ML20002B579
| ML20002B579 | |
| Person / Time | |
|---|---|
| Site: | La Crosse File:Dairyland Power Cooperative icon.png |
| Issue date: | 07/09/1980 |
| From: | Finnan C, Milos R, Yoli A DAIRYLAND POWER COOPERATIVE |
| To: | |
| Shared Package | |
| ML20002B576 | List: |
| References | |
| 5101-058, 5101-58, 81A0037, 81A37, NUDOCS 8012120241 | |
| Download: ML20002B579 (24) | |
Text
m DOCUMENT NO 81A0037 REV. O I
2N NUCLEAR ENERGY SERVICES. INC.
PAGE 0F O
LACROSSE BOILING WATER REACTOR REVIEW OF PLANT TRANSIENTS Project Application Prepared By A //
Date 5101-058 C. F. Finnan C 7. tm 4/jo/go APPROVALS TITLE / DEPT.
SIGN ATU R E DATE l
R$ne r'i sLQperations 7'7'80 Project Manager
/, - / 7-J'd QA Manager
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8012120 g f
g{ylg g DOCUMENT NO.
81A0037 am NUCLEAR ENERGY SERVICES, INC.
PAGE 2
OF 24
"*0 n o,'
DATE DESCRIPTION APPROVAL g
e
DOCUMENT NO.
8W037 my PAGE OF NUCLEAR ENERGY SERVICES, INC.
- 1. INTRODUCTION This report supplies the additional review and analysis of anticipated plant transients required in response to Section 2.1.9 of NUREG 0578, TMI-2 Lessons Learned Task Force Status Report and Short Term Recommendations.
- 2.
SUMMARY
OF RESULTS AND CONCLUSIONS Results of this review confirm and reinforce previous transient analyses of the LACBWR plant (Ref.1, 2, and 3) which demonstrate that fuel cladding integrity is maintained for all anticipated transients. It is shown that this result holds even assuming that the basic transients are compounded by highly unlikely combinations of equipment failures and operator errors.
The LACBWR plant combines an inherently self-controlling reactor with automatic reactor protection and engineered safeguard systems incorporating redundancy at both the system and component level. These features represent the predominant contribution to the safe operating characteristics of the plant. This review indicates, however, that a significant, though difficult to quantify, contribution to safety can be made by astute, well-trained operators who can make judicious use of available instrumentation to quickly diagnose the nature of the off-normal event, and take expeditious remedial action. No specific recommendatiors for improvements in this regard seem warranted for this plant.
Nonetheless, this report identifies specific transient sequences in which operator inter-vention is required to bring the plant to a safe condition, in the interest of promoting
' increased operator awareness of the more troublesome types of transients.
81A0037 DOCUMENT NO.
PAGE OF NUCLEAR ENERGY SERVICES. INC.
- 3. TRANSIENT ANA1.YSIS
3.1 INTRODUCTION
Anticipated operational transients at the LACBWR plant can be classified into the iollowing seven categories:
(1)
Reactor pressure increase (2)
Moderator temperature decrease (3)
Reactor vessel coolant inventory decrease (4)
Reactor pressure decrease (5)
Core coolant flow decrease (6)
Core coolant flow increase (7)
Positive reactivity insertion Previous studies (Ref. I and 2) have identified a spectrum of anticipated transients for the LACBWR plant. Transients in each category are described in brief below.
3.2 IDENTIFICATION OF TRANSIENTS 3.2.1 - Transients Resulting in a Reactor Pressure Increase 3.2.1.1 Generator Loss of Load Loss of electrical load connected to the generator results in acceleration of the turbine to an overspeed condition. As a result, the turbine stop valves close, shutting off steam flow from the reactor. Cessation of steam flow causes a rapid rise in pressure, which is relieved by automatic main steam bypass valve actuation. A partial scram signal is generated upon stop valve closure.
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3.2.1.2 Turbine Trip Excessive turbine overspeed or mechanical or hydraulic f ailures in the turbine or its auxiliaries will result in simultaneous closure of the turbine stop, reheat intercept, and governor valves. This interruption of steam flow causes reactor pressure to rise rapidly, initiating steam dump to the condenser via the main steam bypass valve.
3.2.1.3 Initial Pressure Regulator Failure (Increasing Pressure)
A failure of the initial pressure regulator system is conceivable such that the turbine inlet governing valve closes, causing a rapid rise in reactor pressure. This results in actuation of the main steam bypass valve to control pressure.
