ML20078H583
| ML20078H583 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 10/06/1983 |
| From: | Nelson R ILLINOIS POWER CO. |
| To: | Schwencer A Office of Nuclear Reactor Regulation |
| References | |
| TASK-2.K.3.13, TASK-2.K.3.15, TASK-TM L30-83(10-06)L, L30-83(10-6)L, L30-8310-6L, U-0672, U-672, NUDOCS 8310140228 | |
| Download: ML20078H583 (11) | |
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THinnla Power Company gg672
_g 10-06)t 500 SOUTH 27TH STREET, P. O. BOX 511. DECATUR, ILLINOIS 62525-1805 Docket No. 50-661 October 6, 1983 Director of Nuclear Reactor Regulation Attention:
Mr. A. Schwencer, Chief Licensing Branch No. 2 Division of Licensing U. S. Nuclear Regulatory Commission Washington, D. C. 20555 Subj ect :
Clinton Power Station Unit 1 SER Confirmatory Issues #45 & 46 Modification of RCIC Systems Logic
Dear Mr. Schwencer:
Per our discussions on the resolution of SER issues with the NRC Staff, attached is a draft copy of FSAR page changes on the following subj ects:
Confirmacory Issue #45 TMI-2 Action Plan Item II.K.3.13 - HPCI and RCIC Initiation Levels Pages Revised; 7.4-3 7.4-4 D-80 D-31 Confirmatory Issue #46 TMI-2 Action Plan Item IT.K.3.15 - Isolation of HPCI and RCIC Pages Revised; 7.4-6 7.4-7 i
D-82 D-83 D-84 These confirmatory issues require that appropriate logic modifications, as described in the Clinton SER, be incorporated into the plant design prior to fuel loading, if qualified hardware is available.
,y G310140228 831006
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PDR ADOCK 05000461
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U- 0672 L30-83(10-06)6 October 6, 1983 Page 2 The engineering designs for the above listed modifications have been completed.
Qualified hardware changes are being incorporated at this time and should be completed during the first quarter of 1984.
The above listed pages will revise the FSAR to reflect these changes in the station design and are attached for your early review.
Illinois Power is planning to include these pages in FSAR Amendment 28.
We trust that this information will resolve SER Confirmatory Issues Nos. 45 and 46 for closeout in the next SER Supplement.
Please let us hear soon if you have any questions on this material.
Sincer 1 son Director-Nuclear Licensing and Configuration Nuclear Station Engineering GEW/jmm Attachments l
cc:
G. A. Harrison, NRC Clinton Licensing Project Manager R. A. Kendall, NRC ICSB NRC Resident Office Illinois Department of Nuclear Safety a
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DRAFT DRAFT
. DRAFT CPS-FSAR AMENDMENT 28 7.4.1.1.3.2 Initiating Circuits Reactor vessel low water level is monitored by four level transducers that sense the difference between the pressure to a constant reference leg of water and the pressure due to the actual height of water in the vessel.
Each transducer supplies a signal to analog comparator trip units that energize control logic.
The analog comparator trip units are located in the main control room.
The instrument sense line for the transducers are physically separated from each other and tap off the reactor vessel at widely separated points.
The RCIC system is initiated automatically by a reactor vessel low water level signal utilizing a one-out-of-two twice logic and produces the design flow rate within 30 seconds.
The system will provide design makeup water flow to the reactor vessel until the amount of water delivered to the reactor vessel is adequate to restore vessel level, at which point the RCIC system is automatically placed in a standby condition.
The controls are l
provided to allou remote-manual startup, operation, and shutdown.
The RCIC turbine is controlled as shown in drawing E02-lRI99.
The turbine governor limits the turbine speed and adjucts the turbine steam centrol valve so that design pump discharge flow rate is obtained.
The flow signal used for automatic control of the turbine is derived from a differential pressure measurement across a flow element in the RCIC system pump discharge line.
The turbine is shut down by tripping the turbine trip and throttle valve closed if any of the following conditions are detected:
l l
(1)
Turbine overspeed (2)
High turbine exhaust pressure (3)
RCIC isolation signal from logic "A" or "B"
(4)
Low pump suction pressure (5) lianual trip actuated by the operator.
1 1
I l
Turbine overspeed indicates a malfunction of the turbine control mechanism.
High turbine exhaust pressure indicates a condition that threatens the physical integrity of the exhaust line.
Low pump suction pressure warns that cavitation and lack of cooling can cause damage to the pump which could place it out of service.
l A turbine trip is initiated for these conditions so that if the causes of the abnormal conditions can be found and corrected, the system can be quickly restored to service.
The trip settings are i
I l
7.4-3
)AT Ces-esiR isenoasnT 28 DRUT selected so that a spurious turbine trip is unlikely, but not so that damage occurs before the turbine is shut down.
