ML20042D793
| ML20042D793 | |
| Person / Time | |
|---|---|
| Site: | 05000605 |
| Issue date: | 04/05/1990 |
| From: | Dua S GENERAL ELECTRIC CO. |
| To: | Chris Miller NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML19302D938 | List: |
| References | |
| MFN-030-90, MFN-30-90, NUDOCS 9004090346 | |
| Download: ML20042D793 (13) | |
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April 5,1990 MFN No.030 90 Docket No STN 50 605 EEN 9015 Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Attention. Charles L. Miller, Director Standardization and Non Power Reactor Project Directorate
Subject:
AllWR Reactivity Control System Modif1 cation Enclosed are thirty four (34) copies of a draft amendment to the SSAR which updates Section 4.6,
" Functional Design of Reactivity Control Systems" to incorporate an electro mechanical brake, replacing the original centrifugal brake, as part of the fine motion control rod drive (FMCRD).
This update also provides a means for testing the FMCRD check valve OE intends to amend the affected portion of Chapter 15 (attached) as well as Section 4.6 in the near future.
The above changes werejudged by the Japanese ABWR Project as the optimal epproach for the ABWR with respect to the prevention of a rod ejection accident. This configuration provides a single failure proof protection against rod ejection with both a passive electro mechanical brake and a check va.ve. Further, this configuration allows for annual testing of both of these features.
Sincerely,
/
k Shyam S. Dua, Acting Manager Regulatory and Analysis Services M/C 382, (408) 925 6948 cc: F. A. Ross DOE) i D. C. Scalett(i (NRC) ea i D. R. Wilkins (GE) 7g W J.17. Quirk (GE) f 94
'l 9004090346 900405 PDR ADOCK 05000605 A PDC
. gg BammAard Plant
, aLEVJ (5) Each positioning device shall provide a 4.6 FUNCI10NALDESIGNOF means to prevent or limit the rate of
. REACTIVITY CONTROL SYSTEMS control rod ejection from the core due to a break in the drive mechanism pressure boun.
The reactivity control systems consists of dary. This is to prevent fuel damage re.
contrel rod 6 and eontrel rod drives, sulting from rapid insertion of reactivity.
I supplementary godolinia urania fuel reactivity controlin rods (Section the 4.3), and theform of Power Generstlen Deelga Basis 4.6.1.1J standby liquid control system (described in Subsection 9.3.5). The control rod drive system (CRDS) design shall meet the following power generation design Evaluations of the reactivity control systems bases:
against the applicable General Design Criteria (GDC) are contained in the folowing subsections: (1) The design shall provide for controlling changes in core reactivity by positioning QD.C Subsection neutron. absorbing control rods within the
' core.
23 3.1.23.4 d 25 3.1.23.6 (2) 'Ibe design shall provide for movement and po.
26 f 27 3.1.23.7 3.1.23.8 sitioning of control rods in increments to !
enable optimized power control and core l 28 3.1.23.9 power shaping.
29 3.1.23.10 4.6.1.2 Description ;
4.6.1 Information for Control Rod Drive !
System Tbc CRDS consists of fine ir.otion control rod drive (FMCRD) meAmalems, and the CRD hydraulic 4.6.1.1 Dealga Bases system (including pumps, filters, hydraulle control units, interconnecting piping, instru.
4.6.1.1.1 Safety Design Bases mentation and electrical controls). The CRDS, in conjunction with the rod control and infor.
The control rod drive CRD mechanical system mation system (RC&lS) and reactor protection ,
shall meet the following safety design bases: system (RPS) performs the following functions: !
(1) The design shall provide for rapid control (1) Controls changes in core reactivity by rod insertion (scram) so that no fuel damage positioning neutron. absorbing control rods !
results from any moderately frequent event within the core in response to control (see Chapter 15). signals from the RC&lS.
(2) The design shall include positioning (2) Provides movement and positioning of control devices, each of which individually supports rods in increments to enable optimized power and positions a control rod. control and core power shape in response to control signals from the RC&lS.
j(3) Each positioning device shall be capable of i
holding the control rod in position and (3) Provides the ability to position large preventing it from inadvertently withdrawing groups of rods simultaneously in response to outward during any non accident, accident, control signals from the RC&lS.
post accident and seismic condition.
