ML16134A621
| ML16134A621 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 12/06/1978 |
| From: | Reid R Office of Nuclear Reactor Regulation |
| To: | Parker W DUKE POWER CO. |
| References | |
| NUDOCS 7901160372 | |
| Download: ML16134A621 (9) | |
Text
NR REG 4UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 December 6, 1978 Dockets Nos.:
50-29 50-270 and Mr. William 0. Parker, Jr.
Vice President - Steam Production Duke Power Company P. 0. Box 2178 422 South Church Street Charlotte, North Carolina 28242
Dear Mr. Parker:
By letter dated February 1, 1978, and as supplemented June 19, 1978, Duke Power Company submitted a proposed program for a Safe Shutdown System for the Oconee Nuclear Station. The system will augment existing station capabilities relative to the Fire Protection Program, the Modified Amended Security Plan and Turbine Building flooding.
We have found the conceptual design of the system to be acceptable.
Our review is presented in the enclosed Concept Evaluation. NRC approval of the final design is required before you make any modifications which affect existing safety related structures or systems. Credit cannot be assumed for the effect of the completed modifications on the fire protection, security and flooding consid erations until our final acceptance of the modifications. We request that you identify and justify those portions of the final design not meeting NUREG 75/087. Kindly submit the final design within 15 months of date of this letter.
Sincerely, Robert W. Reid, Chief
/
Operating Reactors Branch #4 Division of Operating Reactors
Enclosure:
Concept Evaluation cc w/enclosures:
See next p ge 11Z oI
Duke Power Company cc:
Mr. William L. Porter Duke Power Company Post Office Box 2178 422 South Church Street Charlotte, North Carolina 28242 J. Michael McGarry, III, Esquire DeBevoise & Liberman 700 Shoreham Building 806 15th Street, N.W.
Washington, D. C.
20005 U. S. Nuclear Regulatory Commission Region II Office of Inspection and Enforcement ATTN:
Mr. Francis Jape 101 arietta Street, Suite 3100 Atlanta, Georgia 30303 Mr. Robert B. Borsum Babcock & Wilcox Nuclear Power Generation Division Suite 420, 7735 Old Georgetown Road Bethesda, Maryland 20014 Oconee Public Library 201 South Spring Street Walhalla, South Carolina 29691
OCONEE NUCLEAR STATION SAFE SHUTDOWN SYSTEM CONCEPT EVALUATION INTRODUCTION The Oconee Nuclear Station is currently being reviewed by the NRC in connection with fire protection, physical security (10 CFR 73.55) and flooding of the turbine building basement. The fire protection and flooding reviews deal with the capability to saiely shut down the plant if vital systems were disabled. The physical security review deals with the definition of vital areas under the rule:
the number of vital areas can be reduced when the standby shutdown system is in operation.
The Safe Shutdown System (SSS), proposed by the licensee will pro vide an alternate and independent means to achieve and maintain a hot shutdown condition for all three Oconee Nuclear Station units. This system is in addition to and independent of the current shutdown capability described in the Oconee FSAR. The SSS will be designed to maintain hot shutdown in all units for a period of approximately three and one-half days. All components of the system and the associated structure necessary to maintain hot shutdown will be designed to withstand a safe shutdown earthquake. The SSS design will serve to resolve the common safe shutdown requirement for fire protection, physical security, and flooding.
DISCUSSION The conceptual design of the SSS has progressed sufficiently to evaluate the feasibility of the design concept.
This evaluation covers our review of the proposed functional aspects of the SSS which will be used to supply adequate primary and secondary system coolant for the removal of decay heat. The planned capability of the SSS is to maintain hot shutdown conditions in all units for approximately three and one-half days following loss of normal power to the reactor coolant pumps (emergency conditions).
-2 EVALUATION Critical Plant Functions An analysis was made by the licensee to determine the plant requirements which must be met to provide adequate cooling.
These critical plant requirements are summarized as follows:
- 1. A certain minimum water level must be maintained above the reactor core.
- 2. The primary coolant system must be maintained filled to a sufficient level in the pressurizer to assure natural convection and core cooling. The steam generators must have sufficient secondary side cooling water available.
- 3. Decay heat from the fuel must be transferred to an ultimate heat sink, through one or more available heat transfer systems.