Turbine overspeed is detected by a standard turbine overspeed mechanical device.
Two pressure sensors are used to detect high turbine exhaust pressure; either sensor can initiate turbine shutdown.
Two pressure sensors are used to detect low RCIC system pump suction pressure.
A high reactor water level signal initiates the closure of the steam supply valve, rather than the turbine trip valve, to shut off the steam to the turbine.
Closure of the steam suoply valve places the RCIC system in a standby configuration until a low reactor water level initiation signal reinstates system operation.
High water level in the reactor vessel indicates that the RCIC system has performed satisfactorily in providing makeup water to the reactor vessel.
Further increase in level could result in RCIC system turbine damage caused by gross carry-over of moisture.
The reactor vessel high water level setting is near l
the top of the steam separators and is sufficient to prevent gross moisture carry-over to the turbine.
Two level transmitters and associated trip units which sense differential pressure are arranged to require that both trip units trip to initiate a steam supply valve closure.
l 7.4.1.1.3.3 Logic and Sequencing The scheme used for initiating the RCIC system is shown in drawing E02-lRI99.
7.4.1.1.3.4 Bypasses and Interlocks To prevent the turbine pump from being damaged by overheating at reduced RCIC pump discharge flow, a pump discharge bypass is provided to route the water discharged from the pump back to the suppression pool.
The bypass is controlled by an automatic, de motor-operated valve whose control scheme is shown in drawing E02-1RI99.
The valve is closed at high flow or when either the steam supply or turbine trip valves are closed.
Low flow combined with high pump discharge pressure opens the valve.
To prevent the RCIC steam supply pipeline from filling up with l
water and cooling excessively, a condensate drain pot, steam line drain, and appropriate valves are provided in a drain pipeline arrangement just upstream of the turbine supply valve.
The control scheme is shown in drawing E02-1RI99.
The controls position valves so that during normal operation steam line drainage is routed to the main condenser.
The water level in the steam line drain condensate pot is normally maintained by a steam trap which is open to the main condenser.
In addition, the water level in the steam line drain condensate pot is controlled by a level switch and a direct acting solenoid bypass l
valve which energizes to allow condensate to flow out of the drain pot.
Upon receipt of an RCIC initiation signal, the drainage path is isolated.
7.4-4
Ih CPS-FSAR AMENDMENT 28 DMR NRC ACTION PLAN (NUREG-0737)
II.K.3.13 Separation of HPCI and RCIC System Initiation Levels NRC Position Currently, the reactor core isolation cooling (RCIC) system and the high pressure coolant injection (HPCI) system both initiate on the same low water level signal and both isolate on the same high water level signal.
The HPCI System will restart on low water level, but the RCIC system will not.
The RCIC system is a low-flow system when compared to the HPCI system.
The initiation levels of the HPCI and RCIC system should be separated so that the RCIC system initiates at a higher water level than the HPCI system.
Further, the RCIC system initiation logic should be modified so that the RCIC system will restart on low water level.
These changes have the potential to reduce the number of challenges to the HPCI system and could result in less stress on the vessel from cold water injection.
Analyses should be performed to evaluate these changes.
The analyses should be submitted to the NRC staff and changes should be implemented if
. justified by the analysis.
CPS Response The response to this task will be divided into two parts:
the first response will address the need to separate the RCIC and HPCS' initiation level, and the second response will address the l
need to provide an auto-restart feature for the RCIC system.
Evaluation of HPCS and RCIC Initiation Level In response to this requirement, Illinois Power Company jointly sponsored through the BWR Owners' Group a program to evaluate l
this concern.
The results of this program were submitted to the NRC via a letter from R. H. Buchholz, General Electric Company, to D. G. Eisenhut, Director of NRC, dated October 1, 1980.
Illinois Power Company endorses the results of this study.
i The conclusion drawn from this analysis is that the separation of HPCS and RCIC initiation setpoints is unnecessary for safety considerations.
The basis for this conclusion, as described in j
the above referenced letter is that for rapid level changes associated with accident scenarios and severe transients, their initiation would be essentially simultaneous in that possible separation distances could not preclude HPCS challenges; likewise, for slow level changes due to small leaks or slow transients, adequate time exists for manual initiation of RCIC by the reactor operator, prior to HPCS auto-initiation.
D-80
The above referenced BWR Ouner's Group analysis addresses the use of both systems.
DRA:T CPS-FSAR AMENDMENT 28 As a result of the above challenges, thermal stresses will occur in the reactor vessel and its internals.
The most severe thermal cycle due to RCIC and HPCS initiation at the current low water level was assessed and compared to the thermal cycle analysis for the limiting reactor components.
