ML20196H288
| ML20196H288 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 06/24/1999 |
| From: | VERMONT YANKEE NUCLEAR POWER CORP. |
| To: | |
| Shared Package | |
| ML20196H285 | List: |
| References | |
| NUDOCS 9907060200 | |
| Download: ML20196H288 (13) | |
Text
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, VERMONT YANKEE NUCLEAR POWER CORPORATION Docket No. 50-271 BVY 99-85 Attachment 3
%nont Yankee Nuclear Power Station Proposed Technical Specification Change No. 214 Turbine Control Valve and Turbine Stop Valve Closure Scram Bypass Marked-up Version of the Current Technical Specifications t
9907060200 990624 PDR ADOCK 05000271 P PDR
l VYNPS l 1.1 SAFETY LIMIT 2.1 LIMITING SAFETY SYSTEM SETTING D. Reactor low-low water level l
Emergency Core Cooling System (ECCS) initiation i shall be at least l 82.5 inches above the top of I the enriched fuel. l E. Turbine stop valve scram ,
shal be less than or equal l t valve closure from j ull open, j
,# F. Turbine control valve fast i closure scram shall, when ;
operatina at creater than i
,when operating at greater than 30t f C u J, trip upon 30% of Rated Thermal Power' ac ion of the turbine nerol valve fast closure relay.
G. Main steam line isolation valve closure scram shall be less than or equal to 10% i valve closure from full open.
H. Main steam line low pressure Rated Thermal Power initiation of main steam l'ine isolation valve closure shall be at least 800 psig. l l 1
a i
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l i
l t
I Amendment No. 64, 84 10
y VYNPS l .-
- BASES: 2.1 (Cont'd)
I metal-water reaction to less than 1%, to assure that core geometry remains intact.
The design of the ECCS components to meet the above criteria was dependent on three previously set parameters: the maximum break size, the low water l level scram setpoint, and the ECCS initiation setpoint. To lower the ECCS l
initiation setpoint would now prevent the ECCS components from meeting their design criteria. To raise the ECCS initiation setpoint would be in a safe direction, but it would reduce the margin established to prevent actuation of the ECCS during normal operation or during normal?y expected transients.
E. Turbine Stop Valve Closure Scram Trip Setting The turbine stop valve closure scram trip anticipates the pressure, neutron flux and heat flux increase that could result from rapid closure of the turbine stop valves. With a scram trip setting of <10% of valve closure from full open, the resultant increase in surface heat flux is limited such that MCPR remains above the fuel cladding integrity safety limit eve ing the worst case transient that assumes the turbine bypass is closed. Thiy (scram bypassed ,en turbine eam flow is) Wlow 30% of rayed, ageured (by rbine fir stage press ey j F. Turbine Control Valve Fast Closure Scram l The control valve fast closure scram is provided to limit the ra 'd increase in pressure and neutron flux resulting from fast closure of the urbine control valves due to a load rejection coincident with failure o the bypass system. This transient is less severe than the turbine stop va e closure with failure of the bypass valves and therefore adequate margin exists.
G. Main Steam Line Isolation Valve Closure Scram The isolation valve closure scram anticipa*
transients which occur during normal or i This scram signal may be With the scram setpoint at 10% of valve e bypassed at S 30% of reactor neutron flux. Rated Thermal Power. j H. Reactor Coolant Low Pressure Initiation of Main Steam isom_.. .__..
Closure The low pressure isolation of the main steam lines at 800 psig is provided to give protection against rapid reactor depressurization and the resulting rapid cooldown of the vessel. Advantage is taken of the scram feature which occurs when the main steam line isolation valves are closed, to provide the reactor shutdown so that high power operation at low reactor pressure does not occur. Operation of the reactor at pressures lower than 800 psig requires that tne reactor mode switch be in the startup position where protection of the fuel cladding integrity safety limit is provided by the IRM high neutron flux scram.