- 4. The available shutdown margin must be maintained at greater than 1% Ak/k with the highest worth control rod assumed to be fully withdrawn.
We have reviewed the conceptual design of the SSS and its potential to meet the above critical functions. Based on the information provided by the licensee, and on our review, we have concluded that the conceptual design can perform these functions. The planned locations of the vital equipment included in the SSS design and the location of a structure entitled the Safe Shutdown Facility (SSF) are provided in References 1, 2, and 3.
System Concept The licensee has stated the the Oconee Reactor Coolant System can rely on primary side natural circulation to remove core decay heat in the event of a loss of normal station power. Following loss of normal power to the reactor coolant pumps, the control rods scram, the pumps coastdown, and the core heat generation due to decay heat decreases with time.
The licensee has also calculated the minimum and maximum expected natural circulation flow as a function of time after loss of power and compared these values to natural circulation flow tests performed on Oconee Unit 1. The measured data and the calculated values of natural circulation flow demonstrate that the core heat can be adequately removed by natural circulation flow. Based on the above, we concur with the licensee's conclusions on the natural circulation capabilities of the Oconee Reactor Coolant
-3 System.
However, long-term cooling at hot standby conditions will be dependent on the water inventory available to the feedwater system. Where there is a limited volume of high-quality water available because the high-quality feedwater will be soon spent by steam release to the atomosphere via the steam generator pressure relief or dump valves, the introduction of poorer quality water could lead to premature degradation of the steam generator and a reduction in heat transfer capabilities and natural circulation flow. Therefore, the licensee should give consideration to this condition in his final design and assess any potential consequences in his final design submittal.
This system would be used only in the most extreme emergency.
Emergency Makeup System The Emergency Makeup System (EMS) is a portion of the proposed shutdown system. The purpose of the EMS is to supply makeup to the Reactor Coolant System (RCS) should the need arise during emergency conditions. Makeup will be added to recover the decrease in the Reactor Coolant System volume that results from going from a hot power operation condition to a hot shutdown condition and to recover normal system leakage. The EMS will use the Spent Fuel Pool as a source of makeup water for the RCS should the need arise such that the normal makeup system is not available.
However, to ensure that the final design will perform as intended, the licensee must include additional information, and engineering evaluations as described in the appropriate sections of NUREG 75/087.
In particular, the licensee must show that the makeup system will provide adequate coolant volume to maintain a sufficient level in the pressurizer to assure natural circulation under the most conser vative conditions. The licensee's final designs should also provide information on the plants design capabilities to transfer to, and to maintain, a cold shutdown mode following implementation of the SSS hot shutdown operations.
Out-leakage from the RCP seals will be routed to and stored in the fuel transfer canal and an emergency makeup pump will be installed to take suction from this stored water. This will allow recirculation of the makeup water; thereby reducing the quantity of water that must be stored and reduces the quantity of water removed from the spent fuel pool.
The shrinkage of the reactor coolant volume should eliminate the need to let down from the RCS while going to the hot shutdown condition, and minimize the possibility of a solid system. Backup protection is provided by existing code relief valves to protect the RCS from over pressurization.
All active components in the EMS will be tested both in performance tests in the manufacturer's shop and through inplace testing after installation. Initial system flow tests will be performed to demonstrate proper dynamic functioning of the system. Means will be included in the design to allow testing of the components under hot shutdown conditions.
-4 Based on our review of the information provided in References 1, 2, and 3, we find the EMS concept acceptable for the removal of decay heat.
High Head Auxiliary Service Water System The High Head Auxiliary Service Water System (HHASW) provides an alternate means of supplying feedwater in the event both the normal and emergency feedwater systems are unavailable. The purpose of the HHASW is to cool the Reactor Coolant System (RCS) and to achieve and maintain a hot shutdown condition for all Oconee units for an extended period of time. Suction for the HHASW pump will be taken from the CCW piping. This source of water will always assure an adequate supply of cooling water.
All active components in the HHASW System will be tested in the manufacturer's shop. Since only the most extreme emergency would require operation of this subsystem, a complete inplace functional test of this system will not be done because it is unacceptable to pump river water into the steam generators, except under these emergency conditions. The motor operated valves will be tested for their ability to function and the pump will be tested in place using an installed test loop.
