Hybrid heat pipe based passive in-core cooling system for advanced nuclear power plant

doi:10.1016/j.applthermaleng.2015.07.045

Applied Thermal Engineering

Volume 90, 5 November 2015, Pages 609-618

https://doi.org/10.1016/j.applthermaleng.2015.07.045 Get rights and content

Highlights

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Hybrid heat pipe is presented as a new concept of passive in-core cooling system.
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CFD analysis has been accomplished to find heat removal capacity.
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1D reactor transient calculation was applied to predict thermal performance.
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Results demonstrate that hybrid heat pipe can delay core heat-up at station blackout.

Abstract

After the Fukushima accident in 2011, passive safety of nuclear reactors available under station blackout accidents like Fukushima has become the most pressing issue in the nuclear energy industry. For passive in-core cooling system (PINCs), the concept of a hybrid heat pipe, which is the combination of the heat pipe and neutron absorber was proposed to enhance the safety of advanced nuclear power plants. With the unique features of heat pipe and control rod, the hybrid heat pipe can remove decay heat directly from the core as it is inserted into the reactor pressure vessel with the same drive mechanism of a control rod. In this study, a two-step numerical analysis was performed for evaluating the concept of the hybrid heat pipe and its applications. The thermal performance of a single hybrid heat pipe was numerically analyzed using a commercial CFD code for designated designed features under reactor operation conditions. As a result, the hybrid heat pipe concept was found to remove 18.20 kW per rod with total thermal resistance of 0.015 °C/W. Using MALTAB, the one-dimensional thermal hydraulic analysis of reactor was conducted for the proposed PINCs to calculate the coolant temperature for evaluating the cooling performance of hybrid heat pipe. It revealed that the hybrid heat pipe was able to delay core heat-up at the station blackout accidents and extensions. If the hybrid heat pipe had enhanced heat removal capacity, it could continue cooling the core during accidents while preventing the core uncovery.

Introduction

In March 2011, a large scale of earthquake of magnitude 9.0 and a tsunami caused severe core damage of the nuclear reactor in Fukushima, Japan. Since all onsite and offsite power was lost, the decay heat generated after reactor shutdown was not adequately removed. Although emergency electricity was provided from storage batteries at that time, the batteries were all failed because of flood following the tsunami. This event showed the vulnerability of the cooling ability of current nuclear power plant during station blackout (SBO) accidents and associated conditions. After Fukushima nuclear power plant accident, the importance of decay heat removal system has become emphasized to cope with the unexpected accident from natural disasters. Existing emergency core cooling system (ECCS) concentrated on the supply of refueling water into the reactor pressure vessel (RPV) to cool the core directly. For normal pressurized water reactors, the coolant is pressurized to approximately 155 bar to prevent coolant boiling and a high-temperature range coolant is used to convert the heat efficiently. However, when depressurization process of the RPV is impossible, the emergency refueling water from the ECCS cannot be injected because of high pressure. To complement this gap, a new concept for passive safety system that can work regardless of the reactor condition is necessary.

Heat pipe is an excellent heat transfer device wherein latent heat of vaporization is used to transport heat over a long distance with a small temperature difference [1]. Since liquid flows by the capillary force from the wick structure and steam flows up due to the buoyant force, external power supply is not necessary. Heat pipes are widely used for removal of local hot spot heat fluxes in CPUs and for thermal management in spacecraft, satellite and other waste heat control systems [2], [3], [4]. Since heat pipes can cool without external power, their applications have been continuously researched about development of passive cooling system in the field of nuclear energy.

Singh et al. suggested the heat pipe cooling method as an emergency core cooling system (ECCS) for spent nuclear fuel pool of nuclear power plants [5]. Long and curved heat pipes were considered for passive cooling of the spent fuel pool.

Mochizuki et al. suggested a loop type heat pipe cooling system for a boiling water reactor decay heat removal system, and found the total thermal resistance and cooling ability of the system [6]. In their study, the evaporator section of loop heat pipe was located near the core, and the condenser section was located outside the containment with air-cooled heat transfer metal plate fins.

Syiridenko researched a passive emergency core cooling system using heat pipes in the water–water energetic reactor (WWER), concentrating on the independent working mechanism [7].

Nam et al. suggested a multi-pod heat pipe cooling system of a containment building and conducted a preliminary analysis on the amount of heat removed and the heat transfer coefficient [8]. Multi-pod heat pipes penetrate the concrete wall to support the containment spray system for cooling during accident to prevent over-pressurization inside the containment building.

