A Conceptual Approach to Eliminate Bypass Release of Fission Products by In-Containment Relief Valve under SGTR Accident

Taeseok Kim,Hoichul Jung,Joongoo Jeon,Wonjun Choi,Nam Kyung Kim,Sung Joong Kim

doi:10.1155/2018/5936214

Taeseok Kim, Hoichul Jung + Show 4 more

Open Access

https://doi.org/10.1155/2018/5936214

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Abstract

During a hypothesized severe accident, a containment building is designed to act as a final barrier to prevent release of fission products to the environment in nuclear power plants. However, in a bypass scenario of steam generator tube rupture (SGTR), radioactive nuclides can be released to environment even if the containment is not ruptured. Thus, thorough mitigation strategies are needed to prevent such unfiltered release of the radioactive nuclides during SGTR accidents. To mitigate the consequence of the SGTR accident, this study was conducted to devise a conceptual approach of installing In-Containment Relief Valve (ICRV) from steam generator (SG) to the free space in the containment building and it was simulated by MELCOR code for numerical analysis. Simulation results show that the radioactive nuclides were not released to the environment in the ICRV case. However, the containment pressure increased more than the base case, which is a disadvantage of the ICRV. To minimize the negative effects of the ICRV, the ICRV linked to Reactor Drain Tank (RDT) and cavity flooding was performed. Because the overpressurization of containment is due to heat of ex-vessel corium, only cavity flooding was effective for depressurization. The conceptual design of the ICRV is effective in mitigating the SGTR accident.

Highlights

Prevention or mitigation of fission product release is very important to guarantee ultimate safety of nuclear power plants (NPPs)
Using the current MELCOR simulation, a steady-state calculation was performed to verify the suitability of the MELCOR nodalization of Optimized Power Reactor 1000 MWe (OPR1000)
It was confirmed that the MELCOR results are in good agreement with the nominal Final Safety Analysis Report (FSAR) values

Summary

Introduction

Prevention or mitigation of fission product release is very important to guarantee ultimate safety of nuclear power plants (NPPs). Many researchers have studied hazardous factor such as direct containment heating [2], steam explosion [3], hydrogen combustion [4], and overpressure [5]. These studies enhance reliability of the containment building. In a hypothesized scenario of containment bypass, even if the containment building is not ruptured, fission products can be released to the environment. SGTR accident can release fission products to environment without containment rupture because pressure boundary of the primary system is not retained due to SGTR [7]. The SGTR accident induced by SBO releases more fission products to environment because many safety features such as auxiliary feed water (AFW) are inoperable. To investigate its effectiveness in Optimized Power Reactor 1000 MWe (OPR1000) consisting of a major fleet of Korean operating NPPs, numerical simulation was conducted using MELCOR code

Numerical Methodologies

Results and Discussion

Conclusions