(4) Provides rapid control rod insertion (scram)
(4) Each positioning device shall be capable of in response te manual or automatic signals detecting the separation of the control rod from the RPS so that no fuel damage results from the drive mechanism to prevent a rod from any plant transient.
drop accident.
Amendment Futur 4t
1 9 31A6100AB EsamAnniPlant arv. c 1 -l
, (8) Provides alternate rod insertion (ARI), an directed to each FMCRD connected to the alternete means of actuating motor driven HCU.lanide each FMCRD, high pressure water lifts j
, rod insertion should an anticipated the hollow piston off the ball sut and drives
. transient without scram (ATWS) occur, the control rod lato the core. A spring washer buffer assembly stops the hollow piston at the (9) Automatically drives in the drive mechanisms end of its stroke. Departure from the ball nut with the electric motors upon scram initia. releases spring loaded latches in the hollow l tion. This provides an additional, diverse piston that engage slots in the guide. tube, means of fully inserting a control rod. These latches support the control rod in the ,
inserted position. The control rod cannot be 1 (10) Provides selected control rod run.in (SCRRI) withdrawn until the ball not is driven up and for reactor stability control. (See engaged with the hollow piston. Stationary subsection 7. 7.1. 2.2. ( 2 )) . fio6ers on the ball out then can the latches out of the slots and hold them la the retracted (11) Prvents rod ejection by a passive motor position. A scram action is complete when every i brake or a seram line inlet check valve. PMCRD has reached their fully inserted position. ;
The design bases and further discussion of The use of the PMCRD mechanisms in the CRD ;
both the RC&lS and RPS, and their control inter- system provides several features which enhance ;
faces with the CRDS, are presented in Chapter 7. both the system reliability and plant ,
operations. Some of these features are listed 4.6.1.2.1 Fine Motion Control Rod Drive and discussed briefly as follows:
Mechanisms (1) Diverse Means of Rod Insertion The fine motion control rod drive (FMCRD) used for positioning the control rod in the reactor The FMCRDs can be inserted either core is a mechanical / hydraulic actuated mechanism hydraulically or electrically. In response (Figures 4.61, 4.6 2 and 4.6 3). An electric to a scram signal, the FMCRD is inserted motor driven ball nut and spindle assembly is hydraulically via the stored energy in the capable of positioning the drive at a minimum of scram accumulators. A signalis also given 18.3mm increments. Hydraulic pressure is used simultaneously to insert the FMCRD for fast scrams. The FMCRD penetrates the bottom eleetrically via its motor drive. This head of the reactor pressure vessel. The FMCRD diversity provides a high degree of does not interfere with refueling and is assurance of rod insertion on demand.
l operative even when the head is removed from the reactor vessel. (2) Absence of FMCRD Piston Seals The fine motion capability is achieved with a The FMCRD pistons have no seals and thus, do i ball nut and spindle arrangement driven by an not require maintenance.
electric motor. The ball nut is keyed to the guide tube (roller key) to prevent its rotation (3) FMCRD Discharge and traverses axially as the spindle rotates. A hollow piston rests on the ball nut and upward The water which scrams the control rod
! potion of the ball nut drives this piston and the discharges into the reactor vessel and does control rod into the core. The weight of the not require a scram discharge volume, thus control rod keeps the hollow piston and ball nut climinating a potential for common. mode in contact during withdrawal. failure.
A single hydraulic control unit (HCU) powers (4) Improved Plant Maneuverability ;
the scram action of two FMCRDs. Upon scram valve initiation, high pressure nitrogen from the HCU The fine motion capability of the FMCRD. J raises the piston within the accumulator forcing allows rod pattern optimization in response 1 water through the scram piping. This water is l'
l Amendment Futur 462
', 'ABWR muun Standard Plant arv. c
. to fuel burnup or load following demands. The basic elements of the FMCRD are at such a feature complements the ability to follows:
load. follow with core flow rate adjustaants. Combining this with Reactor (1) Portions of the FMCRD required for Recirculation System flow control, further hydraulle scram (including hollow piston l improves plant maneuverability, and buffer. 8 (5) Adaptable to Plant Automation (2) Portions of the FMCRD required for electrical rod insertion (including a
- The relatively simple logic of the FMCRD permits plant automation. This feature is motor, brake ball screw release, shaft, ball nut).associated connector, l utilized for automatic reactor startup and shutdowes and for automAlon load following. (3) Rod position indication (position synchronizing signal generators).
