ML20207J864

Suppls 860211 Response to IE Info Notice 86-003, Potential Deficiencies in Environ Qualification of Limitorque Motor Valve Operator Wiring, Per NRC 860206 & 07 Onsite Audit & Insp & IE Bulletin 79-01B

ML20207J864
Person / Time
Site:	Prairie Island
Issue date:	02/21/1986
From:	Larson C NORTHERN STATES POWER CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
IEB-79-01B, IEB-79-1B, IEIN-84-44, IEIN-86-003, IEIN-86-3, NUDOCS 8607290276
Download: ML20207J864 (13)

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Northern States Power Company 414 Nicollet Mall Minneapohs. Minnesota 55401 Telephone (612) 330 5500 February 21, 1986 Mr J G Keppler Regional Administrator-Region III US Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, Illinois 60137 PRAlRIE ISLAND NUCLEAR GENERATING PLANT DOCKET NOS. 50-282 LICENSE NOS. DPR-42 50-306 DPR-60 Information Related to IE Information Notice 86-03, Potential Deficiencies in Environmental Qualification of Limitorque Motor Valve Operator Wiring The purpose of this letter is to supplement our letter of February 11, 1986 and provide assurance to your office that we have placed a high priority on resolution of this issue and that plant operation may safely continue until all environmental qualification concerns with Limitorque valves are resolved.

On February 6 s.nd 7, 1986 the Nuclear Regulatory Commission (NRC) Region III inspectors performed an on-site audit and inspection af the qualifica-tion status of internal wiring installed in Limitorque motor operated valve actuators at the Prairie Island Nuclear Generating Plant (PINGP).

The audit resulted from recent industry knowledge concerning potential uncertainties on the part of the equipment vendor, Limitorque, as to the specific wiring installed during the equipment manufacturing process.

In addition, some nuclear utilities were uncertain about the type of field wiring used during installation and subsequent maintenance activities.

We have actively and aggressively pursued the environnental qualification of Limitorque motor operated valve actuators, including internal wiring, since the issuance of NRC IE Bulletin 79-01B. Considerable effort has been expended over the years in correspondence with Limitorque concerning all aspects of their environmental qualification program and in evaluation of Limitorque qualification test reports. We have responded to each industry issue raised concerning Limitorque environmental qualifica-tion status promptly and in good faith.

8607290276 860221 PDR ADOCK 05000282 G PDR , j;

- I FEB 2 41986 /'

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1.0 INTRODUCTION

This document supplements our February 11,.1986 letter to the NRC and f- summarizes the status of Limitorque internal' wiring qualification at the PlNGP, discusses the operability requirements of safety-related motor operated valve actuators on the PINGP 10CFR50.49 environmental qualifica-tion masterlist, and provides a plan for all corrective actions that have been defined. The discussion provided in this document combined with the support documentation available at the PINGP provides adequate assurance

, that the safety of the general public will not be compromised until all corrective actions have been completed.

The PINGP Operations Committee has formally reviewed this document'and concurs with the conclusions contained herein.

, 2.0 ENVIRONMENTAL QUALIFICATION BASIS FOR LIMITORQUE INTERNAL WIRING 2.1 Overview

. -Prior to November 30, 1985,- all available documentation provided by Limitorque showed that the internal wiring was one of the following:

1. Rockbestos Firewall III

2. Raychem Flamtrol

! 3. Polyvinyl Chloride (PVC) 1 Correspondance with Limitorque provided assurance that these wires were qualified as part of the environmental qualification test programs described in Limitorque-test reports 600376A,'600456, B0009 B0003, and 600198.'Thus, environmental qualification evalua-tions for the PINGP r? cognized the existence of Limitorque supplied internal w1 ring and judged qualification to be demonstrated based on Limitorque testing..

4 In addition to Limitorque provided internal wiring, there is frequently a need to perform wiring additions or modifications during the

, installation process. These modifications were often performed on an as-needed basis using standard electrical construction practices.

At the PINGP, the standard practice'for field wiring of Limitorque i

motor operated valve actuators was to use either Rockbestos SIS

? (Firewall III) wiring or conductors stripped from multi-conductor control wiring. Qualification of this field wiring was evaluated 4 and documented with the set of electrical cables used throughout the plant.

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Page 3 In early October 1985, Commonwealth Edison issued a 10CFR21 report relating to internal wiring of Limitorque motor operated valve actuators for the Zion Generating Plant. Word of this issue spread through the environmental qualification industry and the PINGP took actions to review the existing qualification basis for the internal wiring.