3.2. l A Main Steam Isolation Valve Closure Closure of the main steam isolation valve is initiated by various trip signals such as low reactor water level, low condenser vacuum, or low main steam line pressure (1000 psig)# MSIV closure initiates a full reactor scram and operation of the shutdown condenser. Shutdown condenser operation is initiated since MSIV closure isolates the reactor from its normal heat sink, the main condenser.
3.2.2 Transients Resulting in a Moderator Temperature Decrease 3.2.2.1 Uncontrolled increase in Feedwater Flow Should a failure of the feedwater control system occur such that excessive feedwater is introduced into the reactor, the subcooling of the water entering the ccre will be increased.
This results in a decrease in voids with a resultant increase in reactor power.
3.2.2.2 Loss of Feedwater Heater Loss of a feedwater heater results in a feedwater temperature reduction. This reduces the void content of the core, resulting in an increase in reactor power.
81A0037 DOCUMENT NO.
PAGE OF NUCLEAR ENERGY SERVICES, INC.
3.2.2.3 Liquid Poison Injection or ECCS operation Inadvertant operation of these systems results in direct addition of cold water into the core.
3.2.2.4 Isolated Loop Startup (Cold)
For this transient it is assumed that only one recirculating loop is operating and that the second, which is cold, is started. This results in a small flow of cold water into the core by means of the bypass line around the recirculation pump discharge isolation valve. Interlocks prevent opening of the isolation valve when the temperature of tha water in the recirculating loop is not close to that in the reactor. The decrease in the reactor water inlet temperature results in a power increase.
3.2.3.
Events Resulting in a Reactor Vessel Coolant Inventory Decrease 3.2.3.1 Loss of Feedwater Flow A failure of the feedwater system is assumed such that feedwater flow is completely lost. The reactor will continue to operate until the resulting decrease in water level closes the main steam isolation valve, starts the shutdown condenser, and scrams the reactor.
3.2.4 Events Resulting in a Reactor Pressure Decrease 3.2.4.1 Accidental Ogning of the Main Steam Bypass Valve A malfunction of the main steam bypass valve, causing inadvertant valve opening, will result in a decrease in reactor pressure until a MSIV closure signal is initiated.
This action scrams the reactor and initiates shutdown condenser operation.
3.2.4.2 Initial Pressure Regulator Failure (Decreasing Pressure)
A failure of the initial pressure regulator causing the turbine inlet valves to fail in the wide open position wil' have consequences similar to the case of accidental MSBV opening.
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DOCUMENT NO.
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3.2.5 Events Resulting in a Core Coolant Flow Decrease 3.2.5.1 Loss of Recirculation Flow Loss of one or both recirculation pumps results in a rapid decrease in core coolant flow rate. Loss of both recirculation pumps will result in a reactor scram. Loss of one pump may result in a scram depending on initial flow rate.
3.2.6 Transients Resulting in a Core Coolant Flow Increase 3.2. 6.1 Isolated Loop Startup (Hot)
This transient develops assuming that only one recirculation loop is operating and that a second, which is hot, is started. This results in an increase in core coolant flow rate with a subsequent increase in power.
3.2. 6.2 Recirculation Flow Control Failure (Increasing Flow)
For this transient, it is assumed that the reactor is operating at partial power (approx. 60%) and that the recirculation flow control system fails such that there is an increase in the recirculation flow rate. This results in a reactor power increase.
3.2.7 Transients Resulting in a Positive Reactivity insertion 3.2. 7.1 Control Rod Withdrawal at Power For this transient it is assumed that, due to equipment failure or operator error, a control rod is fully withdrawn while the reactor is operating at full power.
3.2.7.2 Control Rod Withdrawal at Startup This transient results from equ*pment failure or operator error.by which a control rod is fully withdrawn while the reactor is cold and critical.
81A0037 DOCUMENT NO.
PAGE OF NUCLEAR ENERGY SERVICES. INC.
- 4. DISCUSSION OF TRANSIENT SCENARIOS, ANALYS$ OF EFFECTS AND CONSEQUENCES, AND IDENTIFICATION OF REQUIRED OPERATOR ACTIONS 4.i TRANSIENTS RESULTING IN A REACTOR PRESSURE INCREASE Event trees for transient scenarios in this category appear in Figure 4-1.
