ML062840176
ML062840176 | |
Person / Time | |
---|---|
Site: | Calvert Cliffs |
Issue date: | 09/27/2006 |
From: | Calvert Cliffs, Constellation Energy Group |
To: | Office of Nuclear Reactor Regulation |
References | |
Download: ML062840176 (32) | |
Text
SITs B 3.5.1 B 3.5 EMERGENCY CORE COOLING SYSTEM (ECCS)
B 3.5.1 Safety Injection Tanks (SITs)
BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.1-1Revision 2BACKGROUNDThe function of the four SITs is to inject large quantities of borated water to the reactor vessel following the blowdown phase of a large break loss of coolant accident (LOCA) and to provide inventory to help accomplish the
refill phase that follows thereafter.
The blowdown phase of a large break LOCA is the initial period of the transient during which the Reactor Coolant
System (RCS) departs from equilibrium conditions, and heat
from fission product decay, hot internals, and the vessel
continues to be transferred to the reactor coolant. The
blowdown phase of the transient ends when the RCS pressure
falls to a value approaching that of the containment
atmosphere.
The refill phase of a LOCA follows immediately where reactor coolant inventory has vacated the core through steam flashing and ejection out through the break. The core is essentially in adiabatic heatup. The rest of the SITs' inventory is then available to help fill voids in the lower
plenum and reactor vessel downcomer to establish a recovery
water level at the bottom of the core and continue reflood of the core with the addition of safety injection water.The SITs are pressure vessels partially filled with borated
water and pressurized with nitrogen gas. The SITs are
passive components, since no operator or control action is
required for them to perform their function. Internal tank
pressure is sufficient to discharge the contents to the RCS, if RCS pressure decreases below the SIT pressure.
Each SIT is piped into an RCS cold leg via the injection lines utilized by the High Pressure Safety Injection and Low
Pressure Safety Injection (HPSI and LPSI) systems. Each SIT
is isolated from the RCS by a motor
-operated isolation valve and two check valves in series. The motor
-operated isolation valves are normally open, with power removed from
the valve motor to prevent inadvertent closure prior to or
during an accident.
ECCS - Operating B 3.5.2 B 3.5 EMERGENCY CORE COOLING SYSTEM (ECCS)
B 3.5.2 ECCS - Operating
BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.2-1Revision 15BACKGROUNDThe function of the ECCS is to provide core cooling and negative reactivity, to ensure that the reactor core is protected after any of the following accidents:a.Loss of coolant accident; b.Control element assembly ejection accident; c.Secondary event, including uncontrolled steam release or excess feedwater heat removal event; andd.Steam generator tube rupture.
The addition of negative reactivity by the ECCS during a secondary event where primary cooldown could add enough
positive reactivity to achieve criticality and return to
significant power was considered in design requirements for
the ECCS.There are two phases of ECCS operation: injection and recirculation. In the injection phase, all injection is initially added to the RCS via the cold legs. After the refueling water tank (RWT) has been depleted, the ECCS
recirculation phase is entered as the ECCS suction is
automatically transferred to the containment sump.
Two redundant, 100% capacity trains are provided. In MODEs 1 and 2, and MODE 3 with pressurizer pressure 1750 psia, each train consists of HPSI and LPSI charging subsystems. In MODEs 1 and 2, and MODE 3 with pressurizer
pressure 1750 psia, both trains must be OPERABLE
. This ensures that 100% of the core cooling requirements can be provided in the event of a single active failure.
A suction header supplies water from the RWT or the containment sump to the ECCS pumps. Separate piping
supplies each train. The discharge headers from each HPSI
pump divide into four supply lines. Both HPSI trains feed
into each of the four injection lines. The discharge header
which is fed from both LPSI pumps divides into four supply
lines, each feeding the injection line to each RCS cold leg.
ECCS - Operating B 3.5.2 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.2-2Revision 15 For LOCAs that are too small to initially depressurize the RCS below the shutoff head of the HPSI pumps, the steam generators must provide the core cooling function
.During low temperature conditions in the RCS, limitations
are placed on the maximum number of HPSI pumps that may be
OPERABLE. Refer to LCO 3.4.12 Bases, for the basis of these
requirements.
During a large break LOCA, RCS pressure will decrease to 200 psia in 20 seconds. The safety injection systems are actuated upon receipt of a SIAS. If offsite power is available, the safeguard loads start immediately. If
offsite power is not available, the engineered safety
feature (ESF) buses shed normal operating loads and are
connected to the diesel generators. Safeguard loads are
then actuated in the programmed time sequence. The time
delay associated with diesel starting, sequenced loading, and pump starting determines the time required before pumped
flow is available to the core following a LOCA.
The active ECCS components, along with the passive SITs and RWT, covered in LCO 3.5.1 and LCO 3.5.4, provide the cooling
water necessary to meet Reference 1, Appendix 1C, Criterion 44.APPLICABLEThe LCO helps to ensure that the following acceptance SAFETY ANALYSEScriteria, established by Reference 2 for ECCSs, will be met following a LOCA:a.Maximum fuel element cladding temperature is 2200°F;b.Maximum cladding oxidation is 0.17 times the total cladding thickness before oxidation;c.Maximum hydrogen generation from a zirconium water reaction is 0.01 times the hypothetical amount generated if all of the metal in the cladding cylinders surrounding the fuel, excluding the cladding
surrounding the plenum volume, were to react;d.Core is maintained in a coolable geometry; ande.Adequate long-term core cooling capability is maintained.
ECCS - Operating B 3.5.2 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.2-3Revision 15 The LCO also limits the potential for a post-trip return to power, following a steam line break, and ensures that
containment temperature limits are met.
Both HPSI and LPSI subsystems are assumed to be OPERABLE in the large break LOCA analysis at full power (Reference 1, Section 14.17). This analysis establishes a minimum
required runout flow for the HPSI and LPSI pumps, as well as
the maximum required response time for their actuation. The
HPSI pumps are credited in the small break LOCA analysis.
This analysis establishes the flow and discharge head
requirements at the design point for the HPSI pump. The
steam generator tube rupture and steam line break analyses
also credit the HPSI pumps, but are not limiting in their
design.The large break LOCA event with a loss of offsite power and a single failure (disabling one ECCS train) establishes the
OPERABILITY requirements for the ECCS. During the blowdown
stage of a LOCA, the RCS depressurizes as primary coolant is
ejected through the break into Containment. The nuclear
reaction is terminated either by moderator voiding during
large breaks or control element assembly insertion during
small breaks. Following depressurization, emergency cooling
water is injected into the cold legs, flows into the
downcomer, fills the lower plenum, and refloods the core.
