Global and Local Reactivity Assessments for Passive Control Systems of Multi-module HTGR Special Purpose Reactors

Abstract

In this report various categories of Flexible Power Operation (FPO) were defined. For each category the requisite reactivity for meeting the FPO specifications was quantified using a point kinetics reactor model with 3-temperature feedback.

The available reactivity in the reactor through temperature perturbations and the existing control drum systems were then quantified. A comparison of the reactivity from various control drum patterns is shown in Fig. EC.1, and the spatially dependent reactivity coefficients are shown in Figs. EC.2 and EC.3. When evaluating the available reactivity from each of these mechanisms it was found that: • the existing control drum system would be sufficient for meeting reactivity requirements for any of the categorized FPO requirements. • the reactivity available through varying the flow rate was not sufficient for any of the FPO categories. Therefore, work in future milestones for this project will focus on the control drum system and automation for FPO. However, the concept of the passive flow controllers may still have value in other applications in the reactor performance such as: local power shaping, additional margin and protection in over-temperature transients, and small power changes (e.g. < 10% rated power). Likely some additional investigation will be performed to assess this value as well.