RELAP5 Analyses of a Deep Burn High Temperature Reactor Core

Hongbin Zhang*, Michael Pope, Haihua ZhaoIdaho National Laboratory

*Email: Hongbin.Zhang@inl.gov2010 RELAP5 International Users SeminarSeptember 20-23, 2010, West Yellowstone, Montana

Acknowledgement: Authors are grateful for Paul Bayless’s help to set up the RELAP5 input deck.

Prismatic Deep Burn Concept

LWR used fuel

TRU kernelTRU TRISO

Compacts

Fuel ElementsDeep Burn Core

Burn-up to 750 GWD/MT is feasible

Fuel Composition• Packing fraction of TRISO particles is 18%. • Fuel kernel diameter is 200 um.• TRU fuel representative of PWR spent fuel after 5 years of

cooling.

Nuclide Fraction (wt%)Np-237 6.8Pu-238 2.9Pu-239 49.5Pu-240 23.0Pu-241 8.8Pu-242 4.9Am-241 2.8Am-242 0.02Am-243 1.4

2D Lattice Calculations• DRAGON – collision

probability transport code developed by Institut de Génie Nucléaire, École Polytechnique de Montréal, Montréal. 172 energy groups for various temperature and burnups.

• 23 group homogenized cross sections generated for DIF3D.

• Reflector: 1-D model of the core with a representative fuel region and a reflector zone.

Schematic of 1/12 fuel block model used in DRAGON

Full Core Calculations

• DIF3D/REBUS• Axial Shuffle Only

Equilibrium Cycle• Equilibrium cycle is reached after 12 cycles• Cycle length – 300 days• Batch-average discharge 64% FIMA, or 600 MWD/t.

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Decay Heat Curve

Decay heat curve is from calculations by Professor Kostadin Ivanov at Penn State

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Fuel at 7 GWd/ton burnup

RELAP5 Model• Model started from the NGNP Point Design, INEEL/EXT-03-00870 Rev. 1• Core, vessel, reactor cavity and RCCS considered• Core – seven parallel coolant channels• 1-D radial conduction with conduction enclosure to simulate axial direction heat conduction.

RELAP5 Nodalization

Reactor vessel, cavity and RCCS nodalization

RELAP5 Steady State Results• Reactor Power: 600 MWth. • Reactor Inlet Temperature: 491°C.• Reactor Outlet Temperature: 850°C.• Core Flow Rate: 324 KG/S• Bypass Flow Fraction: 12%

Low Pressure Conduction Cooldown Results

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High Pressure Conduction Cooldown Results

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Summary• LPCC (depressurized loss of forced cooling)

transients showed fuel temperatures exceed 1600oC

• However, very conservative consumptions went into the RELAP5 calculations– Burnable poisons and power flattening

measures were not considered– Very conservative decay heat curve was used

• Ongoing promising work by other researchers to use burnable poisons and better fuel shuffling scheme to lower fuel temperature.