As describe above, much research has been conducted on using heat pipes for the development of passive cooling for nuclear power plants. In most of these studies, other structures have to be installed to provide an interface for heat transfer. In addition, the systems developed have to change the existing designs of nuclear power plants, which can affect the integrity of the facilities. Therefore, the ability to apply the concepts suggested by previous studies to current nuclear power plant appears unclear at present. Considering issues that involve the inherent safety of nuclear power plants, the concept of a hybrid heat pipe as passive in-core cooling systems (PINCs) was proposed by our research group. This concept can be applied by simply replacing the existing control rod with the hybrid heat pipe. Hybrid heat pipe has unique features being inserted directly to the core to remove decay heat from nuclear fuel without structural changes of existing nuclear power plant facilities.

In this study, a hybrid heat pipe is suggested as a PINCs and the design features are demonstrated for a heat pipe containing a neutron absorber. Since the hybrid heat pipe has unique operating conditions in a nuclear reactor, it should operate in high-pressure and high-temperature conditions. Using a commercial CFD code, a single hybrid heat pipe was simulated to evaluate thermal performance in designated operating conditions. To examine the cooling effect of the hybrid heat pipe as a PINCs, a one-dimensional reactor transient analysis was performed by calculating the temperature change in the coolant inside RPV using MATLAB.

Section snippets

The concept of a hybrid heat pipe

Hybrid heat pipe is a totally passive decay heat removal device that combines the control rod and heat pipe as a PINCs. The hybrid heat pipe contains a neutron absorber such as B₄C, and has the same driving force of the existing control rod [9]. For pressurized water reactor type, existing target of the ECCS is supply the refueling water when the depressurization of RPV is impossible. Since the control rod is dropped by gravitational force during an unexpected power-off condition, the hybrid

Numerical methods

For evaluating the thermal performance of the hybrid heat pipe as a PINCs, a two-step numerical analysis, which consisted of a single hybrid heat pipe simulation and one-dimensional thermal hydraulic reactor transient analysis, was performed. The analysis model for the hybrid heat pipe simulation was validated through comparison with experimental results for a conventional heat pipe. From the results of the single hybrid heat pipe simulation, the amount of heat removed by hybrid heat pipe is

Validation of heat pipe analysis model

To validate the heat pipe analysis model, results of the single heat pipe simulation were compared with experiments and matched with theoretical results, shown in Fig. 5. Length of heat pipe is total 1000 mm, and those of the evaporator, adiabatic, and condenser regions are 350 mm, 150 mm and 500 mm, respectively. The saturation condition in heat pipe was considered as 323 K and 12.5 kPa. In the experiment, water jacket at 21 °C with a 0.13 kg/s mass flow rate was installed to surround the

Conclusions

Hybrid heat pipe with a combination of heat pipe and control rod was suggested as a PINCs. The hybrid heat pipe has the distinct feature that it can be a unique solution to cool the reactor when the depressurization process is impossible and a conventional ECCS cannot inject refueling water into the RPV. The hybrid heat pipes contain a neutron absorber material, so it can shutdown the reactor and at the same time, remove decay heat in core. For evaluating the concept of hybrid heat pipe,

Acknowledgements

This work was supported by the Nuclear Energy Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT, and Future Planning (no. 2013M2A8A1041442, 2015M2B2A9031869, 2013M2B2B1075734).

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Research paperHybrid heat pipe based passive in-core cooling system for advanced nuclear power plant

Highlights

Abstract

Introduction

Section snippets

The concept of a hybrid heat pipe

Numerical methods

Validation of heat pipe analysis model

Conclusions

Acknowledgements

Appl. Therm. Eng.

Appl. Therm. Eng.

Appl. Therm. Eng.

Appl. Therm. Eng.

Int. J. Heat Mass Transf.

Int. J. Heat Mass Transf.

Heat Pipes

Performance Characteristic of Cylindrical Heat Pipes for Nuclear Electric Space and Undersea Power Plants

Heat pipe based emergency cooling system for removing decay heat from nuclear reactor and spent fuel pool

Conceptual design of passive containment cooling system for APR-1400 using multipod heat pipe

Nucl. Technol.

Research paper
Hybrid heat pipe based passive in-core cooling system for advanced nuclear power plant