ML17158A114
| ML17158A114 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 01/31/1994 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17158A113 | List: |
| References | |
| NUDOCS 9402040275 | |
| Download: ML17158A114 (9) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, O.C. 20565-0001 S
F TY EVA U TION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT N0132 TO FACILITY OPERATING LICENSE NO. NPF-14 AMENDMENT NO.
99 TO FACILITY OPERATING LICENSE NO.
NPF-22 PENNSYLVANIA POWER 5 LIGHT COMPANY ALLEGHENY ELECTRIC COOPERATIVE INC.
SUS UEHANNA STEAM ELECTRIC STATION UNITS 1
AND 2 DOCKET NOS.
50-387 AND 388
- 1. 0 INTRODUCTION By letter dated January 9,
- 1991, as supplemented by letters dated August 19<
- 1991, June 22,
- 1992, and August 3, 1992, the Pennsylvania Power and Light Company (PP8L or the licensee) submitted a request for changes to the Susquehanna Steam Electric Station (SSES),
Units 1 and 2, Technical Specifications (TS).
The requested changes would revise the isolation setpoints for the ambient temperature switches in the High Pressure Coolant Injection (HPCI) and the Reactor Core Isolation Cooling (RCIC) room cooler air inlets.
The application has also requested changes to the isolation setpoints for the ambient and differential tempe} ature detectors in the Reactor Water Cleanup (RWCU) penetration room.
The changes pertaining to the RWCU system were approved by Amendment Nos.
123 and 90 for Units 1 and 2, respectively, issued October 3, 1992.
Section 5.2.5. 1.3 of the Final Safety Analysis Report (FSAR) for the SSES describes the various means used to detect possible abnormal leakage of primary coolant (or steam) outside the primary containment.
There are multiple means used to detect possible
- leakage, including area radiation
- monitors, ambient and differential temperature
- sensors, flow and differential flow elements, and pressure and differential pressure instruments.
This application only involves two temperature sensors and this safety evaluation will primarily discuss the temperature-based leak detection method in the HPCI
-and RCIC rooms.
A differential temperature sensing system is installed in each room containing equipment that interfaces with the reactor coolant pressure boundary.
These are the HPCI, RCIC, Residual Heat Removal (RHR) and RWCU systems equipment
- rooms, and the main steam line tunnel.
Temperature sensors are placed in the inlet and outlet ventilation ducts.
Other sensors are installed in the equipment areas to monitor ambient temperature.
A differential temperature switch between each set of sensors and/or ambient temperature switch initiates an alarm and isolation when the temperature reaches a preset value.
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II RCIC and RHR leak detection area ambient temperature switch setpoints are designed to initiate isolation signals at 167 'F.
This setpoint includes sufficient margin above the post LOCA maximum area temperature to preclude inadvertent isolation signals.
The HPCI, RCIC and RHR ventilation inlet and exhaust differential temperature switch setpoints are designed to initiate isolation signals at a differential temperature of 89 'F.
This setpoint includes sufficient margin to prevent inadvertent isolation signals when the area ventilation exhaust is at the maximum post LOCA temperature, and the ventilation inlet corresponds to the minimum reactor building recirculating ventilation design temperature.
This setpoint will allow wide fluctuations in outside air temperature without causing inadvertent isolation signals.
l.l HPCI System Leak Detection The steamline of the HPCI system is constantly monitored for leaks by the leak detection system.
Leaks from the HPCI steamline will cause a change in at least one of the following monitored operating parameters; sensed area temperature, steam pressure, or steam flow rate.
If the monitored parameters indicate that a leak may exist, the detection system responds by activating an alarm and depending upon the activating parameter, initiates HPCI auto-isolation action.
The HPCI leakage detection system consists of three types of monitoring circuits.
The first of these monitors area ambient and differential temperature, triggering the alarm circuit when the temperature rises above the preset maximum.
The second type of circuit utilized by the leakage detection system monitors the flow rate, or differential pressure, through the steamline, triggering an alarm circuit when flow rate exceeds a preset maximum.
The third type of circuit utilized by the HPCI leakage detection system monitors the steamline pressure upstream of the differential pressure element.
Alarm outputs from all three circuits are also used to generate the HPCI auto-isolation signal.
The two division HPCI temperature monitors work on a one-out-of-two logic that initiates the.isolation logic.
