ML20093A471
| ML20093A471 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 07/03/1984 |
| From: | Andrews R OMAHA PUBLIC POWER DISTRICT |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| LIC-84-207, NUDOCS 8407100543 | |
| Download: ML20093A471 (6) | |
Text
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i Omaha Public Power District 1623 Harney Omaha. Nebraska 68102 402/536 4000 July 3, 1984 L IC-84-207 Mr. Harold R. Denton, Director U. S. Nuclear Regulatory Commission Office of Nuclear Reactor Regulation Division of Licensing Operating Reactors Branch No. 3 Washington, D.C.
20555
Reference:
Docket No. 50-285 l
Dear Mr. Denton:
Environmental Qualification of Safety-Related Electrical Equipment at Fort Calhoun Station - Request for Extension The Omaha Public Power District, in April,1984, (Letter W. C. Jones to H. R.
Denton, dated 4/3/84) requested an exemption from the s:hedule requirements of 10 CFR 50.49.
This extension wa. requested to allow adequate time to complete qualification testing of the electrical penetration subassemblies.
By letter dated May 18, 1984, the District was granted an extension until September 30, 1984, for the qualification of these penetration assemblies.
l During the week of June 18, 1984, the District received preliminary test re-sults from the test laboratory which had been conducting environmental qual-ification testing on the electrical penetration assemblies.
The preliminary results were confinned and to eliminate uncertainty regarding the reportabil-ity of these findings, the District classified the incident as a "significant event" pursuant to 10 CFR 50.72 and made the appropriate 4-hour verbal notifi-cation. This notification was accomplished on June 22, 1984.
As a follow-up to that notification, on Monday, June 25, 1984, the District held a phone conversation with Mr. James R. Miller (Chief, ONRR) and Mr. E. G.
Tourigny (NRC Project Manager for Fort Calhoun) of your of fice to infom the NRC of the problem with the environmental qualification of this electrical equipment and the District's plans for resolution.
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Mr. Harold R. Denton July 3, 1984 Page Two The test results indicated that the failure occurred during the MSLB/LOCA profile test which includes the stress parameters of steam, pressure, and chemical spray. The District inspected the penetration assembly and deter-mined that the teflon insulation on the lead wires had become brittle and had cracked. Based upon this, the penetrations were unable to fulfill their elec-trical function. The failure appears to be due to an interaction between the steam / spray environment and the radiation-weakened lead wire insulation.
The District has concluded that the damage can only occur to the lead wire in-sulation after accumulation of high radiation doses and in the presence of a pressure / steam environment. We also believe that the only DBA for which these conditions will be present is a large Break LOCA accompanied by high radiation resulting from fuel damage. Because the failure mechanism is dependent upon the accumulation of a significant radiation dose, the insulation breakdown is not expected to occur at the onset of a design basis accident. However, some modification is necessary to ensure that the reactor could be maintained in a safe condition following such an event. Accordingly, a two phase approach to resolution of the problem is being pursued.
Phase I consists of modifying those penetrations which are required to ensure the ability to achieve long tem cot e cooling or to provide post-accident mon-itoring capability. These modifications are described in Attachment A.
These modifications either are completed or will be cmpleted prior to achieving Mode 2 as defined in the Fort Calhoun Technical Specifications. The remaining assemblies either do not accmplish a post-LBLOCA mitigation function, cm-plete their accident function prior to the accumulation of a large radiation dose, or can be controlled administrative 1y, as described in Attachment A.
The qualification of the remaining components will be completed in Phase II.
The completion of Phase II will require an extended outage. The District's next refueling outage is scheduled for the fall of 1985.
Therefore, pursuant to 10 CFR 50.49(h), the District respectfully requests an additional extension until November 30, 1985. Attachment B contains the District's revised justi-fication for continued operation until cmpletion of qualification of electri-cal equipment at Fort Calhoun Station can be accomplished.
Sinc rely,
/
/ hM' R. L. Andrews Division Manager Nuclear Production RLA/DJM/rh-B Attachments cc:
LeBoeuf, Lamb, Leiby & MacRae 1333 New Hamshire Avenue, N.W.
Washington, D.C.
