Analysis of DLOFC Accident in HTR-10 Operating at Higher Temperatures

The high-temperature gas-cooled reactor (HTGR) with a high outlet temperature from 700°C to 800°C to 1000°C is expected to be widely used for heat supply, hydrogen production, steelmaking, seawater desalination, thermal recovery of heavy oil, and coal liquefaction and gasification. The 10-MW High Temperature gas-cooled test Reactor (HTR-10), with an outlet temperature of 700°C, has been constructed and operated in China as a pilot plant to demonstrate the inherent safety features of the modular HTGR.

Supported by the Chinese National S&T Major Project and National Key R&D Program of China, some research on HTGR technology with much higher outlet temperatures has been carried out in the Institute of Nuclear and New Energy Technology (INET), Tsinghua University, China, including the preliminary design and analysis of a HTR-10 with an outlet helium temperature of 950°C (HTR-10H).

This paper presents the simulation results of the depressurized loss-of-forced cooling (DLOFC) accident of the HTR-10H. This analysis was performed with two different codes, TINTE and SPECTRA, within a cooperation between the Nuclear Research Group of the Netherlands and the INET. In the past, comparisons between TINTE and SPECTRA have also been performed for the Chinese 200-MW(electric) High Temperature gas-cooled Reactor Pebble bed Module (HTR-PM). The calculation results showed that both the fuel temperature and the reactor pressure vessel temperature remained below the acceptable limits during the DLOFC accident.

The inherent safety of the HTR-10 can be guaranteed in the accident condition. Both the TINTE results and SPECTRA results for the maximum and average fuel temperature agreed well. In both models, the heat carrying capacity of the Reactor cavity cooling system (RCCS) had been underestimated, especially in the SPECTRA model. The RCCS performance needs to be investigated and the models need to be further improved in the future.

The work introduced in this paper shows the feasibility of increasing the outlet helium temperature of the HTR-10 from the current 700°C to 950°C, if further design optimization can effectively reduce the fuel temperature during steady-state operation, or more irradiation tests can be carried out to prove the retention performance of the TRISO particles for the radioactive fission products at temperatures above 1200°C.