ML20081D713
| ML20081D713 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 03/15/1995 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20081D701 | List: |
| References | |
| NUDOCS 9503200373 | |
| Download: ML20081D713 (6) | |
Text
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'e UNITED STATES
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.,E NUCLEAR REGULATORY COMMISSION o
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SAFETY EVALUATION BY.IHE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 77 TO FACILITY OPERATING LICENSE NO. NPF-47 t
ENTERGY OPERATIONS. INC.
RIVER BEND STATION. UNIT I DOCKET NO. 50-458
1.0 INTRODUCTION
By application dated March 15, 1994, Entergy Operations, Inc. (the licensee) requested changes to the Technical Specifications (Appendix A to Facility Operating License No. NPF-47) for the River Bend Station, Unit 1 (RBS). The proposed changes would delete Technical Specification (TS) 3/4.3.8, " Turbine Overspeed Protection System." Surveillance test requirements for the turbine overspeed protection system based on the manufacture's recommendations would be contained in the RBS technical requirements manual (TRM).
Section 182a of the Atomic Energy Act (the "Act") requires that applicants for nuclear power plant operation licenses state TSs and that these TSs be included as a part of the license. The Commission's regulatory requirements related to the content of TSs are set forth in 10 CFR 50.36. That regulation requires that the TSs include items in five specific categories, including (1) safety limits, limiting safety system settings, and limiting control settings; (2) limiting conditions for operation; (3) surveillance requirements; (4) design features; and (5) administrative controls.
It states also that the Commission may include such additional TSs as it finds to be appropriate.
However, the regulation does not specify the particular TSs to be' included in a plant's license.
l The Commission has provided guidance for the contents of TSs in its " Final Policy Statement on Technical Specifications Improvements for Nuclear Power Reactors" (" Final Policy Statement"), 58 FR 39132 (July 22,1993), in which the Commission indicated that compliance with the Final Policy Statement satisfies Section 182a of the Act.
In particular, the Commission indicated that certain items could be relocated from the TSs to licensea-controlled documents, consistent with the standard enunciated in Portland General Electric Co. (Trojan Nuclear Plant, ALAB-531, 9 NRC 263, 273 (1979).
In that case, the Atomic Safety and Licensing Appeal Board indicated that " technical specifications are to be reserved for those matters as to which the imposition of rigid confitions or limitations upon reactor operation is deemed necessary to obviate the possibility of an abnormal situation or event giving rise to an l
immediate threat to the public health and safety."
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I Consistent with this approach, the Final Policy Statement identified four criteria to be used in determining whether a particular matter is required to be included in the TSs, as follows:
(1) installed instrumentation that is used to detect, and indicate in the control room, a significant abnormal degradation of the reactor coolant pressure boundary; (2) a process variabic, design feature, or operation restriction that is an initial condition of a.
design basis acci.ient or transient analysis that either assumes the failure of or presents a challenge to the integrity of a fission product barrier; (3) a structure, system, or component that is part of the primary success path and which functions or actuates to mitigate a design basis accident or transient that either assumes the failure of or presents a challenge to the integrity of a fission product barrier; (4) a structure, system, or component which operatingexperienceorprobabilisticsa[etyassessmenthasshowntobe significant to pubile health and safety.
As a result, existing limiting condition for operation (LCO) requirements which fall within or satisfy any of the criteria in the Final Policy Statement must be retained in the TSs, while those LCO requirements which do not fall within or satisfy these criteria may be relocated to other, licensee-controlled documents.
2.0 EVALUATION The RBS turbine is equipped with several valves which control turbine speed during normal plant operations and protect it from overspeed during abnormal conditions. These valves are the high pressure turbine control' valves, the high pressure turbine stop valves, the low pressure turbine intermediate stop valves, and the low pressure turbine intercept valves. The turbine overspeed protection system consists of separate mechanical and electrical sensing mechanisms which are capable of initiating fast closure of the steam valves.
The mechanical and electrical overspeed control systems, trip criteria, and iie valve operation and closure times are described in Section 10.2.2 of the Rt i Updated Safety Analysis Report (USAR).
TS 3/4.3.8 requires at least one Turbine Overspeed Protection System to be OPERABLE in OPERATIONAL CONDITIONS I and 2 and provides surveillance requirements for periodic testing and inspection of the turbine steam valves.