This included review of walkdown sheets obtained during normal valve maintenance over the past year. NRC IE Information Notice NO. 86-03 '

was issued on January 14, 1986 and formally notified the PINGP of the status of potential Limitorque internal wiring qualification deficiencies.

IE Information Notice No. 86-03 was coupled with information obtained from other nuclear utilities and industry environmental qualification groups to form a data base from which the PINGP could reevaluate the qualification basis for Limitorque internal wiring. This is discussed in detail below.

2.2 Wiring Installed in Limitorque Motor Operated Valve Actuators at the PINGP The following wires are installed as internal wiring in Limitorque motor operated valvo actuators at the PINGP:

2.2.1 Rockbestos Type SIS 600V UL 2.2.2 Rockbestos Type SIS Nuclear 2.2.3 Raychem Flamtrol 2.2.4 GE Vulkene SIS UL INS 2.2.5 GE XHHW SI 58053 2.2.6 Kynar Insulated Wire 2.2.7 600V TFF 2.2.8 600V TW o Items 2.2.1 and 2.2.2 are both of the chemically crosslinked Firewall III formelation. Qualification of this cable has been a generic open item throughout the utility indastry. Rockbestos has recently completed qualification testing and results are under review by the NRC and NRC contractors.

Testing has been performed by other utilities and utility groups that is available to document environmental qualification. This testing documented the successful completion of post-LOCA performance tests after being subjected to thermal aging to simulate 40 years life, radiation exposure to 2.86 E08 rads gamma, and LOCA condition of 360*F and 50 psig. This testing envelopes the postulated accident conditions at the PINGP. No anomalies affecting qualification to the PINGP environments was reported.

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Page 4 The qualification documentation of Rockbestos cables was stated in the audit exit meeting to be an unresolved item pending resolution

/ of NRC IE Information Notice 84-44. The PINGP believes that adequate evidence exists in the testing noted above to support continued operation of the plant without compromising the safety of the general public until this issue is resolved.

1 o Item 2.2.3 has been tested and documentation was reviewed on-site that supports the environmental qualification. There were no unresolved or open items during the audit relating to the qualifica-tion of this cable.

o Items 2.2.4 and 2.2.5 are both manufactured with General Electric (GE) Vulkene insulation. Vulkene is a GE name for chemically cross-linked polyethylene. This wire was originally believed to only be associated with the motor (used as a motor lead) and environmen-tally qualified with the motor. As a pr'ecaution, a separate qualification documentation package was prepared that demonstrated full qualification for the Prairie Island environments. There were ne unresolved or open items during the audit relating to the quali-fication of this cable.

o item 2.2.6 is a Kynar insulated wire. Kynar is produced by the Penwalt Corporation and is the commercial name for polyvinylidene fluoride. Kynar insulated cable has been tested as reported in Conax Corporation's Test Report No. IPS-585, " Coaxial Feedthrough Subassemblies". This cable was subjected to thermal aging at 305* F for 102 hours0.00118 days <br />0.0283 hours <br />1.686508e-4 weeks <br />3.8811e-5 months <br /> with no visible degradation. The cable was then exposed to a total lutegrated dose of 1.1 E08 rads gamma. Again there was no visible degradation of the insulation. The cable was then placed inside a steam chamber to simulate the effects of a design basis accident. Peak temperatures exceeding 400* F. pressure in excess of 70 psig, and 100% relative humidity were achieved simultaneously. The duration of the test was 312 hours0.00361 days <br />0.0867 hours <br />5.15873e-4 weeks <br />1.18716e-4 months <br /> at temperatures above 300* F. The cable functioned throughout the test and was found to be in acceptable condition as determined by dielectric and insulation tests in post DBA functional testing. It should be pointed out that this DBA simulation envelopes the PINGP containment LOCA accident thermalhydraulic conditions. In addition, the duration of the postulated accident is also enveloped by the test. The maximum postulated radiation dose for inside contain-ment is 4.81 E07 rads gamma (one year TID). This requirement is enveloped by this test which irradiated the wire 1.1 E08 rads gamma as described above. The qualified life of Kynar has been determined to be in excess of 40 years using the Arrhenius equation. Therefore, since all the postulated accident conditions for inside containment .

are enveloped by this test, the Kynar insulated wire is qualified for use in Limitorque motor operated valve actuators.

Page 5 o Items 2.2.7 and 2.2.8 are both Polyvinyl Chloride (PVC) wires.

