Various Characteristics of Severely Aged Flame‐Retardant Cross‐Linked Polyolefin

Okada³

2022

Polymers

Self Cite

The polymeric insulation used in nuclear power plants (NPPs) carries the risk of molecular breakage due to oxidation and hydrolysis in the event of an accident. With this in mind, tubular specimens of flame-retardant ethylene-propylene-diene rubber (FR-EPDM) insulation were obtained by taking conductors out of a cable harvested from an NPP. Similar tubular specimens were made from a newly manufactured cable and those aged artificially using a method called the “superposition of time-dependent data.” The inner and outer surfaces of each tubular specimen were subjected to various instrumental analyses to examine their oxidation, moisture uptake, and cross-linking. As a result, it has become clear that oxygen penetrates the cable through gaps between the twisted conductor strands. Meanwhile, water vapor diffuses more often through the sheath than through gaps between the conductor strands. Of the two methods used to simulate design-based accidents in NPPs, the one used to simulate the designed loss-of-coolant accident is more severe to FR-EPDM than the one used to simulate the designed severe accident. In addition, the validity of the method called the “superposition of time-dependent data,” which is used to give artificial aging treatments to cable samples, was confirmed. Measurements of spin-spin relaxation time and residual dipolar coupling using time-domain nuclear magnetic resonance were found suitable to use to obtain information on the cross-linking of FR-EPDM insulation.

Section: Resultsmentioning

confidence: 99%

Section: Superposition Of Time-dependent Datamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Penetration Routes of Oxygen and Moisture into the Insulation of FR-EPDM Cables for Nuclear Power Plants

Okada³

2022

Polymers

Self Cite

“…Regarding this, several research projects such as 'European Tools and Methodologies for an efficient ageing management of nuclear power plant Cables (Team Cables)' conducted mainly by the University of Bologna [1, 2], 'Light Water Reactor Sustainability (LWRS) Programme' organised by the US Department of Energy [3,4], and a Japanese one entrusted by the Secretariat of the Nuclear Regulation Authority in Japan are recently actively involved in the degradation of insulating polymers for use in NPPs. For conducting the last project, we have been doing many pieces of research on the degradation of various insulating polymers used in safety-related cables, such as cross-linked polyethylene (XLPE) [5,6], flame-retardant (FR) XLPE [7], FR ethylene-propylene-diene rubber [8,9], FR cross-linked polyolefin [10,11], and silicone rubber [12,13].…”

Section: Introductionmentioning

confidence: 99%

Thermal ageing of soft and hard epoxy resins

2022

High Voltage

Self Cite

Two kinds of epoxy resin, a soft one with rubber‐based additives and an ordinary hard one, are used as electrical insulators and airtight sealants in electrical penetrations in nuclear power plants (NPPs). Knowing how they behave under adverse environments is important for the safe operation of NPPs. In this regard, we gave artificial thermal ageing treatment to the two resins by heating them in air at various temperatures. The resins were then subjected to mechanical, thermal, and dielectric tests. As a result, it has become clear that the soft epoxy resin becomes hard, while its permittivity and loss factor decrease as the heating becomes longer. The glass transition tends to occur at a high temperature in the soft epoxy resin when it was heated. With these changes, the soft resin tends to exhibit similar behaviour in various properties to that of the unaged hard one. On the other hand, the hard one is hardly affected by the simulated thermal ageing. Therefore, both resins can be useable in NPPs.

“…Much research has also been carried out in Japan to examine the degradation behavior of various insulating polymers such as silicone rubber (SiR), soft epoxy resin (SE), flame-retardant ethylene-propylene-diene rubber (FR-EPDM), flame-retardant cross-linked polyolefin (FR-XLPO), non-flame-retardant cross-linked polyethylene (NFR-XLPE), and flame-retardant cross-linked polyethylene (FR-XLPE) in a project entrusted by the Nuclear Regulation Authority in Japan [6][7][8][9][10][11][12][13][14][15][16][17]. Here, NFR-XLPE and FR-XLPE are used in both pressurized-water type and boiling-water type NPPs, in Japan, depending on the purpose of each cable.…”

Section: Introductionmentioning

confidence: 99%

Degradation of Flame-Retardant Cross-Linked Polyethylene Caused by Heat, Gamma-Rays, and Steam

2022

IEEE Access

Self Cite

Various kinds of polymers are used for electrical insulation in nuclear power plants. They are subjected to thermal and radioactive stresses, depending on their locations. They are also subjected to hightemperature steam in the event of an accident. Regarding this, sheets of flame-retardant cross-linked polyethylene (FR-XLPE) were subjected to heat, gamma-rays, and steam exposure, and their infrared absorption spectra, stress-strain relations, indenter moduli, and permittivity spectra were measured. As a result, we have made clear various degradation-induced property changes of FR-XLPE. In addition, it has also become clear that cross-linked structures are formed by the gamma-ray irradiation in FR-XLPE. In this regard, some aspects of degradation due to subsequent steam exposure are suppressed by the formation of firm three-dimensional cross-linked structures.INDEX TERMS Aging, gamma rays, insulating polymer, mitigation, nuclear power plant, steam exposure