(6) Reduced Time for Reactor Startup (4) Bayonet coupling between the drive and The FMCRDs can be moved in large groups, control rod.
Movements of large groups of control rods (called gangs) is utilized to reduce the (5) Reed position switches for scram time for reactor startup, surveillance. ,
(7) Reduced Rod Drop Accident Consequences (6) Control rod separation detection devices (Dual Class 1E CRD separation switches).
The rod separation detection feature of the FMCRD virtually climinates the possibility (7) Continuous full in indication switch, of a Rod Drop Accident by preventing rod withdrawal when control rod separation is (8) Failed buffer detection (uses the full in detected. Additionally, movement of rods in indication switch.
large groups during reactor startup greatly .
reduces the maximum relative rod worth to (9) Brake mechanism to prevent rod ejection in levels lower than current rod pattern the event of a break in the FMCRD primary controls. Rod pattern controls are retained pressure boundary and ball check valve to in order to verify proper automatic rod prevent rod ejection in the event of a movements and to mitigate the consequences failure of the scram insert line, of a rod withdrawal error (10) Integral laternal shoot out support (to The drives are readily accessible for prevent drive shoot out) inspection and servicing. The bottom location makes maximum utilization of the water in the The most significant features and functions reactor as a neutron shield and gives the least of the FMCRD are described below.
possible neutron exposure to the drive :
components. Using water from the condensate 4.6.1.2.2.1 Components for Fine Motion Control treatment system, and/or condensate storage tanks As the operating fluid eliminates the need for The fine motion capability is achieved with a l special hydraulic fluid, ball nut and spindle arrangement driven by an electric stepper motor. The ball nut is keyed 4.6.1.2.2 FMCRD Components to the guide tube (roller key) to prevent its rotation and it traverses axially as the spindle Figure 4.61 provides a simplified schematic rotates. A hollow piston rests on the ball nut l of the FMCRD for illustration of the drive's and upward motion of the ball nut. drives the !
operating principles. Figure 4.6 2 illustrates control rod in to the core. The weight of the the drive in more detail. control rod keeps the hollow riston and ball nut in contact during withdrawal.
Amendment Futur 463
'. ABWR msma
,' new= d Pl==* mm e l .
The drive motor, located outside the pressure poaltion when the ball sut and hollow piston are boundary, is connected to the spindle by a drive re. engaged.
, abaft. The drive shaft pecettstes the pressure l ,
boundary and is scaled by conventional packings. Re. engagement of the ball nut with the hollow l A splined coupling connects the drive shaft to piston following scram is cutomatic.
I the spindle. The lower half of the splined Simultaneous with the initiation of the coupling is keyed to the drive shaft and the hydraulic scram each FMCRD motor is signaled to upper half keyed to the spindle. The tapered end start in order to cause movement of the ball nut of the drive shaft fits lato a conical seat on upward untilit is in contact with the hollow the end of the spindle to keep the two axially piston This action completes the rod full.in aligned. The entire weight of the control rod insertion and leaves the drives in a condition and drive internals is carried by a drive shaft ready for restarting the reactor. With the thrust bearing located outside the pressure latches in the hollow piston retracted the boundary, permanent magnats in the stepper motor provide the holding torque to maintain the control rods The axially moving parts are centered and fully inserted in the core. When the motor and I guided by radial rollers. The bals aut and brake are deennergized, the passive holding bottom of the hollow piston include radial terque from the brake keeps the rods fully rollers bearing against the guide tube. Radially inserted.
