ML16161A257
| ML16161A257 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 05/16/1997 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML16161A256 | List: |
| References | |
| NUDOCS 9705200380 | |
| Download: ML16161A257 (6) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20655-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 224 TO FACILITY OPERATING LICENSE DPR-38 AMENDMENT NO. 224 TO FACILITY.OPERATING LICENSE DPR-47 AND AMENDMENT NO. 221 TO FACILITY.OPERATING LICENSE DPR-55 DUKE POWER COMPANY OCONEE NUCLEAR STATION, UNITS 1. 2. AND 3 DOCKET NOS. 50-269, 50-270, AND 50-287
1.0 INTRODUCTION
By letter dated April 29, 1997, Duke Power Company (the licensee) submitted a request for changes to the Oconee Nuclear Station, Units 1, 2, and 3, Facility Operating Licenses. The requested changes would incorporate a license condition that will allow revisions to the Oconee Updated Final Safety Analysis Reportto clarify application of the main turbine-generated missile protection criteria to certain portions of the low pressure service water (LPSW) system.
The Oconee Updated Final Safety Analysis Report (UFSAR) currently specifies that all Engineered-Safeguards (ES) structures, systems and components be designed to withstand turbine-generated missiles using shielding or separation. However, the licensee has determined that certain portions of the LPSW system piping do not meet this design criterion if high trajectory turbine missiles are considered. As a result, the licensee considers this to be an Unreviewed Safety Question (USQ) and has submitted license amendments to clarify the USFAR.
To clarify this design criterion, the licensee has determined that additional design options should be provided, consistent with the turbine missile design guidance provided in Regulatory Guide 1.115, "Protection Against Low Trajectory Missiles," and NUREG-0800, "Standard Review Plan."
Revision I of Regulatory Guide 1.115 and Section 3.5.1.3 of NUREG-0800, Revision 2, provide design criteria that are consistent with current industry practice. Use of this methodology will also permit implementation of LPSW modifications as described in the licensee's letter dated December 28, 1995.
2.0 EVALUATION USFAR Section 3.1.40, "Missile Protection," and UFSAR Section 3.5.1.2, "Turbine Missiles," describe the turbine missile design criterion employed by the licensee. The former requires that the ES equipment be protected from missiles resulting from hypothesized plant equipment failure by means of 9705200380 970516 PDR ADOCK 05000269 P.
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-2 physical separation or shielding. It also-references UFSAR Section 3.5 for further details.
UFSAR Section 3.5.1.2 contains a description of the hypothesized turbine missiles at Oconee and focuses on their effects on impacting the Reactor Building. However, this section does not provide clear criteria for designing against damage of ES equipment located outside of the Reactor Building caused by high trajectory or low trajectory missiles generated by a major failure of one of the Oconee main turbine generators.
2.1 High Trajectory Turbine Missile Design UFSAR Section 3.1.40 desGribes design requirements for equipment-generated missiles and is interpreted by the licensee to require that ES equipment must be shielded or separated to protect against.h.igh trajectory turbine missiles.
As a result, the licensee has determined that the Units 1 and 2 main LPSW supply headers do not meet the implied design criteria because they are physically located directly beside each other in two locations. Also, as part of.an extensive Service Water System modification that is underway to install certain equipment, use of the current Oconee licensing basis criteria will require either shielding or separation for protection from high trajectory missiles.
In order to establish adequate separation for ES equipment to protect it against turbine missiles, a minimum separation of 7 feet is specified. This separation criterion is based on protection from missiles of various probable shapes and dimensions that may be produced from broken turbine/generator components. Based-on a review of the licensee's design memorandum, the staff finds this separation criterion to be reasonable and acceptable. The proposed change would add this criterion to UFSAR Section 3.5.1.2.
A proposed change to UFSAR Section 3.1.40 will reference Section 3.5.1.2 regarding the specific requirements for turbine missile design criteria. A new section will be added to Section 3.5.1.2 to describe how to implement the high trajectory turbine design criterion in accordance with that described in NUREG-0800, Revision 2, Section 3.5.1.3, Subsection III, Item No. 5. This guidance allows consideration of a vulnerable target area prior to requiring shielding or separation. The licensee's interpretation of the current Oconee licensing basis does not allow additional design options in the consideration of the probability of equipment being impacted by a high trajectory turbine missile.
