atw - International Journal for Nuclear Power | 05.2020

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atw Vol. 65 (2020) | Issue 5 ı May ENVIRONMENT AND SAFETY 278 limit is shown in Figure 2, which is closely related to the maximum solidity limit. Above this limit, the particulate is the predominant ingredient and the fiber is embedded in the matrix. Such a condition of the debris bed is physically unacceptable. This situation can arise in the plant with a large particulate debris source. Therefore the mass ratio of particulate to fibrous debris is an important parameter in the evaluation of the head loss. Major source of particulate debris is the unqualified coatings in the containment because the generation and transport of unqualified coatings are assumed to be 100 % in the GR [3]. The 4-in and 6-in initial fibrous debris loading lines are shown in Figure 2. USNRC recommended that NUREG/CR-6224 correlations be used within the range of 1/8 to 4 inches initial fibrous debris loading (for NUKON) because it is not fully validated in the range exceeding 4 inches. In that case, the screen size should be increased or NUKON insulation should be replaced by an alternate insulation (i.e., RMI). As mentioned above, the head loss is closely related to the particulate- tofibrous debris mass ratio. The screen size should be determined carefully Amount of Cal-Sil insulation [ft 3 ] 0, 50, 100 Spray Termination Time [sec] Short: 95,000 Long; 1,000,000 Buffer Agent | Tab. 2. Environmental conditions in the present study. considering the cost effects between the reductions of the amounts of fibrous and particulate debris. 3.2 Effects of containment environmental conditions The prediction model for head loss by chemical products is currently not available and its effect on the head loss is evaluated only by the screen vendor’s performance testing. In the present analysis, the amounts of the potential chemical precipitates in the various containment environments are evaluated using WCAP-16530-NP methodology [6]. The amount of three predo minant types of pre cipitates, i.e., sodium aluminum silicate (NaAlSi 3 O 8 ), aluminum oxyhydroxide (AlOOH), calcium phosphate (Ca 3 (PO 4 ) 2 ) after 30 days of ECCS mission time are evaluated under various environmental conditions as shown in Table 2. The typical envi ronmental conditions of a Korean Westinghouse two loop NaOH, TSP nuclear power plant are used as the following input data in the present analysis: (a) pH and temperature profiles of sump and containment during 30 days, (b) The maximum pool volume during the recirculation phase after LBLOCA, (c) Amount of metallic aluminum (submerged and unsubmerged), (d) Amount of E-glass within ZOI (such as NUKON) (e) Concrete surface area within ZOI (submerged and unsubmerged). The presence of Cal-Sil insulation increases the releases of calcium and silicate as shown in Figure 3. For plants with sodium hydroxide (NaOH) buffer, sodium aluminum silicate is the principal precipitant since the insulation mix is a main source of silicon. Both of the presence of Cal-Sil and long spray time could drastically increase the amount of sodium Imprint | Editorial Advisory Board Frank Apel Erik Baumann Dr. Erwin Fischer Carsten George Eckehard Göring Dr. Florian Gremme Dr. Ralf Güldner Carsten Haferkamp Christian Jurianz Dr. Anton Kastenmüller Prof. Dr. Marco K. 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(KTG) | Publisher INFORUM Verlags- und Verwaltungsgesellschaft mbH Robert-Koch-Platz 4, 10115 Berlin, Germany Phone: +49 30 498555-30 Fax: +49 30 498555-18 www.nucmag.com | General Manager Dr. Thomas Behringer | CvD Nicolas Wendler | Advertising and Subscription Petra Dinter-Tumtzak Phone: +49 30 498555-30 Fax: +49 30 498555-18 E-mail: petra.dinter@nucmag.com | Layout zi.zero Kommunikation Antje Zimmermann Berlin, Germany | Printing inpuncto:asmuth druck + medien gmbh Buschstraße 81, 53113 Bonn, Germany | Price List for Advertisement Valid as of 1 January 2019 Published monthly, 9 issues per year Germany: Per issue/copy (incl. VAT, excl. postage) 24.- € Annual subscription (incl. VAT and postage) 187.- € All EU member states without VAT number: Per issue/copy (incl. VAT, excl. postage) 24.- € Annual subscription (incl. VAT, excl. postage) 187.- € EU member states with VAT number and all other countries: Per issues/copy (no VAT, excl. postage) 22.43 € Annual subscription (no VAT, excl. postage) 174.77 € | Copyright The journal and all papers and photos contained in it are protected by copyright. Any use made thereof outside the Copyright Act without the consent of the publisher, INFORUM Verlags- und Verwaltungsgesellschaft mbH, is prohibited. This applies to reproductions, translations, micro filming and the input and incorporation into electronic systems. The individual author is held responsible for the contents of the respective paper. Please address letters and manuscripts only to the Editorial Staff and not to individual persons of the association´s staff. We do not assume any responsibility for unrequested contributions. Signed articles do not necessarily represent the views of the editorial. ISSN 1431-5254 Environment and Safety Physical and Chemical Effects of Containment Debris on the Emergency Coolant Recirculation ı Jisu Kim and Jong Woon Park
