Simulation of the NuScale SMR and Investigation of the Effect of Load-Following on Component Lifetimes

Abstract

The NuScale small modular reactor (SMR) has been modeled using the Virtual Environment for Reactor Applications multiphysics environment and the results compared with the publicly reported data in the Design Certification Application. The results show an excellent agreement for the compared axial and radial power distributions, temperature coefficients of reactivity, boron and control rod worths, and fast neutron flux. This NuScale model is then used to investigate the effect of different operational modes on reactor components to determine how the flexible load-following operation may affect control rod and reactor pressure vessel (RPV) lifetimes. The control rod degradation is confirmed to primarily affect the silver-indium-cadmium rod tip. The degradation rate is observed to follow a nonlinear function of core power level where the increase in degradation decreases with insertion depth.

For the variation in core power levels expected with current load-following schemes, the total control rod degradation is found to be mild, at 5% to 10% of usable life per cycle for a reactor operating at <80% power. Nonetheless, this enables load-following strategies to be confirmed and/or modified to ensure that control rods do not need to be replaced during the 60+ year life of the reactor. The RPV degradation was found to be almost directly proportional to the core power level and was not overly sensitive to flux shape perturbations. Future work is planned using these damage functions to optimize operation over multiple NuScale SMR units and to develop strategies for prognostics and health management.

Keywords:

• Small modular reactors
• load-following
• flexible operation

Acronyms

2-D:	=	two dimensional
3-D:	=	three dimensional
BOEC:	=	beginning of equilibrium cycle
CRA:	=	control rod assembly
DCA:	=	design certification application
DTC:	=	Doppler temperature coefficient
EOEC:	=	end of equilibrium cycle
FPO:	=	flexible power operation
HBWF:	=	Horse Butte Wind Farm
ICI:	=	in-core instrumentation
MOEC:	=	middle of equilibrium cycle
MTC:	=	moderator temperature coefficient
NPP:	=	nuclear power plant
PDIL:	=	power-dependent insertion limit
PWR:	=	ppressurized water reactor
RPV:	=	reactor pressure vessel
RUL:	=	remaining usable life
SMR:	=	small modular reactor
VERA:	=	Virtual Environment for Reactor Applications

Disclosure Statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research made use of the resources of the High Performance Computing Center at Idaho National Laboratory, which is supported by the Office of Nuclear Energy of the U.S. Department of Energy and the Nuclear Science User Facilities under contract number De-AC07-05ID14517.This work was supported by funding received from the U.S. Department of Energy Office of Nuclear Energy’s Nuclear Energy University Program under contract number DE-NE0008975.