The surveillance requirements include weekly cycling of each of the valves through at least one complete cycle. Cycling of the valves introduces the potential for causing plant transients which can be detrimental to plant safety.
' The Commission recently promulgated a proposed change to 10 CFR 50.36, pursuant to which the rule would be amended to codify and incorporate these criteria (59 FR 48180, September 20,1994). The Commission's Final Policy Statement specified that the Reactor Core Isolation Cooling, Isolation Condenser, Residual Heat Removal, Standby Liquid Control, and Recirculation Pump Trip are included in the TSs under Criterion 4 (5B FR 39132, July 22, 1993).
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a L_ty ri 7 I, In its submittal of March 15,1994',.the licensee proposed that TS J/4.3.8 and its associated Bases be deleted. - The proposed change would also relocate the survelliance requirements to the RBS TRM. The relocated surveillance requirements would be-based on the manufacturer's recommendations and-operational experience' Surveillance testing in accordance with the -
manufacturer's r3 commendations will permit RBS to' optimize testing and inspection' frequencies.such that unnecessary testing and inspections.will be
' reduced.' Reduction of unnecessary testing and inspections will assist in reducing plant transients and may thereby enhance safety.
To date, the maintenance and test histories of the turbine steam valves have been good. The problems experienced with these valves to date have been minor and of a nature. expected with valves in this type of service. - There have been no failures of a kind which would have affected its capacity to operate or its ability to prevent an overspeed condition.
The purpose of overspeed protection is to minimize the possible generation of turbine fragment. missiles. -The licensee has proposed the deletion of the turbine overspeed protection system specification based on the low probability of the generation of a damaging turbine missile and other existing performance verifications performed on the.overspeed protection system.
A favorable terbine orientation exists at RBS. The center of the reactor-building is on a line extended through the longest axis of the turbine generator; this orientation minimizes the possible impact of a turbine fragment on safety-related equipment.
Section 3.5.1.3 of the River Bend USAR provides an analysis of the nrobability of turbine missile damage ~ to safety-related components. This analysis considered turbine placement and orientation and the potential generation of low-trajectory and high-trajectory missiles. The probability of turbine missile damage was based on the probabilities of missile generation, of a missile striking a critical-plant region, and of a missile strike damaging its target in a manner leading to unacceptable consequences. The probability of damage to safety-related equipment based pn General Elect
- ic (GE) turbine failure data was calculated to be 1.05 x 10' per year and, based on failure data, was calculated to 7.5 x 10'juREG-0800 (Standard Review Plan) per year.
i The probability results based ca the turbine panufacturer's data is less than the NRC. acceptable risk rate of less than 10' per year for tue loss of an essential system from a single unit. The probability results based on the-NRC's data slightly exceeds the acceptable risk rate. However, the NUREG-08W, Section 2.2.3, provides for an acceptable risk rate of 4
approximately 10 per year provided that, when combined with reasonable qualitative arguments, the realistic probability can be shown to be lower. A discussion of these arguments and the conservatism of the NRC's data is-provided in USAR Section 3.5.1.3.4.4 A summary of these arguments is as follows:
a.
The overall ric estimate included low-trajectory missiles os well as high-trajectory missiles and included missiles from design overspeed failures as well as destructive overspeed failures.
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b.
The turbinc failure rate of 10 per turbine year used in the NRC model was derived from observed turbine failures prior to 1956. Since that time, with improvements in turbine design, preservice and inservice inspections, quality cot. trol, and the use of materials of higher freeture toughness, the turbine failure rate is expected to be significantly less i
than the 10*' per turbine year value suggested by the NRC.
The entire front surfaces and roof areas of all buildings containing the c.
essential systems, rather than the actual areas occupied by the essential systems, were used in the NRC model.
d.
The NRC model assumed every missile penetrated the concrete wall or roof, strikes an essential system and results in unacceptable damage.
Therefore, the realistic probability of turbine missile damage is acceptably low. The transient due to the actuation of the turbine stop valves (in response to a turbine overspeed event) should also be considered.
For this event, the closure of the turbine stop valves initiates the design basis transient (in this case load rejection) and not the turbine overspeed itself.
The overspeed protection system does not perform a subsequent function to l
mitigate the effects of the transient.