High trajectory turbine missiles are characterized by their nearly vertical trajectories. Missiles that are ejected more than a few degrees from the vertical either have sufficient speed such that they land offsite, or their speeds are low enough that their impact on most plant structures is not a significant hazard. The proposed new high trajectory turbine missile design criterion would allow the licensee to use the option of evaluating whether or not a significant probability exists that a high trajectory turbine missile could impact a certain structure, system, or component (SSC). The proposed UFSAR change would adopt the NUREG-0800 guidance that allows the designer to waive shielding or separation requirements if the vulnerable target area (as
-3 viewed from the vertical) is less than 104 square feet, since the expected probability of a turbine missile strike is sufficiently low.
The portions of the LPSW and Service Water system piping that do not meet Oconee's current high trajectory turbine missile design have been evaluated under the new design criterion by the licensee. It has been determined that the vulnerable target area is less than 10' square feet for each item.
Therefore, shielding or separation would not be needed.
2.2 Low Trajectory Turbine Missile Design The UFSAR currently does not explicitly describe the requirements for low trajectory turbine missile design. However, UFSAR Section 3.1.40 describes equipment-generated missile protection design requirements and is interpreted to require that ES equipment be shielded or separated to protect against low trajectory turbine missiles. In addition, UFSAR Section 3.5.1.2 does not provide specific guidance for designing ES equipment outside the Reactor Building for low trajectory turbine missiles.
The existing ES equipment currently meets the design requirements for low trajectory turbine missiles because of shielding. Therefore, no USQ currently exists for low trajectory turbine missiles.
In order to clearly address low trajectory turbine missile design.criteria in the UFSAR, Section 3.1.40 will be revised to reference Section.3.5.1.2 and a new section will be added to Section 3.5.1.2 to describe how to implement the low trajectory turbine missile design criterion. This new section will implement a low trajectory turbine missile design criterion in accordance with that described in Regulatory Guide 1.115, 'Revision 1, dated July 1977, and NUREG-0800, Revision 2, Section 3.5.1.3, dated July 1981.
This guidance allows consideration of equipment locations relative to the likely missile strike zones and probability of a missile strike prior to requiring shielding or separation. It is the licensee's interpretation that other design options are not allowed when considering the location of equipment relative to the missile strike zones or probability of equipment being impacted by a low trajectory turbine missile.
2.3 Summary The licensee has proposed revisions to the Oconee UFSAR to clarify the turbine missile design licensing basis. The revisions will permit application of the turbine missile design criterion to allow exclusion of equipment for which a turbine missile strike is not probable. In addition, certain ES equipment may not be required to be shielded or separated for missile protection. Because this criterion is consistent with industry practice and with guidance provided by the staff, the staff finds use of the guidance to modify the design basis by incorporating it into the UFSAR acceptable.
This change will be incorporated into each Oconee license as a new license condition that authorizes changes to the UFSAR for Units 1, 2, and 3, as described in the licensee's submittal and this safety evaluation.
-4 The licensee is also clarifying UFSAR Section 3.1.40 to better defi ne the scope of equipment that is required to be protected against turbine missiles.
This section identifies engineered safety features as being the scope of equipment requiring turbine missile design. However, "engineered safety features" are defined in other UFSAR design criteria as "Engineered Safeguards Systems." Therefore, to establish consistency, engineered safety features are being defined as Engineered Safeguards Systems. This is consistent with the UFSAR Chapter 6 definition and does not change the licensee's interpretation of the Oconee UFSAR. Therefore, it is acceptable.
3.0 STATE CONSULTATION
In accordance with the Commission's regulations, the South Carolina State official was notified of the proposed issuance of the amendments. The State official had no comments.
4.0 EXIGENT CIRCUMSTANCES
Oconee Units 2 and 3 are currently in a forced outage for repairs on the high pressure injection system. It is the staff's position that a plant in a shutdown condition may not restart if a USQ exists. The USQ associated with high trajectory turbine missiles was self-identified within 2 weeks of the Unit 2 shutdown as a result of engineering design reviews associated with the Oconee Service Water Project that were underway. Prior to the forced shutdown, the licensee was aggressively developing proposed license amendments to resolve the issue, but had not completed the process and, therefore, could not have applied for the amendments sooner. Therefore, the issue was not resolved prior to the shutdown and must be resolved on an exigent basis so that it does not delay restart of Unit 2 or 3 once repairs to the high pressure injection system are completed. Units 2 and 3 are scheduled to be restarted before the expiration of the notice comment period.
