Performance Evaluation of
Improved EPDM Material under
High-temperature Environments
1. Introduction

Winter 2018
No.34

Figure1 schematically illustrates the characteristics of
the improved EPDM material and existing silicone

In the case of a severe accident（hereafter, SA）, therubber and fluororubber sealing materials, based on

primary containment vessel（PCV）is surrounded byprevious evaluation results of each material. The

high-temperature steam at 200ºC and high radiation

horizontal axis represents steam temperature and thedose of several hundred kGy. Therefore, the PCVvertical axis radiation dose. The figure shows that

requires a sealing material that can maintain sealing

silicone rubber and fluororubber cannot maintainperformance even under an SA environment. For suchsealing performance in the event of SA; on the othercases, we evaluated the performance of our improved

hand, the new EPDM material maintains sealing

EPDM material（No. H3070）under high-temperature

performance even in high-temperature steam of overenvironments.

200ºC and γ ray irradiation of over 800 kGy.

Previously, silicone rubber and fluororubber, whichThus, the improved EPDM material was confirmed togenerally have excellent heat resistance, have beenoffer adequate environmental performance in theused as sealing materials for PCV. However, in an

event of SA, and was determined to be used as a newenvironment with high-temperature steam of 200ºC

sealing material for PCV. For this application, it wasand high radiation dose of several hundred kGy, thecrucial to confirm the following two matters:

structural weaknesses of polymers cause theconfirmation of the limit conditions under which theprogression of reduction in molecular weight due toimproved EPDM material can maintain sealinghydrolysis and due to exposure to high energies

performance, and verification of the improved EPDM

including γ rays. This is likely to lead to the loss ofmaterial’s superiority under SA environments.

sealing performance, and so a new material wasTherefore, an evaluation under a high-temperature

considered necessary.

１）

The improved EPDM material was developed on theassumption that it would be used in high-temperature
steam, and we have proposed the new material forsuch applications. We have been conducting variousevaluations to confirm its sealing performance, using asteam environment at a high temperature of 200ºC
and atmospheric pressure of 0.854 MPa as basic
conditions which properly allow a PCV to containradioactive material in the event of SA. Various tests
were conducted under these conditions and theimproved EPDM material was confirmed to haveadequate sealing performance. ２）
15

Figure1

General characteristics of sealing material

Technical Papers

environment in which the temperature significantly２-2）Evaluation method

exceeded SA temperatures was conducted.

2-2-1）Compression-set test

Regarding the evaluation method, the following tests

Two evaluation methods were used to confirm thewere conducted to confirm sealing performance:

performance at 300ºC, one of which was thecompression-set tests, which are effective for verifying

compression-set test, which is very effective forthe lifespan of the seal, and leakage tests using small

confirming the lifespan of a seal.

flanges, which imitate flanges installed on actual

The method of measurement conformed to JIS K

equipment.

6262:2013“Rubber, vulcanized or thermoplastic –Determination of compression-set at ambient, elevatedor low temperatures.”The JIS large specimen

2. Evaluation（cylindrical specimen with a diameter of φ29 mm and２-1）‌Preliminary test to set the evaluation
temperature

thickness of 12.5 mm）was used as the sample shape;This evaluation aimed to confirm the limitation of

Plastic deformation which occurs at high temperatures

sealing performance of the improved EPDM material;and under compressed conditions（but not only high-the evaluation was conducted at temperatures up totemperature conditions） was quantified. The

the temperature at which the improved EPDM

quantification was defined as follows: 0%: the original

material showed no significant material changes.

shape is completely restored; 100%: no shape

Thermogravimetric analysis was used as therestoration occurs. Rubber deterioration can beevaluation method. In Figure2, the purple line

considered to be a chemical reaction. Therefore, therepresents the rate of weight loss due to heat. Weighttime taken to reach a given deformation can beloss begins to occur at a temperature of over 300ºC. No

estimated by plotting a graph with time on themajor change was found to develop in the main

horizontal axis and compression-set rate on the verticalbackbone structure at temperatures up to 300ºC.

axis as shown in Figure3.

the compression rate was 25%.

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temperatures up to 300ºC.