On smaller breaks, RCS pressure will stabilize at a value dependent upon break size, heat load, and injection flow.
The smaller the break, the higher this equilibrium pressure.
In all LOCA analyses, injection flow is not credited until
RCS pressure drops below the shutoff head of the HPSI pumps.
The LCO ensures that an ECCS train will deliver sufficient water to match decay heat boiloff rates soon enough to
minimize core uncovery for a large LOCA. It also ensures
that the accident assumptions are met for the small break
LOCA and steam line break.
For smaller LOCAs the steam generators serve as the heat sink to provid e core cooling.
Emergency Core Cooling System - Operating satisfies
10 CFR 50.36(c)(2)(ii), Criterion 3.
ECCS - Operating B 3.5.2 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.2-4Revision 15LCOIn MODEs 1, 2, and 3, with pressurizer pressure 1750 psia, two independent (and redundant) ECCS trains are required to ensure that sufficient ECCS flow is available, assuming there is a single failure affecting
either train. Additionally, individual components within
the ECCS trains may be called upon to mitigate the
consequences of other transients and accidents.
In MODEs 1 and 2, and in MODE 3 with pressurizer pressure 1750 psia, an ECCS train consists of a HPSI subsystem, and a LPSI subsystem
.Each HPSI and LPSI train includes the piping, instruments, and controls to ensure the availability of an OPERABLE flow
path capable of taking suction from the RWT on a SIAS and
automatically transferring suction to the containment sump
upon a recirculation actuation signal.
During an event requiring ECCS actuation, a flow path is
provided to ensure an abundant supply of water from the RWT
to the RCS, via the HPSI and LPSI pumps and their respective
supply headers, to each of the four cold leg injection
nozzles. In the long-term, this flow path may be switched
to take its supply from the containment sump and to supply
part of its flow to the RCS hot legs via the pressurizer or
the shutdown cooling (SDC) suction nozzles.
The flow path for each train must maintain its designed
independence to ensure that no single failure can disable
both ECCS trains.
In addition for the HPSI pump system to be considered OPERABLE, each HPSI pump system (consisting of a HPSI pump
and one of two safety injection headers) must have balanced
flows, such that the sum of the flow rates of the three lowest flow legs is 470 gpm.APPLICABILITYIn MODEs 1 and 2, and in MODE 3 with RCS pressure 1750 psia, the ECCS OPERABILITY requirements for the limiting DBA large break LOCA are based on full power operation. Although reduced power would not require the
same level of performance, the accident analysis does not
provide for reduced cooling requirements in the lower MODEs.
ECCS - Operating B 3.5.2 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.2-5Revision 15 The HPSI pump performance is based on the small break LOCA, which establishes the pump performance curve and has less
dependence on power.
The requirements of MODE 2, and MODE 3 with RCS pressure 1750 psia, are bounded by the MODE 1 analysis.The ECCS functional requirements of MODE 3, with RCS pressure 1750 psia, and MODE 4 are described in LCO 3.5.3.
In MODEs 5 and 6, unit conditions are such that the probability of an event requiring ECCS injection is
extremely low. Core cooling requirements in MODE 5 are
addressed by LCO 3.4.7 and LCO 3.4.8. MODE 6 core cooling
requirements are addressed by LCO 3.9.4 and LCO 3.9.5.ACTIONSA.1 If one or more trains are inoperable and at least 100% of
the ECCS flow equivalent to a single OPERABLE ECCS train is
available, the inoperable components must be returned to
OPERABLE status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. The 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> Completion
Time is based on an Nuclear Regulatory Commission study (Reference 3) using a reliability evaluation and is a
reasonable amount of time to effect many repairs.
An ECCS train is inoperable if it is not capable of delivering the design flow to the RCS. The individual
components are inoperable if they are not capable of
performing their design function, or if supporting systems
are not available.
The LCO requires the OPERABILITY of a number of independent subsystems. Due to the redundancy of trains and the
diversity of subsystems, the inoperability of one component
in a train does not render the ECCS incapable of performing
its function. Neither does the inoperability of two
different components, each in a different train, necessarily
result in a loss of function for the ECCS. The intent of
this Condition is to maintain a combination of OPERABLE
equipment such that 100% of the ECCS flow equivalent to 100%
of a single OPERABLE train remains available. This allows
increased flexibility in plant operations when components in
opposite trains are inoperable.
ECCS - Operating B 3.5.2 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.2-6Revision 15 An event accompanied by a loss of offsite power and the failure of an emergency diesel generator can disable one
ECCS train until power is restored. A reliability analysis (Reference 3) has shown that the impact with one full ECCS
train inoperable is sufficiently small to justify continued
operation for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
Reference 4 describes situations in which one component, such as a SDC total flow control valve, can disable both
ECCS trains. With one or more components inoperable, such
that 100% of the equivalent flow to a single OPERABLE ECCS
train is not available, the facility is in a condition
outside the accident analyses. Therefore, LCO 3.0.3 must be
immediately entered.
B.1 and B.2 If the inoperable train cannot be restored to OPERABLE status within the associated Completion Time, the plant must
be brought to a MODE in which the LCO does not apply. To
achieve this status, the plant must be brought to at least
MODE 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and pressurizer pressure reduced to 1750 psia within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. The allowed Completion Times are reasonable, based on operating experience, to reach the required unit conditions from full power in an orderly
manner and without challenging unit systems.SURVEILLANCESR 3.5.2.1 REQUIREMENTS Verification of proper valve position ensures that the flow
path from the ECCS pumps to the RCS is maintained.
Misalignment of these valves could render both ECCS trains
inoperable. Securing these valves in position by
interrupting the control signal to the valve operator, ensures that the valves cannot be inadvertently misaligned.
These valves are of the type described in Reference 4, which
can disable the function of both ECCS trains and invalidate
the accident analysis. A 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> Frequency is considered
reasonable in view of other administrative controls ensuring
that a mispositioned valve is an unlikely possibility.
ECCS - Operating B 3.5.2 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.2-7Revision 15 SR 3.5.2.2 Verifying the correct alignment for manual, power-operated, and automatic valves in the ECCS flow paths provides
assurance that the proper flow paths will exist for ECCS
operation. This SR does not apply to valves that are
locked, sealed, or otherwise secured in position, since
these valves were verified to be in the correct position
prior to locking, sealing, or securing. A valve that
receives an actuation signal is allowed to be in a
non-accident position provided the valve automatically
repositions within the proper stroke time. This SR does not
require any testing or valve manipulation. Rather, it
involves verification that those valves capable of being
mispositioned are in the correct position.