Furthermore, operating plant experience was evaluated to estimate the frequency of occurrence ci HPCS and RCIC initiations.
Based on this evaluation, it was concluded that the current design is satisfactory, and a significant reduction in thermal cycles is not necessary.
Evaluation of Proposed Auto-Restart of RCIC In response to this requirement, Illinois Power Company jointly sponsored through the BWR Owners' Group a program to evaluate this concern and develop an appropriate modification.
The results of this program were submitted to the NRC via a letter from D. B. Waters, Chairman of BWR Owners' Group, to D. G.
Eisenhut, Director of NRC, dated December 29, 1980.
An evaluation of modifications to the RCIC system to allow automatic restart following a trip of the system at high RPV water level was conducted.
The evaluation of the automatic restart indicates that it would contribute to improved system reliability and that it could be accomplished without adverse effects on system function and plant safety.
Illinois Power Company has imp-lemented an RCIC automatic restart modification on the Clinton Power Station.
I The modification consists of the relocation of the existing high vessel level trip function from the RCIC turbine trip valve to the RCIC steam supply valve.
This signals the-RCIC steam supply valve to close when the high reactor vessel water level is attained.
Closure of the RCIC steam supply valve also automatically resets many of the functions that allow RCIC to restart when low vessel water level is reached.
Any adverse effects due to increased system complexity are more than offset by the increased safety, reliability and availability created by the change.
This modification enables RCIC to restart on low vessel level (Level 2) because the logic resets or aligns the RCIC valving for startup.
Formerly, this reset was accomplished manually.
This reset condition is indicated on an annunciator in the control room.
The initiating circuits for the RCIC system are described in Subsection 7.4.1.1.3.2.
D-81
, %[
PS-FSAR AFENDFENT 28 To assure that the RCIC can be brought to design flow rate within ~
a
,30 seconds from the receipt of the initiation signal, the following maximum operating times for essential RCIC valves are provided by the valve operation mechanisms:
RCIC turbine steam supply valve 15 seconds RCIC pump discharge valves 15 seconds RCIC pump minimum flow bypass valve 5 seconds The operating time is the time required for the valve to travel from the fully closed to the fully open position, or vice versa.
The two RCIC steam supply line isolation valves are normally open and they are designed to isolate the RCIC steam line in the event of a break in that line.
These valves are operated by ac motors powered from different ac sources and automatically close after a 3-second time delay on receipt of an isolation signal.
A normally closed de motor-operated valve is located in the turbine steam supply pipeline just upstream of the turbine stop valve.
The control scheme for this valve is shown in drawing E02-1RI99.
Upon receipt of an RCIC initiation signal this valve opens and remains open until closed by operator action from the main control room.
The instrumentation for isolation consists of the following:
Outboard RCIC Turbine Isolation Valve (Common Valve to both RCIC Steam Line and RHR Heat Exchanger Line)
(1)
Differential temperature switches-RCIC and RHR equipment area ventilation air inlet and outlet high temperature.
(2)
Ambient temperature switches-RCIC and RHR equipment area high temperature.
(3)
Differential temperature switch-RCIC pipe routing area (main steam line pipe tunnel) ventilation air path high l
temperature.
(4)
Ambient temperature switch-RCIC pipe routing area (main steam line pipe tunnel) high temperature.
(5)
Differential pressure transmitter and trip unit-RCIC or RHR/RCIC steam line high flow or instrument line break.
(6)
Two 3-second time delay break detection logic circuits.
l (7)
Two pressure transmitter and trip unit-RCIC turbine l
exhaust diaphragm high pressure.
Both trip units must activate to isolate, l
(8)
Pressure transmitter and trip unit-RCIC steam supply l
pressure low.
7.4-6
DRAFT DRAFT Ces-esxR m - Da m 28 (9)
Manual isolation if the system operation has been initiated.
Inboard RCIC Turbine Isolation Valve (Common valve to both RCIC steam line and RHR heat exchanger line)
(1)
Except for the manual isolation feature, a similar set of instrumentation causes the inboard valve to isolate.
Two pump suction valves are provided.in the RCIC system.
One valve lines up pump suction from the RCIC storage tank; the other one from the suppression pool.
The RCIC storage tank is the preferred source.
Both valves are operated by de motors.
The control arrangement is shown in drawing E02-lRI99.
Upon receipt of an RCIC initiation signal, the RCIC storage tank suction valve automatically opens.
RCIC storage tank low water level or low water temperature, RCIC tank pump suction line low temperature, or suppression pool high water level automatically opens the suppression pool suction valve.
Full opening of this valve automatically closes the RCIC storage tank suction valve.
A third pump suction valve from the RHR system is located in the RHR system.
One de motor-operated RCIC pump discharge valve in the pump discharge pipeline is provided.
