atw 2018-09v3

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atw Vol. 63 (2018) | Issue 8/9 ı August/September RESEARCH AND INNOVATION 460 | | 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 Therefore, a number of catalysts are withdrawn out of containment during an overhaul period of each plant and their performance is tested in the PAR performance test facility (PPTF) under the natural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
atw Vol. 63 (2018) | Issue 8/9 ı August/September | | Fig. 6. Start-up Delay Times after One Overhaul Period Exposure to VOC. Plant ID Compounds other plants, the re-evaluation has been performed in 2017. Figure 7 shows the hydrogen depletion rates after an overhaul period of exposure to VOCs in containment air. A total of 62 tests are performed with 248 catalyst samples from seventeen (17) plants as described in Table 2. The test results show that the hydrogen depletion rates are much higher than the required depletion rate of 0.2 g/sec that is specified in technical specification of PAR purchase in Koran nuclear power plants. A total averaged value is estimated as 0.270 g/sec with C1 G H1 H2 M1 P Y Estimated Sources of VOCs Benzene ! ! ! ! ! ! ! Paint, Insulation, Glue Docosane ! ! ! ! Oil Eicosane ! ! ! ! ! Oil Heptadecane ! ! ! ! ! ! ! Oil Heptane, 3-methylene- ! ! ! Oil Hexadecane ! ! ! ! ! ! Oil Octadecane ! ! ! ! ! ! Oil 1-Propene, 2-methyl- ! ! ! Paint Dibutylformamide ! ! ! Insulation Diethyl phtalate ! ! ! Paint, Insulation Heneicosane ! ! ! ! Oil Methylstyrene ! ! ! ! Paint, Insulation Nonadecane ! ! ! Oil Tridecane ! ! ! ! Oil Nonaneitrile ! ! ! Oil, Resin Tetradecane ! ! ! Oil Toluene ! ! Paint, Sealing | | Tab. 3. Major Compounds Adsorbed on the Sample Catalyst Surface. a standard deviation of 0.03 sec. The measured hydrogen depletion rates of catalysts exposed to VOCs have no difference with those of new catalysts that is estimated as 0.2687 g/sec with a standard deviation of 0.0108 sec. The recombination reaction takes place on some active sites on the degraded catalyst releasing the heat of reaction. This causes the catalyst surface temperature to increase creating a driving force for convective flow. Increase convective flow accelerates the reaction rate leading to further increase in the catalyst temperature until all the adsorbed | | Fig. 5. Hydrogen Depletion Rates after One Overhaul Period Exposure to VOC. VOCs desorb and all the active sites are free, i.e., the catalyst is fully regenerated. The same conclusion about the hydrogen depletion rate has been reported in reference [6]. The adsorbed airborne substances on the catalyst surface are analyzed qualitatively using GC/MS (gas chromatograph/mass spectrometer) method for selected samples from seven (7) plants. Various VOCs are detected and their major compounds are summarized in Table 3. It is estimated that these compounds are originated from paints, oils, lubricant, insulation, glues, etc., which are commonly used in the plant maintenance. Although benzene, heptadecane etc. are commonly detected, the detected volaticle organic compounds differ from each plants. In the previous results, the plant H1 showed a relatively longer start-up delay time compared to other plants [8]. There was a steam generator replacement in plant G and H when the PARs were installed in 2013. Further tests are performed in next overhaul for plant H. The test results of H 2 represents test results in the second overhaul (2016) in plant H. The detected VOCs are different from the results of the first overhaul (2014) but the start-up delay time still remained in relatively larger value than other plants. The common VOCs detected in plant G, H1 and H2 are benzene, hetadecane, octadecane etc. (the plant G and H are the same type plants). However, these materials are also detected in other plants having a relatively shorter start-up delay time. From the present results, it is considerd that the detected materials are plant-specific and strongly dependent on the maintenance activities. The VOC materials presented in Table 3 are at least not strongly related to the RESEARCH AND INNOVATION 461 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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atw 2018-09v3

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