adjustable rollers at both ends of the labyrinth seal keep the hollow piston precisely centered in The automatic run.in of the ball nur using this region, the electric motor drive following the hydraalic scram provides a diverse means of rod insertion The top of the rotating spindle is supported as a backup to the accumulator scram, against the inside of the hollow piston by a stationary guide. A hardened bushing provides 4.6.1.2.2J FMCRD Preaanre Boondary the circumferential bearing between the rotating spindle and stationary guide. Rollers of the The part of the drive inserted into the guide run in axial grooves in the hollow piston reactor drive housing is contained within the to prevent the guide from rotating with the outer tube. The outer tube is the drive spindle, hydraulle pressure boundary, climinating the need for designing the drive horsing for scram 4.6.1.2.2.2 Components for Scram pressure. The outer tube is welded to the middle flange at the bottom and is attached to a The scram action is initist:d by the hydraulic seal piece at the top. The seal piece bears control unit. High pressure water lifts the against and seals to the CRD housing. The seal hollow piston off the ball nut and drives the piece and outer tube are attached by slip type control rod into the core. A spring washer connection that accounts for any slight buffer assembly stops the hollow piston at the variation in length between the drive and the end of its stroke. Departure from the ball nut drive housing, releases spring loaded latches in the hollow piston that engage slots in the guide tube. The middle and lower housing enclose the These latches support the control rod in the lower part of the drive and are a part of the jnserted position, reactor pressure boundary'. The middle housing 4 is attached to the drive housing by four l The control rod cannot be withdrawn until the threaded bolts. The lower housing (spool piece) l ball nut is driven up and engaged with the hollow is in turn held to the middle housing and piston. Stationary fingers on the ball nut cam secured to the drive housing by a separate set the latches in the hollow piston out of the slots of eight main mounting bolts. This arrangement in the guide tube and hold them in the retracted permits removing the lower housing, drive shaft and seal assembly without disturbing the rest of the drive. Removing the lower housing transfers the weight of the drive line from the drive ;
Amendment Futur u.4
-A.B M
.a..at.., sia. ions.
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- screw out down in to overtravel. After the drive to provide support. This tube which is weighing spring has raised the spindle to the welded to the drive middle flange, attaches by a limit of its travel, further retation of the bayonet lock to the guide tube base. The guide
' spindle in the withdraw direction will drive the tube, being supported by the housing extension, ball aut down away from the piston (assuming the prevents downward movement of the drive in the coupling is engaged). Piston movement, if any, event of housing failure, can then be detected by a reed switch at the zero stroke position. The CRD houslag support is designed to prevent ejection of a CRD and attached control 4.6.1.2.2.8 FMCRD Bruke rod in the unlikely event of failure of the:
The FMCRD design incorporates an (1) Drive housing to vessel attachment weld electromechanical brake keyed to the motor (including a failure through the housing or shaft. The brake is normally engaged by passive along the fusion line of the housing to stub spring force. It is disengaged when the spring tube weld).
load is overcome by the energized magnetic force. The braking torque between the motor (2) Flang* bolting attaching the drive to the shaft and the CRD spool piece is sufficient to housit g, prevent control rod ejection in the event of failure in the pressure retaining parts of the The laternal support concept is illustrated drive mechanism. The brake is designed so that schematically in Figure 4.6.*1. With failure its failure will not prevent the control rod from assume I at point A or B, the sum of the rapid insertion (scram), mechanicalload plus pressure load acting on the drive and houslag would tend to eject the The electromechanical brake is shown in Figure drive. In any of these failures, the drive 4.6 6. It is located between the stepper motor middle flange would be prevented from modng by and the synchronizing signal generators. The the outer tube (which, in turn, is attached to stationary spring loaded disk and coil assembly the upper guide which is locked to the fulde is contained within the brake mounting bolted to tube base). This guide tube is supported by the the bottom of the stepper motor. Tbc rotating stub tube welded to the RPV bottom head through disk is keyed to the stepper motor shaft and the CRD housing. In the event of total failure synchro shaft, of the housing to stub tube weld, the housing would be driven downward by the weight plus vessel pressure. After moving a short distance (0.3 inch), the flange of the guide tube contacts the core plate, stopping further movement. As stated above, the CRD is positively locked to the guide tube base and it cannot move further. In this way the housing is prevented from leaving the penetration, thereby ,
restricting the leak path to the area of the l annulus between the CRD housing and the hole in t the reactor pressure bottom head. An orderly
' shutdown would result even if this failure would i
occur since leakage from this annulus is less 4.6.1.2.2.9 Integral internal Blowout Support than the supply from the normal make up systems. The components that provide the An internal CRD housing support has been anti. ejection function are the guide tube, core adopted to replace the support structure of plate, housing and CRD outer tube. The l
beams, hanger rods, grids and support bars used materials of these components are specified to '
in previous product lines. quality requirements consistent with that function.