The 31 day Frequency is appropriate because the valves are operated under procedural control and an improper valve
position would only affect a single train. This Frequency
has been shown to be acceptable through operating
experience.
SR 3.5.2.3 Periodic surveillance testing of the HPSI and LPSI pumps to detect gross degradation caused by impeller structural
damage or other hydraulic component problems is required by
the American Society of Mechanical Engineers Code,Section XI. This type of testing may be accomplished by
measuring the pump developed head at only one point of the
pump characteristic curve. This verifies both that the
measured performance is within an acceptable tolerance of
the original pump baseline performance and that the
performance at the test flow is greater than or equal to the
performance assumed in the unit safety analysis.
Surveillance Requirements are specified in the Inservice
Testing Program, which encompasses American Society of
Mechanical Engineers Code,Section XI. American Society of
Mechanical Engineers Code,Section XI provides the
activities and Frequencies necessary to satisfy the
requirements.
ECCS - Operating B 3.5.2 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.2-8Revision 15 SR 3.5.2.4 The Surveillance Requirement was deleted in Amendment Nos. 260/237.
SR 3.5.2.5, SR 3.5.2.6, and SR 3.5.2.7 These SRs demonstrate that each automatic ECCS valve actuates to the required position on an actual, or simulated
SIAS, and on a recirculation actuation signal; that each
ECCS pump starts on receipt of an actual or simulated SIAS;
and that the LPSI pumps stop on receipt of an actual or
simulated recirculation actuation signal. This Surveillance
is not required for valves that are locked, sealed, or
otherwise secured in the required position under
administrative controls. In order to assure the results of
the low temperature overpressure protection analysis remain
bounding, whenever flow testing into the RCS is required at RCS temperatures 365F (Unit 1), 301F (Unit 2), the HPSI pump shall recirculate RCS water (suction from the RWT isolated) or the requirements of LCO 3.4.12, shall be
satisfied. The 24 month Frequency is based on the need to
perform these surveillance tests under the conditions that
apply during a plant outage and the potential for unplanned
transients if the surveillance tests were performed with the
reactor at power. The 24 month Frequency is also acceptable
based on consideration of the design reliability (and
confirming operating experience) of the equipment. The
actuation logic is tested as part of the Engineered Safety
Feature Actuation System testing, and equipment performance
is monitored as part of the Inservice Testing Program.
SR 3.5.2.8 Periodic inspection of the containment sump ensures that it is unrestricted and stays in proper operating condition.
The 24 month Frequency is based on the need to perform this
surveillance test under the conditions that apply during an
outage, on the need to have access to the location, and on
the potential for unplanned transients if the surveillance
test were performed with the reactor at power. This
Frequency is sufficient to detect abnormal degradation and
is confirmed by operating experience.
ECCS - Operating B 3.5.2 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.2-9Revision 15 SR 3.5.2.9 Verifying that the SDC System open-permissive interlock is OPERABLE ensures that the SDC suction isolation valves are
prevented from being remotely opened when RCS pressure, is
at or above, the SDC System design suction pressure of
350 psia. The suction piping of the LPSI pumps, is the SDC
component with the limiting design pressure rating. The
interlock provides assurance that double isolation of the
SDC System from the RCS is preserved whenever RCS pressure, is at or above, the design pressure. The 309 psia value
specified in the Surveillance is the actual pressurizer
pressure at the instrument tap elevation for PT-103 and
PT-103-1 when the SDC System suction pressure is 350 psia.
The procedure for this surveillance test contains the
required compensation to be applied to this value to account
for instrument uncertainties. This surveillance test is
normally performed using a simulated RCS pressure input
signal. The 24 month Frequency is based on the need to
perform this surveillance test under conditions that apply
during an outage. The 24 month Frequency is also acceptable
based on consideration of the design reliability (and
confirming operating experience) for the equipment.REFERENCES1.UFSAR2.10 CFR 50.46, "Acceptance Criteria for Emergency Core Cooling Systems for Light Water Nuclear Power Plants"3.Nuclear Regulatory Commission Memorandum to V. Stello, Jr., from R. L. Baer, "Recommended Interim Revisions to
LCOs for ECCS Components," December 1, 19754.Inspection and Enforcement Information Notice No. 87-01, "RHR Valve Misalignment Causes Degradation of ECCS in PWRs," January 6, 1987 ECCS - Shutdown B 3.5.3 B 3.5 EMERGENCY CORE COOLING SYSTEM (ECCS)
B 3.5.3 ECCS - Shutdown
BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.3-1Revision 2BACKGROUNDThe Background S ection for B 3.5.2, is applicable to these Bases, with the following modification.
In MODE 3 with pressurizer pressure 1750 psia and in MODE 4, an ECCS train is defined as one HPSI subsystem. The HPSI flow path consists of piping, valves, and pumps that enable water from the RWT to be injected into the RCS following the accidents described in B 3.5.2.APPLICABLEThe Applicable Safety Analyses section of B 3.5.2 isSAFETY ANALYSESapplicable to these Bases.
Due to the stable conditions associated with operation in MODE 3 with RCS pressure 1750 psia and MODE 4, and the reduced probability of a DBA , the ECCS operational requirements are reduced. Included in these reductions is that certain automatic SIASs are not available. In this MODE, sufficient time exists for manual actuation of the
required ECCS to mitigate the consequences of a DBA.
Only one train of ECCS is required for MODE 3 with RCS pressure 1750 psia and MODE 4. Protection against single failures is not relied on for this MODE of operation.Emergency Core Cooling System - Shutdown satisfies 10 CFR 50.36(c)(2)(ii), Criterion 3.LCOIn MODE 3 with pressurizer pressure 1750 psia and MODE 4, an ECCS subsystem is composed of a single HPSI subsystem.
Each HPSI subsystem includes the piping, instruments, and
controls to ensure an OPERABLE flow path capable of taking
suction from the RWT and transferring suction to the
containment sump.
During an event requiring ECCS actuation, a flow path is required to supply water from the RWT to the RCS via the
HPSI pumps and their respective supply headers to each of
the four cold leg injection nozzles. In the long
-term, this flow path may be switched to take its supply from the ECCS - Shutdown B 3.5.3 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.3-2Revision 2 containment sump and to deliver its flow to the RCS hot and cold legs.
