乙丙橡胶绝缘电缆的全称是交联乙烯—丙烯橡胶绝缘电缆。它的工作温度范围:-50℃至+150℃,短路热稳定允许温度为250℃,是国内外核电站电缆使用最多的一种绝缘材料,正是因为是核电站关键电缆,特别是核岛内电缆的安全重要性,所以世界各地对该材料的电缆都进行了很多的测试和研究,下面的文章是美国核管会(NRC)在2000年和2002年对这个电缆的一个测试报告和公告,以提醒核电站从业者关注乙丙橡胶绝缘电缆的安全性问题,以防出现重大质量安全问题。

原文地址或下载:

http://www.nrc.gov/reading-rm/doc-collections/gen-comm/reg-issues/2000/ri00025.html

原文大意如下:

OKONITE公司的单导体控制电缆的潜在质量隐患（于2000年12月26日）。

BROOKHAVEN国家实验室（BNL）在美国核管会NRC的合同授权下对核电站的电器做环境资格评估时，低压仪表控制电缆的评估也是该合同的一部分。

在1999年后期，在WYLE实验室进行了这些电缆的LOCA（冷却剂泄露意外）测试，电缆样品是乙丙橡胶绝缘，氯磺化聚乙烯粘合护套的仪表控制电缆，取自几个不同的生产商，包括OKONITE公司的12AWG电缆，测试先进行热加速老化，然后是辐射老化，最后是暴露在模拟LOCA情况的测试，热加速老化和辐射老化的参数取决于各个供应商的EQ测试报告。OKONITE公司的样品测试参数分20年和40年寿命两个不同的情况，对于40年寿命的老化参数是： 150 °C下504小时，然后是辐射老化：在6.5 kGy/hr (0.65 Mrad/hr)的辐射剂量速度下总共500 kGy (50 Mrads)的GAMMA辐射。

模拟的LOCA测试是在7.5kGy/hr (0.75 Mrad/hr)的辐射剂量速度下总共1500 kGy (150 Mrads)的GAMMA辐射，接着是双峰蒸汽暴露，基于IEEE-323-1974标准，峰值蒸汽温度是 174 °C (346 °F)，蒸气压强是779.1 kPa (113 psig)，在测试容器的压强下降到220.6 kPa (32 psig)时喷洒硼酸基化学喷雾，并延续24小时，蒸汽暴露的延续时间是10天。经过上面测试的电缆样品再做浸水耐压测试，测试电压2400V AC (等于 80 v/mil AC)，与IEEE-323-1974标准一致。

OKONITE公司的全部3根40年老化实验样品和2根中的1根20年老化样品在LOCA实验前的反复老化实验就已经失效，LOCA实验前就出现了环型裂纹，在LOCA实验后出现纵向裂纹。

后来在2002年，NRC就此事情有一个跟进报告》》》，OKONITE公司做了有效的改进并成功通过测试。但从跟进报告可以看出，后来的测试参数已经下降了，原来在1999年的测试基准是：150 °C下504小时＋200 Mrads,在这种情况下是测试不通过的。而后来则改为:150 °C下225小时＋200 Mrads和150 °C下300小时＋200 Mrads,当然就容易通过测试了。虽然这个事情就这样结束,但也看得出来,实在有些勉强! 因为通过降低测试标准来通过测试,那该电缆的质量隐患也是一样存在的。

通过上面的事例，我们应该高度重视在核电站，特别是核岛反应堆里面电缆的质量问题，以100%确保在整个寿命期（包括延寿期），电缆都不能有任何的性能上的下降和将就。

原文如下:

Potential Deficiency in Qualifition of Okonite Single-Conductor Electrical Control Cables

December 26, 2000
? ADDRESSEES
? INTENT
? BACKGROUND INFORMATION
? SUMMARY OF ISSUE
? BACKFIT DISCUSSION
? FEDERAL REGISTER NOTIFICATION
? PAPERWORK REDUCTION ACT STATEMENT

ADDRESSEES
All holders of operating licenses for nuclear power reactors, except those who have permanently ceased operations and have certified that fuel has been permanently removed from the reactor vessel

INTENT
The U.S. Nuclear Regulatory Commission (NRC) is issuing this regulatory issue summary (RIS) to notify addressees of a potential deficiency in the environmental qualification (EQ) of certain singleconductor Okonite electrical cables used for instrumentation and control (I&C) applications in nuclear power plants. The NRC is
continuing to work with the nuclear power industry to reach closure in this matter. Consequently, this RIS only presents the current status of the NRC/industry effort; a supplement to this RIS will be issued when a satisfactory basis for closure is identified. This RIS does not transmit any new requirements or staff positions. No
specific action or written response is required.

