ML20214F564
| ML20214F564 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 05/18/1987 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20214F558 | List: |
| References | |
| NUDOCS 8705260151 | |
| Download: ML20214F564 (6) | |
Text
__
'o UMTED STATES
~
8" o
NUCLEAR REGULATORY COMMISSION g
.E WASHINGTON, D. C. 20555
\\...+/
SAFETY EVALUATION ON CLINTON POWER STATION E
COMPLIANCE WITH ATW5 RULE - 10 CFR 50.62 DOCKET NO. 50-461
1.0 INTRODUCTION
On July 26, 1984, the Code of Federal Regulation-(CFR) was amended to include Section 10 CFR 50.62, " Requirements for Reduction of Risk from Anticipated Transients Without Scram (ATWS) Events for Light-Water-Cooled Nuclear Power Plants" (known as the "ATWS Rule"). An ATWS is an expected operational transient (such as loss of feedwater, loss of condenser vacuum, or loss of offsite power) which is accompanied by a failure of the reactor trip system (RTS) to shutdown the reactor. The ATWS Rule requires specific improvements in the design and operation of commercial nuclear power facilities to reduce the likelihood of failure to shutdown the reactor following anticipated transients, and to mitigate the consequences of an ATWS event.
For each boiling water reactor, three systems are required to mitigate the consequences of an ATWS event.
1.
It must have an alternate rod injection (ARI) system that is diverse (from the reactor trip system) from sensor output to the final actuation devices. The ARI system must have redundant scram air header exhaust valves. The ARI must be designed to perform its function in a reliable manner and be independent (from the existing reactor trip system) from sensor output to the final actuation device. By letters dated October 16, 1985 and March 5, 1987, Illinois Power Company provided information to address the Clinton Power Station (CPS) implementation of the ARI system. The staff's evaluation is addressed in this SER.
2.
It must have a standby liquid control system (SLCS) with a minimum flow capacity and boron content equivalent in control capacity to 86 gallons per minute of 13 weight percent sodium pentaborate solution.
The SLCS and its injection location must be designed to perform its function in a reliable manner. The staff's evaluation on the-Clinton's SLCS was addressed in the Safety Evaluation Report Supplement Number 7 dated September 1986. The staff has concluded that the applicant's proposed design for the SLCS is acceptable.
3.
It must have equipment to trip the reactor coolant recirculating pumps automatically under conditions indicative of an ATWS. This equipment must be designed to perform its function in a reliable manner. The staff's evaluation on the Clinton's recirculating pump trip (RPT) system was addressed in the Safety Evaluation Report Supplement Number 6 dated July, 1986. The staff has concluded that the RPT design is acceptable.
8705260151 870518 PD ADOCK 05000461 Wr PDR
1 2.0 ARI SYSTEM REVIEW CRITERIA i
The systems and equipment required by 10 CFR 50.62 do not have;to meet all of.the stringent requirements normally_ applied to' safety-relat9d equipment.
'However,' this equipment is part of the broader class of structures, systems, and components.important to safety defined in the introduction to 10 CFR, Appendix A, General Design Criteria (GDC). GDC-1 requires that ~ _
" structures, systems, and components important to safety shall be designed, fabricated, erected, and tested to quality standards'~ commensurate with the -
importance of the safety functions to be performed." Generic Letter-85-06
" Quality Assurance Guidance for ATWS Equipment.that is not Safety Related" details the quality _ assurance that must be applied to this equipment.
In general, the equipment to be installed in accordance with the ATWS Rule is. required to be' diverse from the existing RTS, and must be testable at power. This equipment is intended to provide needed diversity (where only minimal diversity currently exists in the RTS) to reduce the potential 4
for common mode failures that could result in an ATWS leading to unacceptable plant conditions..
The criteria used in evaluating the licensee's submittal include 10 CFR 50.62 " Rule Considerations Regarding Systems and Equipment Criteria" published in Federal Register Volume 49, No. 124 dated June 26, 1984-and Generic Letter 85-06 " Quality Assurance Guidance for ATWS Equipment that is not Safety Related."
n 3.0 CLINTON ARI SYSTEM DESCRIPTION i
Clinton Power Station has an ARI system which is;non-safety related. The ARI system provides an alternate means of venting the scram air headers 3'
by opening the redundant scram valves. The ARI function is initiated manually, or automatically by either Reactor Pressure Vessel (RPV) high i
pressure or RPV low water level. The ARI design consists ofitwo
. independent subsystem. Each subsystem consists of two RPV low level channels arranged in a two-out-of-two energize-to-actuate configuration in parallel with two RPV high pressure channels also arranged in a two-out-of-two energize-to-actuate configuration.