atw Vol. 65 (2020) | Issue 5 ı May | Fig. 3. Comparison of the chemical precipitates with various plant environments. aluminum silicate precipitates because long spray time increases dissolution of aluminum as well as silicon. The precipitation of aluminum oxy hydroxide is negligible in the present analysis because the concentration of aluminum is not sufficiently lager than that of silicon. The quantity of sodium aluminum silicate is limited by the amount of silicon available in solution, if the silicon concentration is less than 3.12 times the aluminum concentration as shown in Eq. (7). Any remaining aluminum in solution will precipitate as aluminum oxyhyroxide. If the concentration of silicon is greater than 3.12 times the aluminum concentration, then the quantity of sodium aluminum silicate generated is limited by the concentration of aluminum available. For plants using trisodium phosphate (TSP), calcium phosphate is generated in addition to sodium aluminum silicate and aluminum oxyhydroxide. When CalSil and TSP co-exist, significant amount of calcium phosphate is generated with increasing amount of Cal-Sil as shown in Figure 3. It has been known that calcium phosphate has a significant impact on the head loss because its characteristics are like a gum. Therefore, above-mentioned three parameters, i.e., the amount of Cal-Sil, long spray termination time, use of TSP as a buffer agent has a most negative effect on the recirculation sump performance. Through the present study, the following recommendations are made: (a) Reduce the amount of Cal-Sil insulation (b) Replace TSP with alternate buffer agent (c) Reduce spray time by operation 3.3 Debris interceptor There may be various design options to reduce the head loss across the sump screen such as an active strainer and a specially designed screen surface to prevent the thin bed effects. The adoption of a debris interceptor is another viable option for reducing particulate debris such as unqualified coatings. The detailed effects on the debris transport are dependent on the specific debris interceptor design. For example, if the debris interceptor can reduce the particulate debris from 3,000 lbm to 1,000 lbm, the head loss can be reduced form 3.98 ft to 0.87 ft for 400 ft 3 fiber debris loading as shown in Figure 1. 4 Conclusions A parametric study is performed on the effects of debris source, containment environments and debris interceptor on the overall performance of ECCS recirculation sump. The key parameters of each effect are deduced and the recommendations for reducing their adverse effects are made through the present ana lysis. Following conclusions can be made: (a) The amount of unqualified coating debris has a great adverse effect on the screen head loss by reducing porosity in the fibrous insulation, (b) Cal-Sil insulation reacts with TSP buffer and significantly increases the generation of a gum-like chemical precipitate, (c) Spray time increases the chemical by-products but the effect is smaller than that of buffer agent type and unqualified coating. (d) The debris interceptor, when verified, may play a vital role reducing head loss generated by coatings and fibrous debris mix. The cost of reducing debris sources, removal of Cal-Sil insulation and installation of debris interceptor should be compared with the benefit of reducing number of suction strainers to select design change options for a particular plant. For this, the present parametric analysis method are being used for Korean nuclear power plants. Acknowledgments This work was supported by a grant from the nuclear safety research program of the Korea Foundation of Nuclear Safety with funding by the Korean Government’s Nuclear Safety and Security Commission (Grant Code: 1307008-0719-CG100). Nomenclature A effective screen area [ft 2 ] K constant depending insulation type S v surface-to-volume ratio of the debris [ft 2 /ft 3 ] U Q c v fluid approach velocity [ft/sec] volumetric flow rate [ft 3 /sec] compression rate microscopic volume of the debris constituent ∆H head loss [ft-water] ∆L m actual mixed debris bed thickness [in] ∆L o theoretical fibrous debris bed thickness L conversion factor L = 1 for SI units, and L = 4.1528E-05 (ft-water/inch)/(lbm/ft 2 /sec 2 ) for English units. a o solidity of the original fiber blanket (i.e., the “as-fabricated” solidity) a m mixed debris bed solidity h μ m p /m f , the particulate-to-mass ratio in the debris bed (i.e., total particulate mass/total fibrous mass) dynamic viscosity of water [lbm/ft/sec] r density of water [lbm/ft 3 ] r ƒ fiber density [lbm/ft 3 ] r p average particulate material density [lbm/ft 3 ] References [1] NUREG-0933, A Prioritization of Generic Safety Issues, Supplements 28, USNRC, Aug. 2004. [2] USNRC Generic Letter 2004-02, Potential Impact of Debris Blockage on Emergency Recirculation during DBA at PWR, USNRC, Sep. 13, 2004. [3] NEI 04-07, Pressurized Water Reactor Sump Performance Evaluation Methodology, Rev. 1, Nov. 2004. [4] Safety Evaluation by the USNRC related to NRC NRC Generic Letter 2004-2 NEI Guidance Report (NEI-04-07) Pressurized Water Reactor Sump Performance Evaluation Methodology, Dec. 2004. [5] NUREG/CR-6224, Parametric Study of the Potential for BWR ECCS Strainer Blockage due to LOCA Generated Debris, Sep. 1995. [6] WCAP-16530-NP, Evaluation of Post-Accident Chemical Effects in Containment Sump Fluids to Support GSI-191, Westinghouse, Feb. 2006. Authors Jisu Kim Jong Woon Park Dongguk University, 123 Dongdae-ro, Gyeongju, Gyeongbuk 38066, South Korea kimjs@dongguk.ac.kr ENVIRONMENT AND SAFETY 279 Environment and Safety Physical and Chemical Effects of Containment Debris on the Emergency Coolant Recirculation ı Jisu Kim and Jong Woon Park
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