BACKGROUND INFORMATION
The Brookhaven National Laboratory (BNL), under contract to the NRC, has been conducting research on low-voltage I&C cables to support the resolution of Generic Safety Issue (GSI) 168, "Environmental Qualification of Electric Equipment." As part of this research, in late 1999, a loss-of-coolant-accident (LOCA) test (Test #5) was conducted on I&C cables having ethylene propylene rubber (EPR) insulation and covered with a bonded chlorosulfonated polyethylene (CSPE) outer jacket. The purpose of the test was to determine whether cables with bonded jackets would experience a failure mechanism that is unique, that is, a failure mechanism other than what unbonded jacketed cables have shown under postulated LOCA conditions. The
testing was performed at the Wyle Laboratories in Huntsville, Alabama, using cable samples obtained from several manufacturers, including Okonite. The Okonite samples were single conductor, #12 American wire gauge (AWG) cable, with the insulation and bonded jacket covering noted above. For the test, the cable samples were first subjected to accelerated thermal and radiation aging, and then exposed to simulated LOCA conditions. The accelerated thermal and radiation aging parameters were selected on the basis of each vendor's original EQ test report. For the Okonite cable samples, preaging was conducted to demonstrate 20-year and 40-year qualification. The parameters for demonstrating 40-year qualification of Okonite cable included elevated temperature exposure for 504 hours at 150 °C (302 °F), followed by exposure to 500 kGy (50 Mrads) of gamma radiation at a dose rate of 6.5 kGy/hr (0.65 Mrad/hr).
The simulated LOCA test consisted of exposing the cable samples to 1500 kGy (150 Mrads) of gamma radiation at a dose rate of 7.5 kGy/hr (0.75 Mrad/hr), followed by exposure to a double-peak steam profile, as described in Institute of Electrical and Electronic Engineers (IEEE) Standard 323-1974. The peak temperature and pressure conditions of the steam profile were, respectively, 174 °C (346 °F)
and 779.1 kPa (113 psig). A boric-acid based chemical spray was initiated when the test chamber pressure decreased to 220.6 kPa (32 psig), and was continued for twenty-four hours. The duration of the steam exposure was 10 days. Following the exposure of the cable samples to the simulated LOCA conditions, the specimens were submerged in water and subjected to voltage-withstand testing at a test voltage of 2400 volts ac (equivalent to 80 v/mil ac), as described in IEEE Standard 383-1974.
All three Okonite specimens that underwent 40-year equivalent preaging, and one of two Okonite specimens that underwent 20-year equivalent preaging, failed instantaneously. The artificial aging is believed to have contributed to the failure mechanism since circumferential cracks were observed following cable preaging.Longitudinal splits were observed on the cable jackets following exposure to the simulated LOCA conditions. The details of this test are discussed in a letter report from Robert Lofaro, BNL, to Satish Aggarwal, NRC, "Results of Test 5 on Bonded Jacket Electric Cables,"

dated March 6, 2000 (ADAMS accession number ML003709449).

