Development of Heat Pipe Reactor Modeling in SAM

About: The article was published on 2019-06-01 and is currently open access. It has received 13 citations till now. The article focuses on the topics: Heat pipe.

Figures

Figure 2: Schematic of a conventional heat pipe

Figure 10: Schematic of the heat pipe reactor 7-cells model.

Table 7: Material properties for heat pipe reactor fuel cell

Figure 9: Schematic of the heat pipe reactor single-cell model. Radial dimension is scaled by 5 times.

Figure 11: Transient average temperature at different regions for the single-cell model for Option 1 (left, SAM 2D-RZ) and Option 2 (right, SAM 3D-1D)

Figure 4 Schematic of the mesh for 2D-RZ heat conduction model

Full text

ANL/NSE-19/9
Development of Heat Pipe Reactor Modeling in SAM
Nuclear Science and Engineering Division

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prepared by
G. Hu, R. Hu, and L. Zou
Nuclear Science and Engineering Division, Argonne National Laboratory
June 2019
ANL-NSE-19/9
Development of Heat Pipe Reactor Modeling in SAM

Development of Heat Pipe Reactor Modeling in SAM
June 2019
i ANL-NSE-19/9
EXECUTIVE SUMMARY
System Analysis Module (SAM) is under development at Argonne National Laboratory as
a modern system-level modeling and simulation tool for advanced non-light water reactor safety
analyses. It utilizes the object-oriented application framework MOOSE to leverage the modern
software environment and advanced numerical methods available in PETSc. The capabilities
of SAM are being extended to enable the transient modeling, analysis, and design of various
advanced nuclear reactor systems. This report presents the development of new capabilities for
modeling the heat pipe type reactor systems.
The need for power at remote locations away from a reliable electrical grid is an important
niche for nuclear energy. Heat pipe-cooled fast-spectrum nuclear reactors are well suited for
these applications. The key feature of the heat pipe reactors is the use of heat pipes for heat
removal from the reactor core. The heat pipe makes use of the phase change of the working
fluid and transports a large amount of heat from the evaporator to the condensation end with
very small temperature drops. In contrast to the traditional nuclear reactor system that makes
use of pumped loop for extracting the thermal power, the heat pipe reactors make use of
hundreds of heat pipes for removing the thermal power (including the decay heat) passively.
This could potentially significantly improve the reliability and safety of the reactor systems.
The essential part in the analysis of a heat pipe type reactor is the modeling of heat transport
inside the heat pipe. The capability of SAM is extended in this work to enable the modeling of
the conventional heat pipe. Two alternative modeling options, 2D-RZ Heat conduction and 3D-
1D coupling, are developed, which are both based on the assumption that the heat pipe vapor
core can be modeled as a superconductor of extremely high thermal conductivity. Both
modeling options are verified with a simplified thermal resistance model. The heat pipes are
also coupled with the fuel region of a prototype micro reactor under both normal and off-normal
conditions. It is confirmed that both modeling options can correctly model the heat transport in
the heat-pipe reactors.

Frequently asked questions

Q1. What are the contributions mentioned in the paper "Development of heat pipe reactor modeling in sam" ?

In this paper, the authors presented the new heat pipe modeling capabilities of SAM in the analysis of a made-up heat pipe reactor. 

Q2. What is the stability condition for the vapor core?

Since the vapor volume is fixed and the vapor density is usually small, the stability condition requires that the specific heat capacity is large enough. 

Q3. What is the thermal resistance of a heat pipe?

The thermal fluid phenomena in a heat pipe can be divided into four basic categories: 1) heat conduction in the heat pipe wall; 2) liquid flow and heat transfer in the wick structure; 3) interfacial mass, momentum, and energy transfer in the liquid vapor interface; and 4) vapor flow in the heat pipe core. 

Q4. What is the main approximation for modeling the heat pipe in SAM?

The main approximation for modeling the heat pipe in SAM is that the vapor core can be modeled as a superconductor with a very large thermal conductivity. 

Q5. What are the advantages of using a heat pipe over other conventional methods?

The advantages of using a heat pipe over other conventional methods include for example exceptional flexibility, simple construction, easy maintenance, and easy control with no external pumping power. 

Q6. Why is the capability of SAM extended?

Because of the increasing interests in heat-pipe type micro-reactors, the capability of SAM has been extended in this work to enable the modeling of the conventional heat pipe and the heat pipe type reactor. 

Q7. What is the boundary condition between the wick and the vapor core?

The boundary condition between the wick and the vapor core is𝑞Q = ℎn ⋅ (𝑇Q − 𝑇n) (2-10)where 𝑇Q and 𝑞Q are the wall temperature and wall heat flux at the wick-vapor boundary, respectively. 

Q8. What is the temperature gradient at the bottom and top of the heat pipe?

At the bottom and top end, the temperature gradient is zero, which represents that there is no heat loss from the bottom and top of the heat pipe. 

Q9. What is the vapor core's thermal conductivity?

In general, the effective thermal conductivity of the vapor core has to be very large, e.g. 107 W/(m-K) is used in the verification tests. 

Q10. What is the overall conductance of a condenser heat pipe?

The overall condenser heat transfer capability is variable and thus provide a variable total conductance, which will control the operating temperature. 

Q11. What is the prediction of the failure of a single heat pipe?

The prediction shows that the failure of a single heat pipe causes a local peak in the fuel temperature, where the peaking factor is mainly determined by the inter-assembly heat transfer characteristic of the reactor. 

Q12. What is the primary goal of the developed heat pipe modeling capability?

It should also be noted that the primary goal of the developed heat pipe modeling capability is to enable the transient safety analyses of the heat-pipe-type reactor systems, not to design a heat pipe. 

Q13. How long does the flow of the working fluid last?

This process will continue as long as the capillary pressure is enough to drive the condensed working fluid back to the condenser region. 

Q14. What is the effective heat transfer coefficient between the wick and the vapor core?

The solution of the heat conduction equation in the 3D structure requires the vapor temperature while the solution of the vapor temperature equation requires the wall heat flux at the wick and vapor core boundaries. 

Q15. What is the main parameter that governs the stability condition of the vapor core?

It is observed that the main parameters that governs stability condition is the total heat capacity of the vapor core, i.e. 𝜌𝑉𝐶o.