Caple AUF900 Uživatelský manuál stáhnout pdf (Strana 233)

231

ENSI Erfahrungs- und Forschungsbericht 2011

oxidation in steam, followed by a low flow rate of

air leading to an extended period of oxygen starva-

tion, in order to examine the interaction between

nitrogen with the pre-oxidised bundle. The ex-

periment conduct and results are ilustrated in fig-

ure 1. QUENCH-16 thus complemented the earli-

er experiments CODEX-AIT [16], QUENCH-10 [17]

and PARAMETER-SF4 [18]. Collectively these ex-

periments examine the effect of air covering the

whole spectrum from very low to high levels of

preoxidation.

A clearly exhibited feature of QUENCH-16 is nitrid-

ing of the cladding, particularly in the upper eleva-

tions which were most strongly affected by the ox-

ygen starvation. The oxygen starvation and nitrid-

ing lasted about 850 s and may have been the driv-

ing force for the strong oxidation excursion dur-

ing reflood, which did not occur in QUENCH-10

where the starvation period was very short. Pre-

test analytical support to QUENCH-16 was pro-

vided by PSI, using SCDAP/Sim and MELCOR, EDF

using MAAP-4 and GRS using ATHLET-CD. Prelimi-

nary post-test analyses have been performed [19].

Current status of model development

Validation of the PSI model has continued. A full

implementation in a developmental version of

SCDAP/Sim has been successfully completed by

Innovative Software Services (ISS). The new code

version has been used for further post-test anal-

yses of PARAMETER-SF4 [20, 21] successfully re-

producing the air ingress thermal transient (fig-

ures 2, 3) and oxygen consumption (figure 4). The

same version is also being used for the analysis of

QUENCH-16, currently in progress.

In parallel with the above work, the model has

been implemented into a special version of MEL-

COR 1.8.6 by the Russian Academy of Science

(RAS). The model is identical to the one success-

fuly implemented in SCDAP. A trial version was

provided to PSI for verfication of the implementa-

tion. Verification of the model as applied to oxida-

tion in steam has been successfuly carried out, as

shown in figure 5. However, the features needed

to simulate the heater rods in QUENCH and PA-

RAMETER are not included in this version and so

the model cannot yet be fully validated within the

MELCOR code. Efforts to rectify this deficiency are

in progress.

An initiative is being planned within the Euro-

pean Framework SARNET-2 Programme to per-

Figure 2:

Thermal response in

upper elevations of bundle

during PARAMETER-SF4

air ingress phase. Change

in slope indicates onset of

local oxygen starvation.

Figure 3:

Thermal response

in lower elevations

of bundle during

PARAMETER-SF4 air

ingress phase. Change in

slope indicates onset of

local oxygen starvation.

Figure 4:

Oxygen consumption

during PARAMETER-SF4

air ingress phase. Base

case, S1 and S2 used

the PSI model and kine-

tic parameters; S3 and

S4 used the Benjamin

correlation (MELCOR

default parameters) in

conjunction with the PSI

model.

Figure 5:

Verification of PSI model

implementation in

MELCOR 1.8.6: Sample

problem comparison for

hydrogen production

during steam oxidation.

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