With RCS pressure 1750 psia, one HPSI pump is acceptable without single failure consideration, based on the stable reactivity condition of the reactor
, and the limited core cooling requirements. The LPSI pumps may therefore be released from the ECCS train for use in SDC. In MODE 3 with RCS cold leg temperature 365 F (Unit 1), 301 F (Unit 2), a maximum of one HPSI pump is allowed to be OPERABLE in
accordance with LCO 3.4.12.
The LCO is modified by a Note which allows the HPSI train to
not be capable of automatically starting on an actuation signal when RCS cold leg temperature is 385 F (Unit 1), 325 F (Unit 2), during heatup and cooldown and when 365 F (Unit 1), 301 F (Unit 2), during other conditions.
This allowance is necessary to ensure low temperature overpressure protection analysis assumptions are maintained.
The LCO Note provides a transition period
[between 385 F and 365 F (Unit 1), between 325 F and 301 F (Unit 2)
] where the OPERABLE HPSI pump will be placed in pull-to-lock on a cooldown and restored to automatic status on heatup (see LCO 3.4.12
). At 365 F and less (Unit 1), 301 F and less (Unit 2), the required HPSI pump shall be placed in pull-to-lock and will not start automatically. The HPSI pumps and
HPSI header isolation valves are required to be out of
automatic when o perating within the MODE s of Applicability for the Low Temperature Overpressure Protection System (LCO 3.4.12).APPLICABILITYIn MODE s 1, 2, and 3 with RCS pressure 1750 psia, the OPERABILITY requirements for ECCS are covered by LCO 3.5.2.
In MODE 3 with RCS pressure 1750 psia and in MODE 4, one OPERABLE ECCS train is acceptable without single failure consideration, based on the stable reactivity condition of the reactor
, and the limited core cooling requirements.
In MODE s 5 and 6, unit conditions are such that the probability of an event requiring ECCS injection is
extremely low. Core cooling requirements in MODE 5 are ECCS - Shutdown B 3.5.3 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.3-3Revision 26 addressed by LCO 3.4.7 and LCO 3.4.8. MODE 6 core cooling requirements are addressed by LCO 3.9.4 and LCO 3.9.5.
ACTIONS A Note prohibits the application of LCO 3.0.4.b to an inoperable ECCS HPSI subsystem. There is an increased risk associated with entering MODE 4 from MODE 5 with an inoperable ECCS HPSI subsystem and the provisions of LCO 3.0.4.b, which allow entry into a MODE or other specified condition in the Applicability with the LCO not met after performance of a risk assessment addressing inoperable systems and components, should not be applied in this circumstance.
A.1 With no HPSI pump OPERABLE, the unit is not prepared to respond to a LOCA. The one hour Completion Time to restore
at least one HPSI train to OPERABLE status, ensures that
prompt action is taken to restore the required cooling
capacity or to initiate actions to place the unit in MODE 5, where an ECCS train is not required.
B.1 When the Required Action cannot be completed within the required Completion Time, a controlled shutdown should be
initiated. Twenty-four hours is reasonable, based on
operating experience, to reach MODE 5 in an orderly manner and without challenging plant systems.SURVEILLANCESR 3.5.3.1 REQUIREMENTS The applicable SR descriptions from B 3.5.2 apply.REFERENCESThe applicable references from B 3.5.2 apply.
SITs B 3.5.1 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.1-2Revision 2 Additionally, the isolation valves are interlocked with the pressurizer pressure instrumentation channels
, to ensure that the valves will automatically open as RCS pressure
increases above SIT pressure
, and to prevent inadvertent closure prior to an accident. The valves also receive a
safety injection actuation signal (SIAS) to open. These features ensure that the valves meet the requirements of Reference 1 for "operating bypasses" and that the SITs will be available for injection without reliance on operator
action.The SIT gas and water volumes, gas pressure, and outlet pipe size are selected to allow three of the four SITs to
partially recover the core before significant clad melting
or zirconium water reaction can occur following a LOCA. The
need to ensure that three SITs are adequate for this
function is consistent with the LOCA assumption that the
entire contents of one SIT will be lost via the break during
the blowdown phase of a LOCA.APPLICABLEThe large break LOCA analyses at full power (Reference 2
, SAFETY ANALYSES Section 6.3
) credits the SITs. This is the Design Basis Accident (DBA) that establishes the acceptance limits for
the SITs. Reference to the analysis for this DBA is used to
assess changes to the SITs as they relate to the acceptance
limits.In performing the large break LOCA calculations, conservative assumptions are made concerning the
availability of safety injection flow. These assumptions include signal generation time, equipment starting times, and delivery time due to system piping. In the early stages
of a large break LOCA with a loss of offsite power, the SITs
provide the sole source of makeup water to the RCS. (The
assumption of a loss of offsite power is required by
regulations.) This is because the LPSI pumps, HPSI pumps, and charging pumps cannot deliver flow until the diesel
generators start, come to rated speed, and go through their
timed loading sequence. In cold leg breaks, the entire
contents of one SIT are assumed to be lost through the break
during the blowdown and reflood phases.
SITs B 3.5.1 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.1-3Revision 2 The limiting large break LOCA is a double ended guillotine cold leg break at the discharge of the reactor coolant pump.
During this event, the SITs discharge to the RCS as soon as
RCS pressure decreases to below SIT pressure. As a
conservative estimate, no credit is taken for safety injection pump flow until the SITs are empty. This results in a minimum effective delay of over 60 seconds, during
which the SITs must provide the core cooling function. The
actual delay time is less. No operator action is assumed
during the blowdown stage of a large break LOCA.
This Limiting Condition for Operation (LCO) helps to ensure that the following acceptance criteria, established by Reference 3 for the Emergency Core Cooling System (ECCS), will be met following a LOCA:a.Maximum fuel element cladding temperature is 2200°F;b.Maximum cladding oxidation is 0.17 times the total cladding thickness before oxidation;c.Maximum hydrogen generation from a zirconium water reaction is 0.01 times the hypothetical amount that would be generated if all of the metal in the cladding cylinders surrounding the fuel, excluding the cladding
surrounding the plenum volume, were to react; andd.The core is maintained in a coolable geometry.
Since the SITs discharge during the blowdown phase of a LOCA, they do not contribute to the long
-term cooling requirements of 10 CFR 50.46.
Since the SITs are passive components, single active failures are not applicable to their operation. The SIT
isolation valves, however, are not single failure proof;
therefore, whenever the valves are open, power is removed
from their operators and the switch is key locked open.
These precautions ensure that the SITs are available during an accident (Reference 2, Section 14.17
). With power supplied to the valves, a single active failure could result
in a valve closure, which would render one SIT unavailable
for injection. If a second SIT is lost through the break, only two SITs would reach the core. Since the only active SITs B 3.5.1 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.1-4Revision 2 failure that could affect the SITs would be the closure of a motor-operated outlet valve, the requirement to remove power from these eliminates this failure mode.