These wires had qualification documentation prepared utilizing type testing and materials testing information that was available in i

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various industry publications. There was an unresolved. item in the audit concerning applicability.of. qualification documentation. The

, PINGP has committed to inspecting and replacing ell PVC insulated ,

I- wires in Limitorque motor operated valve. actuators (see NSP letter

_ dated February 11, 1986). In Unit 1, this inspection and replacement will take place during the 1986 refueling outage now' scheduled to begin on March 5, 1986. In Unit 2, the inspection and replacement will be completed during the next scheduled cold shutdown lasting 10 days or more. The latest.this work will be completed will be during the 1986 refueling outage now scheduled to begin on October 22, 1986.

The primary concern raised in the audit was the similarity of the installed PVC wiring to the tested wiring. Specifically,,the concern was that the formulations of the PVC in the tested and installed specimens were not identical and, therefore, the qualification documentation may be inadequate. We believe that this level of-detailed examination is beyond the requirements of the. DOR Guidelines and is not consistent with direction given by the NRC in previous years for DOR Guideline qualifications, nor with general industry

practice.

The objective of the D0R Guideline was to give licensees guidance and direction in evaluating the environmental qualification of equipment to provide reasonable assurance of qualification. Appendix

. C of the DOR Guidelines provides a partial list of materials commonly used in nuclear power plant applications. A review of this listing shows materials specified in terms of their base compound, e.g., nylon, Buna-N, Silicone Rubber, etc. It is our opinion that this provides a reflection as to the level of detail of materials identification and evaluation required to satisfy the requirements of-the D0R Guidelines. There has never been a requirement stated to perform qualification to the D0R Guidelines to the level of detail l where specific compound formulatic.ns of cable insulation, gaskets, 0-rings, etc. are evaluated for similarity to the tested compounds.

The focus of qualification questions on the PVC centered around the

! radiation qualification of the wire and potential for degradation.

The basis for concern is that potential degradation of the PVC wiring could occur when wires were exposed to the one-year Total Integrated Dose (TlD) of 4.81 E07 Rads gamma at the containment 1

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Page 6 centerline. Table 1 has been developed since the audit and provides further clarification of the expected TID based on equipment operating time and location. This review has categorized the valves into the following groups:

1. Radiation exposure is not a requirement for valves not required to be repositioned. This includes ten (10) valves per unit.

2. Radiation exposure is less than IE04 Rads for valves required to realign for recirculation mode and valves that operate on a safety injection signal and are located in the Auxiliary Building. This includes twenty-one (21) valves per unit.

3. Radiation exposure of 3 x 10 Rads for valves located in the Reactor Building and required to operate on a safety injection signal. This includes five (5) valves per unit.

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4. Radiation exposure of 8 x 10 Rads for valves opened to provide additional safety injection flow to the reactor vessel. This includes two (2) valves per unit.

5. Radiation exposures greater than 8 x 10 Rads for valves required for longer term operation. All valve operators in this category were recently re-placed (1984 and 1985) and do not contain PVC wiring.

This includes seven (7) valves per unit.

The PINGP qualification review to the D0R Guidelines has documented qualification levels to TID's as high as 5E07 Rads gamma. However, there are several generally accepted industry references available to show qualification well above the 8E05 Rad level. Some are itemized below:

EPRI NP-2129 " Radiation Effects In Organic Materials in Nuclear Power Plants," Nov. 1981 o 80% retention of elongation @ IE07 Rads o 80% retention of elongation @ 7E07 Rads EPRI NP-1558 "A Review of Equipment Aging Theory and Technology," Sept. 1980 o Incipient to Mild damage @ IE07 Rads o Mild to Moderate damage @ 8E07 Rads s e, ,_ . - . _ ~ , _ , . _ . _ _ ., -

Page 7 CERN 79-04 (European Organization for Nuclear Research)

" Compilation of Radiation Damage and Test Data, Part 1: Cable Insulating Materials,"

June 1979 o Not recommended for use as cable insula-tion at greater than IE08 Rads CERN 70-5 (European Organization for Nuclear Research)

" Effects of Radiation on Materials and Components" Feb. 1970 o Incipient to Mild damage @ IE07 Rads o Mild to Moderate damage @ 8E07 Rads REIC Report (Radiation Effects Information Center)

No. 46 "The Effects of Radiation on Electrical Insulating Materials" June 1969 o Incipient to Mild damage @ 1E07 Rads o Mild to Moderate damage 8E07 Rads It is also important to understand the failure mode of cable insula-tion in a high radiation environment. Most test data available suggests that embrittlement (reduction of elasticity) is the principal effect of high radiation exposure. Once embrittled, the insulation may crack under stress that could expose the metal conductor leading to a short if touched to other wire or metal, or if exposed to a high degree of moisture. Some mechanical stress must be present to induce insulation cracking once it has become embrittled. The installation of wiring internal to Limitorque motor operated valve actuators is installed in a relatively stress free condition. There is no mechanical operation or function of the internal wiring during valve actuation. Once installed, the internal wiring is not moved.