20036 Mr. E. G. Tourigny, NRC Project Manager Mr. L. A. Yandell, Senior Resident Inspector
--mmumm-mm
Attachment A Technical Discussion of Environmental Qualification Testing of Electrical Penetrations The Fort Calhoun Station containment electrical penetration system provides a dual function of passing electric power into containment and instrument sig-nals out of containment via insulated conductors, and at the same time sealing the conductors to provide containment integrity (refer to USAR Section 5.9.3 for a description of the penetrations). This function is accomplished by the use of subassemblies which are inserted in a penetration canister. Each sub-assenbly is made up of a stainless steel tube (sheath) through which a lead wire, or wires (depending on the type) are run and see. led at both ends. The penetration system subassembly types are multiconductor low voltage (600 V),
single conductor low voltage, medium voltage (4160V), coaxial, triaxial, and thermocouple lead wires. The subassemblies under discussion are the multi-conductor low voltage (120V and 480V single and three phase power, A.C. con-trol, D.C. control, and instrumentation) and/or thermocouple configurations.
These particular multiconductor penetrations use FEP teflon as the lead wire insulation, and TFE teflon as the seal material in the subassembly.
Because the D0R Guidelines for electrical equipment qualification require the sequential testing of equipment containing materials which are susceptible to radiation damage, the District is conducting an environmental qualification test of the low voltage multiconductor penetration subassembly. The sequen-tial test procedure uses IEEE 317-1976 and IEEE 323-1974 as a guide.
Plant specific parameters are used to envelope the sequentially applied environ-mental stress parameters (aging, short circuit and short time overload, seis-mic, radiation, and MSLB/LOCA, short circuit).
The District was notified by the test laboratory that after irradiation was perfomed and during the initial MSLB/LOCA profile test (steam, pressure, chemical spray) an insulation breakdown had occurred. Af ter an inspection by the District and after an evaluation of the infomation resulting from that inspection, it was detemined that the teflon lead wire insulation had becane brittle and cracked.
It is the District's judgement, based on test evidence, that the penetrations failed to perfom their electrical function. The fail-ure appears to be an interaction of the steam / spray environment and the radi-ation weakened lead wire insulation. The penetration had in fact passed func-tjonal tests following radiation exposure, using the outboard (auxiliary build-ing side) seal as the pressure boundary.
It is the District's conclusion that damage to the lead wire insulation occurs only after accumulation of a high radiation dose and a pressure / steam environment.
It is also the District s judgement that this environment is present only during LBLOCA in which fuel damage occurs releasing fission products.
It should be noted that even in the case of a LBLOCA, all equipment is expected to complete its immediate accident function (e.g., reactor trip, safeguards initiation, etc.).
The District is taking a two phase approach to achieve qualification.
Phase I, as discussed in the following paragraphs, modifies selected electrical pen-etrations needed to accomplish long tem core cooling or accomplish post-acci-dent monitoring af ter a large Break LOCA (LBLOCA). Additionally, administra-tive control will be established for dealing with the assemblies not required
after a LBLOCA. These controls will be established prior to achieving Mode 2 as defined in the Fort Calhoun Station Technical Specifications.
Phase II will address and resolve the Electrical Equipment Qualification-related cir-cuits not modified in Phase I by the requested extension date of November 30, 1985.
Phase I The District will have upgraded all subassemblies associated with equipment which must be energized to accomplish long tenn core cooling or accomplish post-accident monitoring prior to Mode 2.
The balance of equipment which is Electrical Equipment Qualification (EEQ) related either does not accomplish a mitigation function in a LBLOCA (e.g., the Auxiliary Feedwater Systen), com-pletes its function before failure (e.g., reactor trip) or can be dealt with administratively. The modifications to the subassemblies are designed to en-sure electrical integrity and in doing so also ensure containment integrity.
The modifications-used a combination of qualified heat shrink tubing to sleeve the lead wires and qualified room temperature vulcanizing (RTV) silicone rub-ber to seal the heat shrink covered lead wire interface at the subassembly seal by sealing the area between the heat shrink and the stainless steel sheath. Both materials were designed for the purpose which the modifications require. The Raychem heat shrink tubing is qualified for a LOCA in Wyle Laboratories report number 58442-1, including electrical properties. The Dow Corning RTV is qualified by a combination of testing and District analysis.
The RTV seals and provides additional electrical insulation at the interface as discussed in Dow Corning Bulletin 61-016a. The RTV has been checked to insure bonding on the Raychem heat shrink tubing and stainless steel subassem-bly sheath. The teflon has been completely surrounded by the RTV or Raychem.