The minimum volume requirement for the SITs ensures that three SITs can provide adequate inventory to reflood the
core and downcomer following a LOCA. The downcomer then
remains flooded until the HPSI and LPSI systems start to
deliver flow.
The maximum volume limit is based on maintaining an adequate gas volume to ensure proper injection and the ability of the
SITs to fully discharge, as well as limiting the maximum
amount of boron inventory in the SITs.
A minimum level, corresponding to 1090 cubic feet of borated water is used in the safety analysis as the volume in the
SITs. To provide margin, the low level alarms are set at
187 inches (corresponding to 1113 cubic feet) and 199 inches (corresponding to 1179 cubic feet). The analyses are based
upon the cubic feet requirements; the level (inches) figures
are provided for operator use because the level indicator
provided in the C ontrol R oom is marked in inches, not in cubic feet.
The minimum nitrogen cover pressure requirement ensures that the contained gas volume will generate discharge flow rates
during injection that are consistent with those assumed in
the safety analyses.
The maximum nitrogen cover pressure limit ensures that excessive amounts of gas will not be injected into the RCS
after the SITs have emptied.
A minimum pressure of 195 psia is used in the analyses. To allow for instrument accuracy, a 200 psig minimum and
250 psig maximum are specified. The maximum allowable boron
concentration of 2700 ppm is based upon boron precipitation
limits in the core following a LOCA. Establishing a maximum
limit for boron is necessary since the time at which boron
precipitation would occur in the core following a LOCA is a
function of break location, break size, the amount of boron
injected into the core, and the point of ECCS injection.
SITs B 3.5.1 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.1-5Revision 2 Post-LOCA emergency procedures directing the operator to establish simultaneous hot and cold leg injection are based on the worst case minimum boron precipitation time.
Maintaining the maximum SIT boron concentration within the
upper limit ensures that the SITs do not invalidate this
calculation. An excessive boron concentration in any of the
borated water sources used for injection during a LOCA could
result in boron precipitation earlier than predicted.
The minimum boron requirements of 2300 ppm are based on beginning-of-life reactivity values and are selected to ensure that the reactor will remain subcritical during the
reflood stage of a large break LOCA. During a large break
LOCA, all control element assemblies are assumed not to
insert into the core, and the initial reactor shutdown is
accomplished by void formation during blowdown. Sufficient
boron concentration must be maintained in the SITs to
prevent a return to criticality during reflood.
The SITs satisfy 10 CFR 50.36(c)(2)(ii), Criterion 3.LCOThe LCO establishes the minimum conditions required to ensure that the SITs are available to accomplish their core cooling safety function following a LOCA. Four SITs are
required to be OPERABLE to ensure that 100% of the contents
, f o r three of the SITs
, will reach the core during a LOCA.
This is consistent with the assumption that the contents of
one tank spill through the break. If the contents of fewer
than three tanks are injected during the blowdown phase of a
LOCA, the ECCS acceptance criteria of Reference 3 could be violated.For an SIT to be considered OPERABLE, the isolation valve must be fully open, power removed above 2000 psig, and the
limits established in the Surveillance Requirement (SR) for contained volume, boron concentration, and nitrogen cover pressure must be met.APPLICABILITYIn MODE s 1, 2, and 3 the SIT OPERABILITY requirements are based on an assumption of full power operation. Although cooling requirements decrease as power decreases, the SITs SITs B 3.5.1 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.1-6Revision 2 are still required to provide core cooling as long as elevated RCS pressures and temperatures exist.
In MODE s 4, 5, and 6, the SIT motor
- operated isolation valves are closed to isolate the SITs from the RCS. This allows RCS cooldown and depressurization without discharging
the SITs into the RCS or requiring depressurization of the SITs.ACTIONSA.1 If the boron concentration of one SIT is not within limits it must be returned to within the limits within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
In this condition, ability to maintain subcriticality or
minimum boron precipitation time may be reduced, but the reduced concentration effects on core subcriticality during reflood are minor. Boiling of the ECCS water in the core
during reflood concentrates the boron in the saturated
liquid that remains in the core. In addition, the volume of
the SIT is still available for injection. Since the boron
requirements are based on the average boron concentration of
the total volume of three SITs, the consequences are less
severe than they would be if an SIT were not available for
injection. Thus, 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> is allowed to return the boron
concentration to within limits.
B.1 If one SIT is inoperable, for reasons other than boron concentration, the SIT must be returned to OPERABLE status
within one hour. In this Condition, the required contents of three SITs cannot be assumed to reach the core during a
LOCA. Due to the severity of the consequences should a LOCA
occur in these conditions, the one hour Completion Time to open the valve, remove power from the valve, or restore
proper water volume or nitrogen cover pressure
, ensures that prompt action will be taken to return the inoperable
accumulator to OPERABLE status. The Completion Time
minimizes the exposure of the plant to a LOCA in these
conditions.
SITs B 3.5.1 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.1-7Revision 2 C.1 and C.2 If the SIT cannot be restored to OPERABLE status within the associated Completion Time, the plant must be brought to a
MODE in which the LCO does not apply. To achieve this
status, the plant must be brought to at least MODE 3 within
6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and MODE 4 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. The allowed Completion
Times are reasonable, based on operating experience, to
reach the required plant conditions from full power
conditions in an orderly manner and without challenging
plant systems.
D.1 If more than one SIT is inoperable, the unit is in a condition outside the accident analyses. Therefore, LCO 3.0.3 must be entered immediately.SURVEILLANCESR 3.5.1.1 REQUIREMENTS Verification every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> that each SIT isolation valve is
fully open, as indicated in the C ontrol R oom, ensures that SITs are available for injection and ensures timely
discovery if a valve should be partially closed. If an
isolation valve is not fully open, the rate of injection to
the RCS would be reduced. Although a motor
-operated valve should not change position with power removed, a closed
valve could result in not meeting accident analysis
assumptions. A 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> Frequency is considered reasonable
in view of other administrative controls that ensure the
unlikelihood of a mispositioned isolation valve.
SR 3.5.1.2 and SR 3.5.1.3 S afety injection tank borated water volume and nitrogen cover pressure should be verified to be within specified limits every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> in order to ensure adequate injection
during a LOCA. Due to the static design of the SITs, a
12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> Frequency usually allows the operator sufficient
time to identify changes before the limits are reached.
Operating experience has shown this Frequency to be
appropriate for early detection and correction of off normal
trends.