The control scheme for this valve is shown in drawing E02-1RI99.
This valve is arranged to open upon receipt of the RCIC initiation signal and closes autcmatically upon receipt of a turbine trip signal.
7.4.1.1.3.7 separation As in the emergency core cooling system, the RCIC system is separated into divisions designated 1 and 2.
The RCIC is a Division 1 system, but the inboard steam line isolation valve, the steam line warmup line isolation valve, the inboard vacuum breaker isolation valve, the inboard turbine exhaust drain isolation valve, and the inboard steam supply drain isolation valve are Division 2; therefore, part of the RCIC logic is Division 2.
The inboard and outboard steam supply line isolation valves, the steam line warmup line isolation valve and the inboard and outboard vacuum breaker isolation valves are ac powered valves.
The rest of the valves are de powered valves.
In order to maintain the required separation, RCIC trip channel and logic components, instruments and manual controls are mounted so that separation from Division 2 is maintained.
All power snd signal cables and cable trays are clearly identified by division.
The auxiliary systems that support the RCIC system are:
the gland seal system (which prevents turbine steam leakage) and the lube oil cooling water system.
An RCIC initiation signal activates the gland seal compressor and opens the cooling water
'.4-7
CPS-FSAR AMENDMENT 28 NRC ACTION PLAN (NUREG-0660 as clarified by NUREG-0737)
II.K.3.15 Modify Break Detection Logic to Prevent Spurious Isolation of HPCI and RCIC NRC Position The high-pressure coolant injection (HPCI) and reactor core isolation cooling (RCIC) systems use differential pressure sensors on elbow taps in the steam lines to their turbinc drives to detect and isolate pipe breaks in the systems.
The pipe-break-detection circuitry has resulted in spurious isolation of the HPCI and RCIC systems due to the pressure spike which accompanies startup of the systems.
The pipe-break-detection circuitry should be modified so that pressure spikes 4
resulting from HPCI and RCIC system initiation will not cause 1.tadvertent system isolation.
CPS Response The BWR/6 design at Clinton Power Station does not utilize the turbine-driven HPCI system but rather the motor-driven HPCS system for high pressure coolant injection.
Hence, the only system impacted by this proposed modification is the turbine driven RCIC system.
In response to this requirement, Illinois Power Company jointly sponsored through the BWR Owners' TMI Group a program to evaluate the inadvertent trip concern and develop an appropriate modification.
As a result of this generic program, the Clinton Plant design includes a provision for the presentation of spuriaus isolation i
of the RCIC system as a result of pressure spikes which may occur during start-up of that system.
This involves installation of a 3 second solid state time delay in the isolation logic j
which will avoid the RCIC isolation due to any short duration l
l pressure spikes during system startup.
This time delay is short enough such that for postulated system pipe breaks, the system l
will isolate in time to prevent unacceptable radiological releases to the environment.
Releases due to a 3 second time I
delay will still be less than the design basis conditions and within existing safety analyses.
Figure D-1 shows a portion of the RCIC elementary diagram which was changed when the time delay device was added to the existing isolation logic.
Figure D-2 summarizes in schematic form the sequence of events that will occur during the starting of the RCIC system with the time delay D-82
.y
gg
%[{
CPS-FSAR AMENDMENT 28 added.
The timer will be started when the flow rate sensed I
by elbow flow meters exceeds the trip setpoint.
At the end of the timer period, system isolation will occur only if the flow meters are still reading at or above the trip setpoint.
As demonstrated in Figure D-2, this will ensure that isola-tion of a pipe break will occur.
It is noted that the RCIC system has two break detection circuits each of which controls one of the two isolation valves.
Both circuits have been modified in order to successfully implement this change.
The instrumentation for isolation of the RCIC system is listed in Subsection 7.4.1.1.3.6.
I t
I l
I I
l D-83 i
7 17.
DRAFT h
CPS-FSAR AMENDMENT 28 RCIC Steam Supply Pressure ATM E31-N685B ~
Is < Low Set Point 1
RHR and RCIC Equipment Area Ambient Temperature 7 High Set Point Temperature Switch "B" on RCIC Pipe In Steam Tunnel Is > High Set Point RCIC Steamline Differential N6 3 Pressure Is> High Set Point Or Instrument Line Break RCIC Steamline Differential ATM E31-Pressure Is7 High Set Point N690B Or Instrument Line Break
'B Sec.
De$ay RClC Steamline Differential ATM E31-Pressure Is> High Set Point N684B l
Or Instrument Line Break RCIC Steamline Differential ATM E31-Pressure Is> High Set Point N691B Or Instrument Line Break FIGURE D-1 RCIC Steamline Break Detection Logic Diagram D-84