ML17332A910
| ML17332A910 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 09/01/1995 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML17332A909 | List: |
| References | |
| NUDOCS 9509080301 | |
| Download: ML17332A910 (6) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON> D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.
>85 TO FACILITY OPERATING LICENSE NO.
DPR-74 INDIANA MICHIGAN POWER COMPANY DONALD C.
COOK NUCLEAR PLANT UNIT NO.
2 DOCKET NO. 50-316
1.0 INTRODUCTION
By letters dated February 15,
- 1994, and June 29, 1995, the Indiana Michigan Power Company (the licensee) requested an amendment to the Technical Specifications (TS) appended to Facility Operating License No.
DPR-74 for the Donald C.
Cook Nuclear Plant, Unit No. 2.
The proposed amendment would revise the TS by eliminating the requirements for the Turbine Overspeed Protection System.
Section 182a of the Atomic Energy Act (the "Act") requires that applicants for nuclear power plant operating licenses state TS to be included as part of the license.
The Commission's regulatory requirements related to the content of TS are set forth in 10 CFR 50.36.
That regulation requires that the TS 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.
However, the regulation does not specify the particular requirements to be included in a plant's TS.
The Commission has provided guidance for the contents of TS 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 TS to licensee-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 conditions or limitations upon reactor operation is deemed necessary to obviate the possibility of an abnormal situation or event giving rise to an immediate threat to the public health and safety."
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 TS, as follows:
(1) Installed instrumentation that is used to detect, and indicated in the control
- room, a significant abnormal 950908030i 95090i PDR'DQCK 050003ib
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degradation of the reactor coolant pressure boundary; (2) a process
- variable, design feature, or operating restriction that is an initial condition of a Design Basis Accident 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 operating experience or probabilistic safety assessment has shown to be significant to public health and safety.
As a result, existing TS requirements which fall within or satisfy any of the criteria in the Final Policy Statement must be retained in the TS, while those TS requirements which do not fall within or satisfy these criteria may be relocated to other, licensee-controlled documents.
- 2. 0 EVALUATION The turbine overspeed protection systems are designed to prevent damage to the turbine by terminating an overspeed transient.
Operation of the overspeed protection system is designed to minimize the potential for a turbine missile.
Loss of electrical load or malfunction of the control system can cause the turbine to overspeed.
The emergency overspeed protection systems operate to limit the maximum turbine speed under fault conditions.
Currently, Section 3/4.3.4 of the D. C.
Cook Unit 2 TS requires at least one turbine overspeed protection system to be operable.
The licensee has proposed the deletion of the turbine overspeed protection system specification based on other existing performance verification performed on the overspeed protection system.
The basis of TS 3/4.3.4, "Turbine Overspeed Protection" involves maintaining the turbine overspeed protection system to reduce the hazards of turbine missiles.
This function is discussed in Standard Review Plan Sections 3.5. 1.3 and 10.2.3.
The licensee provided an analysis in Section 14.1.13 of the Updated Safety Analysis Report (USAR) which deals with a safety analysis of the main turbine-generators and presents the results of the study of the consequences of a failure.
That analysis indicated that although large energetic fragments could be generated, the probability is extremely small.
The plant is designed to prevent a turbine missile from endangering the reactor and associated nuclear systems.
The Commission recently adopted amendments to 10 CFR 50.36, pursuant to which the rule was revised to codify and incorporate these criteria.
See Final Rule, "Technical Specifications,"
60 FR 36953 (July 19, 1995).
The Commission indicated that reactor core isolation cooling, isolation condenser, residual heat removal, standby liquid
- control, and recirculation pump Trip are included in the TS under Criterion 4, although it recognized that other structures, systems and components could also meet this criterion.
The D.
C.
Cook Unit 2 turbine is equipped with several turbine valves which control turbine speed and load during normal plant operations and protect it from overspeed during abnormal conditions.
These valves are the high pressure turbine control valves and main stop valves, and the low pressure turbine reheat stop valves and reheat intercept valves.
The turbine overspeed protection system consists of two independent mechanical sensing devices which are capable of initiating fast closure of the turbine valves through two independent trip circuits.
Each of these circuits are exercised weekly to verify their operability.
The D.
C.
Cook Unit 2 turbine has two independent mechanical overspeed trips, one set at 110X and the other at 112X of rated speed.
They are installed on a
stub shaft gear, driven by the main turbine shaft.
Each overspeed trip device has a spring-loaded bolt with its center of gravity eccentric to the axis of rotation.
