Caple AUF900 Manual de usuario descargar pdf (Pagina 243)

241

ENSI Erfahrungs- und Forschungsbericht 2011

nisms determine the particle retention close to

the break where major retention takes place.

2. Even with a very low submergence significant

aerosol retention takes place. With high flow

rate and large spherical particles, aerosol trans-

port efficiency through the flooded bundle is

very low underlining the importance of the jet

– bundle interactions close to the tube break

on the aerosol retention in the flooded bundle.

3. Droplets are entrained from the water surface

with high gas flow rates. They carry aerosol par-

ticles with them and once the droplets evap-

orate, aerosol particles are released to the gas

flow. However, compared to particle retention

in the water due to inertial effects close to the

tube break, the effect of droplet entrainment on

particle transport is small. However, further work

would be recommended to determine this effect

when the aerosol loading in the water is high

at the later stages of the accident progression

when cumulative released aerosol mass is high.

4. Based on these tests as well as earlier data [vii],

the increasing submergence of the break in-

creases the particle retention in the water, and

the effect is much stronger in the flooded bun-

dle than in bare pools. This is presumably due to

the jet – bundle interactions, creating very com-

plex two-phase flows. This indicates that mod-

els developed for bare pools should be adapted

for calculation of aerosol retention in the flood-

ed bundle even in the regions far away from the

tube break.

When the steam generator secondary side was

filled with water up to the dryer section inlet

(Phase VIII, flooded separator), aerosol retention

was even higher than in the flooded bundle. The

effect of different gas flow rates and particle siz-

es was investigated. The decontamination fac-

tor in the flooded separator was found to be very

high in all the tests. No significant difference in DF

was measured with different flow rates or differ-

ent particle sizes. The high aerosol retention in the

flooded separator was mainly due to the large wa-

ter submersion of the break, combined with the

complex flow pattern inside the flooded separator.

Modeling of aerosol retention by pool scrubbing

in a wet SG faces two challenging conditions: gas

injection under the jet regime and the presence of

tube surfaces. The approach adopted to extend

the current capabilities of estimating pool scrub-

bing DFs (Decontamination Factors) has been to

extend a previous developed tool to accommo-

date the specific features of the SGTR scenario:

SPARC90 [viii]. So far the major progress has been

achieved in the adaptation of the particle trap-

ping as a consequence of water droplets entrained

within the gas jet at the inlet point. Decontamina-

tion by droplet entrainment is strongly dependent

on droplet features such as the number of drop-

lets entrained, their diameter and the relative ve-

locity. The equations embedded within SPARC90

have been reviewed and, when necessary, updat-

ed with alternative equations better fitted to the

conditions expected in the SGTR scenario. Present-

ly this work is still in progress and will be continued

in the ARTIST-extension project.

Droplet retention in the steam generator

dryer, DBA accident conditions

Rupture of one or more steam generator tubes re-

sults in leakage of primary coolant to the second-

ary side, and consequently, pressure increase in the

secondary side of the steam generator. The pres-

sure increase may be sufficient to cause a pres-

sure relief valve to open thereby providing a di-

rect pathway for the radioactive primary coolant

to the environment. The radioactivity release re-

sulting from such incidents depends strongly on

the conditions in the primary and secondary side

of the steam generator. For most of the condi-

tions, radioactivity release can be calculated based

on existing data [ix], however, under non-recircu-

lating conditions in the dry secondary side, no ex-

perimental data are available to assess the reten-

tion of radioactivity in the steam generator. Under

these conditions, release takes place mainly in the

form of droplets formed when the primary coolant

is released to the secondary side as a flashing jet.

The retention of droplets in the upper structures

Projekt XY

SQRT(Stk)

Flooded bundle, agglomerates

Flooded bundle, spherical

Figure 5:

The decontamination

factor DF in the tests in

the flooded bundle.

1 2 ... 238 239 240 241 242 243 244 245 246 247 248 ... 303 304

Caple AUF900 Manual de usuario Pagina 243

Comentarios a estos manuales

Caple AUF900 Manual de usuario Pagina 243

Comentarios a estos manuales

Relacionado con productos y manuales para No Caple AUF900