Experience of other nuclear plants shows that embrittled cables still perform their required function if installed in a mechanical stress free environment. It's not until the cable is pulled during the replacement process that the insulation actually cracks or falls off the cable. The logical conclusion of this discussion is that even if the internal wiring does become embrittled, it will likely perform its function because there is no induction of mechanical stress to actually cause insulation cracking.

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Page 8 3.0 LIMITORQUE VALVE OPERABILITY REQUIREMENTS Table 1 provides a summary of the Limitorque motor operated valve actuators on the PINGP environmental qualification masterlist. The summary provides the following information:

o Valve ID

-o Function o Installed Location o Operating Requirements including required radiation dose at valve operating time The purpose of developing this summary is to review the potential for failure of an operator due to PVC wiring failure and, assumirg failure occurs, the impact of that failure on plant safety.

From a review of Table 1, it can be seen that with the exception of two (2) valves per unit, all motor operated valve actuators fall into one or more of the following categories:

i o Valves are already in their safeguards position and do not require operation, o Valve location and operating requirements are such that the TID is less than 3E04 Rads, o Valve operators-were recently-replaced with new operators that do not contain PVC wiring, o Valves have redundant valves in non-harsh environments.

s Therefore, the only concern from an operability standpoint assuming internal wiring failure is the Safety Injection to the Reactor Vessel valves (32067, 32069, 32170, 32172). The TID at the valve operating time

! is 8E05 Rads. Assuming wiring failure leading to valve operator failure, the valves can be operated from the motor control center which is located in a non-harsh environment. The Operational Support Center (OSC) is manned by personnel familiar with this method of valve operation and the personnel are available for this activity.

This valve operability summary provides the conclusion that the ability to shut down the plant and the safety of the general public will not be compromised in the unlikely event of valve failure due to PVC wiring failure.

4.0 CONCLUSION

This discussion has provided an overview of the present status of wiring installed in Limitorque motor operated valve actuators at the PINGP.

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The use of PVC wiring has been the focus of the NRC audit and has, therefore, been highlighted in the discussion provided herein. The.

• PINCP corrective action plan-has committed to replacing all PVC wiring g installed in Limitorque valve actuators during the next extended outage (March 1986 for Unit 1 and noc later than October 1986 for Unit 2). We ,

-believe the operation of the plant until the next outage to replace this.

wiring poses no threat to the ability of the plant to safely shutdown following a postulated accident, and to the safety of the general'public

for the following reasons

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1. Adequate documentation exists to provide reasonable assuranceLof environmental qualification of the PVC i . wiring when evaluated against the requirements of the DOR Guidelines.

2. There is a very small probability that failure of the

PVC wiring will lead to failure of.the valve actuator

.at the conditions expected during a postulated accident, should they occur.

3. In the unlikely event of wiring failure. leading to failure of the valve actuator, there is sufficient

! redundancy in system design, or available and existing methods to operate the non-redundanc valves from Motor Control Centers-located in non-harsh environ-

{ ments.

Please contact us if you have any questions related to the supplemental informa-tion we have provided.

l O d M* n= ~-

) C E Larson Vice President NLulear Generation c: Director of NRC (Attn: G E Lear)

.NPR Project Manager, NRC Resident Inspector, NRC G Charnoff 1

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e TABLE 1 OPERATING REQUIREMENT FUNCTIONAL EVALUATION UNIT 1 2 ID ID FUNCTION LOCATION OPERATING REQUIREMENT 32016 32019 Main Steam to Stm Driven Aux These are new operators purchased in 1984 32017 32020 AFW Pump Aux and qualified to Limitorque Report No.

600376A. Internal wire is not PVC.

32023 32028 FW to Stm Gen Isolation Aux Valves closa automatically on SI actuation 32024 32029 Aux and will complete their safety functions prior to significant exposure to harsh environment. The valves are not required to operate thereafter and subsequent failure will not mislead plant operators or adversely affect safety related equipment.

Radiation exgosure including background is less than 10 Rads. Redundant function is provided by FW Reg valve closure, FW pmp trip and FW pap discharge valve closure.