This test loop will have a manual valve to adjust the back pressure on the pump to simulate pumping through the actual lines to the steam generators.
System Design Criteria The system design criteria proposed by the licensee for the SSS are as follows:
- 1. The Safe Shutdown System will be designed to meet or exceed the applicable criteria contained in the Oconee FSAR including provisions for inservice inspection set forth in the ASME Code Section XI for Class 2 components.
Additionally, the appropriate ASME Codes, based on Reg. Guide 1.26 and applicable IEEE Codes will be utilized in the design of various sybsystems and components. Part of this system (RC Emergency Makeup) will be under Quality Group B and will be designed in accordance with ASME Code Section III Class 2.
The High Head Auxiliary Service Water System has a portion (crossover between emergency feedwater lines) in each reactor building that will be under Quality Group B and designed to
ASME Code Section III Class 2. The remainder of tKe High Head Auxiliary Service Water System will be under Quality Group C and will be designed in accordance with ASME Code Section III Class 3 since this is an auxiliary feedwater system. The SSF has a small cooling water system for the HVAC and diesel generator. This system, with the exception of the diesel generator and HVAC components, will also be under Quality Group C and will be designed in accordance with ASME Section III Class 3.
- 2. The Safe Shutdown Facility foundation walls will be waterproofed by standard waterproofing techniques to an elevation slightly above yard grade to prevent inflow of yard surface waters. Flooding sources from within the structure will be limited to normal equipment drainage which will be handled by installation of a sump.and sump pump. The sump pump will discharge to the yard drain system.
The sump pump discharge line will be designed to prevent back flow into the sump from outside sources.
- 3. The Safe Shutdown Facility Structure and associated components the Safe Shutdown System will be designed to withstand the Safe Shutdown Earthquake.
- 4. The system will be designed such that failures.in the system do not cause failures or inadvertent operations in existing plant systems.
- 5. Major components of the Safe Shutdown System will be located in a separate structure independent of fire damage in existing plant areas. Cabling for the Safe Shutdown System will not be located in areas containing existing safety system equipment or cabling, with the exception of electrical penetration area and inside containment. In the electrical penetration area, a three-hour fire wall will be provided between existing safety system cabling and Safe Shutdown System cabling. Inside containment, maximum possible separation will be maintained between existing safety system cabling and Safe Shutdown System cabling so that fires in containment will not cause loss of both existing cabling and Safe Shutdown System cabling.
With the exception of meeting the single failure criterion, DPC proposes to implement a design criteria that meets or exceeds-the design criteria for the existing Oconee units. Since the SSS is planned as a standby system which backs up existing redundant safety systems, the proposed system serves to add an extra dimension to the "Defense-in-Depth" protection to the public; thus application of the single failure criterion is not required. We find the criteria acceptable, subject to the following conditions:
a) DPC stated in their June 19, 1978 submittal that they would selectively apply portions of NUREG 75/087 to their design.
We have requested that the licensee identify and justify those portions of the design not meeting NUREG 75/087.
b) Any deviations from the above listed four criteria, and/or the criteria specified in the Oconee FSAR, and/or the criteria described in NUREG 75/087, shall be identified by the licensee
-6 and submitted for NRC review in the final design submittal.
CONCLUSIONS The conceptual design of the SSS will result in a final design that will provide a dedicated independent shutdown system if the licensee designs it to the above mentioned criteria and follows the NRC conditions appended to the criteria. The conceptual design, as conditioned above, will meet the Fire Protection Program requirements of the NRC August 11, 1978 License Amendment, provide relief from the requirements of the Modified Amended Security Program in regard to designation of vital areas and provide adequate protection against flooding of vital systems in the Turbine Room basement by providing alternate shutdown capability. We conclude the conceptual design is acceptable.
0 0
-7 References
- 1. Presentation of Conceptual Safe Shutdown System by Duke Power Company to NRC, dated January 18, 1978.
- 2. Letter, W. 0. Parker (DPC) to E. G. Case (NRC), dated February 1, 1978.
- 3. Letter, W. 0. Parker (DPC) to E. G. Case (NRC), dated June 19, 1978.