atw 2018-09v3


atw Vol. 63 (2018) | Issue 8/9 ı August/September


| | Fig. 4.

Tempearature and Hydrogen Concetration at the Exit of Test Device of Periodic Inspection

(New Catalyst: 3 % hydrogen and air mixture at 60 °C and 1 bar).

shows temperature rise behavior of

new catylists, which shows a similar

trend with time. Therefore, the PAR

supplier suggested the accepatance

criteria of the periodic inspection as

the temperature rise at a given time

(The exact values of temperature rise

and time are not described in this

paper because that information is a

supplier’s proprietary). Figure 5

shows temperature rise bebavior of

catylists that were exposed to containment

air during one overhaul period.

The behavior of temperature rise is

affected by the existence of VOC.

Some catalysts showed delayed startup

of hydrogen recombination and

others showed further increase of

temperature by combustion of VOC

itself. Figure 5 also shows the hydrogen

volume faction of air-hyrogen

mixture at the outlet of the test device.

It showed that the hydrogen recombination

already started although

the temperature does not reach the

required value. Therefore, there is a

possibility of unneccesary failure of

plant inspection with the current

method by temperature rise. This

method requires relatively long test

time because of larger heat capacity of

ceramic structure. In addition, it is

­difficult to correlate the hydrogen

recombination performance with the

amount of temperature rise and test

time. Threfore, we decided to change

the inspection method from the temperature

rise to the direct measurement

of hydrogen concentration with

new acceptance criterion.

Under the VOC-affected conditions,

the performance of PAR is hard

to identify through the current perioic

inspection method because the startup

delayed time and the hydrogen

­removal rate are defined under the

| | Fig. 5.

Tempearature and Hydrogen Concetration at the Exit of Test Device of Periodic Inspection

(After the Exposue of One Overhaul Period to Containment Air, 3 % hydrogen and

air mixture at 60 °C and 1 bar).

natural convection conditions. Therefore,

a number of catalysts are withdrawn

out of containment during an

overhaul period of each plant and

their performance is tested in the PAR

performance test facility (PPTF) under

the natural convection conditions.

A total of 152 tests are performed

with 608 catalyst samples to investigate

the effect of volatile organic

compounds (VOC) on the startup

performance on the hydrogen

removal. The catalyst samples are

taken from seventeen (17) plants with

four (4) different reactor types. For

plants C, D, F, H and M, the tests are

performed twice in the first and

second outage period to compare test

resuts between the first and the

second outages in the same plant.

Figure 6 shows the measured start-up

delay times in conditions of hydrogen

of 3 vol. %, temperature of 60 °C and

pressure of 1.5 bar. These test conditions

are selected because a start-up

delay time is considered after the

hydrogen concentration and the

temperature reached at both 3 vol. %

and 60 °C in the analysis of hydrogen

control to determine the capacity

and locations of PARs as a hydrogen

mitigation system [2]. Fifteen (15)

minutes of the start-up delay time are

assumed in severe accident analyses

while 12 hours of the start-up delay

time is assumed in design basis accident

analysis [12]. For new catalysts a

certain time is required until the flow

is fully developed by naural convection.

This time has been measured as

about 404 sec with a standard deviation

of 66.9 sec. As shown in Fig. 6,

the start-up delay times are well

within 15 minutes except the plants G

and H. The start-up delay times for

plant G and H1 show an average time

of 1,006 sec and 893 sec with a

standard deviation of 160 sec and

215 sec, respectively. The total averaged

start-up delay time for all plants

is estimated as 660.6 sec with a standard

deviation of 237.8 sec. For plants

C, D, F, H and M, the second tests does

not show a noticeable difference

­compared to its first tests.

In the design basis accident such as

a loss-of-coolant-accident (LOCA),

the hydrogen is generated gradually

and the hydrogen concentration could

be reached at 4 vol. % after several

days without a hydrogen mitigation

system after a LOCA takes places. In

the analysis of hydrogen concentration

in the LOCA, twelve (12) hours of

the start-up delay time were assumed

after the hydrogen concentration and

the catalysts temperature reach at

both 3 vol. % and 60 °C. Although the

start-up delays of 12 hours are considered,

there is a sufficient margin to

maintain the hydrogen concentration

below the regulatory limit of 4 vol. %.

However, in the severe accident conditions,

the hydrogen concentration in

the containment abruptly increases at

the timing of the reactor vessel failure

so that the margin for start-up delay

for hydrogen removal may not be

­sufficient compared to the situation of

a design basis accident. The regulatory

position in Korea is that the startup

delay times should be verified and

compared to the assumptions used in

the analysis of hydrogen control in

DBA and severe accident conditions.

In the case of plant G, H and N, the

analysis of hydrogen control in severe

accident conditions has been re-evaluated

with a longer delay time of

30 minutes in consideration of the

results of the start-up delay time

measurement tests in 2014. For the

Research and Innovation

Effects of Airborne Volatile Organic Compounds on the Performance of Pi/TiO 2 Coated Ceramic Honeycomb Type Passive Autocatalytic Recombiner ı Chang Hyun Kim, Je Joong Sung, Sang Jun Ha and Phil Won Seo

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