**2. HTTR-GT/H2 Dispatch Model Methodology**

The HTTR-GT/H2 dispatch model was developed to generate insights into the optimal dispatch of nuclear IES and how different factors can affect that dispatch. As such, this model demonstrates how the HTTR-GT/H2 might best be dispatched in response to fluctuating hourly electricity prices throughout the year. The model also allows for the investigation of different input assumptions and their effects on the stochastic optimization of decisions to dispatch hydrogen or electricity.

#### *2.1. Modeling Framework*

The RAVEN framework is a multi-purpose optimization, data analysis, and uncertainty quantification code. It can be used in conjunction with the HERON plugin to develop economic dispatch models.

HERON creates a two-loop dispatch algorithm that incorporates RAVEN's optimization and synthetic time history generation abilities. The general structure of the stochastic dispatch model is given in Figure 1. The outer loop optimizes some grid parameter(s) (e.g., generator capacity), while the inner loop samples synthetic time histories, performs the economic dispatch, and tracks discounted cash flows via the TEAL plugin.

The HERON plugin was used to build the HTTR-GT/H2 dispatch model in RAVEN. HERON simplified the creation of this model, which might otherwise have proven complicated for typical RAVEN users. HERON enables users to quickly develop inputs based on technology prices, commodities such as electricity or hydrogen, and the hydrogen and electricity markets. HERON then translates these user-friendly inputs into RAVEN scripts

that utilize RAVEN's sampling, data transfer, and stochastic optimization capabilities to perform the dispatch.

**Figure 1.** General schematic of the HERON dispatch model workflow [15].

Figure 2 shows the decision process for the HTTR-GT/H2 dispatch model. This specific dispatch model utilizes an inner loop to perform the hydrogen/electricity (e- in Figure 2) dispatch and an outer loop to track hydrogen prices.

**Figure 2.** Algorithm used in the HTTR-GT/H2 price-taker dispatch model. The model can run a different inner loop for each stochastic time history in order to generate an expected net present value.