The NRC statf also notes that the proposed deletion of TS 3/4.3.8 would make the RBS TSs consistent with the guidance provicied in the NRC's Standard Technical Specifications, General Electric Plants, BWR/6 (NUREG-1434) in that the NRC's Standard Tevinical Specifications do not include TSs requiring the operability of a turbine overspeed protection system.
The licensee has proposed changes to TS 3/4.3.8 to remove the requirements related to the operability of the turbine overspeed controls, and related surveillance requirements.
In the amendment application, the licensee committed to include the surveillance program into a licensee controlled i
document; the RBS TRM. The TRti was established for the purpose of relocating TS requirements which are identified through various line item improvements.
As proposed in a letter dated January 14, 1954, for LAR 91-11 (RBG-39894), the information being relocated to the TRM is controlled and subsequent changes will be reviewed in accordance with the change control program described in Specification 6.5.2.
The turbine is equipped with control valves and stop valves which control turbine speed during normal plant operation and protect it from overspeed during abnormsl conditions.
The turbine overspeed protection system consists i
of separate si.echanical and electrical sensing mechanisms which are capable of initiating fast closure of the steaa valves. Currently, TS 3/4.3.8 requires particular operability and surveillance requirements for these steam control and stop valves to minimize the potential for fragment missiles that might be generated as the result of a turbine overspeed event.
The licensee has proposed to relocate these provisions to the TRM such that future changes to
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'the operation and surveillance of the turbine overspeed features can be l
reviewed in accordance with.the change control program described in i
- Specification 6.5.2.
.Although the. design basis accidents and transients include a variety of system failures and conditions.which might result from turbine missiles striking various. plant systems and equipment, system failures and plant conditions..
could be caused by other events as well as turbine failures.. In view of the low likelihood of turbine missiles this scenario does not constitute a part of 1
the primary success path to-prevent or mitigate such design basis accidents and transients.
Similarly, the turbine overspeed control is not part of an i
initial condition of a design basis accident or transient that'either assumes 1
the failure of or presents a challenge to the integrity of a. fission product 1
barrier.
Probabilistic safety assessments (PRA) and operatir.g experience have U
demonstrated that proper maintenance of the turbine overspeed control valves
'is important to minimize the potential for overspeed events and turbine 1
damage; however,.that experience has also demonstrated that there is low likelihood of significant risk to public health and. safety because of turbine overspeed events.
Further,'the potential for and consequences of turbine j!
overspeed events i e diminished by the favorable orientation of the turbine, relative t0 the likely path of any turbine missiles, and the licensee's 1
inservice inspection program, which must comply with 10 CFR 50.55(a), and a l
surveillance program for the turbine control and stop valves derived from the manufacturers recommendations, i
Accordingly, the staff concluded that the requirements for turbine overspeed' l
controls do not meet the TS criteria'in the Final Policy Statement. The
-i limiting conditions for operation and surveillance requirements for turbine overspeed controls were removed from the standard TSs.
On this basis, the staff concludes that these requirements are not required to be in the TSs under 10 CFR 50.36 or Section 182a of the Atomic Energy Act, and are'not required in order to~ provide adequate protection to the health and i
safety of the public. Further, they do not fall within any of the four' criteria set forth in the Commission's Final Policy Statement, discussed i
above.
In addition, the NRC staff finds that sufficient regulatory controls j
exist under the provisions of Section 6.5.2 of the facility operating license to ensure that future changes to these requirements are acceptable.
Accordingly, the staff has concluded that these requirements may be relocated from the Tis to the TRM.
The NRC staff has no objection to the deletion of.the Bases associated with i
TS 3/3.3.8. This change is administrative in nature and supports the proposed changes.
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3.0 STATE CONSULTATION
In'accordance with the Commission's regulations,'the Louisiana State Official was notified of the proposed issuance of the amendment. The State official had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
b The amendment changes a requirteent with respect to installation or use of a.
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facility component locat?d within the restricted area as defined in 10 CFR Part 20 and changes sur,9111ance requirements. The NRC staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluent that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure.
The Commission has previously issued a proposed finding that the amendment involves no significant hazards i
consideration, and there has been no public comment on such finding (59 FR 27056). Accordingly, the amendment meets 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 amendment.
5.0 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 amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
Edward Baker, NRR David L. Wigginton, NRR k
Date: March 15,1995 5
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