It is apparent that the loss of external load and initial pressure regulator failure transient sequences are equivalent to, or quickly evolve into, turbine trip sequences. Turbine trip and MSIV closure are the only two distinct, independent transient scenarios in this category. These are examined below.
4.1.1 Turbine Trip 4.1.1.1 Normal Plant Response A turbine trip results in the closure of the reheat intercept, turbine inlet, and turbine stop valves. In addition, a signal for a partial scram is generated as the turbine stop valve leaves the full open position.
Steam flow from the reactor is completely interrupted, causing a rapid rise in reactor pressure. For initial power levels greater than about 60%, this increase in pressure may result in an increase in reactor power levei sufficient to initiate a second (full) scram signal. The main steam bypass valve opens, d' umping steam to the condenser to control pressure.
4.1.1.2 Description of Alternate Sequences Arising From Postulated Equipment Failures or Operator Errors l
A conceivable alternate abnormal transient sequence can be constructed based l
upon failure of the main steam bypass valve to open as required upon rising main
DOCUMENT NO.
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steam line pressure (see Figure 4-1.2). For this scenario, if no manual action is taken to open the valve, a scram will occur and shutdown condenser operation will automatically be initiated when reactor pressure increases to 1325 psig. The consequences of this accident have been found to be similar to the case of the MSIV closure transient. CPR remains well above the Jesign basis MCPR of 1.32.
No damage to the fuel will occur.
4.1.1.2 Requirements for Operator Action For the case in which shutdown condenser operation is automatically initiated, operator intervention to modulate steam flow to the condenser is the prescribed and correct course of action. This precludes cooldown rates which exceed the maximum rate permitted by the technical specifications.
No adverse conse-quences result from failure of the operator to take this action, however, since valve-wide-open shutdown condenser cooldown is self-limiting, and resulting cooldown rates will not cause f ailure of the reactor coolant pressure boundary nor result in f ailure of any saf ety related systems.
4.1.2 Main Steam Isolation Valve Closure l
l 4.1.2.1 Normal Plant Response Closure of the main steam isolation valve terminates steam flow from the reactor and completely isolates the reactor from its primary heat sink, the main l
condenser. Signals calling for full reactor scram and for shutdown condenser operation are initiated simultaneously with the MSIV leaving the " full open" position, thus limiting reactor heat input and providing an alternate heat sink for reactor pressure control.
Simulation of a MSIV closure transient for LACBWR transient using digital computer codes (Ref.1) indicates that no damage to the fuel will occur. With the shutdown condenser handling the decay heat load, a stable condition is main-tained.
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4.1.2.2 Alternate Sequences Arising from Postulated Equipment Failure or Operator Errors Possible variation on the basic MSIV closure scenario are indicated in the MSIV closure event tree of Figure 4-1.3. The upper branch proceeds as in the " normal" sequence, i.e., all automatic actions occur as required. At this point the reactor is scrammed and a sink is available for removal of decay heat.
Nevertheless, a completely stable state has not been reached at this point, since the shutdown condenser with inlet valves wide-open represents a heat removal capability in excess of the decay heat generation rate.
Operator action to manually throttle the steam flow to the shutdown condenser is therefore needed to maintain a stable hot shutdown condition (heat removal rate equal to decay heat generation rate at desired reactor pressure), or to achieve a cooldown within technical specification cooldown rate limitations.
The lower branch of the event tree in Figure 4-1.3 follows a sequence based upon the assumption that equipment failure occurs, such that signals for reactor scram and shutdown condenser operation are not generated on main steam isolation valve closure. This results in a pressure rise which increases reactor power due to a decrease in moderator voids. Reactor scram occurs at 120% of full power at
(
about 1.5 seconds af ter MSIV closure.
Pressure continues to increase until shutdown condenser operation is initiated at 1325 psig at approximately T = 6.00 seconds. While scram and shutdown condenser operation are somewhat delayed in this scenario, computer simulation (Ref.1) has shown that no damage to the core will occur.
l 4.1.2.3 Requirements for Operator Actions l
There are no initially required operator corrective actions for the MSIV closure transient.
Having recognized the incident as a MSIV closure transient, the operations shoud verify that all automatic safety actions have occured as l
required.
Subsequent to automatic shutdown condenser initiation, however, l
7 manual operator control of steaming rate to the shutdown condenser should be established to preclude excessive reactor cooldown rates.
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DOCUMENTr.O.
1 1I 24 PAGE OF NUCLEAR ENERGY SERVICES. INC.