This system utilizes the outer tube of the Amendment Futur 4.66
. J
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MM Me==A- d Plant
- sA6100AB nerv. e Pressure in the charging header is monitored pressurlied water for hydraulle scram, on in the control room with a pressure indicator and signal, to two drive units. Additionally, each !
low pressure alarm. HCU provides the capability to acQust purge flow l to the two drives. A test port is provided on l
During normal operation, the flow control the HCU for connection of a portable test l valve maintains a constant system flow rate. station to allow controlled venting of the scram l This flow is used to purge the drives to prevent lasert line to test the FMCRD ball check valve l reactor water from entering the drive mechanisms. ' during plant shutdown. Operation of the electrical system that supplies scram signals to 44.1.2JJJ Purge Water Hender the HCU is described in Chapter 7.
The purge water header is located downstream The basic components in each HCU are: (1) from the flow control valve. The flow control manual, pneumatic and electrical valvest (2) en valve adjusts automatically to maintain constant accumulator; (3) related piping; (4) electrical flow as reactor vessel pressure changes. Because conaec Ioas; (5) fitters; aod (6) :
flow is constant, the differential pressure instrumentation (Figure 4.6 8). The components between the reactor vessel and CRD bydraulle and their functions are described in the system is maintained constant independent of following paragraphs. >
rector vessel pressure. A flow indicator in the control room monitors purge water flow. A (1) Scram Pilot Valve Assembly ;
differential pressure indicator in the control room indicates the difference between reactor The scram pilot valve assembly is operated vessel pressure and drive purge water pressure, from the RPS. The scram pilot valve assembly, ,
with two solenoids, controls the scram inlet A high differential pressure between the valve. The scram pilot valve assembly is reactor vessel and drive purge header could cause solenold operated and is normally energized. On control rods te drift inward. An alarm in the loss of electrical signal to the solenoids, such control room will alert the operator of high as the loss of external AC power, the inlet port differential pressure at a value below that at closes and the exhaust port opens. The pilot '
which actual rod drift will occur. Should high valve assembly (Figure 4.6 8) is designed so
- differential pressure occur, for example by that the trip system signal must be removed from failure of the flow control valve in a full open both solenoids before air pressure can be position, the existence of rod drift would be discharged from the scram valve operators. This .
sensed by the control rod drive separation prevents the inadvertent scram of both drives ;
switches and alarmed to the operator in the associat:d with a given HCU in the event of a control room. Simultaneously, the control system failure of one of the pilot valve solenoids, i would impose an automatic rod withdrawal block.
The ability of the system to provide hydraulle (2) Scram lnlet Valve l scram would not be affected by this condition. .
The scram inlet valve opens to supply Conversely, a failure of the flow control pressurized water to the bottom of the drive valve in the full closed position would result piston. This quick opening globe valve is in the loss of purge flow to the individual operated by an internal spring and system i drives. The drives are fully capable of pressure. It is closed by air pressure applied ,
functioning without purge water; however, loss of to the top of its diaphragm operator. A purge flow will result in increased drive position indicator switch on this valve ;
contamination by leakage of reactor water in to energizes a light in the control room as soon as the drives. The CRD system's scram function the valve starts to open.
l would not be affected by the loss of purge flow.
(3) Scram Accumulator l 4.6.1.2.3.2.4 Hydraulle Control Units {
The scram accumulator stores sufficient l Each hydraulic control unit (HCU) furnishes energy to fully insert two control rods at any (
l l
Amenomeni ruiu, na l
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3sA6100AB !
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accumulator charging line prevents loss of water water header is indicated in the control room.
l pressure in the event supply pressure is lost. An alara is provided to indicate escessive differential pressure which will lif t the ,
During normal plant operation, the accumulator contrel rods if aot limited. !
, piston is seated at the bottom of its cylinder. . '
I Loss of nitrogen decreases the nitrogen pressure, The pump purge water is furnished to the RIPS . . :
I which actuates a pressure switch and sounds an and RWCU pumps at the required flow rates as i i
alarm in the control room, specified on the CRDS process flow diagram I t (Figure 4.6 9). ,
To ensure that the accumulator is always able to produce a scram,it is continuously monitored To assure the continuous ability to trip, the for water leakage. A float. type level switch charging water header maintains the HCU :
actuates an alarm if water leaks past the piston accumulato S at a high pressure. The scram ;
barrier and collects in the accumulator valves remain closed sacept during and after e instrumentation block, trip operation, so that no flow passes through ,
the charging water header. Pressure in the ;
4.6.1.2.4 Control Rod Drive System Operation charging water header is monitored. A significant degradation in the charging header !
