacks, efforts have been 

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Wherever possible the design of SSCs should be a failure tolerant design. That is, should these items fail, their failure would tend to move the plant towards a safe plant condition. This technique has broader application to areas other than protection against internal hazards, but where vaUd it may help in mitigating the effects of postulated internal hazards. 

For the seismic design of SSCs, external events such as floods or fires assumed to occur at the site as a consequence of an earthquake should be taken into account. They should be defined on the basis of probabilistic considerations. These loadings as a consequence of an earthquake should be combined with either SL-1 or SL-2 loadings, with due account taken of event timing and duration. 

Additionally, a set of specific design requirements shall be applied as appropriate to the design of SSCs for particular reactor types. 

In accordance with para. 3.13, acceptance criteria shall be established for operational states and for DBAs. In particular, the DBAs considered in the design of the research reactor and selected BDBAs shall be identified for the purposes of establishing acceptance criteria. For the design of SSCs, acceptance criteria may be used in the form of engineering design rules. These rules may include requirements in relevant codes and standards established in the State or internationally. The regulatory body shall review the acceptance criteria. 

In the design of SSCs of the RCSASs important to safety, account should be taken of all external hazards such as seismic hazards (for further information see under Seismic considerations in this section, paras 3.24-3.27), tornadoes, missiles, floods and hurricanes that may possibly be encountered in all operational states and in design basis accident conditions. 

The circumstances considered make it actual to search for the concept of NP development during the gas pause period, which enables to overcome arising difficulties. One of possible concepts has been designed by SSC RF IPPE [27]. The main concept goal is to increase sharply the efficiency of natural uranium energy potential utilization without radio-chemical fuel reprocessing and fuel cycle closing for gas pause elimination. 

Step 1 specifies that, for each DBE, classify as "safety-related" those design selections chosen for compliance with the lOCFRlOO region dose criteria. More specifically, for each DBE, various functions can be identified which must be performed if the consequences of the event are to remain within those allowed by the dose criteria. For the Standard HHTGR, these functions, as discussed previously in Section 3.2.2, are the retention of radionuclides in the fuel and, to maintain the fuel within its design conditions to assure such retention, the removal of core heat, control of the core heat generation rate, and prevention of chemical attack on the fuel. Step 1 requires that a set of SSCs which are capable of performing these functions for all DBEs for which they are required be classified as "safety-related."... 

The design and arrangement of SSCs is such that all required ISI and SS can be carried out. 

Although their application to non-ideal cases is relatively rare, SSCs can also be economical under certain process conditions and design requirements, with some of the criteria that favor the use of SSCs as follows (Rooks et al, 1996) ... 

Retrofit of SSCs to DWCs, which is an important breakthrough in both grassroots and retrofit designs, is becoming a promising trend. A retrofit design procedure, which utilizes shortcut. 

The reliability of SSCs may be adversely affected if technological limits defined by the designer are exceeded. These limits should be considered in the surveillance procedures, which should include acceptance criteria if appropriate. 

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. 

DOE Order 420.1, Facility Safety, requires the detailed application of that order s requirements to be guided by safety analyses that establish the identification and functions of safety (safety class and safety significant) structures, systems, and components (SSCs) for a facility and establish the significance of safety functions performed by those SSCs. It specifies that nuclear facilities shall be designed with the objective of providing multiple layers of protection to prevent or mitigate the unintended release of radioactive materials to the environment. The safety analyses must consider facility hazards, natural phenomena hazards, and external man-induced hazards. Paragraph 4.4.1 requires safety analyses for hazardous facilities to include the ability of SSCs and personnel to perform their intended safety functions under the effects of natural phenomena. DOE O 420.1 (DOE 1995) incorporates requirements from the cancelled DOE Orders 5480.28, 5480.7A, and 6430.1A(DOE 1993). 

The purpose of this chapter is to identify and describe structures, systems, and components (SSCs) that were assumed explicitly in the hazard/accident analysis to have provided a safety function that is, they were considered necessary in order to satisfy Evaluation Guidelines (EGs), provide defense in depth, or contribute to worker safety. Each of these SSCs is described along with the basis for designating the SSC as safety-related. Also provided are the applicable functional requirements, interfaces vwth other SSCs, and evaluations required to demonstrate performance of the SSCs safety functions under all expected accident or environmental conditions. 

It is important to realize that classification for the sake of classification or the assignment of preconceived requirements to SSCs could make the design and construction of new facilities or the modification of existing ones and their operational costs prohibitive for little risk reduction gained. Therefore, the classification of SSCs and the implementation of requirements should be applied in a graded approach. The classification is therefore based on results of hazard or accident analyses. 

The objective of the review of the design of the nuclear power plant is to determine the adequacy of the design and its documentation in an assessment against current international standards and practices. (The term nuclear power plant includes all SSCs on the site, as stated in para. 3.1.)... 

The objective of the review is to determine the actual condition of SSCs important to safety and whether it is adequate for them to meet their design requirements. In addition, the review should confirm that the condition of SSCs is properly documented. 

The objective of the review of the deterministic safety analysis is to determine to what extent the existing deterministic safety analysis remains valid when the following aspects have been taken into account actual plant design the actual condition of SSCs and their predicted state at the end of the period covered by the PSR current deterministic methods and current safety standards and knowledge. In addition, the review should also identify any weaknesses relating to the application of the defence in depth concept. 

In the early stages of the design of the plant, a preliminary layout of the main facilities should be prepared this should be periodically reviewed to achieve the most suitable solution for the seismic design. All procedures for seismic design should be firmly based on a clear appreciation of the consequences of past destructive earthquakes, and this knowledge should be adopted and realistically applied. In this preliminary work, the considerations mentioned in this section should be taken into account to reduce the effects of earthquakes on SSCs. 

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