The District has also shortened the teflon insulated lead wires.
Administrative controls will be established prior to Mode 2 to provide dir-ection to operating personnel in the event it becomes necessary to assure proper positioning of pilot-solenoid air-operated valves following a LBLOCA.
An analysis of the failiure mechanism indicates the possibility for three instances where this administrative control would be required. The first possibility is that of shorting the solenoid lead wire with the position indication lead wire, causing the valve to change position.
Secondly, short-ing may cause the loss of position indication. Thirdly, shorting may cause the operator to receive misleading indication (e.g., the valve is indicated to be both open and closed at the same time). The administrative controls are procedural in nature and direct the operator to fail the instrument air supply to containment in the event undesired valve repositioning occurs, or mislead-ing infonnation is indicated. This allows the operator to achieve the desired valve position, regardless of indication.
Phase II The District will complete the environnental qualification of the renaining penetration assemblies by the requested extension date of November 30,,1985.
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Attachment B Justification for Continued Operation 10 CFR 50.49(i) provides guidance concerning those items which should be con-sidered in development of a justiff ation for continued operation until that time when equipment qualification can be established. The justification should include consideration of the following items:
(1)
Accomplishing the safety function by some designated alternative if the principal equipment has not been demonstrated to be fully qualified:
District's Position:
Those assemblies which must function following a DBA of the type expected to induce the failure (i.e., Large Break LOCA) have been modified to alle-viate this concern. Administrative controls will be established prior to achieving Mode 2 for a limited number of situations where the failure of electrical equipment has the potential for providing the operator with misleading information.
It is expected that solenoid-operated valves will fail in their accident positions.
For any indication to the con-trary, the operators are instructed to fail the instrument air to contain-ment, thus ensuring the valve is positioned in its desired position. The remaining EEQ-related assemblies will be qualified by the end of the next scheduled refueling outage.
(2)
The validity of partial test data in support of the original qualifica-tion:
District's Position:
Preliminary test data indicates that the failure was induced by stresses which would only be present as a result of a large Break LOCA (i.e., high radiation levels combined with a steam environment).
Equipment required to mitigate a LBLOCA has been modified. The remaining equipment can be justified for continued operation based upon the fact the failure mechan-ism is due to DBA conditions for which that equipment is not required.
Further, the Phase I modification utilizes qualified components and methods previously found acceptable.
(3)
Limited use of administrative controls over equipment that has not been demonstrated to be fully qua1171ed:
District's Position:
Administrative controls will be established prior to achieving Mode 2 for a limited number of situations where the failure of electrical equipment has the potential for providing the operator with misleading infonnation.
It is expected that solenoid-operated valves will fail in their accident positions.
For any indication to the contrary, the operators are in-structed to fail the instrument air to containment, thus ensuring the valve is positioned in its position.
~
Additionally, any electrical shorting between the solenoid-operated valve and its position indication is not expected to cause valve repositioning.
Circuit design is such that shorting would result in either loss of posi-tion indication or indication that the valve was simultaneously opened
and closed.
In either of these instances, procedures call for the oper-ator to fail instrument air to containment, thus ensuring that no valve repositioning takes place.
(4)
Completion of the safety function prior to exposure to the accident envi-ronnent resulting from a design basis event and ensuring that the subse-quent failure of the equipment does not degrade any safety function or afslead the operator:
District's Position:
Certain of the subassemblies could not be classified as completing their design function prior to exposure to the failure-inducing LBLOCA environ-ment. These subassemblies have been modifled as a part of Phase I.
The remaining assemblies (those assemblies who will complete their accident function prior to exposure to the failure-inducing enviroment or those whose accident function is not required after a LBLOCA - the only DBA expected to induce failure) can be justified for continued operation until qualification.
(5)
No significant degradation of any safety function or misleading informa-tion to the operator as a result of failure of equipment under the acct-dent environment resulting from a design basis event:
District's Position:
Phase I modified all subassemblies whose failure (post-LOCA) would ad-versely af fect a post-LBLOCA safety function. The remaining assemblies are justified for continued operation until qualified.
Additionally, administrative controls will be established prior to achieving Mode 2 to ensure that the operator is not misled by confusing i
information resulting from the failure of any of these subassemblies.
(See (3) above) l Based upon these five items, continued operation of the Fort Calhoun Station until the requested extension date of November 30, 1985, is justified.
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