The operating modes of the control rod drive pressure will result in a low pressure warning !
system (CRDS) are normal operation, rod lasert. alarm and rod withdrawal b'ock, and, eventually, ,
tion / withdrawal, and scram. These operational re. actor scram if further degradation occurs, modes are described in the following sections. .
4.6.12.4.2 Control Red Immortion/ Withdrawal 4.6.1.2.4.1 Normal Operation Normal insertion and withdrawal of the 't During normal operation the CRDS provides the control rods is provided by the electric stepper i proper arnount of flow required for drive purging motor on the FMCRDs. The motors receive their and for pump purging (RIPS plus RWCU pumps). A insert / withdraw commands via signals from the multi stage centrifugal pump pressurites the rod control and information system (RC&lS). The system with water from the treated makeup water objective of the RC&lS is to provide the system (de. oxygenated) and/or condensate storage operator with the means to make changes in tank. CRD pump minimum bypass flow to the nuclear reactivity so that reactor power level condensate storage tank is utilized to prevent and distribution can be controlled. The system ;
pump overheating if the pump discharge is allows the operator to manipulate control rods, blocked. The total pump flow is the sum of this The design bases and further discussion of the '
bypass flow, the CRD purge flow through the flow RC&lS are covered in Chapter 7.
control valve, and the recirculation and reactor water cleanup pump purge flows. A full. capacity 4.6.1.2.43 Scram standby pump is available. Condensate water is processed by filters (drive water filters)in the Upon loss of electric power to both scram pump suction and discharge. A redundant set of pilot valve solenoids, the associated HCU drive water filters are provided and are normally applies the drive insert forces to its on standby. Differential pressure monitoring respective drives using a precharged accuraulator jdevices and control room alarms are used to contained within the HCU (The N.,/H2O monitor the filter elements to detect plugging of accumulator having previously been charg1d with the filters. charging water from the CRDS). The drives >
insert the control rod blades rapidly. The The purge water for each drive is provided water displaced from the drives is discharged through the purge water header. The purge water into the reactor vessel. Also, on receipt of a control valve automatically controls purge water scram signal, each FMCRD will automatically flow to the drive mechanisms. Differential start and the ball nut on each drive will be {
pressure between the reactor vessel and the purge driven upward by the screw shaft until it is Amendment Futur 4.69
'., 3sAs100AB
. .. ..a pi... m ;
l
. back in contact with the hollow piston. This materials, B,C powder, austealtic stainless !
completes the rod full.in lasertion and places steel, and in The case of the alternate control j
, the CRDS in a condition ready for restarting the rod, Hefalum have boon found suitable in meeting ;
. reactor, the demands of the BWR environment. 1 Specifically the B4 C containing tees are RAD After reactor scram, indication that the scram RESIST
- high purity 304 stainless steel with v has gone to completion (rods in full in position) special chemistry control on carbon and lowered ,
is displayed to the operator, impurity lisuits to resist irradi. tion assisted i atress corrosion cracking. The sheaths are type l Following scram completion (each ball out 316L stainless steel and the structure is type '
re.cageged with its hollow piston), the scra.n 504,304L or type 316L stainless steel.
signals are reset and each accumulator is e recharged with water from CRDS. 4.6.23.1J Diesmaleanl and Tolorsnee Analysis l
4.6.1.2.5 lastrumentation Layout studies are done to assure that, given I the worst combination of part tolerance ranges ;
The instrumentation for the CRDS is defined on at assembly, no laterference exists which will i the system P&lD, Figure 4.6 8. Supervisory restrict the passage of control rods. In instrumentation and alarms such as accumulator ' addition, preoperational verification is made on ;
trouble, low charging header pressure, purge each control blade system to show that the water / reactor vessel high differential pressure acceptable levels of operational performance are are adequate and permit surveillance of the CRD m et.
System's readiness.
4.6JJ.13 Thermal Analysis of the Tendency -
The design bases and further discussion are to Warp covered in Chapter 7.
