When steam generator tube rupture (SGTR) occurs in the lead-bismuth cooled fast reactor, high pressure water/steam flows into the primary side filled with high temperature liquid metal. According to the location and size of the rupture, the leakage behaviors of the rupture may involve leak-before-break (LBB), single-phase critical flow or two-phase critical flow. Under the action of high temperature liquid metal, different forms of heat and mass transfer behaviors occur in the two-component multiphase system of water-metal, which has an important influence on the safe operation of the lead-bismuth cooled fast reactor.

This study aims at the bubble dynamic behavior in the descending flow field of liquid lead-bismuth alloy (LBE) in the tube bundle in different stages of SGTR caused by microcrack on the surface of the heat transfer tube during the drying stage and low flow single phase steam permeates the primary side.

Based on the VOF method, a numerical simulation model of steam-LBE two-phase flow and phase interface capture was established to study the bubble growth and transport behaviors from single tube or 3×3 tube bundle in the downward flow field of high temperature LBE. The SST k- ω model was employed to solve the turbulence equation. The physical law of steam bubble movement was analyzed and its influence on the heat transfer and operation stability of steam generator was evaluated.

The results show that the dynamics behaviors of steam bubbles in the descending flow field are quite different from these in static liquid or upward flow. The steam bubbles may slide along the heat transfer tube surface after departure from the crack under the actions of LBE descending flow field and buoyancy. The steam bubbles may form a steam film covering the heat transfer tube surface or accumulate by quantity in the bundle.

These phenomena adversely affects the flow stability of the LBE and the heat transfer of the steam generator.

The superconducting third harmonic cavity has been developed independently in Shanghai Synchrotron Radiation Facility (SSRF) and passed beam tests. The cavity electric field needs to be precisely controlled during operation to achieve the goal of stretching beam cluster and improving beam life.

This study aims to design a digital low level radio frequency (DLLRF) controller for superconducting third harmonic cavity at SSRF.

The hardware of controller was based on a field-programmable gate array (FPGA) board and a front-end board whilst in-phase/quadrature (I/Q) demodulation techniques were implemented in the software of controller. A synergistic strategy was adopted for driving the stepper motor with slow tuning speed and piezoelectric ceramic with fast tuning speed, and an algorithm for the quench detection for passive cavity. Finally, experimental tests were performed to verify the effectiveness of this designed DLLRF.

When the state is in top-up mode over 120 mA, the amplitude stability has improved form ±5% with open loop to less than ±1% with close loop, the voltage of piezo has varies smoothly and stably within 120 V, and the beam life has improved more than doubled.

A digital low level radio frequency controller for the superconducting third harmonic cavity has been designed and satisfies the requirements for SSRF.

Hefei Advanced Light Facility (HALF) is a fourth-generation synchrotron radiation light source based on diffraction-limited storage ring. The timing system provides trigger signals for the HALF injector, storage ring and beamline, coordinates injection and beam measurement, and achieves filling of the storage ring bucket with any designated bunch pattern.

This study aims to design a timing system for HALF to reduce the trigger signal jitter of the HALF device to less than 30 ps, and stabilize the signal drift caused by the optical fiber length change.

Based on the MTCA.4 event-driven products from Micro-Research Finland Oy (MRF), the event timing technology scheme was adopted to implement the timing system. Appropriate system frequencies for electron gun, microwave system and storage ring were selected to achieve different modes of storage ring bucket filling scheme. The timing system software was developed under Experimental Physics and Industrial Control System (EPICS) to coordinate with the control system of HALF, including an EPICS driver, database records, and operation interfaces. Delay compensation was applied to signal drift caused by the variation of optical fiber length. Finally, a prototype of the timing system was developed for performance tests.

The results show that the jitter of the trigger signal is less than 24 ps, and the signal drift is controlled at about 3 ps after delay compensation, both meet the design requirements of HALF timing system.