4.2 TRANSIENTS RESULTING IN A MODERATOR TEMPERATURE DECREASE Characteristic of all transients in this category is a rapid increase in reactor power due to the increese in reactor inlet subcooling. For the more severe transients an overpower scram occurs at 120% of full power.
Of the four transients in this category listed in paragraph 3.2.2, only two are significant enough to result in a reactor scram. These are the uncontrolled feedwater addition and the inadyertent ECCS actuation.
These have similar consequences. Of the two, the uncontrolled feedwater addition transient is the more severe and is discussed below.
4.2.1 Increase in Feedwater Flow 4.2.1.1 Normal Plant Response Under the assumption that a f ailure in the feedwater control system occurs such that feedwater flow increases at the maximum rate to the maximum available for both feedwater pumps, a reactor scram on overpower will occur af ter a time I
delay of approximately nine.,econds (Ref.1). The CPR during the transient remains above 1.32. No damage occurs to the core. At this point the core is in a safe stable condition with adequate cooling available.
4.2.1.2 Alternate Transient Sequences l
Reactor scram does not end the transient, as feedwater flow still proceeds uncontrolled. From this point several alternative pathways exist as indicated in Figure 4-2.1.
Inspection of the event tree indicates that operator intervention is required to either reestablish control of feedwater flow, or to terminate feed-l water flow completely.
l 4.2.1.3 Requirements for Operator Action For this transient, active operator intervention is required to controf or terminate feedwater flow to the reactor. Failure to correct the feedwater-to-steam flow imbalance will result in extensive damage to the turbine from water carryover. If j
l the feedwater flow rate cannot be manually reduced and maintained at an 1
i equilibrium value, power to the feedwater pumps should be terminated.
81A0037 DOCUMENT NO.
NUCLEAR ENERGY SERVICES. INC.
PAGE OF 4.3 EVENTS RESULTING IN A REACTOR VESSEL COOLANT INVENTORY DECREASE These are potentially severe transients, since insufficient coolant inventory can lead directly to fuel damage. To ensure that an adequate core coolant inventory exists during both normal and off-normal operation, LACBWR design incorporates redundant reactor water level safety channels which automatically initiate the following action if reactor water level decreases to a pre-determined value: (1) reacter scram; (2) high pressure core spray; (3) main steam isolation valve closure.
The latter action initiates shutdown condenser operation.
4.3.1 Loss of Feedwater Flow 4.3.1.1 Normal Plant Response This scenario assumes that a failure in the feedwater system occurs such that feedwater flow to the reactor is completely cut off, and that no corrective action is taken by the operators initially to restore level. With the reactor still steaming at full power, the loss of feedwater will result in a steady decrease in water I
inventory. When the low level set-point for Reactor Level Channels 1 and 2 or 3 is reached, redundant signals are generated to scram the reactor, isolate the
(
reactor from the generator plant via MSIV closure, and initiate high pressure core I
spray to restore level. Shutdown condenser operation is initiated concurrent with l
MSIV closure to provide a sink for core af terheat. At this point the reactor is in a l
safe, stable configuration, cooldown may continue by means of shutdown con-denser and decay heat removal system, or the plant may be returned to power assuming the feedwater system fault can be expeditiously corrected.
4.3.1.2 Alternate Transient Sequences and Required Operator Actions Alternate (more severe) transient scenarios can be generated by assuming failure of each of the automatic safety features (singly) to perform when required.
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(1) Failure of High Pressure Core Spray System to Actuate Since MSIV closure terminates the decrease in reactor coolant inventory well before core uncovery, failure of the HPCS to actuate is inconsequential in this scenario. Decay heat is removed in a closed cooling path in which the shutdown condenser serves as the heat sink.
(2) Failure of the Scram System to Shut Down the Reactor This scenario has beei analyzed in Reference 2 under the assumptions that: (a) feedwater flowrate goes to zero in 2 seconds; (b) recirculation pumps are not cut back to 80% of rated speed when the low level scram setpoint is reached; (c) at 1350 psig, the recirculation pumps are tripped. Results of a computer simulation show that approximately 9 seconds af ter the feedwater pumps trip, reactor power begins to decrease due to the decrease in inlet subcooling. At 14 seconds, the reactor water level reaches the low water level scram set-point. The main steam isolation valve begins to close and reactor vessel pressure begins to rise. At 26 seconds the vessel pressure reaches 1406 psia and the relief valves open. Pressure peakr at 1420 psia and then decreases, the relief valves closing at 44 seconds into l
the transient. the MCHFR remain:, above the steady-state level during this accident and there is no damage to the core.
l (3) Failure of the MSIV to Close The assumed complete loss of the feedwater pumps limits use of the main l
condenser as a heat sink during this transient. It is therefore necessary to isolate the turbine from the reactor and to establish a closed cooling circuit through the shutdown condenser. If MSIV closure is not accomplished automatically, then manual action to close the MSIV, the turbine building steam isolation valve, or turbine stop valve is called for.