The various parts of the control rod assembly 4.6.2 Evaluations of the CRDS remain at approximately the same temperature during reactor operation, negating the problem i 4.6.2.1 Fallure Mode and Effects Analysis of distortion or warpage. What little differential thermal growth could exist is '
This subject is covered in Appendix 15B. allowed for in the mechanical design. A minimum ;
axial gap is maintained between absorber rod ,
4.6.2.2 Protection from Common Mode Failures tubes and the control rod from assembly for the purpose. In addition, to further this end, The position on this subject is covered in dissimilar metals are avoided.
Appendix ISB.
4.6.23.1.4 Forces for Expulsion 4.6.23 Safety Evaluation An analysis has been performed which Safety evaluations of the control rods and evaluates the maximum pressure forces which control rod drives are deteribed below. Further could tend to eject a control rod from the description of the control rodt is contained in core. The results of this analysis are given in Section 4.2. Subsection 4.6.2.3.2.2.2.- In summary, if the check valve in the drive flange were to fall to 4.6.23.1 Control Rods close, which is unlikely, calculations and tests i indicate that the maximum ejection velocity )
4.6.23.1.1 Materials AdequacyThroughout would exceed allowable rates. However, a i Design Lifetime passive brake in the FMCRD prevents the rod I l ejection motion. !
The adequacy of the materials throughout the !
design life was evaluated in the mechanical 1 design of the control rods. The primary I
Amendment Futur 4.6 10
SaA6100AB dadandard Plant an c
, operating buffer under criteria for normal 4A23.2.2.2 Rapture of Hydraulic ume to and upset events and for an abnormally Detve Meeslag Flange
. operating buffer under criteria for upset
. events. For the case of a scram insert line break, a partial or complete circumferential opening is (5) The control rod is designed for lateral postulated at or near the point where the line displacements due to the maximum fuel enters the housing flange. This failure, if not channel deflection allowed within fuel mitigated by special design features, could channel design criteria under upset (OBE) result in rod ejection at speeds encoeding maal-events and faulted (SSE) events, mum allowable limits of 4 in/sec (assuming rod pattern control) or 6 inches maximum travel 4.6.23.2 Control Rod Deives distance before full stop. Failure of the scram insert line would cause loss of pressure to the 4.6.23.2.1 Evaluation etScrom T1me underside of the hollow piston. The force resulting from full reactor pressure acting on The rod scram function of the CRD system the cross. sectional area of the hollow piston, provides the negative reactivity insertion plus the weights of the control rod and hollow required by safety design basis 4.6.1.1.1(1), piston, is imposed on the ball nut. The ball The scram time shown in the description is out in turn translates this resultant force into adequate as shown by the transient analyses of a torque acting on the spindle. When this Chapter 15. torque exceeds the motor residual torque and seal ftlctics, reverse rotation of the spindle 4.623.2J Analysis of Malfunction Relating to will occur permitting rod withdrawal. Analyses Rod Withdrawal show that the forces generated during this post.
D ulated event can result in rod ejection speeds There are no known single malfunctions that which exceed the maximum allowable limits, cause the unplanned withdrawal of even a single control rod. However, if multiple malfunctions The FMCRD design provides two diverse means are postulated, studies show that an unplanned of protection against the results of a rod withdrawal can occur at withdrawal speeds postulated scram insert line failure. The first that vary with the combination of malfunctions means of protection is a ball check valve postulated. located in the middle flange of the drive at the scram port Reverse flow during a line break 4.6.23.2.2.1 Drive Housing Fallure will cause the ball to move to the closed position. This will prevent loss of pressure to l The bottom head of the reactor vessel has a the underside of the hollow piston, which in penetration for each CRD location. A drive turn will prevent the generation of loads on the housing is raised into position inside each drive which could cause rod ejection.
penetration and fastened by welding. The drive is raised into the drive housing and bolted to a The second means of protection is the FMCRD ,
flange at the bottom of the housing, brake described in Subsection 4.6.1.2.2.8. In i the event of the failure of the check valve, the l In the unlikely event of a failure of the passive brake will prevent the ball spindle
/ drive housing to vessel attachment weld rotation and rod ejection. ;
(including a failure through the housing or along !
the fusion line of the housing to stub tube weld) or th'e flange bolting attaching the drive to the housing, ejection of the CRD and attached control 4.6.23.2.23 Total Fallure of All Drive l rod is prevented by the integral internal blowout Flange Bolts 1 support. The details of the this internal blowout support structure are contained in The FMCRD design provides an anti rotation Section 4.6.1.2.2.9. j Amendment Futur 4.6 12 l
BM pi...