Figure2

Winter 2018

Therefore, the performance was evaluated at

Results of thermogravimetric analyses
16Performance Evaluation of Improved EPDM Material under High-temperature Environments

imitate the flanges installed on actual equipment, wereused to confirm whether the sealing performance
could be maintained at the temperatures andpressures of SA. Figure4 schematically illustrates thesmall flange and Table2 shows their sizes. The crosssectional shape and size of the flange’s groove are
equivalent to those of the actual equipment; the crossFigure3

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No.34

Compression-set test and expected lifespansectional shape and size of gaskets were also
equivalent to those of the actual equipment. In theTable1 shows the evaluation conditions. To take theevent of SA, the flanges of the PCV open due to innerconditions in the event of SA into consideration, thepressure. To imitate this phenomenon, an adjustingevaluation was conducted under the following

shim was inserted into the smooth part in the small

conditions: atmosphere: saturated steam environment,flange, and the opening area was then adjusted. After

exposure dose of γ rays: 800 to 1000 kGy, temperature:

the adjustment, He gas was used to apply pressure to

200 to 300ºC. Regarding the environment within a PCV

the inside of the small flange. This pressurizationin the event of SA, the maximum atmosphericenabled leakage tests to be conducted underpressure was assumed to be 0.854 MPa. On the otherconditions imitating those in the actual equipment.

hand, this evaluation was conducted under a saturatedAs Table3 shows, the test conditions were as follows:

steam environment, resulting in much greaterpressure applied to the specimens（saturated steampressure at 200ºC: 1.6 MPa, at 300ºC: 8.6 MPa）.
Therefore, the environment is much more severe thanin a PCV in the event of SA.
2-2-2）Leakage tests using small flanges

Leakage tests using small flanges were conducted as
the second evaluation method. Small flanges, which
Table1

Conditions for compression-set tests

Figure4

Outline of a small flange

Table2

Sizes of small flanges

Table317Conditions for leakage tests

Technical Papers

After the flange temperature reached a given
temperature, He atmosphere of 1 MPa was used topressurize the inside of the flange for 10 minutes.
After the pressurization, the presence of leakage wasconfirmed. If He gas leaks in this test, the leakage canbe confirmed from the outside of the flange. Therefore,
the leaked He gas was collected through water as a
substitute to calculate the hourly leakage rate of He.
Figure 5 outlines the test equipment.

Figure6

Specimen after Test No. 6-3 test

Figure6 shows an external view of a specimen tested
under the most severe conditions with a temperatureof 300ºC and duration of 168 hours（Test No. 6-3）.
Figure5 Outline‌of test equipment to determine leakage
from a small flange

dents were found around the center of the sealing
surface. Therefore, the specimen was cut and thecross section was checked. Although the dents were３-1）Compression-set testcaused by a crack that had developed inside, theTable4 shows the results of the compression-set tests.

crack was confirmed not to have penetrated into theIn the table, Cs represents the compression-set rate.

sealing surface. The cause of the crack appeared to be

The following trends were confirmed: under aa rapid expansion of compressed steam while theconstant temperature, the compression-set ratepressure was being reduced under highly-pressurized

increases over time; within a given time period, thesaturated steam. To be more specific, the crack iscompression-set rate increases with increasing

considered to have developed as follows: 1）Steamtemperature.

pressure of 8.6 MPa was applied to flanges for theTable 4

Results of compression-set tests

evaluation under a saturated steam environment at300ºC. 2）The steam pressure also compressed steam
contained in the rubber. 3）After the evaluation wascompleted, the highly-pressurized steam was released
from the pressure container. 4）During steam release,
rapid decompression occurred. 5） The rapid
decompression caused steam, which had been
compressed in the rubber, to expand rapidly. 6）The
rapid expansion caused the crack in the rubber.
In this evaluation, the crack was caused by a physicalfactor stemming from the evaluation equipment. On
the other hand, in the event of SA, the maximum
pressure is expected to be 0.854 MPa, and so it isconsidered that no crack will develop in actual
18

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3. Evaluation results

Although no abnormality was found on the side face,

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Performance Evaluation of Improved EPDM Material under High-temperature Environments

compression-set rate of 80%. ３）２）Time duration wasset such that a compression-set rate of 80% could beachieved within the time duration. 3） Eachtemperature was arranged according to the timeduration. As a result, the plot demonstrates that acollinear approximation can be made with very highcorrelation coefficients.
Since thermal deterioration is a chemical reaction, theprogress of deterioration varies depending on theamount of thermal energy which is applied to thematerial. Therefore, regular deterioration behaviors
are likely to be detected provided that thetemperature range does not significantly exceed thethermal limit for the material and the evaluation
Figure7Winter 2018
No.34

