foreign body：
It refers to all substances that enter, remain or exist outside the system or equipment itself, which may adversely affect the operation and performance of the system and equipment. The main foreign bodies are listed below (not limited to): tool materials for foreign body prevention; work kits, procedures, drawings, record books, etc.; parts and components removed from equipment; spare parts and their packages; solvents; cutting debris and debris, welding slag, etc.; sediment, cement debris and stones, water grass, marine organisms in seawater system; light water in heavy water system; Suspended substances, soluble impurities, microorganisms, corrosion products, activation products, harmful chemicals not allowed in the system, such as halogen, sulphur, sodium, lead, cobalt and other impurities introduced into the process system due to impurities in chemicals, incorrect addition of chemicals, system leakage, cross-contamination and other reasons, these impurities will increase the corrosion of equipment or cause the rise of radiation field. High; Personnel entering system pipes or containers;
Foreine Material Exclusion：
It refers to the adoption of certain methods to prevent foreign objects from entering the system or equipment due to personnel negligence, or to reduce their probability.
Foreign body control area or foreign body prevention area：
An established area to control the access of tools, equipment, materials and personnel to an open system, thereby reducing the possibility of leaving any items in the system due to negligence.
Foreign body incidents are often found in the commissioning process of nuclear power plants. If foreign body control (FME) is not strengthened and necessary measures are taken to prevent foreign body from entering structures, systems and equipment that should not be entered, such as turbogenerators, reactor cores and primary circuits, it will pose a great threat to the subsequent safe and stable operation of nuclear power units, causing significant economic losses and, in serious cases, leading to nuclear safety accidents. Occurrence.
The following are six typical foreign body incidents found during the recent commissioning of nuclear power plants in China.
On May 1, 2016, when the Commissioner made an important system valve on-line after the pressure vessel was fastened, he found that the valve was leaking, and there was greater resistance in the process of closing the valve, so the valve could not be closed completely. Subsequently, the maintenance department dismantled the valve and found a bolt (25mm in length, 7.9mm/9.01mm in narrowest/widest bolt head) and metal sheet (fan-shaped, 7mm in radius, 7mm in arc, 0.5mm in thickness) in the valve seat. After analysis, the most likely source of foreign body is the cover bolt of a certain equipment in the same room with the valve, and the most likely source of foreign body is the metal debris produced by the drill bit opening in the pipeline prefabrication stage.
On May 1, 2016, a plate heat exchanger of equipment cooling water system (CCS) was being retrofitted in a nuclear power plant. A broken spring arm, a semi-circular foreign body (baffle component) and a hexagonal bolt (M12*25) were found at the entrance of CCS side of the heat exchanger. The damage of the titanium cover of the blind plate on the baffle of the moving end of the heat exchanger was found. At the same time, a black suspected rubber strip object was found, but because the foreign body has been discarded by the construction personnel, after investigation, it was treated as an external foreign body of the system for analysis. On June 1, another broken long spring arm (length 90 mm, diameter 5 mm) was found at the bottom of the heat exchanger. After that, the maintenance personnel dismantled and inspected a check valve in the same system. It was found that the valve spring also broke in two places, and the block and tightening bolt did not fall off. On July 1, the staff removed the valve which had replaced the spring and found that the spring of the valve broke again. Five arms were found to have broken. After analysis, the source of foreign matter in plate heat exchanger is the broken parts on the check valve at the outlet of a pump in the same system.
On July 1, 2016, when debuggers cleaned up the bottom shell of a system B diesel engine of Unit 1, they found a broken drill bit adhering to the inside of the cover plate of A5 crankcase. On August 1, in the process of opening the cover of the diesel engine camshaft box to extract desiccant, four bolts were found in the B6 cam box. After analysis, the source of foreign body is that the drill bit was broken when the nameplate of the unit was installed on the A5 cam box by the nameplate installer of the manufacturer. The foreign body of four bolts was introduced into the A5 cylinder crankcase before the equipment went out of the factory.
On January 19, 2017, a piece of metal block and several pieces of metal filament were found in the filter of the fluctuating tube orifice at the bottom of the regulator when the internal inspection of the regulator was carried out in the nuclear power plant. The source of foreign matter is the processing of pipe side groove of nozzle, pipe group, and the possibility of foreign matter entering the regulator from outside of the system/equipment during pipe welding in the stage of installation of the regulator.
In March 2017, during the internal inspection of condenser in nuclear power plant, it was found that there were welding rod head and rust slag foreign bodies at the bottom of condenser A heat trap, scaffold fastener, concrete block, wire rod, grinding wheel cutting piece, welding rod head and rust slag foreign bodies at the bottom of condenser B heat trap, and welding rod head and rust slag foreign bodies at the bottom of condenser C heat trap. The source of foreign bodies may be that foreign bodies are left on the internal parts of the condenser in the early stage of the work, and fall into the condenser heat trap in the process of system flushing, steam turbine flushing, flutter and other factors.
In March 2017, in the process of large-scale washing of equipment cooling water system (CCS), large foreign bodies were washed out at the filter screen of equipment cooling water pump B three times before and after. On March 16, five foreign bodies with sizes ranging from 30 to 60 mm were washed out, one scaffold fastener was washed out on March 17, and the whole fastener factory was 110 mm, with a width of 95 mm; on March 31, plastic was washed out. One temporary pipe cap with a diameter of 79 mm. The foreign bodies produced in the construction of surrounding intersections are the possible sources of foreign bodies.
Through the common cause analysis of the six foreign body incidents found in the commissioning process of the nuclear power plant, it can be found that the foreign body prevention control measures are imperfect; the foreign body inspection in the system is not in place; and the staff are not aware of the risk of foreign body prevention.