Am..a sissions. !
am e
. aucle.ar instrumentation; and The after.lastellation, prestartup tests (Chapter 14) include normal and scram motion and (b) when the rod is fully withdrav>a the
. are primarily intended to verify that piping, first time, observe that the drive will ,
valves, electrical components and instrumentation mot 30 to the overtravel posillon. )
are properly lastelled. The test specifications Observation of the separation switches ;
include criteria and acceptable ranges for drive provides direct ladication that the speed, scram valve response times, and control control rod is followlsg the drive pressures. These are tests intended more to during withdrawal, but does not provide J document system condition rather than tests of a direct check on coupling integrity, i performance. Additionally , observation of a response I from the suelear lastrumentation during As fuel is placed in the reactor, the startup as attempt to withdraw a control rod i test procedure (Chapter 14) is followed. The provides another ladirect indication I tests in this procedure are istended Io that the rod and drive are coupled. The )
demonstrate that the initial operational overtravel position feature provides a characteristics meet the limits of the positive check on the coupling :
specifications over the range of primary coolant integrity, for only an uncoupled drive l temperatures and pressures from ambient to can reach the overtravel position. !
operating. The detailed specifications and j procedures are similar to those in BWRs presently (4) During operation, accumulator presst.re and I under construction and in operation. level at the normal operating value are 1 verifled.
4.6.3.1J Surveillance Tests Experience with CRD systems of the same type The surveillance requirements (SR) for the CRD ladicates that weekly verification of ,
system are described below. While these accumulator pressure and level is sufficient requirements have not yet been formallred the to assure operability of the accumulator latent is to follow the general pattern portion of the CRD system, established for surveillance testing in BWRs presently under construction and in operation. (5) At the time of each major refueling outage, each op:rable control rod is subjected to (1) Sufficient control rods shall be withdrawn, scram time tests from the fully withdrawn following a refueling outage when core position, alterations are performed, to demonstrate with adequate shutdown margin that the core Experience indicates that the scram times of
! can be made suberitical at any time in the the control rods do not significantly change I subsequent fuel cycle with the one control over the time interval between refueling rod pair (having the same HCU) or one rod of outages. A test of the scram times at each maximun worth withdrawn and all other refueling outage is sufficient to identify operable tods fully inserted. any significant lengthening of the scram times.
- (2) Each partially or fully withdrawn control l j rod is exercised one or two steps at least 4.6.3.1.6 Functional Testa once each week.
l The detailed requirements for functional l (3) The coupling integrity shall be verified for testing have not as yet been formally each withdrawn control rod as follows: established, but the intent is to follow the general pattern established for such testing in l (a) when the rod is first withdrawn, observe BWRs currently under construction and in the control rod separation switch operation. As such, it is anticipated that the ;
response and discernible response of the functional testing program of the CRDS will '
consist of a five year maintenance life test and Amendment Futur 4 15 l
t BA6100AB WPlant aw e
,- a 1.5 times design life test program. In addition to maintenance and design life tests, ,
the program covers crud / contamination testing, '
. seismic misalignment, channel bulge, failed buffer, rod drop (to test hollow piston latch -
l functionality), and rod ejectioa (to test FMCRD l brake and scram inlet check valve functionality).
4.6.4 laforination for Combined Performano of Reactivity Control Systems 44.4.1 Velmerobility to Common Mode Failures The reactivity control system is located such that it is protected from common mode failures ;
due to missiles, failures of moderate and high ;
energy piping, and fire. Sections 3.4,3.5 and ,
3.6, and subsection 9,5.1 discuss protection of
~
essential systems again;t missiles, pipe breaks and fire. ,
t 44.4.2 Accidents Taking Credit for Multiple Reactivity Systems t There are no postulated accidents evaluated in Chapter 15 that take credit for two or more reactivity control systems preventing or mitigating each accident. '
4.6.5 Evaluation of Combined Performance As indicated in Subsection 4.6.4.2, credit is not taken for multiple reactivity control systems for any postulated accidents in Chapter 15.
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Figure 4.6-1 FINE MOTION CONTROL ROD DRIVE SCHEMATIC 4,6 17 Amec*at 10 i
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