A plot of the results of compression-set tests

environment is not unstable.
Therefore, in this evaluation, which was conductedequipment in the event of SA.

under a saturated steam environment of 200 to 300ºC,

Figure7 illustrates the results of the compression-set

the deterioration had developed according to thetests. The horizontal axis represents time; the verticalchemical-reaction theory, and was not likely to cause

axis represents compression-set rate. Under suchsudden and abnormal deterioration. Therefore, lifetime

conditions, the resulting data were plotted to produce

estimation was confirmed to be possible with thisan approximation curve for each temperature. Asdeterioration.

Figure7 shows, each curve shows a very highcorrelation coefficient, and the slopes of the respective３-2）Leakage test using small flanges

approximation curves are approximately the same.

The results from leakage tests using small flanges

Figure8 is an Arrhenius plot of the results of theshowed that no leakage occurred from the specimen

Arrhenius equation under the following conditions: 1）

which had been exposed to the saturated steam

Sealing performance can be secured at theenvironment at 280ºC and 300ºC for 168 hours.
After the evaluation had been completed, the small
flanges were dismantled to check the appearance ofthe gaskets. Figure9 shows a photograph of aspecimen which was exposed to 280ºC for 168 hours;
no abnormality was found in the appearance.
Similarly, regarding a specimen which was exposed to
300ºC for 168 hours, cracks were confirmed on part of
the gasket in the direction of the outer circumference;
however, no cracks or damages, which affect leakage,were confirmed in the direction of inner or outercircumference. Regarding the abovementioned cracks,
like the internal cracks in the compression-set tests,
rapid expansion of compressed steam due to rapid

Figure8 Arrhenius‌plot based on data at temperatures of
200 to 300ºC
19

decompression appears to have caused the cracks.
Therefore, at 168 hours after the initiation of exposureTechnical Papers

・These results indicate that the improved EPDM
material can be used in a stable manner undersaturated steam environments at temperatures up
to 300ºC.

5. Conclusion
In this evaluation, the improved EPDM material wasconfirmed to maintain its sealing performance evenunder the very severe environment of 300ºC, provided
the environment was limited to that used in thisevaluation. This finding highlighted the importance ofFigure9

Specimen after Test No. 7-1 leakage tests

continuing with development and verification based on
unconventional, free-thinking without bias, as well as

under saturated steam environments at 280ºC andlistening to users’requests. We will continue to strive

300ºC, no significant defect of sealing material washard to produce such reports in the future.

confirmed. Therefore, the sealing performance

Note that this report is an edited version of a paper

appears to have been maintained.

presented at the autumn academic lecture session of

4. Summary
The results of the compression-set tests and leakage

Lastly, we sincerely thank the staff of Chubu ElectricPower Co., Inc. for their assistance in publishing thisreport.

tests using small flanges under high-temperaturesaturated steam environments were as follows.

6. References

・The mechanism of deterioration of our improved
EPDM material（No. H3070）appeared to be the１）Koji Ito,“Radiation Resistance of Elastomer forsame at temperatures ranging between 200 andVacuum Seals,”Proceedings of the 27th Linear

300ºC; the possibility of sudden abnormal

Accelerator Meeting in Japan, 7P-19.

deterioration developing due to temperature２）Ken Suzuki, Valqua Technology News, No. 30, 14-19

changes is low.

（2016）.

・The results of the leakage tests using small flanges３）Toshio Kawamura,“O-ring’s life span and reliability,”

showed no leakage when the flanges had been

Valqua Review, Vol. 26（1982）.

exposed to saturated steam at 300ºC for 168 hours.

Ken Suzuki
Corporate Research andDevelopment Group
Product Development DivisionⅠ

Winter 2018

the Atomic Energy Society of Japan in 2017.

Shinichi Matsuda
CHUBU Electric Power Co.,Inc.

CHUBU Electric Power Co.,Inc.

Takuya Sugimura

20No.34