81A0037 DOCUMENT NO.
14 24 PAGE OF NUCLEAR ENERGY SERVCES. INC.
(4) Failure of Shutdown Condenser to Initiate Automatically on MSIV Closure Under the circumstances of the given scenario, failure of a shutdown condenser actuation signal to be generated by MSIV closure results in loss of heat sink for reactor core decay heat. As a result, reactor pressure will rapidly increase. A second, redundant signal to establish steam flow to the shutdown condenser will be generated, however, when reactor pressure reaches 1325 psig. This arrests the pressure surge well below the set-point of the main steam safety valves and reestablishes a heat sink for decay he't.
Nn direct operation intervention is rect" red initially under this scenario to avc:c adverse consequences. Cooldown or hot shutdown can subsequently be achieved through manual control of decay heat removal through the shutdown condenser.
4.4 EVENTS RESULTING IN A REACTOR PRESSURE DECREASE Event trees for these transients appear in Figure 4-4.
In general, these transients are characterized by an initial decrease in reactor power due to an increase in reactor moderator voids. Subsequent plant response depends on the specific transient scenario.
4.4.1 Inadvertent Opening of the Turbine Bypass Valve 4.4.1.1 Normal Plant Response Inadvertent, full opening of the main steam bypass valves results in a decrease in pressure and a rapid decrease in reactor power. Within 3 seconds the turbine inlet valves close due to the decreased reactor pressure.
At 9 seconds into the transient, the subcooling of the water entering the reactor increases, resulting in an increase in reactor power. The magnitude of this power increase is sufficient l
to initiate a reactor high power level scram at approximately 10 seconds into the transient.
Reactor pressure will continue to decrease until MSIV closure is automatically initiated at the low pressure trip point of 1000 psig. Reactor decay l
heat is dissipated by means of the shutdown condenser.
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4.4.1.2 Alternete Triubient Sequences Variant transient sequences resulting from various assumed equipment failures are shown graphically in Figure 4-4.1. Due to the redunduncy and depth of the safety systems and the inherent self-controlling feature of the reactor, no adverse consequences arise for a wide-range of assumed single failures.
4.4.1.3 Requirements for Operator Action Assuming no operator intervention at the outset of the transient to close the turbine bypass valve, plant protective features will automatically actuate to bring the plant to a safe condition.
No direct manual operator action is initially required.
Through the transient, the operators role is supervising, watching process variables and ensuring that required safety system actuations occur as required.
4.4.2 Initial Pressure Regulator Failtre (Decreasing Pressure) 4.4.2.1 Normal Plant Response Failure of the initial pressure regulator such that the turbine inlet valves open fully results in an increase in steam flow from the reactor with a consequent decrease in reactor pressure.
Reactor power decreases through the first few seconds of the transient due to the increase in moderator void content. At 9 seconds into the transient, the subcooling of the water entering the core increases, causing reactor power to undergo a transient increase (9 seconds is the transport time of the recirculation loops).
This power surge peaks out at approximately 102% of full power at 12 seconds into the transient.
Reactor power and pressure continue to decrease from this point until at 19 seconds into the transient the main steam isolation valve closes at its low pressure closure set-point of 1000 psig.
MSIV closure simultaneously initiates reactor scram and shutdown condenser operation.
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4.4.2.2 Alternate Tranrient Sequences These are shown graphically in Figure 4-4.2. As for the case of inadvertent main steam bypass valve opening this transient does not progress in directions which would yield adverse consequences or require extraordinary operator perception or action.
4.4.2.3 Requirements for Operator Action As for the case of inadvertent turbine bypass valve opening, operator intervention can arrest the course of the transient in its early stages; on the other hand, initial operator inaction does not lead to adverse consequences. Automatic shutdown condenser operation should be followed by manual operator control of the reactor cooldown rate via modulation at steam flow through the tube side of the shutdown condenser.
