Analysis of VTR Primary Pump Coastdown
- Argonne National Lab. (ANL), Argonne, IL (United States)
Simulations were performed to evaluate how different flow coastdown rates impact transient results. These simulations were performed with a preliminary SAS4A/SASSYS-1 model of the VTR to assess the advantages and disadvantages of delaying a pump trip following a control rod scram. When the control rods are inserted into the core by the reactor protection system, fission power will drop quickly. Pumps should be tripped soon after to avoid decreasing the power-to-flow ratio too much and preventing thermal shock of components in and above the core. The primary motivation for this report is characterizing the temperatures of these components with various delays between the control rods scramming and the primary pumps tripping. In the simulations with a control rod scram and a delayed pump trip, even if one of the pump coastdown mechanisms fails, a faster pump trip and coastdown is preferable. This can be achieved both by shortening the delay between the scram and trip as well as by decreasing the inertia provided by the coastdown mechanism. Based on the results of these simulations, there is no benefit to delaying when the pumps trip following a control rod scram. In other scenarios, however, a slow flow coastdown rate is preferable. Results from unprotected loss of flow simulations are presented to demonstrate that a slower coastdown reduces how much temperatures increase within the core. An initial flow halving time of between five and seven seconds was predicted to produce peak in-core temperatures with sufficient margins to the limiting criteria. For halving times less than five seconds, peak temperatures significantly reduce margins. For halving times greater than seven seconds in the unprotected loss of flow cases, the resulting peak temperatures are lower, but this leads to unfavorable results for the previous cases with a control rod scram. In order to achieve an acceptable balance between cases with and without a preceding control rod scram, the results presented in this report support an initial flow halving time in the five-to-seven second range, although ongoing PRA analysis could produce results that support a coastdown beyond this range.
- Research Organization:
- Argonne National Laboratory (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE Office of Nuclear Energy (NE)
- DOE Contract Number:
- AC02-06CH11357
- OSTI ID:
- 1868341
- Report Number(s):
- ANL-VTR-17; 152269
- Country of Publication:
- United States
- Language:
- English
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