Dr. Ondrej Chvala ( [ Ссылка ] ) a full time faculty member of the Department of Nuclear Engineering at The University of Tennessee Knoxville presented at Thorium Energy Alliance Conference #10 (TEAC10) at Oak Ridge on 2019-10-01.

A modern version of ORNL’s MSRE dynamic modeling by Syd Ball and Tom Kerlin (ORNL-TM-1070, 1965).

Downloadable Slides:
[ Ссылка ]

Why Dynamic System Modeling?
- Simple and adaptable modeling approach that captures underlying physics.
- Ascertain transient behavior during normal operation and accident scenarios. Useful for I&C development.
- Determine safety limits and parameter sensitivities.
- Develop a validated open-source tool with accessible computational requirements.

MSR Dynamic Models Developed
- Molten Salt Reactor Experiment (PKE for core; PHX; radiator, validated with MSRE data).
- Molten Salt Breeder Reactor (Two-fluid modular MSBR, 1000MWe/4, ORNL-4528, 1970).
- Molten Salt Demonstration Reactor (Single fluid MSDR, 350MWe, ORNL-TM-3832, 1972).

Full power plant modeling: MSDR, ORNL-TM-3832

The OTSG combines the subcooled, boiling, and superheating regions into a single component body. The moving boiling and superheating boundaries allow the OTSG model to change the average heat transfer coefficient and thus function at different power levels.

The balance-of-plant system is composed of a nozzle chest, high-pressure turbine, moisture separator, reheater, low-pressure turbine, condenser, and two feedwater heaters.
These components together operate the superheated steam working fluid flowing from the OTSG through the reheated-regenerative Rankine cycle.
In this variation of the Rankine cycle two turbines work in series. The exhaust steam from the HPT is dried and reheated using a bypass flow before expansion in the LPT.
Furthermore, bleed flows and bypass steam are used to preheat feedwater that is pressurized via pumping to the steam generator.
These steps combine to increase the thermal efficiency of the Rankine cycle while providing practical advantages such as a higher quality exhaust at both turbines, which increases their lifetime, and a larger pressure difference between the boiler and condenser.

The full model consists of some 100 state variables.

When modeling a reactor plant, incorporating the full steam generator and balance-of-plant components can be burdensome.
Moreover, if the design for the turbine cycle is not finalized, adding an OTSG and BOP may not be ideal.
For these reasons, previous models included only the fuel salt and coolant loops.
Doing so, however, ignored some of the dynamic features which may have considerable impact on the power response.
So we calculated power-to-reactivity frequency response for three tertiary loop boundary conditions: constant energy removal from the Hitec loop, constant feedwater inlet temperature to the OTSG, and the full OTSG and BOP model.
For the most part, the behavior of the plant with only OTSG is indistinguishable from the full system model implying that most of the dynamics of interest are in the OTSG.
On the other hand, the behavior of MSDR with constant heat removal is similar but with important distinctions. Namely, the gain is lower than the cases with OTSG and full BOP and is seen to converge with the two at lower frequencies. However, the phase diverges at lower frequencies, but converges at higher frequencies.
Hence, a constant heat removal system simplifies the secondary side behavior, leads to an overestimation of feedback response, and is, in general, not fully accurate for modeling such systems for control studies.

CONCLUSIONS
- MSRs: tremendous progress in the last 10 years!
- Dynamic modeling characterizes system behavior in time.
- Useful for instrumentation and control.
- Accident scenarios, parameter sensitivity to guide research.
- Novel methods of safeguards.
- Functional requirements for a decay heat removal system.
- Well designed MSRs are stable and can rapidly follow demand load.
- Low pressure system with constant flow rates.

Thorium Energy Alliance: [ Ссылка ]

This video captured for future use in Thorium Remix projects: [ Ссылка ]

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