4.5 EVENTS RESULTING IN A CORE COOLANT FLOW DECREASE 4.5.1 Loss of Recirculation Flow Coolant flow through the reactor core at LACBWR is supplied by two vertical, mixed-flow centrifugal pumps in two coolant loops.
Loss of power to one or both pumps, pump seizure, or shaf t breakage could result in partial or complete loss of core coolant flow.
Nominal flow per pump at full power is 15,000 gpm.
Starting conditions and assumptions for this transient are as follows:
(1) The reactor is initially operating at 102% of rated power (2) Both recirculation pumps are lost abruptly and simultaneously.
4.5.1.1 Normal Plant Response This transient has been previously analyzed in Reference 1.
Results of a computer simulation demonstrate that immediately following loss of the pumps, reactor power decreases rapidly due to the increase in moderator voids. When the recirculation flow decays to 30% of its full flow value, the reactor is automatic-ally scrammed. CPR calculations indicate that no damage will occur to the fuel as the CPR remains above 1.32 at all times. Cooldown proceeds via the main or shutdown condenser.
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4.5.1.2 Alternate Transient Sequences Figure 4-5.1 shows an alternate transient path based upon a failure of the reactor protection system to scram the reactor as would normally occur when recircula-tion flow decays to 30% of full flow.
This transient has been analyzed in Reference 2. Results of the analysis indicate that for the case of loss of flow without scram, the MCHFR (minimum critical heat flux ratio) decreases rapidly and attains a minimum value in about 3 seconds. It remains, however, above 1.0, so that no damage to the fuel will occur.
Eventually, heat flux decreases significantly and natural circulation flow is enough to maintain adequate thermal margin.
4.5.1.3 Requirements for Operator Action For the normal plant response, no operator action is required. However, attempts should be made to manually initiate scram if automatic scram does not occur.
4.6 EVENTS RESULTING IN A REACTOR CORE COOLANT FLOW INCREASE Of the two transients identified in this category, the isolated loop startup is more severe.
The analysis for this category will therefore be limited to this transient only.
4.6.1 Isolated Loop Startup (Hot)
LACBWR has two forced circulation pumping loops that connect to the common inlet and outlet manifolds outside the reactor vessel. As a precaution against excessive, inadvert-ent positive reactivity insertion, interlocks have been provided which: (a) prevent starting a pump motor unless its associated discharge valve is closed; (b) prevent the discharge j
valve from opening unless the temperatures of the two recirculation loops are nearly l
l equal. Additionally, the opening time of the recirculation pump discharge roto-valves is greater than four minutes by design.
l For this analysis it is assumed that full flow is inadvertently established in an idle loop when the reactor is at power. Initial power level is assumed to be at 52% of rated power; recirculation flow increases from 15,000 gpm to 30,000 gpm in 20 seconds; the isolated l
loop is 25 F colder than the operating loop. Refer to Figure 4-6.1.
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4.6.1.1 Normal Plant Response Power increases rapidly due to the positive reactivity contribution of the colder fluid as it reaches the core. At approximately 16 seconds into the transient a scram signal will be generated on high neutron flux level. This terminates the transient. No damage to the core will result from this transient as the CPR remains above 1.32 at all times.
4.6.1.2 Alternate Transient Sequences The only definable alternative sequence for this transient is to assume the transient occurs without the scram on high neutron flux. This situation, which has been previously analyzed in Reference 2, indicates that, assuming no operator action, the power rises rapidly but then is reduced and attains a steady-state value of about 90% of full power. Critical heat flux calculations indicate that no damage to the core will occur. There are no requirements for operator action.
4.7 EVENTS RESULTING IN POSITIVE REACTIVITY INSERTION The only significant transient in this category is the uncontrolled r od withdraassi at power.
This event has been analyzed in References 1 and 2.
There are no adverse consequences, no automatic safety system actuations, and no requirements for operator action.
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- 5. REFERENCES 1.
NES Report 0 81 A0025, Response to Question 4 - Transient Analysis for LACBWR Reload Fuel, February 18,1977.
l 2.
Gulf Nuclear Fuels, Co. Report 5S-1178, Anticipated Transients Without Scram at the LaCroste Boiling Water Reactor, February 28,1974.
3.
Safety Analysis Report for the Lacrosse Boiling Water Reactor, Chapter 14.