SUMMARY OF ISSUE
Following receipt of the test results from BNL, the NRC held meetings with representatives from Okonite and the nuclear industry on February 8, and 16, 2000, respectively. It was determined that the composite EPR with CSPE jacket in Okonite's original qualification test report NQRN-1 is a bonded jacket system that is almost identical to the specimens tested by BNL. Okonite single-conductor, #12 AWG cables with EPR insulation and bonded CSPE jacket are used in electrical equipment important to safety, which are located in areas of nuclear power plants that are exposed to harsh environments.
Okonite test report NQRN-1 is the basis for environmental qualification of this cable under 10 CFR 50.49, "Environmental Qualification of Electric Equipment Important to Safety for Nuclear Power Plants." On June 22, 2000, the NRC staff met with representatives of the Nuclear Energy Institute (NEI), the Okonite Company (Okonite), and licensees to discuss the BNL LOCA test (Test #5) results. The
industry noted that the BNL test, which duplicated the original Okonite qualification test, may have been conservative, and presented data from other documented EPR test reports to support this contention. These reports, according to the industry representative, show that EPR insulated cables consistently passed LOCA tests where the cables were preaged to a 40-year equivalent at 60 °C (140 °F). NEI has since issued a survey to licensees asking them to identify
any Okonite single conductor cables (conductor size 8 AWG and smaller) in 10 CFR 50.49 applications that may be exposed to average service conditions more severe than 60 °C (140 °F) and to provide the average temperature, service duration, and safety function supported by the cable. By letter dated July 14, 2000, Okonite informed the NRC staff that it will develop revised aging parameters that are based on the results of the NEI survey to requalify Okonite single-conductor cable. On October 12, 2000, NRC staff met with representatives of NEI and the Okonite Company to discuss NEI's preliminary survey results.
By letter dated November 9, 2000 (ADAMS accession number ML003769561), NEI transmitted to the NRC its report titled "NEI Survey Results on Okonite Okolon Single-Conductor Cables," dated November 1, 2000. The staff is considering further evaluations to validate the 60 °C (140 °F) threshold that was the focus of the survey questions. Based on the NEI survey, 30 of the 103 operating reactors use Okonite Okolon single-conductor cable in 10 CFR 50.49 applications. Four units have
the cable installed in environments that are 60 °C (140 °F) or greater, which may affect the service life of the cable. One unit has a 0.76 mm (30 mil) Jacket on the cable, which is thicker than that on the tested cable. One unit will replace the cable and another unit may replace it following an inspection in 2001. The fourth unit will determine a course of action following issuance of this RIS. In addressing this matter, the staff identified concerns regarding the comprehensiveness of the NEI survey request and the summary results. In particular, the Okonite cables that are routed in localized adverse environments (hot spots) at reactor facilities were not identified and the technical basis for the threshold temperature of 60 °C (140 °F ) used in the survey requires further evaluation. The staff plans to articulate its concerns in a letter to NEI following issuance of this RIS. The staff will determine whether further regulatory action is necessary after it has received the Okonite report on the subject cable. The basis for allowing continued operation of nuclear power plants pending the NRC's efforts to reach closure in this matter was addressed in an NRC memorandum from Brian W. Sheron to Samuel J. Collins, "Action Plan to Address Failures of Bonded-Jacket Okonite Single-Conductor Cables During Loss-of-Coolant-Accident Testing by the Office of Nuclear Regulatory Research," dated May 9, 2000 (ADAMS accession number ML003711726). In essence, continued operation of nuclear power plants is warranted while the staff, in conjunction with the industry, continues to evaluate the potential deficiency of the subject cables. This assessment is based on industry statements regarding the limited application of single conductor EPR/Hypalon
bonded-jacket cables in harsh environments and staff acknowledgment that most of these cables would not be in an operating environment as severe as that simulated during pre-test aging. In addition, the staff is not aware of any installed cables that yet experienced the same thermal and radiation aging that was used for the LOCA qualification test.
The generic implications of similar Okonite cable of different wire gage size, similar cable of other manufacturers, and similar multiconductor cable of all manufacturers are outside the scope of this RIS. They are, however, being considered in the resolution of GSI 168.

BACKFIT DISCUSSION
This RIS requests no action or written response. Consequently, the staff did not perform a backfit analysis.
FEDERAL REGISTER NOTIFICATION
A notice of opportunity for public comment was not published in the Federal Register because this RIS is informational.
PAPERWORK REDUCTION ACT STATEMENT
This RIS does not request any information collection. If there are any questions concerning this RIS, please contact the person listed below.
(ADAMS Accession Number ML003749767)

/RA/D. B. Matthews
David B. Matthews, Director
Division of Regulatory Improvement Programs
Office of Nuclear Reactor Regulation
Technical
contact:
Paul C. Shemanski, NRR
301-415-1377
E-Mail: pcs@nrc.gov
Attachment: List of Recently Issued NRC Regulatory Issue Summaries