Results 1 - 10 of 19945
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[en] Conclusions: Proposed V-1 ALS can cope with 2 x DN 500 DBA. Work on V-1 ALS able to cope with DN 200 DBA and to mitigate DN 500 BDBA will have been finished by April 1994. Further leaktightness improvements are going on on the V-1 HZ boundary during outages with the aim to reduce the existing leak rate by 50%
[en] This report deals with the development of a thermal hydraulic code system for Loss-of-Coolant Accidents of the Advanced Thermal Reactor (ATR). The code system consists of the blowdown analysis codes for large Break LOCA (SENHOR) and Small Break LOCA (LOTRAC), the heatup code (HEATUP) and the reflooding code (FLOOD). Basic models within the codes have been developed and verified by separate effects tests for the important thermal hydraulic phenomena which are expected to occur during an accident in an ATR. The codes are composed of basic models, and have been verified by test on integral facilities, changing the position and the size of the break
[en] Melting ultimately requires the heat production rate to exceed the removal rate. In a nuclear reactor this situation is initiated by either overpower or undercooling conditions. The latter is related to reduced cooling through loss of coolant flow or loss of coolant itself and may lead to general meltdown of the reactor core. Molten material is accumulated in the lower plenum of the reactor pressure vessel. The separation of phases results from different components densities of molten material. High temperature molten UO2 will slowly melt through the wall of RPV lower plenum. To avoid disruption of RPV, an instantaneous heat transfer is needed. To simulate the situation described above, general multiphase flow equations were developed. In order to describe the multiphase flow fully, the continuity, momentum and energy equations were derived using ensemble averaging rather then time or spatial averaging. Because of geometry of the lower plenum a spherical coordinate system was used, to enhance the accuracy of the calculation on the border. (author)
[en] Effects of Residual Power. Several experiments of hot leg small and medium LOCA have been conduction using UUTR.Mod-I test facility. The break sizes are 5 mm and 10 mm, which are equivalent to 0.86% of hot leg pipe cross section area. Beside break size, other experimental variable is residual power, i.e. 2-4% of initial power. In small break experiments, residual power 25 k W did not cause any heated rods burnout, at least during observation time interval. However, residual power of 38 k W caused burnout. In medium break experiments, both 25 k W and 32 k W of residual power caused burnout. The results indicate the importance of simulation of decay heat in order to get the experimental results close to the real condition
[en] The main purpose of this work is to analyse the pressure and temperature behaviour of the metalic containment of a PWR building, submitted to a postulated loss-of-coolant accident (LOCA) caused by a double-ended rupture in the main line of the primary circuit. The scope of the study was directed to verify the Final Safety Analysis Report (FSAR) results for the integrity of the metalic containment of the Angra I power plant. The highest containment pressure peak for this unit is expected for a break in the suction line of one of the main pumps of the primary coolant. Using the same input data, our results are very similar to those presented in the FSAR which shows a reasonable equivalence between the two analytical models. Using as input data the results of a previous LOCA study at CNEN, which yields to more conservative boundary conditions than those presented by the FSAR, the pressure and temperature peak values determined by our model are quite larger than those presented by the cited Safety Report. (author)
[pt]A presente tese teve como objetivo analisar o comportamento de pressao e temperatura no edificio da contencao metalica do predio de um reator a agua leve pressurizada, sob os efeitos de um acidente postulado de perda de refrigerante (LOCA), provocado por uma ruptura total do tipo 'guilhotina' na tubulacao principal do circuito primario. Tal estudo foi aplicado no sentido de verificar os resultados constantes do Relatorio Final de Analise de Seguranca (RFAS), no que se refere a contencao metalica do predio do reator da central Angra I. O acidente mais limitante para aquele tipo de projeto consta de uma ruptura na linha de succao de uma das bombas do refrigerante primario do reator. Nosso modelo fornece resultados bastante proximos daqueles constantes do RFAS, desde que os dados utilizados para os calculos sejam os mesmos, o que indica uma razoavel equivalencia entre os modelos analiticos adotados nos dois estudos. Entretanto, utilizando um estudo anterior de LOCA da CNEN, que fornece condicoes de contorno bem mais conservativas em comparacao aquelas do RFAS, os valores de pico de pressao e temperatura na contencao, determinados pelo modelo do presente estudo, sao bastante superiores aqueles apresentados no referido Relatorio Final de Analise de Seguranca. (autor)
[en] The paper is an approach to calculate the response of Cernavoda NPP Unit 2 RCW System to transient regimes during normal and abnormal regimes. Then one started to analyse the system response to reactor trip on class III and IV of power, LOCA on class IV of power, LOCA on class III power, LOIA on class IV of power, and LOIA on class III power. Moreover, one analysed the system transient due to requirement of changeover of a RCW operating pump, planned and unplanned changeover. This is the first transient approach to this system that took in consideration all building of the system, obtaining a very large system model, with over 900 pipe, 4 pumps, 50 consumers, 21 control valves. The changeover procedure was required to be analysed in order to change the nominal operating mode for Unit 2, from current 2 pumps in operation to 3 pump operations during summer operating mode. (authors)
[en] Highlights: • Review of the requirements and recommendations for BEPU methodology. • Summary of the advantages and limitations of the current deterministic bounding method for non-LOCA transient analysis. • Description of a pragmatic, graded approach for application of the BEPU methodology to non-LOCA transient analysis. • Proposal for a demonstration case. - Abstract: Since 1990’s, the use of best estimate plus uncertainty (BEPU) methodology is becoming a common practice for large-break Loss-Of-Coolant Accident (LOCA) analysis. However, the development and application of BEPU methodology requires a higher-level requirement on the verification and validation, and uncertainty quantification (VVUQ) of the used calculational method and computer codes. This may result in a high-cost for BEPU methodology development, and hence prevent the industry to take full benefit from the BEPU applications. This paper proposes a pragmatic, graded approach for application of the BEPU methodology to non-LOCA transient analyses.
[en] A postulated double-ended guillotine break of an AP600 direct-vessel-injection line has been analyzed. This event is characterized as an intermediate-break loss-of-coolant accident. Most of the insights regarding the response of the AP600 safety systems to the postulated accident are derived from calculations performed with the TRAC-PF1/MOD2 code. However, complementary insights derived from a scaled experiment conducted in the ROSA facility, as well as insights based upon calculations by other codes, are also presented. Based upon the calculated and experimental results, the AP600 will not experience a core heat up and will reach a safe shutdown state using only safety-class equipment. Only the early part of the long-term cooling period initiated by In-containment Refueling Water Storage Tank injection was evaluated. Thus, the observation that the core is continuously cooled should be verified for the later phase of the long-term cooling period when sump injection and containment cooling processes are important
[en] Highlights: •ECC condensation research based on China PWR- CPR1000. •The correlation of condensation based on XJTU-ECC test was proposed. •Wide range of RT number from 0 to 3.5 were analyzed within condensation. •A new analysis method was proposed by using the mass fraction and RT number. •The test report a conservative results on ECC component than RELAP5 calculation.