GFR: Gas-cooled Fast Reactors

Selection of Materials for a Supercritical CO₂ Cooled

Program: 

Type: 

  • TR

RPT. No.: 

1

Authors:: 

S.THON
M. J. DRISCOLL

Report Date: 

August 2002

Abstract

An initial survey was made of published literature on candidate materials for service as structure, cladding, and fuel in a supercritical CO2 gas-cooled fast reactor. A principal emphasis was placed on corrosion resistance relying heavily on British AGR experience. The evidence strongly suggests that available steels will prove suitable for use in the core, reactor pressure vessel, and gas turbine power cycle. There is, however, a lack of corrosion data at the high CO2 pressures of current interest, 20 MPa, or in CO2 subjected to the intense fast neutron fluxes in a GCFR.

UC and US fuels are neutronically superior to UO2, which has proven to be otherwise suitable. However, both US and UC are oxidized by CO2, which probably limits them to use as cermets.

Zirconium and its alloys appear to be neutronically superior to steels, but convincing evidence that its corrosion resistance in CO2 is acceptable has not been found. Thus, the use of zirconium may be limited to fuel concepts where a protective clad layer is employed or where operating temperature is reduced below the current reference conditions of 550oC coolant outlet, 700 oC clad hot spot.

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h1 report title: 

Selection of Materials for a Supercritical CO₂ Cooled

Analysis of a Natural Convection Loop for POST-LOCA GCFR Decay Heat Removal

Program: 

Type: 

  • TR

RPT. No.: 

2

Authors:: 

J. Eapen
M. J.Driscoll

Report Date: 

December 2002

Abstract

Interest has grown over the past few years in the re-assessment of gas-cooled fast reactors (GCFR) for service in the future evolution of the nuclear power industry. The GCFR has been identified as one of the six concepts deserving further
evaluation in the GEN-IV downselection process. It is widely recognized that the principal technical challenge for reactors of this type is the reliable removal of post- LOCA decay heat. This realization motivated the present study of a realistically modeled convection loop for such service in which energy is removed by a water boiler heat exchanger ten meters above the core thermal center.

The approach followed in this evaluation is to improve a pre-existing in-house computer code which carries out a quasi steady-state analysis of convection in a closed loop. Special attention has been paid to the selection of the correlations for friction factors and heat transfer coefficients, since the parameter space of interest spans virtually all convection flow regimes associated with sub-sonic gas flow.

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h1 report title: 

Analysis of a Natural Convection Loop for POST-LOCA GCFR Decay Heat Removal

Address: 

Massachusetts Institute of Technology, Cambridge, MA 02139

Aerodynamic Design of Turbine for S-CO₂ Brayton Cycle

Program: 

Type: 

  • TR

RPT. No.: 

3

Authors:: 

Y. Wang
M.J. Driscoll

Report Date: 

June 2003

 

Introduction

The supercritical CO2 (S-CO2) Brayton cycle is proposed for Generation IV reactor applications because of its simplicity, high efficiency, compactness and thus potential to cost reduction. To achieve an attractive cycle efficiency (~ 45%), highly efficient cycle components must be guaranteed. Hence the turbine, the main design objective is to achieve high efficiency while maintaining the turbine at a reasonable size. Due to the high power and high mass flow rate demands of the present application an axial-flow turbine was employed. Two NASA Glenn Research Center (GRC) developed codes (TURBAN and AXOD) were modified and implemented to perform the aerodynamic design. TURBAN is a preliminary axial-flow turbine design code. AXOD is a multi-stage turbine off-design performance code. Both codes were developed for airbreathing aircraft engine and ideal gas applications. Since CO2 exhibits significantly nonideal behavior under S-CO2 cycle operating conditions, both codes were modified to apply for real gas applications. The NIST pure fluid properties database was implemented into the codes for this purpose. TURBAN-MOD and AXOD-MOD are the modified versions respectively. TURBAN-MOD determines the stage velocity diagrams, stage and overall efficiencies and simple blade geometry at a design-point. AXOD-MOD calculates the off-design performance at optimum incidence angles based on the design-point and generates characteristic maps. The off-design performance maps can be used for cycle control analysis. 

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h1 report title: 

Aerodynamic Design of Turbine for S-CO₂ Brayton Cycle

Design of Shell and Tube Heat Exchanger for the S-CO₂ Cycle and Laminar Flow in Microchannel Heat Exchangers

Program: 

Type: 

  • TR

RPT. No.: 

4

Authors:: 

K. Gezelius
V. Dostal
M.J. Driscoll
P. Hejzlar

Report Date: 

May 2003

Abstract

The main purpose of this study is to design a shell and tube intermediate heat exchanger (IHX) for the S-CO2 cycle.

Initially, the reasons for an indirect cycle approach are described.  Next, the work presents the design contraints and thereafter describes the actual modeling process.  The heat exchanger coolants examined were helium (primary side) and carbon dioxide (secondary side).  The modeling assumes helium on the shell-side and carbon dioxide in the tubes.  