SITs B 3.5.1 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.1-8Revision 14 SR 3.5.1.4 Six months is reasonable for verification by sampling to determine that each SIT's boron concentration is within the required limits, because the static design of the SITs
limits the ways in which the concentration can be changed.
This Frequency is adequate to identify changes that could occur from mechanisms, such as stratification or inleakage.
Verification consists of monitoring inleakage or sampling.
The inleakage is monitored every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> by monitoring tank level. Sampling of each tank is done every six months.
All intentional sources of level increase are maintained
administratively to ensure SIT boron concentrations are
within technical specification limits.
The boron concentration of each tank is verified prior to startup from outages.
A sample of the SIT is required, to verify boron concentration, if 10 inches or greater of inleakage has
occurred since last sampled.
Sampling the affected SIT (by taking the sample at the discharge of the operating HPSI pump) within one hour prior
to a 1% volume increase of normal tank volume, will ensure
the boron concentration of the fluid to be added to the SIT
is within the required limit prior to adding inventory to
the SIT(s).
SR 3.5.1.5 Verification every 31 days that power is removed from each SIT isolation valve operator, by maintaining the feeder
breaker open under administrative control, when the pressurizer pressure is 2000 psig ensures that an active failure could not result in the undetected closure of an SIT motor-operated isolation valve. If this were to occur, only
two SITs would be available for injection, given a single
failure coincident with a LOCA. Since installation and
removal of power to the SIT isolation valve operators is
conducted under administrative control, the 31 day Frequency
was chosen to provide additional assurance that power is
removed.This SR allows power to be supplied to the motor-operated isolation valves when RCS pressure is < 2000 psig, thus SITs B 3.5.1 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.1-9Revision 14 allowing operational flexibility by avoiding unnecessary delays to manipulate the breakers during unit startups or
shutdowns. Even with power supplied to the valves, inadvertent closure is prevented by the RCS pressure
interlock associated with the valves. Should closure of a
valve occur in spite of the interlock, the safety injection
signal provided to the valves would open a closed valve in the event of a LOCA.REFERENCES1.Institute of Electrical and Electronic Engineers Standard 279-1971, "IEEE Standard: Criteria for Protection Systems for Nuclear Power Generating
Stations"2.Updated Final Safety Analysis Report (UFSAR)3.10 CFR 50.46, "Acceptance Criteria for Emergency Core Cooling Systems for Light Water Nuclear Power Plants" RWT B 3.5.4 B 3.5 EMERGENCY CORE COOLING SYSTEM (ECCS)
B 3.5.4 Refueling Water Tank (RWT)
BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.4-1Revision 2BACKGROUNDThe RWT supports the ECCS and the Containment Spray System by providing a source of borated water for ESF pump operation.
The RWT supplies two ECCS trains by separate, redundant supply headers. Each header also supplies one train of the
Containment Spray System. A motor
-operated isolation valve is provided in each header
, to allow the operator to isolate the usable volume of the RWT from the ECCS after the ESF
pump suction has been transferred to the containment sump
, following depletion of the RWT during a LOCA. A separate header is used to supply the Chemical and Volume Control
System from the RWT. Use of a single RWT to supply both
trains of the ECCS is acceptable
, since the RWT is a passive component, and passive failures are not assumed to occur
coincidentally with the Design Basis Event during the
injection phase of an accident. Not all the water stored in the RWT is available for injection following a LOCA; the location of the ECCS suction piping in the RWT will result
in some portion of the stored volume being unavailable.
The HPSI , LPSI , and containment spray pumps are provided with recirculation lines that ensure each pump can maintain minimum flow requirements when operating at shutoff head
conditions. These lines discharge back to the RWT, which
vents to the atmosphere. When the suction for the HPSI and
containment spray pumps is transferred to the containment
sump, this flow path must be isolated to prevent a release
of the containment sump contents to the RWT. If not
isolated, this flow path could result in a release of
contaminants to the atmosphere and the eventual loss of
suction head for the ESF pumps.
This LCO ensures that:a.The RWT contains sufficient borated water to support the ECCS during the injection phase;b.Sufficient water volume exists in the containment sump to support continued operation of the ESF pumps at the RWT B 3.5.4 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.4-2Revision 14 time of transfer to the recirculation mode of cooling; andc.The reactor remains subcritical following a LOCA.
Insufficient water inventory in the RWT could result in insufficient cooling capacity of the ECCS when the transfer
to the recirculation mode occurs. Improper boron
concentrations could result in a reduction of SDM or
excessive boric acid precipitation in the core following a
LOCA, as well as excessive caustic stress corrosion of mechanical components and systems inside Containment.APPLICABLEDuring accident conditions, the RWT provides a source ofSAFETY ANALYSESborated water to the HPSI, LPSI, containment spray, and charging pumps when level is low in the boric acid tanks.
As such, it provides containment cooling and
depressurization, core cooling, and replacement inventory, and is a source of negative reactivity for reactor shutdown (Reference 1). The design basis transients and applicable
safety analyses concerning each of these systems are
discussed in the Applicable Safety Analyses Section of
B 3.5.2 and B 3.6.6. These analyses are used to assess
changes to the RWT in order to evaluate their effects in
relation to the acceptance limits.
The volume limit of 400,000 gallons is based on two factors:a.Sufficient deliverable volume must be available to provide at least 32 minutes (plus a 10% margin) of full flow from all ESF pumps prior to reaching a low level switchover to the containment sump for recirculation;
andb.The containment sump water volume must be sufficient to support continued ESF pump operation after the
switchover to recirculation occurs. This sump volume
water inventory is supplied by the RWT borated water
inventory.
When ESF pump suction is transferred to the sump, there must
be sufficient water in the sump to ensure adequate net
positive suction head for the HPSI and containment spray
pumps. The RWT capacity must be sufficient to supply this RWT B 3.5.4 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.4-3Revision 2 amount of water without considering the inventory added from the SITs or RCS , but accounting for loss of inventory to containment subcompartments and reservoirs due to
containment spray operation and to areas outside containment
due to leakage from ECCS injection and recirculation
equipment.
The 2300 ppm limit for minimum boron concentration was established to ensure that, following a LOCA with a minimum
level in the RWT, the reactor will remain subcritical in the
cold condition following mixing of the RWT and RCS water
volumes with all control rods inserted, except for the
control element assembly of highest worth, which is withdrawn from the core. The most limiting case occurs at
beginning of core life.