There are five temperature monitors per division which consist of three area (two ambient and one differential) and two tunnel (one ambient and one differential) temperature monitors.
The tunnel temperature signals are time delayed before initiating the isolation logic.
1.2 RCIC System Leak Detection The steamlines 'of the RCIC system are constantly monitored for leaks by the leak detection system.
Leaks from the RCIC will cause a change in at least one of the following monitored operating parameters; area temperature, steam pressu, e, or steam flow rate.
If the monitored parameters indicate that a
leak may exist, the detection system responds by activating an annunciator and initiating a RCIC isolation trip logic signal.
The RCIC leak detection subsystem consists of three types of monitoring circuits.
The first of these monitors ambient and differential temperature, triggering an annunciator when the temperature rises above a preset maximum.
The second type of circuit utilized by the leak detection system monitors the flow rate (differential pressure) through the steamline, triggering an annunciator when the differential pressures rises above a preset maximum.
The third type of circuit utilized by the leak detection system monitors the steamline pressure upstream of the differential pressure element and also is annunciated.
Alarm outputs from all three circuits are also used to generate the RCIC auto-isolation signal.
The RCIC area temperature monitoring circuit is similar to the one described above 'for the HPCI area temperature monitoring system.
Using one-out-of-two logic, the RCIC area temperature monitoring circuit activates an annunciator and initiates a
RCIC isolation signal when the temperature rises above a
preset limit.
2.0 EVALUATION In both the HPCI and RCIC rooms, there is a room cooler that sits on the floor.
Inside each cooler is a fan that pulls air from the room across the heat exchanger coils and discharges the air back into the room.
The fans are i.interlocked with the HPCI and RCIC pumps, so that the fans only operate when the HPCI or RCIC system is operating.
The heat exchangers are cooled by the Emergency Service Mater (ESW) system.
The purpose of the heat exchangers is to reduce the heat input into the room from the steam line and turbine when the HPCI or RCIC system are operating.
Mounted on the outside of each heat exchanger (upstream of the fan) is a temperature element.
As might be expected when you see the arrangement, the temperature sensors on the outside of the coolers are monitoring room air temperature.
Located around each room are other temperature sensors which also monitor room air temperature.
Since both sets of sensors are monitoring air temperature in the same room, the temperature readings on both sets of sensors are not significantly different from one another.
In Table 3.3.2-2 of the TSs, the isolation trip setpoint for both the HPCI and RCIC room temperature sensors is 167 'F (with an allowable value of 174 'F).
(In the Table, items 5f and 6d are referred to as "Pipe Routing Area Temperature-High.")
The isolation trip setpoint in the same table for the temperature sensors on the outside of the room coolers is
0
now 147 'F, with an allowable value of 154 'F.
(In the TSs, these temperature sensors are referred to,as "Emergency Area Cooler Temperature-High.")
As stated in the Introduction above, the FSAR states that:
"the HPCI, RCIC and RHR leak detection area ambient temperature switch setpoints are designed to initiate isolation signals at 167 'F."
There is no mention made of any other temperature for the isolation setpoint for the room air sensors.
The change in the TSs proposed by the licensee is to change the trip setpoints for the sensors on the outside of the room area coolers (items 5h and 6f in Table 3.3.2-2) from 147 'F to 167 'F to be identical to the room area sensors.
Also, the licensee proposes to change the allowable value for these same sensors to 174 'F to be the same as for the room area sensors.
A steam leak detection task force was formed in 1988 when the licensee found miswiring of the Reactor Building Steam Tunnel Temperature elements.
One of the actions of this task force was to confirm, via task team walkdowns, that all steam leak detection temperature elements were properly located.
In addition to the steam tunnel errors, this walkdown identified additional problems with temperature element locations in the Unit 2 HPCI and the Unit 1:
RWCU rooms.
These temperature elements have since been relocated to their proper location.
All other temperature element locations were confirmed to be correct.
As part of this program, the lice'nsee also reconstituted the design bases for the temperature based steam leak detection and isolation circuitry in rooms within secondary containment which interface with the reactor coolant system.
Reconstitution of the design bases started with modeling each room in which steam leak detection circuitry is installed, and calculating room temperature response to postulated leak rates.
Initial analyses used leak rates of 5 gpm and 25 gpm.
