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Investigation into the impacts of distributed inlet temperature on thermal limit during LFWH event in Chinshan plant

Untersuchung der Wirkung der Eintrittstemperaturtransiente auf die thermischen Grenzwerte während eines LFWH-Ereignisses in der Chinshan-Anlage
Shao-Shih Ma, Keng-Hsien Hsu, Bo-Yan Chen and Shi-Sen Hsu
From the journal Kerntechnik

Abstract

The Condensate and Feedwater System of the Chinshan BWR units is used to provide reliable and high-quality water to maintain the reactor water level during operation. If a Loss of Feedwater Heating (LFWH) event occurs, the core inlet subcooling increases and then induces corresponding power excursion and the reactor pressure rise. In the Chinshan Final Safety Analysis Report (FSAR), a loss of the feedwater temperature of 55.6°C (100°F) is conservatively assumed in the event. This study analyzes the integral reactor system response with RETRAN. Furthermore, a partial vessel model (PVM) of CFD is used to acquire the conditions of the fuel channel inlet to compensate the weakness of the RETRAN system model to generate detailed thermal-hydraulic conditions. The evaluation shows that the feedwater temperature drop is about 40°C which is lower than the FSAR value. In addition, the sensitivity study shows that the hot channel method underestimates the ΔCPR about 0.025, and there is no direct relation between ΔCPR and either of inlet subcooling or power fraction in transient, which is quite different from the conclusion of the hot channel method. Finally, the sensitivity study also proves the ΔT of 55.6°C (100°F) used in FSAR analysis conservative enough to cover the worst channel with a margin of 0.015 in ΔCPR.

Kurzfassung

Das Kondensat- und Speisewassersystem des Siedewasserreaktors Chinshan gewährleistet zuverlässige Versorgung des Reaktors mit Wasser hoher Qualität während des Betriebs. Beim Ausfall eines Speisewasservorwärmers (LFHW) entsteht die Eintrittsunterkühlung und verursacht eine entsprechende Leistungsabweichung, wodurch der Druck im Reaktor steigt. Im Chinshan-Sicherheitsanalysebericht (FSAR) wird im Ereignisfall eine Speisewassertemperaturtransiente von 55.6°C (100°F) angenommen. Diese Studie analysiert das integrale Reaktorsystemverhalten mit RETRAN. Des Weiteren wird ein partielles CFD-Reaktordruckbehältermodell (PVM) verwendet, um die Schwäche des RETRAN-Modells in Bezug auf die Simulation detaillierter thermohydraulischer Bedingungen zu kompensieren. Die Auswertung zeigt, dass der Temperaturabfall des Speisewassers etwa 40°C beträgt, was niedriger als der Wert im FSAR ist. Die Sensitivitätsstudie zeigt, dass die Methode des heißen Kanals die ΔCPR um 0.025 unterschätzt und es keine direkte Beziehung zwischen ΔCPR und der Eintrittsunterkühlung gibt, was sich von den Rückschlüssen der Methode des heißen Kanals unterscheidet. Die Sensitivitätsstudie zeigt auch, dass das in der FSAR-Analyse verwendete ΔT von 55.6°C (100°F) ausreichend konservativ ist, um den schlechtesten Kanal mit einer Marge von 0.015 in ΔCPR abzudecken.


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Received: 2017-08-10
Published Online: 2017-12-09
Published in Print: 2017-12-18

© 2017, Carl Hanser Verlag, München