ML17258A012
| ML17258A012 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 09/26/2017 |
| From: | Eric Benner, John Lubinski Division of Engineering, Division of Operating Reactor Licensing |
| To: | |
| Johnston J | |
| References | |
| Download: ML17258A012 (15) | |
Text
Committee to Review Generic Requirements Meeting on Oconee Nuclear Station Cable Separation TIA September 26, 2017 John Lubinski Division of Engineering Eric Benner Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation
Agenda
- Background
- Key CRGR Questions
- Key Technical and Licensing Issues
- Path Forward
- Recommendation 2
Background
- CDBI at Oconee Nuclear Station (ONS) (7/27/2014) identified an unresolved item (URI) involving the licensing bases for cable configurations in recently installed underground raceways
- The URI questioned whether ONS appropriately considered electrical system design requirements and licensing basis when implementing this modification under 50.59.
- On October 16, 2014, Region II requested assistance from the Office of Nuclear Reactor Regulation (NRR) to provide answers to questions related to the URI in task interface agreement (TIA) 2014-05.
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Background
- On August 2, 2016, the draft TIA response was sent to Duke Power for a fact check and made publicly available.
- As a part of the fact check Duke Power indicated a number of disagreements with NRC interoperation of both technical issues and the ONS licensing basis
- Consistent with the recent CRGR recommendations to improve oversight in identifying potential backfitting issues, the proposed TIA response will be issued only after CRGR review 4
Background
Configuration prior to installing Configuration after installing cables in common trench cables in common trench Safety related 125V DC power/control cables and safety The licensee rerouted directly buried cables to trench # 3 related 120V AC ESPS cables directly buried in ground and Manhole 6 which included the following safety with adequate separation between the two trains related and non-safety related cables:
Adequately separation from power cables (4.16kV and Safety related cables:
13.8kV AC) such that a fault in one train would not
- 13.8 kVac Emergency power from KHU to Transformer adversely impact redundant trains (approximately 10 feet CT4 apart between redundant trains)
- 4.16 kVac CX Auxiliary Power from Transformer CT4 Separation between medium voltage and low voltage switchgear to KHU power/control cables such that a single failure would not - 125 Vdc supervisory cables A adversely impact redundant trains - 125 Vdc control and power cable for A and B trains Safety related 4.16kV and 13.8kV AC power cables Non-safety related cables:
directly buried with adequate separation -13.8 kVac PSW Power Cables from KHU to Transformer Both trains of ESPS A and B are interconnected at KHS CT6 and CT7 And ONS panels -13.8 kVac PSW Power Cables from Fant line Both trains of ESPS A and B are interconnected at KHS And ONS panels - configuration in panels did not change.
- The non-safety related 13.8 kVac PSW cables were not part of the original licensing basis 5
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Key CRGR Questions
- The TIA response:
- addresses site-specific licensing basis questions and applies only to ONS
- does not communicate a new requirement or staff position
- does not increase, reduce, or modify existing requirements or NRC staff positions
- is not a request for information
- is not a backfit
- TIA response will support RII office actions to close out existing Unresolved Items.
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Key Technical and Licensing Issues
- ONS licensing basis with respect to IEEE Std. 279
- Use of cable shielding vice cable armor
- Evaluation of timing of single failure is not limited to the event start time
- No distinction between passive and active electrical single failures
- Treatment of non-safety related cables in the ONS licensing basis 9
ONS licensing basis with respect to IEEE Std. 279
- NRC and ONS agree IEEE Std. 279-1968 is the licensing basis
- NRC and ONS agree, based on August 5, 1974 Duke letter (The Oconee ECCS actuation system conforms to the single failure requirements of IEEE 279-1971.) that the single failure requirements of IEEE Std. 279-1971 are the licensing basis.
- ONS believes Section 4.2, IEEE Std. 279-1971, is the only section that is part of the licensing basis
- NRC believes Sections 4.2, 4.7, 4.11, and 4.17, IEEE Std. 279-1971, are part of the licensing basis.
- Even if NRC agreed with ONS on the applicability of IEEE Std. 279-1971 (i.e., only Section 4.2), the conclusions in the TIA regarding single failure would be the same.
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Use of cable shielding vice cable armor
- Cable armor is a mechanically strong and flexible sheath which can be applied over a variety of cable cores to protect from failure of nearby cables
- ONS licensing basis allows the use of interlocked armor cable to provide mechanical protection
- Bronze tape is not equivalent to interlocked armor cable and cannot be credited to prevent consequential damage to nearby cables
- Cable shielding of an electric power cable is the practice of confining the electric field of the cable to preclude excessive voltage stress on voids between conductor and insulation
- Neither interlocked armor cable nor bronze tape provides cable shielding 11
Evaluation of timing of single failure is not limited to the event start time
- ONS licensing basis includes the single failure requirements of IEEE Std. 279-1971 and it does not allow restricting the timing of when single failures may occur.
- Postulating the single failure immediately on demand of a component to function, the licensee failed to establish the most limiting single failure that could occur, as required 12
No distinction between passive and active electrical single failures
- The basic design criterion for the electrical portion of the emergency electric power system of a nuclear unit, including the generating sources, distribution system, and controls is that a single failure of any component, passive or active, will not preclude the system from supplying emergency power when required.
- NRCs position on the definition of single failure and how single failure was evaluated during the licensing of plants was discussed in SECY-77-439
- Single Failure Criterion to systems evaluation depends not only on the initiating event that invokes safety action of these systems, together with consequential failures, but also on active or passive electrical failures, which can occur independent of the event 13
Treatment of non-safety related cables in the ONS licensing basis
- Only safety related or Class 1E designated components are credited to mitigate design basis events. The single failure criteria requirements of IEEE Std. 279-1971 apply to Class 1E
- The non-safety related power cables in Trench #3 and Manhole
- 6 are not credited in the ONS licensing basis for mitigating design basis events
- However, the license must account for the impacts of worst-case credible failures of non-safety equipment on Class 1E circuits as required by IEEE Std. 279-1968 (Section X)
- In addition the interconnected nature of the Class 1E DC systems in the ONS KHU start panels and the Keowee hydro-station KHU start panels present vulnerabilities where DC to DC interactions could disable the Keowee emergency power systems 14
Path Forward
- Duke may request a public meeting with CRGR to present their perspectives
- Region II will conduct exit meeting (addressing URI) with licensee and, as appropriate, will communicate apparent violations to Duke Energy.
- Region II will evaluate Oconees operability determinations for the affected systems and equipment
- Region II will disposition the findings in accordance with IMC 0612, conduct appropriate follow-up inspections
- The process would allow Duke an opportunity to dispute any violations, including providing any claims of backfitting.
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