The staff has reviewed the licensee's proposed amendments and finds (1),that exigent circumstances exist, as provided for in 10 CFR 50.91(a)(6),
in that the licensee and the Commission must act quickly and that time does not permit the Commission to publish a Federal Register notice allowing 30 days for prior public comment, and (2) that the licensee has not failed to use its best efforts to make a timely application and avoid creating the exigent circumstance. The Commission noticed the licensee's April 29, 1997, application for amendments in the Federal Register on May 5, 1997 (62 FR 24512), at which time the Commission made a proposed finding that the amendments involved no significant hazards condition and there has been no public comment in response to the notice.
5.0 CHANGE IN CIRCUMSTANCES When the notice was published in the Federal Register, the staff believed that startup of the Oconee units would not occur until the notice period had expired. Normally, the Commission will not issue the amendments until the expiration of the 14-day notice period. However, as stated in the Notice, should circumstances change during the notice period, such that failure to act in a timely way would result, for example, in derating or shutdown of the facility, the Commission may issue the license amendments before the expiration
-5 of the 14-day notice period, provided that its final determination is that the amendments involve no significant hazards consideration. The staff has learned that repairs that prompted the shutdown of Unit 2 have been completed on a more rapid pace than expected and that it will be ready to restart prior to the expiration of the notice period. Therefore, failure to approve the amendments in a more timely manner will unnecessarily delay restart of the unit.
6.0 FINAL NO SIGNIFICANT HAZARDS CONSIDERATION
DETERMINATION The Commission's regulations in 10 CFR 50.92 provide that the Commission may make a final determination that a license amendment involves no significant hazards considerations if operation of the facility in accordance with the amendment would not:
- 1.
Involve a significant increase in the probability or consequence of an accident previously evaluated[.]
...The proposed license amendment proposes the use of less restrictive guidance with respect to application of the turbine missile design criterion. Oconee's current licensing basis is to protect ES [Emergency Safeguards] equipment against turbine missiles by use of shielding or separation. The proposed changes to the Oconee licensing basis would allow Oconee to use NRC approved methodology, as described in Regulatory Guide 1.115, Revision 1 and NUREG-0800 Revision 2 (for low trajectory turbine missiles) and NUREG-0800 Revision 2 (for high trajectory turbine missiles) in evaluating the credibility and probability of a turbine missile strike on ES equipment prior to imposing a separation or shielding design requirement. If the probability is sufficiently low of a turbine missile strike, then shielding or separation would not be required. Therefore, the separation and shielding design requirements would only be waived on equipment which has a very low probability of being struck by a turbine missile.
Design to protect ES equipment against a turbine missile as described above is not an accident initiator. In addition, under this new license amendment, some ES equipment would be exempted from separation and shielding design.requirements for turbine missiles. The basis for this exemption is that the probability of this equipment being hit by a turbine missile is very low as evaluated through NRC approved methods.
Therefore, based on this analysis and the information presented in [of the licensee's submittal], the probability or consequences of an accident previously evaluated will not be significantly increased by the proposed change.
- 2.
Create the possibility of a new or different kind of accident from the accidents previously evaluated[.]
...Design to protect ES equipment against a turbine missile as described above is not an accident initiator.
-6 Therefore, based on this analysis and the~supporting information in Attachment 2, no new failure modes or credible accident scenarios are postulated.
- 3.
Involve a significant reduction in a margin of safety[.]
...Under this new license amendment, some ES equipment would be exempted from separation and shielding design requirements for turbine missiles. The basis for this exemption is that the probability of this equipment being hit by a turbine missile is very low as evaluated through NRC approved methods.
Therefore, based on this analysis and the supporting information in Attachment 2, the margin of safety is not significantly reduced as a result of this proposed amendment.
7.0 ENVIRONMENTAL CONSIDERATION
The amendments change requirements with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. The NRC staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has made a final finding that the amendments involve no significant hazards consideration. Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.
8.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor: David E. LaBarge Date:
May 16, 1997