Inherent safety features

Most of the principles of inherent safety are useful in the preliminary design phase even most process details are still missing. This is represented in Table 4 which shows in which project phase each inherent safety feature should be considered. In fact the opportunities for installing inherent safety features decrease as the design progresses (Kletz, 1991). It can be seen from Table 4 that most features can be considered in the conceptual and flow sheet stage. 

Normally where it is necessary, fireproofing is preferred over water spray for several reasons. The fireproofing is a passive inherent safety feature, while the water spray is a vulnerable active system that requires auxiliary control to be activated. Additionally the water spray relies on supplemental support systems that may be vulnerable to failures, i.e., pumps, distribution network, etc. The integrity of fireproofing systems is generally considered superior to explosion incidents compared to water spray piping systems. The typical application of water sprays in place of fireproofing is for vessel protection. 

The MHR-T refers to HTGR facilities representing one of the advanced areas of new-generation nuclear power development and having inherent safety feature. The technical concept is based on ... 

Three main options from different possible combinations of process units have been previously studied (Khan and Amyotte, 2005, Palaniappan et al., 2002b). The first option is the base case with no additional inherent safety features. The second and third options are revised versions of the first one. Modifications can include some or all of the following a quench tower to reduce the temperature, change of solvent to lower the severity of the operating conditions, an extraction column, a solvent mixer to optimize the use of solvent and efficiency of acid extraction and the use of solvent recycle. 

Figure 1. Aclyric acid production route including all inherent safety features.

The safety demonstration tests in the HTTR are conducted to demonstrate an inherent safety feature, that is an excellent feature in Shutdown of the HTGRs, as well as to obtain the core and plant transient data for validation of safety analsis codes and for establishment of safety design and evaluation technologies of the HTGRs. The safety demonstration tests consist of Reactivity insertion test - control rod withdrawal test and Coolant flow reduction test as shown in Figure 6. In the control rod withdrawal test, a central pair of control rods is withdrawn and a reactivity insertion event is simulated. In the gas-circulators trip test, primary coolant flow rate is reduced to 67% and 33% of rated flow rate by running down one and two out of three gas-circulators at the Primary Pressurized Water Cooler without a reactor scram, respectively. 

LMRs with oxide-fueled core Models modified and newly developed mto the code so far mclude models for reactivity feedback effects and pool thermal-hydraulics In order to venfy the logic of the models developed, and to assess the effectiveness of the inherent safety features based upon the negative reactivity feedbacks m achieving the safety design objectives of passive safety, a preliminary analysis of UTOP and ULOF/LOHS performance has been attempted... 

Besides the demonstration of the heat utilization system, the JAERI plans to carry out safety demonstration tests to confirm the salient inherent safety features of the HTGR. In addition material and fuel irradiation tests as upgrading HTGR technologies after attaining rated power will be conducted. Preliminary tests on selected research subjects such as composite material and ZrC coated fuel developments, have been carried out at high temperature and under irradiation. 

The following safety demonstration tests are planned in the HTTR to verity inherent safety features of HTGRs. 

To verify the inherent safety features of the Modular HTGR... 

In the 90s, industry and research have invested efforts in order to further develop nuclear technol< y in the direction of a "new safety quality while preserving or even regaining m-petitiveness against today s most economic energy carriers (e.g. natural gas). Different plant concepts rely on different approaches (evolutionary - innovative), focxis on diverging realisation periods and use passive systems or inherent safety features to a different extent. There are also considerable differences between fuel cycles either in the basic eipproach or in the details. 

The appropriate combination of inherent safety features and engineered ones should be necessary to prevent the extension of anticipated transients and also postulated accidents within the system. As an example of inherent safety features, one should mention Doppler reactivity that is effective against criticality events, which is a basis to ensure the reactor shut down function. Natural circulation is also an inherent safety feature to enhance the cooling capability of the reactor core. The nuclear energy system should be designed in such a way that severe core damage leading to the release of massive amounts of radioactive materials could be avoided. 

Inherent safety features as well as the use of passive tystems, e.g. natural heat dissqration and natural circulatirm fw core cooling, should as fsir as possible be enqrfiasized in the design. Complexity, cost and the need for manual intervention would be lowered by the absence of large numbers of active systems. 

This reactor, named LEADIR-PS, (an acronym for LEAD-cooled Integral Reactor, Passively Safe) incorporates the inherent safety features of the Modular High Temperature Gas Cooled Reactor (MHTGR), while avoiding the cost of reactor and steam generator pressure vessels, and the safety concerns regarding pressure vessel rupture. 

Safety. Most SMRs make extensive use of inherent safety features and passive safety systems. Such systems are appropriate to SMRs and are harder, if not impossible, to engineer on large reactors. They tend to be simpler than active systems resulting in a simpler safety case and easing the problems of public acceptability. 

Station blackout Natural coolant circulation, passive safety systems, reactor inherent safety features R... 

The reactor plant safety is ensured without power supply or personnel intervention for not less than 72 hours following all possible disturbances and accidents (positive reactivity insertion, loss of heat removal, primary circuit depressurization) by means of the reactor inherent safety features and by using the complex of interconnected passive safety systems and devices. 

The RUTA-20 reactor concept is based on long-term successful experience in operating pool-type research reactors. In addition, RUTA-20 reactor safety has been particularly enhanced due to technological progress in manufacturing of different reactor units, as well as modem approaches to the reactor design process with emphasis on inherent safety features based on fundamental laws of nature. 

Safety concept and design philosophy Provisions for simplicity and robustness of the design Active and passive systems and inherent safety features Structure of the defence-in-depth Design basis accidents and beyond design basis accidents Provisions for safety under seismic conditions... 

Active and passive systems and inherent safety features... 

The inherent safety features of the ELENA-NTEP are a negative temperature reactivity coefficient, a large secondary water inventory (68 m ), a near-zero bum-up reactivity swing, a very small (near iPeir) operating reactivity margin in the core, and negative coolant density and void reactivity effects. 

The localizing safety systems provide the defence in depth and secure the plant safety based on inherent safety features and predominantly passive phenomena they require no human intervention or external power sources. 

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