32040 32046 .Stm Gen Blowdown Rx Valves close automatically on SI actuation 32043 32049 Isolation Rx and will complete their safety functions 32044 32051 Aux ' prior to significant exposure to harsh 32058 32059 Aux environment. The valves are not required to operate thereafter and subsequent 32166 32194 Cntant Isolation Excess Aux failure will not mislead plant operators or 32199 32210 Letdown Line Rx adversely. affect safety related equipment.

Redundant train valves are not exposed to harsh environment. Radiation exposuge including background is less than 10 Rads for motor operators located in the Aux 4

Building and 3 x 10 Rads for operators located in the Rx Building.

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UNIT 1 1 2 l ID ID FUNCTION LOCATION OPERATING REQUIREMENT 1

1 32064 32167 RHR to Rx Val Rx Valves open automatically on SI actuation 32065 32168 Rx and will complete their safety functions j prior to significant exposure to harsh j environment. The valves are not required j to operate thereafter and. subsequent failure 4

will not mislead plant operators or adversely affect safety related equipment. Radiagion i exposure including background is 3 x 10 Rads.

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32067 32170 SI to the RX Vs1 Rx These valves are opened following a LOCA to

} 32069 32172 Rx provide additional SI flow to the vessel to j prevent boron precipitation. Radiatignex-posure including background is 8 x 10 Rads.

In the event the valves cannot be operated due to wire failure, sufficient time is available to operate them from the motor

! control center by Onsite Emergency

, Operational Support Personnel.

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32071 32174 Accumulator to Cold Rx These valves are normally open. In the 32072 32175 Leg Isol Rx event of a small break LOCA in which

! primary system pressure remains in the i neighborhood of 1000 psia it is desir-

. -able to close these valves and isolate l the accumulator to achieve cold shutdown.

Radiation exgosure including background is

. less than 10 Rads. . Subsequent failure

will not mislead plant operators or affect

{ safety related equipment.

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UNIT 1 2 ID ID FUNCTION LOCATION OPERATING REQUIREMENT 32073 32176 SI to Cold Leg Ann Valves are in safeguards position and not required to change position during an accident. Failure will not mislead plant operators or affect safety related equipment.

32074 32177 SI to Ex Vsl Ann Valves are in safeguards position and not required to change position during an Req accident. Failure will not mislead plant operators or affect safety related equipment.

32132 32147 Fan Coil Unit Cooling Rx Valves are in safeguards position and not 32135 32150 Water Return Rx required to change position during an 32138 32153 accident. Failure will not mislead plant 32141 32156 operators or affect safety related equipment.

32195 32197 Przr Pwr Op Isolation Rx These are new operators purchased in 32196 32198 Vlv Rx 1984 and qualified to Limitorque Report No. 600456. Internal wire is not PVC.

32271 32290 Post-LOCA Hydrogen Rx These valves are in their required position 32273 32292 Control Vent Isol Rx and are not required to operate thereafter.

32274 32293 Ann The primary method of hydrogen removal is 32276 32295 Ann internal electric recombiners (two trains).

These valves could also be used for supple-mental sampling during post LOCA operation.

In that event radiation levels to the con 5 tainment operators will not exceed 8 x 10 Rads, and they may be operated from the motor control center in the event of wire failure.

Failure will not mislead plant operators or adversely affect safety related equipment.

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i UNIT

) 1 2 ID ID FUNCTION LOCATION OPERATING REQUIREMENT 32075 32178 Reactor Sump B to RHR Rx The only harsh environment at these motor 32076 32179 Pmp Suction Rx operators is radiation which does not exist 32077 32180 Aux until the operators have been positioned for 32078 32181 Aux ECCS recirculation. Total radiation exposure, i including background and shine from contain-4 32084 32187 RWST to RHR Pmp Aux ment is less than 10 Rads. Following 32085 32188 Aux alignment for ECCS recirculation mode these valves are not required to operate. Subse-

32096 32108 Cntant Spray Pmp Suct Aux quent failure will not mislead plant operators 32097 32109 From RHR Hx Aux or adversely affect safety related equipment.

32103 32114 Cntmt Spray Pmp Disch Aux 32105 32116 Isol Aux 32162 32190 SI Pmp Suct Isol Aux 32163 32191 Aux 32206 32208 RHR to SI Pmp Aux 32207 32209 Aux i 32400 32406 Pressurizer Liquid, Rx These are new operators purchased in 32402 32408 Steam Space and RC Hot Rx 1985 and qualified to Limitorque

! 32404 32410 Leg Sample Rx Report No. 600456. Internal wire is i not PVC.

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