Aqueos Solutions

DOE-HDBK-3010-94

3.0 Liquids; Aqueous Solutions

3.2

A Q U E O U S S O L U T I ON S

3.2.1

T h erm al S tress: E vap oration an d B oilin g

Under most realistic scenarios involving the heating of aqueous solutions during postulated

accidents in nonreactor fuel cycle facilities, the relative vapor pressures of the solvent (water)

and the solute (various compounds of radionuclides, generally acidic nitrate) preclude

evaporation of the solute as a viable mechanism for the airborne release of the solute.

Instead, the airborne release is postulated to result from the entrainment of minute drops of

the bulk liquid formed by the mechanical disintegration of the surface of the bulk liquid.

Mechanical disintegration mechanisms include bubble breakup during boiling, jet drops

formed from the collapse of the crater remaining after bubble breakup, and secondary drops

from the reentry of jet drops. Drops are carried to the bulk flow by convective and vapor

flow away from the heated liquid. An increase in surface disruption would increase the

airborne release, although capture of secondary drops by the large number of primary

particles may place a limit on the release.

Kataoka and Ishii (April 1983) reviewed the literature and data on the entrainment of liquid

droplets from the surface of a bubbling or boiling pool. Droplets are generated by bubble

bursting, splashing or foaming. Some of the entrained droplets fall back into the pool and

some are carried away by the streaming gas. Entrainment, Efg, is defined as:

Efg = droplet upward mass flux/ the gas mass flux = (ρf jfe)/(ρg jg)

(3-1)

ρf

where:

fluid density

jfe

superficial velocity of liquid flowing upward as droplets

ρg

gas density

superficial gas velocity.

Two levels of the gas flow through the liquid upon the surface were noted:

bubbly flow (condition postulated for nonreactor facility accidents): small gas

flow (<0.1 m/s); droplets generated by discrete bubbles rising to surface of

pool and collapsing; initial velocity of entrained droplets is a function of

bubble burst time, bubble diameter, density of liquid and pressure around

bubble; transition to next level at ~0.1 m/s and liquid void fraction 0.3.

churn turbulent flow: may be dominant mechanism for post-Loss of Coolant

accident in light water reactor accident conditions; initial velocity of droplets

determined by momentum exchange mechanism (during breakup of liquid

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