-l The ARI logic for each subsystem is designed to perform the following _
l three functions:
(1) activate two scram pilot' air header solenoid operated vent valves (one per header) to exhaust the air from the pilot scram air header, (2) block the instrument air supply line to the pilot -
scram valves, and (3) exhaust air from the air header to the scram discharge volume vent and drain valves.
Each solenoid valve is furnished
- l with two 125 Vdc solenoid coils and both coils must be energized to open the valve. The ARI function for each subsystem is capable of being i
c - -,. --,
~. -
. manually initiated from the main control room. The operator ha5 to arm the system by rotating the collar and depressing both pushbutton switches to initiate the ARI function.
Indicting lights on this panel 'mform the operator of the system status including all the solenoid valveP open and close position indications.
The automatic and manual actuation signals to the ARI solenoid valves seal-in for a minimum of two minutes to allow that all control rods have time to fully insert.
The ARI system sensors are separated and diverse from reactor protection system sensors. Cables from these sensors are routed separately to the ATWS panels which are located in the TMI/ isolator panel room in the control building.
Provisions for testing the system control logic and valve solenoid coil continuity is provided at these panels. During testing, a signal is injected into the trip units for either two reactor pressure signals or two reactor level signals to simulate a trip condition.
Relay contacts that energize the solenoid valves and the activating relays are checked and then returned to normal.
Indicating lights show the ARI systems are in test.
Two separate and independent non-safety related 125 Vdc power sources are provided for the transmitters, control logic and solenoid coils. The system shall remain functional following an ATWS event including loss of offsite power.
4.0 EVALUATION OF ARI SYSTEM 4.1 SAFETYRELATEDREQUIREMENTS(IEEESTANDARD-279)
The ATWS Rule does not require the ARI system to be safety grade, but the implementation must be such that the existing protection system continues to meet all applicable safety related criteria. The Clinton ARI system is classified as a non-safety related system which does not conform to all the requirements of IEEE Standard-279. However, the ARI system uses separate sensors, logic circuitries, cabinets, and scram valves. There is no direct interface between the ARI system and the existing protection system. Therefore, the implementation of the ARI system allows the existing protection system to continue to meet all applicable safety related criteria. The staff finds this acceptable.
4.2 REDUNDANCY The ATWS Rule requires that the ARI system must have redundant scram air header exhaust valves, but the ARI system itself does not need to be redundant. The Clinton ARI system has redundant scram air header exhaust valves. The design includes two ARI subsystems. A two-out-of-two logic for each subsystem is initiated by either RPV high pressure or RPV low water level. Each solenoid valve is furnished with two 125 Vdc solenoid coils. The preoperational test results verified that the ARI system function time will begin within 15 seconds and be completed within 25 seconds from ARI initiation. The staff finds this acceptable.
. 4.3 DIVERSITY FROM EXISTING REACTOR TRIP SYSTEM (RTS)
E The ATWS Rule requires that the ARI system should be diverse fiom the existing reactor trip system. The Clinton design uses diversepsignal from RTS.
It uses energize-to-function valves instead of deenergize-to-function valves.
It uses DC power instead of AC power. The staff finds this acceptable.
4.4 PHYSICAL SEPARATION FROM THE EXISTING REACTOR TRIP SYSTEM The ATWS Rule guidance states that the implementation of the ARI system must be such that separation criteria applied to the existing protection system are not violated. The Clinton design uses four locally mounted (outside primary containment) pressure transmitters and four level transmitters (differential pressure) at four physically separated locations. _These transmitters sense pressure (or differential pressure) from the same sensing lines used for the reactor protection system (RPS),
but cables from these transmitters are routed separately from the RPS.
The logic circuitries are located in the ATWS panel which are separated from the RPS. The ARI. scram air header exhaust valves are separated from RPS. The electrical components and wirings assigned to two ARI subsystems are separated from _each other by six inches or a metallic barrier. The ARI components and wirings are separated from RPS components and wirings by six inches or a metallic barrier. The staff finds this acceptable.
4.5 ENVIRONMENTAL QUALIFICATION The ATWS Rule guidance states that the qualification of the ARI_ system is for anticipated operational occurrences only, not for accident. The Clinton ARI system equipment are qualified to meet these conditions. The staff finds this acceptable.
