The Investigation of Nonavailability of Passive Safety Systems Effects on Small Break LOCA Sequence in AP1000 Using RELAP5 MOD 4.0

Abstract

The passive safety systems of AP1000 are designed to operate automatically at desired set-points. However, the unavailability or failure to operate of any of the passive safety systems will change the accident sequence and may affect reactor safety. The analysis in this study is based on some hypothetical scenarios, in which the passive safety system failure is considered during the loss of coolant accidents. Four different cases are assumed, that is, with all passive systems, without actuation of one of the accumulators, without actuation of ADS stages 1–3, and without actuation of ADS stage 4. The actuation of all safety systems at their actuation set-points provides adequate core cooling by injecting sufficient water inventory into reactor core. The LOCA with actuation of one of the accumulators cause early actuation of ADS and IRWST. In case of LOCA without ADS stages 1–3, the primary system depressurization is relatively slow and mixture level above core active region drops much earlier than IRWST actuation. The accident without ADS stage 4 actuation results in slow depressurization and mixture level above core active region drops earlier than IRWST injection. Moreover, the comparison of cladding surface temperature is performed in all cases considered in this work.

Keselamatan Reaktor Nuklir: Kecelakaan Dasar Desain dan Kecelakaan Parah

“…DVI terdiri dari sistem aktif dengan pompa injeksi tekanan tinggi dan sistem pasif dengan menggunakan safety injection tank (SIT) yang beroperasi pada tekanan lebih rendah. Di samping itu, LOCA tetap merupakan kunci untuk evaluasi desain reaktor baru, khususnya jenis reaktor air ringan, apakah dapat dikatakan meme nuhi tingkat keselamatan yang dipersyaratkan oleh Badan Pengawas atau tidak sehingga analisis LOCA tetap dilakukan pada desain baru generasi III seperti AP1000 dan European Pressurized Reactor (EPR) (Gurcacz dkk., 2015;Hussain & Nawaz, 2016), termasuk juga mempelajari fenomena spesifik yang mengikuti LOCA seperti loop seal clearing and refill karena spesifik untuk desain tertentu seperti APR-1400 (Kang dkk., 2020). Analisis LOCA yang dilakukan akhir-akhir ini juga telah memanfaatkan codes yang telah berkembang lebih baik sehingga dapat dilakukan analisis dengan hasil yang lebih baik seperti pada (Yousif dkk., 2016).…”