The maximum boron limit of 2700 ppm in the RWT is based on boron precipitation in the core following a LOCA. With the
reactor vessel at saturated conditions, the core dissipates
heat by pool nucleate boiling. Because of this boiling
phenomenon in the core, the boric acid concentration will
increase in this region. If allowed to proceed in this
manner, a point will be reached where boron precipitation
will occur in the core. Post
-LOCA emergency procedures direct the operator to establish simultaneous hot and cold
leg injection to prevent this condition by establishing a
forced flow path through the core regardless of break
location. These procedures are based on the minimum time in
which precipitation could occur, assuming that maximum boron
concentrations exist in the borated water sources used for
injection following a LOCA. Boron concentrations in the RWT
in excess of the limit could result in precipitation earlier
than assumed in the analysis.
The upper limit of 100F (only required for MODE 1 operation) and the lower limit of 40F (RWT temperature
), are the limits assumed in the accident analysis.
The RWT satisfies 10 CFR 50.36(c)(2)(ii), Criterion 3.LCOThe RWT ensures that an adequate supply of borated water is available to
- cool and depressurize the C ontainment in the event of a DBA , to cool and cover the core in the event of a RWT B 3.5.4 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.4-4Revision 2 LOCA, ensure that the reactor remains subcritical following a DBA, and ensure that an adequate level exists in the containment sump to support ESF pump operation in the recirculation mode.
To be considered OPERABLE, the RWT must meet the limits established in the SRs for water volume, boron concentration, and temperature.APPLICABILITYIn MODE s 1, 2, 3, and 4, the RWT OPERABILITY requirements are dictated by the ECCS and Containment Spray System OPERABILITY requirements. Since both the ECCS and the
Containment Spray System must be OPERABLE in MODE s 1, 2, 3, and 4, the RWT must be OPERABLE to support their operation.
Core cooling requirements in MODE 5 are addressed by LCO 3.4.7 and LCO 3.4.8
. MODE 6 core cooling requirements are addressed by LCO 3.9.4 and LCO 3.9.5
.ACTIONSA.1 With RWT boron concentration or borated water temperature
not within limits, it must be returned to within limits
within eight hours. In this condition neither the ECCS nor the Containment Spray System can perform their design
functions; therefore, prompt action must be taken to restore
the tank to OPERABLE condition. The allowed Completion Time
of eight hours to restore the RWT to within limits was developed considering the time required to change boron
concentration or temperature
, and that the contents of the tank are still available for injection.
Required Action A.1 only applies to the maximum borated water temperature in MODE 1.
B.1 With RWT borated water volume not within limits, it must be returned to within limits within one hour. In this condition, neither the ECCS nor Containment Spray System can perform their design functions; therefore, prompt action must be taken to restore the tank to OPERABLE status or to
place the unit in a MODE in which these systems are not
required. The allowed Completion Time of one hour to RWT B 3.5.4 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.4-5Revision 2 restore the RWT to OPERABLE status is based on this condition simultaneously affecting multiple redundant
trains.C.1 and C.2 If the RWT cannot be restored to OPERABLE status within the associated Completion Time, the plant must be brought to a
MODE in which the LCO does not apply. To achieve this
status, the plant must be brought to at least MODE 3 within
6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and to MODE 5 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. The allowed
Completion Times are reasonable, based on operating
experience, to reach the required plant conditions from full
power conditions in an orderly manner and without challenging plant systems.SURVEILLANCESR 3.5.4.1 and SR 3.5.4.2 REQUIREMENTS Refueling water tank borated water temperature shall be verified every 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to be within the limits assumed in the accident analysis. This Frequency has been shown to be
sufficient to identify temperature changes that approach
either acceptable limit.
The SRs are modified by a Note that eliminates the requirement to perform this s urveillance test when ambient air temperatures are within the operating temperature limits
of the RWT. With ambient temperatures within this range, the RWT temperature should not exceed the limits.
Surveillance Requirement 3.5.4.2 is modified by an additional N ote which requires the S R to be met in MODE 1 only. A S R is "met" only when the acceptance criteria are satisfied. Known failure of the requirements of a S R , even without a s urveillance test specifically being "performed," constitutes a S R not "met." This reflects the maximum coolant temperature assumptions in the LOCA analysis.
SR 3.5.4.3 Above minimum RWT water volume level shall be verified every seven days. This Frequency ensures that a sufficient initial water supply is available for injection and to
support continued ESF pump operation on recirculation.
RWT B 3.5.4 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.4-6Revision 2 Since the RWT volume is normally stable and is provided with a Low Level Alarm, a seven day Frequency is appropriate and has been shown to be acceptable through operating
experience.
SR 3.5.4.4 Boron concentration of the RWT shall be verified every seven days to be within the required range. This Frequency ensures that the reactor will remain subcritical following a
LOCA. Further, it ensures that the resulting sump pH will
be maintained in an acceptable range such that boron
precipitation in the core will not occur earlier than
predicted , and the effect of chloride and caustic stress corrosion on mechanical systems and components will be
minimized. Since the RWT volume is normally stable, a
seven day sampling Frequency is appropriate and has been shown through operating experience to be acceptable.REFERENCES1.
UFSAR , Chapter s 6 , "Engineered Safety Features," and 14 , "Safety Analysis" TSP B 3.5.5 B 3.5 EMERGENCY CORE COOLING SYSTEM (ECCS)
B 3.5.5 Trisodium Phosphate (TSP)
BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.5-1Revision 2BACKGROUNDTrisodium phosphate dodecahydrate is placed in baskets on the floor of the C ontainment B uilding to ensure that iodine, which may be dissolved in the recirculated reactor cooling water following a LOCA , remains in solution. Trisodium phosphate also helps inhibit stress corrosion cracking (SCC) of austenitic stainless steel components in C ontainment during the recirculation phase following an accident.
Fuel that is damaged during a LOCA will release iodine in several chemical forms to the reactor coolant and to the
containment atmosphere. A portion of the iodine in the
containment atmosphere is washed to the sump by containment
sprays. The emergency core cooling water is borated for
reactivity control. This borated water causes the sump
solution to be acidic. In a low pH (acidic) solution, dissolved iodine will be converted to a volatile form. The
volatile iodine will evolve out of solution into the
containment atmosphere, significantly increasing the levels
of airborne iodine. The increased levels of airborne iodine
in C ontainment contribute to the radiological releases and increase the consequences from the accident due to
containment atmosphere leakage.
After a LOCA, the components of the core cooling and containment spray systems will be exposed to high
temperature borated water. Prolonged exposure to the core
cooling water combined with stresses imposed on the
components can cause SCC. The SCC is a function of stress, oxygen and chloride concentrations, pH, temperature, and
alloy composition of the components. High temperatures and
low pH, which would be present after a LOCA, tend to promote SCC. This can lead to the failure of necessary safety systems or components.
