Nuclear power is an important component of the national energy strategy, and China's nuclear power has become a new force in the development of nuclear power in the world (second only to the United States). Nuclear power safety concerns public safety and human living environment. As a typical radioactive particle contaminant, nuclear dust protection is very important. At present, the nuclear radioactive particle protection material commonly used in nuclear power plants is disposable nonwoven polyolefin, which is easy to produce a huge amount of waste that is difficult to degrade after use, landfill treatment consumes a lot of land resources, and incineration treatment is easy to produce waste gas pollution.
Polyvinyl alcohol (PVA) has typical characteristics such as pure water solubility, adjustable dissolution temperature, easy degradation, and easy separation from nuclear radioactive particles, which provides ideas for the development of degradable nuclear radioactive particles protective materials and waste efficient cleaning and reduction treatment. The project proposed the preparation of two kinds of protective materials, water-soluble PVA nonwoven materials and water-soluble PVA microporous films, and the creation of a set of high volume reduction ratio reduction treatment equipment for nuclear protective waste, which solved the outstanding contradiction between water-soluble PVA fiber and spunle-forming, and broke through the limitation of difficult thermoplastic processing of PVA films. It has solved the problem that nuclear protection waste is difficult to reduce the ultra-high volume reduction ratio, and formed the industrial processing technology system of soluble PVA nonwoven protection materials for nuclear protection. The project has made breakthroughs in spunlaced materials and key equipment and process technology for film forming and waste capacity reduction, and the overall technology has reached the international advanced level. The product of the project will gradually replace the non-degradable polyolefin protective clothing, effectively promote the technological progress of the nuclear radioactive particle pollutant protection material industry, and is of great significance to safeguard national energy security and support the high-quality development of nuclear power.
PVA fiber has strong water absorption and is easy to swell, which makes it difficult to fully adapt to the conventional spunling processing, especially the first pre-spunling and then the main spunling easily lead to fiber compaction, and the fiber will even dissolve under the conventional high pressure spunling friction, resulting in uneven processing, and then affect the forming of nonwoven materials. The project innovatively developed the spray roller pressure drum, which replaced the conventional prepricking by spraying prewetting to avoid the loss and displacement of PVA fibers in the fiber network; The pre-water removal device was created, and the conventional process of "main needle-drying (> 120 ℃)" was changed to the process of "main needle-pre-water removal - low temperature drying (100 ℃)". Through pre-water removal, the problem of dissolution and adhesion of PVA fiber in the drying process could be solved, and low temperature drying could be realized.
PVA molecular chain contains a large number of strong polar hydroxyl, easy to form intramolecular and intermolecular hydrogen bonds, so that the molecular chain stacking regular, high crystallinity, resulting in its melting temperature (220~230 ° C) and decomposition temperature (230~250 ° C) close, difficult to thermoplastic processing. Based on the principle of "similar phase dissolution", the project adopts the piecewise plastic increase strategy to prepare PVA melt with wide melt processing window, and creates a uniform melt distribution die to form a water-soluble PVA film formed by thermoplastic processing.
Aiming at the problems of high mellowing PVA with large molecular weight and high viscosity of high concentration solution, which lead to difficult separation of nuclear dust, difficult spray of solution during combustion and insufficient combustion, the project studied the solution-degradation-decomposition mechanism of PVA, invented the viscosity reduction technology of high concentration solution, and formed an integrated capacity reduction equipment including dissolution viscosity reduction, thermal combustion decomposition, catalytic purification of tail gas and other devices. The developed soluble PVA nuclear protection materials (PVA spunspunned nonwovens and PVA films) can achieve high volume reduction ratio reduction treatment after waste, reduce the total amount of landfill land by 2 orders of magnitude, and save 90% investment cost compared with conventional incineration. The project was authorized 6 invention patents, 9 utility model patents; Published 5 journal articles; Formulate 1 national standard and 2 industry standards. Four production lines of PVA spunlace nonwoven materials, two PVA film production lines and two ultrasonic composite production lines have been built. The process technology is mature and the equipment runs stably. The type 2 nuclear protective clothing products formed by the selective combination of spunlace materials and films are applied to nuclear power plants at home and abroad.