Release from containment

On the other hand, if the hazard is toxicity, process alternatives can be compared by assessing the mass of toxic material that would enter the vapor phase on release from containment, weighting the components according to their lethal concentration. 

The amounts of material released from a damaged plant are usually expressed in fractions of the isotopic quantities in the core. These source terms (meaning source for the ex plant transport) depend on accident physics, amount of core damage, time at elevated temperatures, retention mechanisms, and plate-out deposition of material as it transports from the damaged core to release from containment. This section gives an outline of early source term assessments, computer codes used in calculations, and some comparisons of result.s. 

Section 8.1 provided a description of a core melt. This section backs up to describe thermal-hydraulic calculations of the phenomena before, during, and after the accident, and other calculations to estimate the radioactive release from containment. In this accident physics cannot be analyzed separately from in-plant transport. 

Many industrial chemicals are toxic or flammable, or sometimes both. Regardless of whether the chemical is toxic or flammable, it can present a danger to plant operators and the public if it is released from its container. Substantial efforts are taken to assure that toxic or flammable materials are not spilled or released from containment. There is always a chance, however, that such materials might be released. Therefore, provisions must be made to protect the plant operators and anyone who lives or works in the vicinity. 

An important hazard in the process industry is the boiling liquid expanding vapour explosion (BLEVE). This is understood to be the explosively rapid vaporization and corresponding release of energy of a liquid, flammable or otherwise, upon its sudden release from containment under greater-than-atmospheric pressure at a temperature above its atmospheric boiling point [37]. It is a physical explosion which is a consequence of sudden pressure relief. If a flammable material is involved a chemical explosion or a fireball can follow. 

VII.3 Annotated Bibliography on Mitigation of Release from Containment... 

Estimate the source term (source term modeling), i.e., how much material in what form (gas/liquid/two-phase) is being released from containment as a function of time, and develop the release scenarios or possible hazard outcomes (toxic cloud, fire, explosion, etc.) following the release. (A powerful tool to develop and keep track of possible outcomes following a release is an event tree event trees are commonly used in quantifying the frequency of these various outcomes and were therefore described in Section 10.2.8.)... 

Figure 5.56. Top video snapshots showing the self-assembly of a lithographically fabricated template into a 3D hollow container. Reproduced with permission from Adv. Drug Deliv. Rev. 2007, 59, 1547. Copyright 2007 Elsevier Science. Bottom optical images of chemical release from containers (a) isotropic release of a dye from a container with identical porosity on all faces (b) anisotropic release of a dye from a container with varied porosity (five faces with an array of 5 pm pores the sixth face has a 160 pm window). Reproduced with permission from J. Am. Chem. Soc. 2006, ]28, 11336. Copyright 2006 American Chemical Society.

Use water fine spray to reduce vapors do not put water directly on point of material release from container. 

Fractional releases from containment are larger, so for single unit plants the ECC must be designed to limit the number of fuel failures and the associated fission product release. 

Transient fission product release from containment ... 

The chemical interactions between fission products can have an important effect on the timing, chemical form, and quantity of products that could be released from the RCS in the case of a severe reactor accident. Each of these factors affects the potential for release from containment into the environment. Two areas of particular importance are the chemical form of iodine (which affects its volatility) and the quantity and composition of deposited aerosols. The latter are important because of the possibility of re-entrainment or revaporization after vessel or RCS failure. An assessment of these areas of concern requires detailed consideration of chemical interactions within the fuel, within the gas, and between gas and vessel structures. 

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