4.6 SEISMIC QUALIFICATION No seismic qualification is required for the ARI system hardware.
4.7 QUALITY ASSURANCE The licensee is required to follow the NRC quality assurance guidance outlined in the Generic Letter 85-06 dated April I6, 1985. The 1
implementation and effectiveness of the licensee's quality controls for these improvements will be verified by Region III.
4.8 SAFETY RELATED (IE) POWER SUPPLY The ATWS Rule guidance states that the ARI system must be capable of performing its safety functions with loss of offsite power, and that the power source should be independent from existing reactor trip system.
~.
I The Clinton ARI system uses two separate _and independent non-sEfety related 125 Vdc power sources for the transmitters, control lo ic and solenoid coils. The battery capacity will support the system ollowing an ATWS event including loss-of-offsite power throughout the firs 20 minutes of the event. The staff finds this acceptable.
4.9 TESTABILITY AT POWER The ATWS Rule guidance states that the ARI system should be testable at~
power.
Provisions are provided for testing the ARI system control logic and. valve solenoid coil continuity during plant operation. A test switch activates relay logic which inhibits the solenoid valve coils and the ARI activating i
relays from being energized. -Then a test signal is injected to simulate a 3
trip condition.
Indicating lights confirm the test was perfonned.
Returning the system from the test mode to normal mode requires the resetting of both the test switch and _the test circuit seal-in switch.
This two-step process is designed to prevent inadvertent scram when i
performing a system test. The licensee also performs a functional test which includes the scram valves (CPS Procedure No. 9434.03) of the ARI i
system at least once per 18 months. The staff finds this acceptable.
4.10 INADVERTENT ACTUATION The ATWS Rule guidance statos that the inadvertent ARI ectuation which challenges other safety systems should be mirimized.
The Clinton ARI system uses a two-out-of-two actuation logic which will minimize inadvertent actuation. The manual initiation requires aming the stvitch and depressing two pushbuttons to initiate the action. -The licensee has established an unavailability goal of inadvertent actuation of 1 x 10~6 spurious actuetions per year, assuming the system is tested on a quarterly basis. The staff finds this acceptable.
4.11 MANUAL INITIATION TheClintondesignhastwosetsofmanual_initiationswitches(twoswitches in each subsystem) in the control room. The operator first rotates the pushbutton's collar to arm the switches, then depress both switches to initiate the protective actions. The staff finds this acceptable.
4.12 INFORMATION READ 0UT The Clinton design provides the operator with the complete status of the ARI system which includes the reactor low level and reactor high pressure trip status, valve position, system under testing, maintenance, or inoperable status. The audible alarms are provided when the ARI system has been initiated, or the ARI system is inoperative. The staff finds the design acceptable.
i n
--,.--n.-
,,,,. ~ - -
,-,,-n_c,,
- ~-.. ~ - -
a
i
. 4.13 COMPLETION OF PROTECTIVE ACTION ONCE IT IS INITIATED g
The Clinton design has a seal-in feature to ensure the completion of protective action once it is initiated. After initial conditigs return to normal, deliberate operator action is required to reset the system -
logic to normal. The staff finds this acceptable.
4.14 MAINTENANCE BYPASS The Clinton ARI system uses a two-out-of-two trip logic for actuation.
Any single transmitter or trip unit can be repaired or calibrated without affecting the operation of the overall system. Test switches are provided to prevent the solenoid valve coils and activating relays from being energized. The test switch requires a two-step process to return the system logic to normal operation. This prevents an inadvertent actuation of the system while performing system testing.- The bypass status is annunciated in the control room. The staff finds this acceptable.
5.0 CONCLUSION
S ON ARI SYSTEM Based on its review, the staff concludes that the ARI design basis for Clinton is in compliance with ATWS Rule 10 CFR 50.62 paragraph (c)(3) and the guidance published in Federal Register Volume 49 No.124 dated June 26, 1984, and is therefore acceptable.
6.0 TECHNICAL SPECIFICATIONS The equipment required by the ATWS Rule to reduce the risk associated j
with an ATWS event must be designed to perform its functions in a reliable manner. A method acceptable to the staff for demonstrating that the equipment satisfies the reliability requirements of the ATWS Rule is to provide ARI Technical Specifications which include operability and surveillance requirements. The staff will provide guidance regarding Technical Specification requirements for ARI at a later date.
Principal Contributor:
H. Li Dated:
May 18, 1987
-