Radioactive Fission Gas Detection System Gas-Liquid Circuit (gas-liquid control unit)
During the normal operation and maintenance of nuclear power plants, it is difficult to avoid the damage of nuclear fuel assembly cladding. Once the nuclear fuel assembly is damaged, it is bound to cause the leakage of radioactive components, which has a bad impact on the control of radioactive components. In order to control the leakage incident as much as possible, during the overhaul, the nuclear fuel assembly needs to be tested offline through this system. Its working principle is: the nuclear fuel assembly to be tested is placed in the underwater sipping device located at the bottom of the spent fuel pool, and the pressure boundary in the underwater sipping device is changed by controlling the relevant detection loop system to create a vacuum environment, so as to release the fission gas in the fuel cladding of the nuclear fuel assembly. After the gas release reaches equilibrium, the air pump in the loop and the valve of the sipping device are opened to promote the uniform mixing of the gas in the loop, and the mixed gas is transported to the detection chamber of the target radioactive nuclide detection system to accurately measure the radioactive activity of the target nuclide in the detected gas, thereby determining the degree of damage to the fuel assembly.
Technical Parameters:
1. Sealing cover drive related parameters
lWater depth at the sealing cover is 8m;
lThe weight of the sealing cover is 80kg ;
l Sealing cover upper surface size: 400mmx400mm;
lSealing cover opening time: ≤15s;
lSealing cover closing time: ≤15s;
l Sealing cover drive cylinder stroke: 270mm;
lSealing cover drive cylinder installation distance: 350mm;
lSealing cover drive cylinder installation form: hinged at both ends;
lSeal cover drive circuit medium: SED.
2 Sealing airbag related parameters
lSealed airbag cavity volume: 0.3L ;
l Sealing airbag working pressure: 0.336MPa~0.40MPa ;
lWorking medium of sealed airbag circuit: SAR.
3. Parameters related to radioactive gas detection circuit
l Target radionuclide detection unit operating temperature range: 5~40℃;
l Working pressure range of target radionuclide detection unit: 0.08-0.5MPa;
l Gas flow rate when the target radionuclide detection unit is working normally: 35 L/min:
l Particles contained in the gas to be tested: ≤10um;
l Ensure the tightness of the radioactive gas detection circuit under positive and negative pressure. Even when some components fail, the system can guarantee the sealing effect and ensure that the detection work can continue after the failure is repaired. The airtightness requires a test pressure of 1MPa, and the pressure drop in 1 hour shall not be greater than 0.005MPa;
lThe ultimate pressure of the vacuum pump is not more than 0.001MPa;
lAdd appropriate gas treatment equipment to the loop for gas filtration, drying, cooling, etc. The components of the gas treatment equipment should not adsorb the target nuclides, cause gas leakage, or introduce other gases when in working condition;
l Ensure that the system can achieve gas circulation effect according to the detection process;
l Consider the feasibility of condensate return to the suction tube, and ensure that the liquid level in the suction tube drops within the control range so that the fuel assembly does not appear above the water surface .
4. Sealing cover drive circuit
lAccording to the needs of the system process, the sealing cover drive cylinder is extended and retracted in time to open and close the sealing cover, and no malfunction is allowed; the system has no jamming or delay. There are no abnormal phenomena such as creeping and knocking during the operation of the drive cylinder; the drive cylinder can be reliably locked at any position:
lIn the event of a system failure, emergency measures can be taken to open the sealing cover to ensure that the fuel assembly can be safely removed from the sipping cylinder.
5. Sealed air bag circuit
lAccording to the needs of the system process, the sealed airbag should be inflated and depressurized in a timely manner, and no malfunction is allowed;
lWhen a slight leak of sealing gas occurs, the system can still maintain normal sealing effect, and feedback the system pressure, flow, etc. to the electrical control system to remind the user that there may be a slight leak in the system ;
l Design safety valves to ensure that the sealed airbags will not be over-pressurized and cause damage;
lWhen a system failure occurs, emergency measures can be taken to relieve the pressure of the sealed airbag , making it easier to open the sealing cover and ensure that the fuel assembly can be safely removed from the sipping tube.
6. Other requirements
lAll pipes, joints, pumps, valves and other components of the system should meet the requirements of corrosion resistance and radiation. Pipes with relative motion should use corrosion-resistant hoses;
l Rubber seals and hoses should be resistant to radiation and corrosion, and should be used normally in an environment of 0-80℃ and 2500ppm boric acid water. They should not be hardened, aged, or fail within at least two overhaul periods. The halogen content of the materials, including ammonia, gas, and sulfur ions, should comply with ASME standards. CI - +F - ≤200mg/Kg, S ≤200mg/Kg;
lThe cumulative radiation dose of underwater sensors is not less than 106Gy;
lThe system adopts A/8 two-way design, A/8 two-way is not divided into main and auxiliary, and can be controlled separately. When conducting radioactive gas detection, the isolation effect of the circuit to be detected should be ensured, and other irrelevant gas and liquid branches are not allowed to enter and affect the detection.
PS: All solenoid valves should have status feedback function.