If the turbine overspeeds, the centrifugal force on the bolt will cause it to extend past the edge of the rotating cylinder.
Once the bolt comes out of the cylinder it strikes a latch which opens a drain on the emergency circuit depressurizing it.
Each overspeed trip device operates through a separate channel to trip the turbine if its setpoint is reached.
When the emergency circuit is depressurized, all of the control, main stop, reheat
- stop, and reheat intercept valves are closed.
Each major steam line entering the turbine has two independent valves in series such that a failure of one in each steam line would not necessarily cause a turbine to overspeed.
Therefore, because of the redundancy and diversity of the overspeed protection
- systems, the possibility of an overspeed condition occurring which could potentially generate a turbine missile is extremely remote.
In addition to the turbine over speed
- system, the normal control system would act to limit any excessive increase in turbine speed and the acceleration limiter would act to limit any rapid increase in turbine speed.
Both of these systems use the control valves to adjust steam flow to the turbine and the acceleration limiter also uses the intercept valves.
The maintenance and test history of the control, main stop, reheat stop, and reheat intercept valves has been good with few instances of repairs required.
Host work has been related to items found during routine inspections and maintenance and did not affect valve operability.
The surveillance for the turbine overspeed protection on Unit 2 will be performed as a plant procedure as part of the Preventive Haintenance Program in accordance with operating experience at the Cook Nuclear Plant, applicable industry experience, and consideration of the turbine manufacturer's recommendations.
This is in accordance with the maintenance program requirements of 10 CFR 50.65.
This is also consistent with the actions for D.
C.
Cook Unit 1, which has never had TS requirements for the turbine overspeed system.
Changes to the plant procedure will receive a technical review in accordance with TS 6.5.3. 1 and will require an independent technical review by an individual qualified to appropriate standards.
The elimination of the TS requirement for overspeed protection will allow the licensee to perform testing and inspection of the system at frequencies based upon manufacturer's recommendations and operational experience or constraints.
4 This will allow an appropriate decrease in the weekly testing frequency which will reduce the challenges to plant equipment and personnel and by so doing, the potential of a plant transient is reduced and safety is enhanced.
Probabilistic safety assessments (PRA) and operating experience have demonstrated that proper maintenance of the turbine overspeed control valves
. is important to minimize the potential for overspeed events and turbine damage; however that experience has also demonstrated that there is low likelihood of significant risk to public health and safety because of turbi'ne overspeed events.
The Cook Nuclear Plant Individual Plant Examination of External Events examined the potential for turbine missile generation from normal operating conditions, and found the probability of turbine missile-induced core damage to be significantly less than the individual plant safety objective of 10 /year.
- Further, the potential for and consequences of turbine overspeed events are diminished by the licensee's inservice inspection
- program, which must comply with 10 CFR 50.55(a),
and a surveillance program for the turbine control and stop valves derived from the manufacturer's recommendations.
The NRC staff also notes that the proposed deletion of TS 3/4.3.4 would make the D.
C.
Cook Unit 2 TS consistent with the guidance provided in the NRC's Standard Technical Specifications, Westinghouse
- Plants, NUREG-1431, in that the NRC's Standard Technical Specifications do not include TS requiring the operability of a Turbine Overspeed Protection System.
Accordingly, the staff concluded that the requirements for turbine overspeed controls do not meet the TS criteria in the Final Policy Statement.
The limiting conditions for operation and surveillance requirements for turbine overspeed controls were removed from the Standard Technical Specifications.
On this basis, the staff concludes that these requirements are not required to be in the TS 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 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 above.
In addition, the NRC staff finds that sufficient regulatory controls exist under TS 6.5.3. 1 and 10 CFR 50.65 to ensure that future changes to these requirements are acceptable.
Accordingly, the staff has concluded that deletion of TS 3/4.3.4 and its associated Bases is acceptable.
3.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Michigan State official was notified of the proposed issuance of the amendments.
The State official had no comments.
- 4. 0 ENVIRONMENTAL CONSIDERATION The amendment changes a requirement with respect to the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and changes surveillance requirements.
The staff has determined that the amendment involves no significant increase in the amounts, and no
5 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 consideration and there has been no public comment on such finding (59 FR 14890).
The June 29, 1995 supplement provided additional supporting information for the request, did not change the scope of the request, and did not affect the no significant hazards consideration.
Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51 '2(b),
no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment
5.0 CONCLUSION
The staff 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:
John Hickman, NRR Date:
September 1,
1995
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