Adjusting the pH of the recirculation solution to levels 7.0 prevents a significant fraction of the dissolved iodine from converting to a volatile form. The higher pH thus decreases the level of airborne iodine in C ontainment and reduces the radiological consequences from containment
atmosphere leakage following a LOCA. Maintaining the TSP B 3.5.5 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.5-2Revision 2 solution pH above 7.0 also reduces the occurrence of SCC of austenitic stainless steel components in C ontainment.
Reducing SCC reduces the probability of failure of
components.
Granular TSP dodecahydrate is employed as a passive form of pH control for post
-LOCA containment spray and core cooling water. Baskets of TSP are placed on the floor in the
C ontainment B uilding to dissolve from released reactor coolant water and containment sprays after a LOCA.
Recirculation of the water for core cooling and containment sprays then provides mixing to achieve a uniform solution
pH. The dodecahydrate form of TSP is used because of the
high humidity in the C ontainment B uilding during normal operation. Since the TSP is hydrated, it is less likely to
absorb large amounts of water from the humid atmosphere and
will undergo less physical and chemical change than the anhydrous form of TSP.APPLICABLEThe LOCA radiological consequences analysis takes credit forSAFETY ANALYSESiodine retention in the sump solution based on the recirculation water pH being 7.0. The radionuclide releases from the containment atmosphere and the
consequences of a LOCA would be increased if the pH of the
recirculation water were not adjusted to 7.0 or above.
Trisodium phosphate satisfies 10 CFR 50.36(c)(2)(ii), Criterion 3.LCOThe TSP is required to adjust the pH of the recirculation water to 7.0 after a LOCA. A pH 7.0 is necessary to prevent significant amounts of iodine released from fuel failures and dissolved in the recirculation water from
converting to a volatile form and evolving into the
containment atmosphere. Higher levels of airborne iodine in
C o ntainment may increase the release of radionuclides and the consequences of the accident. A pH 7.0 is also necessary to prevent SCC of austenitic stainless steel
components in C o ntainment. Stress corrosion cracking increases the probability of failure of components.
The required amount of TSP is based upon the extreme cases of water volume and pH possible in the containment sump TSP B 3.5.5 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.5-3Revision 2 after a large break LOCA. The minimum required volume is
, the volume of TSP that will achieve a sump solution pH of 7.0 when taking into consideration the maximum possible sump water volume
, and the minimum possible pH. The amount of TSP needed in the C ontainment B uilding is based on the mass of TSP required to achieve the desired pH. However, a required volume is specified, rather than mass, since it is
not feasible to weigh the entire amount of TSP in C ontainment. The minimum required volume is based on the manufactured density of TSP dodecahydrate. Since TSP can have a tendency to agglomerate from high humidity in the
C ontainment B uilding, the density may increase and the volume decrease during normal plant operation. Due to
possible agglomeration and increase in density, estimating
the minimum volume of TSP in C ontainment is conservative with respect to achieving a minimum required pH.APPLICABILITYIn MODE s 1, 2, 3, and 4, the RCS is at elevated temperature and pressure, providing an energy potential for a LOCA. The
potential for a LOCA results in a need for the ability to
control the pH of the recirculated coolant.
In MODE s 5 and 6, the potential for a LOCA is reduced or non-existent due to the reduced pressure and temperature limitations of these MODE s , and TSP is not required.ACTIONSA.1 If it is discovered that the TSP in the C ontainment B uilding sump is not within limits, action must be taken to restore the TSP to within limits. During plant operation the
containment sump is not accessible and corrections may not
be possible.
The Completion Time of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> is allowed for restoring the TSP within limits, where possible, because 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> is the
same time allowed for restoration of other ECCS components.
B.1 and B.2 If the TSP cannot be restored within limits within the Completion Time of Required Action A.1, the plant must be
brought to a MODE in which the LCO does not apply. To
achieve this status, the plant must be brought to at least TSP B 3.5.5 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.5-4Revision 23 MODE 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and to MODE 5 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. The allowed Completion Times are reasonable, based on operating
experience, to reach the required plant conditions from full
power in an orderly manner and without challenging plant
systems.SURVEILLANCESR 3.5.5.1 REQUIREMENTS Periodic determination of the volume of TSP in Containment
must be performed due to the possibility of leaking valves and components in the Containment Building that could cause dissolution of the TSP during normal operation. A Frequency
of 24 months is required to determine visually that a
minimum of 289.3 cubic feet is contained in the TSP baskets.
This requirement ensures that there is an adequate volume of
TSP to adjust the pH of the post-LOCA sump solution to a value 7.0.The periodic verification is required every 24 months, since access to the TSP baskets is only feasible during outages, and normal fuel cycles are scheduled for 24 months.
Operating experience has shown this SR Frequency acceptable, due to the margin in the volume of TSP placed in the
Containment Building.
SR 3.5.5.2 Testing must be performed to ensure the solubility and buffering ability of the TSP after exposure to the
containment environment. A representative sample of 3.43 0.05 grams of TSP, from one of the baskets in Containment is submerged in 1.0 0.01 liters of water at a boron concentration of 3106 50 ppm, and at the standard temperature of 120 5 F. Within four hours without agitation, the solution is decanted and mixed, the
temperature adjusted to 77 2 F, and the pH measured. The solution pH should be 6.0. The representative sample weight is based on the minimum required TSP weight of 14,371 lbm, which at manufactured density corresponds to the
minimum volume of 289.3 cubic feet, and maximum possible
post-LOCA sump volume of 4,503,500 lbm, normalized to buffer a 1.0 0.01 liter sample. The boron concentration of the test water is representative of the maximum possible boron TSP B 3.5.5 BASESCALVERT CLIFFS - UNITS 1 & 2B 3.5.5-5Revision 23 concentration corresponding to the maximum possible post-LOCA sump volume. Agitation of the test solution is
prohibited, since an adequate standard for the agitation
intensity cannot be specified.
A test time of four hours would allow time for the dissolved TSP to naturally diffuse through the sample solution.
A test time of less than four hours is more conservative than a test time of longer than four hours because the longer time could permit additional TSP to dissolve, if excess TSP was available.
In the post-LOCA containment sump, rapid mixing would occur, significantly decreasing the actual amount of time before the required pH is achieved. This would ensure compliance with the Standard Review Plan requirement of a pH 7.0 by the onset of recirculation after a LOCA.REFERENCESNone