PP&L used the Compartment Transient Temperature Analysis Program (COTTAP) computer program to generate room thermal response curves under postulated leak conditions.
The 25 gpm postulated leak rate is the General Electric (GE) design basis for calculating isolation setpoints as described in GE document EDE-17-0689.
This design basis is utilized by other BWRs such as Perry, Grand Gulf, Clinton and River Bend.
The use of this postulated leak rate is reasonable, considering that the piping is austenitic stainless
- steel, a very ductile material, the general acceptance of leak-before-break for this material and that a leak rate of 25 gpm has been demonstrated to be well below the leak rates associated with the onset of unstable pipe rupture.,
The COTTAP computer program was described in detail in Attachment A to the licensee's response of August 19, 1991 to our request of June 13, 1991 for additional information.
The "Theory and Input Description Manual" for COTTAP-2,. Revision 1 along with the computer printouts,
- curves, input parameters, etc.
was provided by the licensee's letter of June 23, 1992.
For the HPCI room, the current TS high ambient trip point is 167 'F.
The computer calculations on temperature.
response at a presumed leakage rate of 25 gpm at rated process conditions shows that the existing setpoint (167 'F) is reached at about 18 minutes.
A smaller leak rate of 12-15 gpm would cause the setpoint to be reached in 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.
For the RCIC area, the c'urrent TS high ambient trip point is also 167 'F.
The calculated temperature response in the COTTAP model with a presumed leakage rate of 25 gpm shows that the existing setpoint (167 'F) is reached in about 10 minutes.
A smaller leak rate of 10 gpm would cause the setpoint to be reached in 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.
As discussed
- above, the extensive computer modeling was a two-year effort by the licensee to redefine the design base for the bulk of the temperature isolation setpoints as described in the FSAR.
The objective was to establish an analytically consistent and uniform design basis for the bulk of the existing temperature-based isolation circuit setpoints without changing those setpoints.
The only change requested to the isolation setpoints is to eliminate the inconsistency between the isolation setpoints for the temperature sensors mounted on the air inlets to the room coolers and the setpoints for the wall mounted temperature sensors in the same room.
The isolation setpoints for the wall-mounted circuits in the TSs is 167 'F for both the HPCI and RCIC rooms.
The isolation setpoints for room cooler circuits for the current TSs is 147 F.
- However, both sensors are monitoring the same room air temperature and historically have recorded essentially the same'temperature.
The writer -'
personally examined the room arrangements.
Considering the layout of the steam lines to the turbine, it does not appear that the sensors mounted on the room coolers would detect a steam leak any sooner than the wall-mounted
, sensors.
We agree with the licensee that the isolation setpoints for both circuits should be the same.
The analyses submitted by the licensee have demonstrated that establishing isolation setpoints based on a postulated 25 gpm leak rate is reasonable and will isolate any leak well before it would lead to a pipe break.
Both the
'procedures require operator rounds into the HPCI and RCIC areas once-per-day.
All areas with steam.leak detection circuitry have their temperatures (and differential temperatures) available in the main control room for monitoring.
The alarm response procedures identify specific action required, including observation, confirmation, isolation, and repair of leaks.
Visual observation of a steam leak, or rising room temperatures, or the occurrence of a pre-isolation temperature alarm in the main control room would invoke operator action without attempting to quantify the leak rate, or waiting for the temperature to reach the isolation setpoint.
Prolonged operation with any significant leak is not anticipated.
The HPCI and RCIC system are the only two high pressure emergency core cooling systems.
The automatic isolation setpoint should not be so low as to take these important systems out of service for minor steam leaks such as from valve packing.
Raising the isolation setpoint for the temperature sensors on the two-room coolers to be the same as the isolation setpoint for the room temperature sensors eliminates an inconsistency and has been justified by the licensee.
The proposed changes to the TSs are acceptable.
3.0 STATE CO SU TATION In accordance with the Commission's regulations, the Pennsylvania State official was notified of the proposed issuance of the amendments.
The State official had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
The amendments change a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20.
'The NRC staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any efflue its 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 amendments involve no significant hazards consideration, and there has been no public comment on such finding (58 FR 32389).
Accordingly, the amendments meet 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 amendments.
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 i'ssuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
R. Clark Date:
january 31, 1994
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