Barrier concept

The SS/SH barrier concept is based on the assumption that two reactive materials placed in layers will react at the interface to form an insoluble precipitate. The precipitate is designed to form a seamless, impermeable seal that will prevent the transmission of leachate and contaminants to the surrounding media. 

Bacteria, use of antimicrobial proteins for control, 6 Bacteriocins Escherichia colU 304 lactic acid bacteria, 304-307t Barrier concept, use of antimicrobial peptides, 303... 

Fig. 9. The diffusion barrier concept for ACZ compared with CZ. (a) ACZ the sintering of CZ is inhibited by A1203 particles dispersed among CZ particles and (b) CZ sinter easily without any dispersal.

A new material ACZ for a TWC with high thermal stability is developed based on a novel concept, i.e. the diffusion barrier concept. Diffusion... 

Fig. 8-4. Kovalevsky s barrier concept, showing responses of plants to increasing metal concentrations in soils. L0 is the background value of the element in the plant tissue L, is the limiting value of the element in the plant tissue. A, LfL0 > 300 (barrier-free) B, Lt/LQ > 30 < 300 (high-barrier) C, L,/L0 > 3 < 30 (medium-barrier) D, L /L0 > 2 < 5 (low-barrier) (adapted from Brooks, 1993).

Over the last decade numerous publications have dealt with the functional barrier concept from different points of view and with different scientific... 

Containment can normally be achieved by application of the displacement concept (low pressure differential, high airflow), or the pressure differential concept (high pressure differential, low airflow), or the physical barrier concept. 

The design modifications investigated fell into two categories. (1) Mat mount density such as increasing the mount density from 4070 g/m to 4300 g/m, gradual reduction in the mat gap, and internal ribs. (2) Gas barrier concepts comprised a range of seals. All these modifications resulted in mat loss. 

Universal Precautions Specimen Handling and Laboratory Testing AIDS, hepatitis B, and other bloodbome pathogens pathogen types routes of entry barrier concepts and protective measures disposal of sharps and other contaminated items personal hygiene and emer-... 

Figure 1. Schematic Showing Tri-layer Hydrogen Barrier Concept...

Concerning radiation protection outside the plant, a barrier concept with progressive rates of vacuum from inside (e.g., glove boxes) to the outer atmosphere in connection with the ventilation system and treatment of off-gas by HEPA filters will achieve protection of the population. Emission of airborne radioactivity is monitored and the radioactivity of liquid effluents is controlled. 

The above categories are treated below in more detail. In the course of time a barrier concept has been developed. It comprises several levels, as shown in Table 4.1. 

In modem technology, which is characterized amongst others by the use of nuclear power, the operation of complex process plants and air and space travel, failure can hardly be tolerated because its consequences may be large. They can be economic, such as unplanned shut-downs or destraction of plants, or endanger humans and environment. Accidents do happen despite the numerous safety measures described in the preceding chapters. The reason is that technical measures and human interventions for avoiding accidents can never be perfect. They fail with a certain probability. This is the rationale for the barrier concept presented in Sect. 4.2. 

This understanding is then put in contrast to the Risk/Barrier concepts as indicated by Reason (1996)... 

Deep geological disposal concepts, in particular for alpha bearing (low or medium level) waste and heat generating high level waste, were developed mainly based on the multi-barrier concept. In this concept, the protection of humans and the environment should be guaranteed by an optimal combination of a number of barriers consisting of the waste matrix, container, buffer and backfill material, the repository structures and the geological environment. 

The geological barrier plays the main role in the multi-barrier concept, in particular where it concerns the long term. Various geological formations are under consideration such as clay, salt, crystalline rocks, tuff, etc. The enqjhasis put in the various national programmes on >ecific rock formations depends on the presence of one or another formation at the national territories [4]. Therefore, there is no best or second best rock formation but each of them has its own advantages and disadvantages. 

Ciurent deep repository projects are based on a multi-barrier concept aiming at ensuring the containment of radioactive substances ... 

The overall safety of a deep repository system relies on a multi-barrier concept including the geological barrier. 

---