ML17305A755
| ML17305A755 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 05/09/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17305A754 | List: |
| References | |
| GL-89-19, NUDOCS 9005150166 | |
| Download: ML17305A755 (6) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 ENCLOSURE SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION PALO VERDE NUCLEAR GENERATING STATION
RESPONSE
TO GENERIC LETTER 89-19 1.0 INRODUCTION By Generic Letter (GL) 89-19
, the NRC recommended that a system be provided to mitigate main feedwater overfill events for all boiling and pressurized water reactors (BWRs 5 PWRs) that currently do not have such protection.
This action was part of the technical resolution of Unresolved Safety Issue (USI) A-47, "Safety Implications of Control Systems in LWR Nuclear Power Plants."
Furthermore, it was reauested that all LWR plants have Technical Specifications that address the operability of the overfill protection systems that are provided in response to the Generic Letter on USI A-47.
2.0 DISCUSSION AND EVALUATION 2.1 Overfill protection for each LWR consists of protection channels that initiate the termination of main feedwater flow to the reactor vessel for a
BWR or to the steam generators for a
- PWR, on sensing a hioh water level condition.
The overfill protection mitigates the consequences of main feedwater control system failures as an event which could lead to overfill conditions, as well as limiting the operating water level to within the bounds of the assumptions used in the safety analysis.
Both functions fall within the scope of the criteria for determining the content of Technical Specifications as established by Pe Commission's Interim Policy Statement on Technical Specifications The action set forth by GL 89-19 on Technical Specifications for overfill protection is that license amendment requests be submitted that encompass requirements for limiting conditions for operation, setpoints, and surveillance requirements which are commensurate with the safety actions required by the existing Technical Specifications.
By letter dated January 22, 1990, APS provided a discussion of the existing automatic steam generator overfill protection scheme at Palo
- Verde, and a justification of how the system meets the main feedwater overfill protection objectives of the GL.
SYSTEM DESIGN Per the GL, an acceptable overfill protection system design is one which (a) is separate from the feedwater control system so that it is not powered from the same source, (b) is not located in the same cabinet as the feedwater control system, and (c) the cables are not routed so that a
fire is likely to affect both the feedwater control system and the overfill protection system siniultaneously.
Common-mode failures, however, that could disable overfill protection and the feedwater control system, but would still cause a feedwater pump trip, are considered acceptable failure modes.
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2.2 Palo Verde provides automatic steam generator overfill protection by initiating a reactor trip and main steam isolation signal (MSIS) on high steam generator level.
These functions are safety-related.
On an MSIS both the main steam isolation valves and the feedwater isolation valves close.
The high steam generator level has a setpoint of 91 percent of narrow range of steam generator level to initiate both a reactor trip and a MSIS actuation.
The trip and MSIS actuation operate on a two-out-of-four initiating logic.
The MSIS isolates the main feedwater from the steam generator by closing feedwater isolation valves when steam generator level reaches the setpoint.
The Palo Verde design achieves the same results as tripping the main feedwater pumps by isolating main feedwater to the steam generators on high level.
The Palo Verde reactor trip and MSIS functions are included in the Plant Protection System (PPS), which is separated from control systems.
A loss of power, loss of ventilation, or a fire in the feedwater control system (FWCS), will not affect the operation of the high steam generator level trip or the MSIS actuation.
The PPS is powered by class lE power and is electrically isolated and physically separated from the FWCS.
Based upon the above, we conclude that the existing automatic steam generator overfill protection design at Palo Verde is acceptable.
TECHNICAL SPECIFICATIONS 2.3 Palo Verde's existing Technical Specifications define requirements for the overfill protection system which the NRC has previously reviewed and found to be acceptable.
The reactor trip functions and main steam isolation signal actuation as related to high steam generator level are addressed by Technical Specification Sections 3/4.3.1, "Reactor Protective Instrumentation,"
and 3/4.3.2, "Engineered Safety Features Actuation System Instrumentation.
As such, the Palo Verde Technical Specifications do not need to be modified in order to meet the objectives of the GL, and are acceptable as is.
SMALL BREAK LOCA SCENARIOS APS stated that the discharge pressure of the high pressure injection pumps at Palo Verde are greater than 1275 psi.
Therefore, reassessment of emergency procedures and operator training programs to ensure operator's capability to handle the full spectrum of possible small-break loss of coolant accident scenarios is not required in accordance with GL 89-19, Item 4.c of Enclosure 2.
3.0 CONCLUSION
Based on the above, we conclude that the cur rent steam generator overfill protection design and associated Technical Specification requirements at Palo Verde satisfy the objectives of GL 89-19, and are therefore, acceptable.
PRINCIPAL CONTRIBUTOR:
T.
Chan Dated:
May 9, 1990
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REFERENCES 1.
U. S. Nuclear Regulatory Commission, Generic Letter 89-19, "Request for Action Related to Resolution of Unresolved Safety Issue A-47,
'Safety Implication of, Control Systems in LWR Nuclear Power Plants,'ursuant to 10 CFR 50.54," dated September 20, 1989.
2.
"Interim Policy Statement on Technical Specification Improvements for Nuclear Power Reactors,"
52 FR 3788, February 6, 1987.
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