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81A0037 DOCUMENT NO.
PAGE OF NUCLEAR ENERGY SERVICES. INC.
, FIGURE 4-1.1 GENERATOR LOSS OF LOAD Turbine inlet Figure 4-1.2 Valve Closes a
Turbine-Generator Load Rejection Turbine Inlet Valve Turbine Trip f ails to close rapidly - (Figure 4-1.2) enough to prevent overspeed condition (106% rated speed)
FIGURE 4-1.2 TURBINE TRIP Main Steam Bypass Valve opens
/
to relieve pressure l
Full scram on Turbine Trip w/ simul 2 MSBV fails to open taneous partial scram MSBV open to relieve
[ pressure No scram on high flux Full reactor scram MSBV fails to on high pressure; open shutdown condenser initiation on high pressure (1325 psig)
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FIGURE 4-1.3 MSIV CLOSURE Operator takes manual l
control of the S.C. to-(A) i Reactor scram, S.C.
regulate rate of heat I
initiation upon MSIV removal leaving full open pos. \\
No operator action a(B)
MSIV Closes Operator takes manual
'o scram or S.C.
Reactor scram, S.C.
control of the S.C.-(A) initiation on MSIV initiation on high to regulate rate of closure reactor pressure heat removal No operator action-(B)
(A)
Cooldown proceeds normally, or hot shutdown maintained (B)
Unsupervised cooldown of reactor occurs FIGURE 4-1.4 INITIAL PRESSURE REGULATOR FAILURE (INCREASING PP. ESSURE)
Initial Pressure Turbine Inlet Reg. Failure Valve closes
- Figure 4-1.2 l
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FIGURE 4-2.1 FEEDWATER CONTROL SYSTEM FAILURE (INCREASING FLOW)
Operator throttles feedwater control valve & reestablishes level p (A)
Feedwater Control System f ails, pumps go to Operator trips RFW pumps
> (B) maximum speed A
Operator takes no action p (C)
Reactor scram on high power (A)
Cooldown progresses normally (or hot shutdown maintained) from this point using main condenser as heat sink.
Operator closes MSIV &
Cooldown progresses (or hot shutdown verifies S.C. initiation maintained) using shutdown condenser as heat sink.
(B)
Operator takes no MSIV closes on low Cooldown progresses further action Rx level, initiating (or hot shutdown S.C. operation rpaintained) using l
shutdown condenser (C)
Reactor level increases uncontrolled:
steam lines flood, extensive turbine damage from water carryover likely. No damage to core, as excess feedwater ensures core cooling.
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FIGURE 4-3.1 FAILURE OF FEEDWATER PUMP (S)
(DECREASING FLOW)
High pressure core spray actuates
- Reactor water Reactor Feedwater l
level decreases d
MSIV closes
- Pumps fail Shutdown condenser actuates
- Rx scram on low level *
- See text for consideration of f ailure of each of these automatic safety actuaticns to occur (singly).
FIGURE 4 4.1 INADVERTENT OPENING OF THE TURBINE BYPASS VALVE Operator closes valve; transient ends.
Bypass Valve opens MSIV closes on low MSBV remains open reactor pressure (1000 psi)
Reactor scram, shutdown con-denser cooling initiated.
FIGURE 4-4.2 INITIAL PRESSURE REGULATOR FAILURE (DECREASING PRESSURE)
MSIV clos'es on TIV remains low Rx pressure; shutdown open condenser cooling initiated Turbine Inlet Valve Manual control of turbine f ails open load established by operator Operator trips turbine x Figure 4-1.2 mo.....e e - - - -,
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81A0037 DOCUMENT NO.
PAGE OF NUCLEAR ENERGY SERVICES. INC.
FIGURE 4-5.1 LOSS OF RECIRCULATION FLOW Reactor scram Transient terminated (Iow flow)
Recirculation Pumps trip Low flow scram Reactor power drops to =10%
f ails to occur rated power within 2 seconds; MCHFR decreases rapidly &
attains a minimum value
>l.0. Heat flux subsequently decreases significantly &
natural circulation is enough to maintain adequate thermal margin.
FIGURE 4-6.1 ISOLATED LOOP STARTUP (HOT)
Reactor scram 1
(high neutron flux)
Transient terminated Isolated Recirc.
Pump starts High flux scram Power increases rapidly, then f ails to occur drops back & stabilizes at 90% of rated power. No core damage occurs.
)