According to the analysis the modeled shell and tube IHX had a length of 7.4 m with a bundle volume of 57 m3. The pumping power of the primary and the secondary side was calculated to 4.6 and 2.4 MW, respectively.  

In addition to the shell and tube heat exchanger, the report also addresses the issue of laminar flow in microchannel heat exchangers.  This part of the investigtion aims at presenting convincing theoretical support for highly efficient heat exchangers in laminar flow regime.  

Using the properties of the media for the proposed IHX design, the analysis showed that the number of tubes in the compact heat exchanger for this large scale applicaiton was very big - on the order of millions for a tube inner (hydraulic) diameter of 0.73 mm. In spite of the large number of tubes, the length of the HX was approximately 4 m for an efficency of 85%.

 

 

 

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Neutronic Evaluation of GFR Breed and Burn Fuels

Program: 

Type: 

  • TR

RPT. No.: 

5

Authors:: 

P. Yarsky
M. J. Driscoll

Report Date: 

May 2023

Abstract

Breed and Burn operation refers to the equilibrium operation of a fast reactor where sufficiently large amounts of plutonium are bred in-situ such that the core can be reloaded with low enrichment fuel (< 5 w/o U235) and core criticality is sustained through a discharge burnup on the order of 150 MWD/kgHM. Hence economic operation and improved uranium utilization are achieved without a requirement for reprocessing.

In the present work neutronics screening of potential nuclear fuels was carried out using a code coupling MCNP and ORIGEN. Fuel performance was measured as a function of burnup for a variety of ceramic and metallic alloy fuels.

The reactivity histories, flux spectra, and conversion ratio histories for each fuel type were evaluated and based on the results a short list of potential fuels having superior performance was developed, including: UN-15, UC, US, and U-10Zr. The neutronics studies show that high heavy metal density is a key factor in good fuel performance, which favors a metallic. For a final selection, additional evaluation must be carried out
on the basis of mechanical performance and the chemical properties of the fuel.

Use of the Prestressed Cast Iron Vessel in Nuclear Reactor Applications

Program: 

Type: 

  • TR

RPT. No.: 

6

Authors:: 

L. B. Fishkin
M. J.Driscoll

Report Date: 

April 2004

Abstract

Prestressed Cast Iron Vessel (PCIV) use for advanced nucelar reactor applications, epecially for the Gas-Cooled Fast Reactor (GFR), is reviewed. Particular attention is given to the extensive work in Germany, which includes design analysis and the construciton and test of semi-scale PCIVs.  Several proposed applications worldwide to HTGR, BWR, and PWR units are also documented.  IT is concluded the PCIV is a prime candidate for GFR applications because of its exceptionally high assurance against coolant leakage at a cost that is competitvie with that of PCRVs or convenitonal forged steel vessels.

 

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Evaluation of Uranium Carbide and Sulfide Fuels for a Gas-Cooled Fast Reactor Utilizing Dry Reprocessing

Program: 

Type: 

  • TR

RPT. No.: 

7

Authors:: 

J. W.Plaue
K.R. Czerwinski
M.J.Driscoll

Report Date: 

October 2023

Abstract

Chemical aspects of uranium carbide (UC) and uranium sulfide/carbide solid solution (UCUS) fuels for a gas-cooled fast reactor were examined. Samples of the fuels were synthesized and then characterized. The fuels were then evaluated for compatibility with carbon dioxide (CO 2 ), the proposed reactor coolant. In addition, an initial examination of a one-step CARbon Dioxide
Oxidation (CARDIO) dry reprocessing scheme was performed. 

Based upon an evaluation of practices in the literature, carbothermic reduction of uranium oxide (UO 2 ) with graphite was chosen as the synthetic route for production of UC. A novel volatile metal process was used to create UCUS through the replacement reaction of UC with zinc sulfide. Results of the fuel
characterization showed the presence of significant quantities of UO2 contamination. A reaction between either the graphite or the UC and the alumina furnace boats was the suspected source of the oxygen.

Kinetic parameters for the oxidation of UC and UCUS under CO 2 were determined through offgas analysis of non-isothermal tube furnace experiments under flowing conditions. Results confirmed the formation of UO 2 , but suggested a different reaction mechanism than previously found in the literature. Rather than forming a free carbon reaction intermediate, the data indicated the reaction of UC with CO 2 in a 1 to 3 ratio, directly forming UO2 and carbon monoxide. Activation energies for the reaction with UC were found to range from 399.3 to 326.1kJ/mol, and for US from 111.6 to 117.3 kJ/mol. No significant correlation between UC and US ratios and oxidation behavior was observed.

The CARDIO process was evaluated through volatility experiments under CO 2 using a powdered spent fuel simulant consisting of UO2 and stable isotopes of silver, cesium, europium, gadolinium, molybdenum, neodymium, and samarium. Near complete removal of Ag, Cs, and Mo was observed. Lanthanide removal fractions were found to be unusually high; near seventy
percent at 1000°C for Eu, Nd, and Sm, and ninety percent for Gd. The high removal was suspected to be the result of a catalytic effect of noble metals causing the lanthanide oxides to form carbonates, which then decompose to the metal at lower temperatures.

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