~
'Thus, the combination of main steam line low pressure isolation and isolation valve closure scram assures the availability of neutron scram I
- l. protection over the entire range of applicability of the fuel cladding
! integrity safety limit.
l
. Amendment No. M, M, 44, 164 17
VYNPS TABLE 3.1.1 NOTES (Cont'd)
C ^
- 9. Channel signals for the turbine control valve fast cl'osure trip shall be derived from the same event or events which cause the control valve fast closure.
- 10. A turbin stop valve clo re and generator ad rejection as is permi d when the fir stage turbine y sure is less 30% of I no (220 psia).
u
- 11. The IRM scram is h a:ssed when the APRMs are on scale and the mode switch is in the run positlion.
- 12. While performing roluel interlock checks which require the mode switch to be in Startup, the uced APRM high flux scram need not be operable provid:4: .
- a. The following tri functions are operable:
- 1. Mode switch i shutdown,
- 2. Manual scram,
- 3. High flux IRM cram
- 4. High fJuq JRM ram in noncoincidence, S. Scram discharge volume high water level, and;
- b. No more than two (2) control rods withdrawn. The two (2) control rods that can be wit drawn cannot be faced adjacent or diagonally adjacent.
i Turbine stop valve closure and turbine control valve fast closure scram signals may be bypassed at < 30% of reactor Rated Thermal Power.
h Amendment No. H, M, 64, M, 90 24
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1 l
- vrups
< , , ge - 3 .1 ~ (Cont'd)-
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' all of the water Tb- .
mmodated in
- closure scram signals may be bypassed at5 30% of reactor Rated Thermal Power since, at low thermal power levels, the margins to fuel thermal-
, hydraulic limits and reactor primary coolant boundary pressure limits are
' '~
large and an immediate scram is not necessary. This bypass function is.
'n'o rmally accomplished automatically by pressure switches sensing turbine first stage pressure. The turbine first stage pressure setpoint controlling the bypass of the scram signals on TCV fast closure and TSV closure is derived from analysis of reactor pressurization transients. Certain operational factors, such as turbine bypass valves open, can influence the relationship between turbine first stage pressure and reactor Rated Thermal Power. However, above 30% of reactor Rated Thermal Power, these scram functions must be enabled. .
. ant
. ..er's i
An their L v. Systeam*,
genet.
dated'Decew-. '
Loss of condenser vacuum occurs when the condenser can no longer handle the heat input. Loss of condenser vacuum initiates a closure of the turbine stop valves and turbine bypass valves which eliminates the heat input to the condenser. Closure of the turbine stop and bypass valves l
causes e pressure transient, neutron flux rise, and an increase in ..
l surface heat flux. To prevent the clad safety limit from being exceeded I if this occurs, a reactor scram occurs on turbine stop valve closure.
The turbine stop valve closure scram function alone is adequate to prevent the clad safety limit from being exceeded in the ' event of a turbine trip transient without bypass.
High radiation levels in th'e m'ain s' team line tunnel above that due to the normal nitrogen and oxygen radioactivity is an indication of leaking fuel. A scram is initiated whenever such radiation level exceeds three times normal background. The purpose of this scram is to reduce the source of such radiation to the extent necessary to prevent release of l radioactive materials to the turbine. An alarm is initiated whenever the l
radiation level exceeds 1.5 times normal background to alert the operator *<
i to possible serious radioactivity spikes due to abnormal core behavior. l The air ejector off-gas monitors serve to back up the main steam line l monitors to provide further assurance against release of radioactive i materials to site environs by isolating the main condenser off-gas line '
to the main stack.
The main steam line isolation valve closure scram is set to scram when the isolation valves are 10 percent closed from full open in 3-out-of-4 lines. This scram anticipates the pressure and flux transient, which would occur when the valves close. By scranusing at this setting, the resultant transient is insignificant.
A reactor mode switch is provided which actuates or bypasses the various
= scram functions appropriate to the particular plant operating status.
The manual scram function is active in all modes, thus providing for '
manual means of rapidly inserting control rods during all modes of reactor operation.
30 Amendment No. H, 76 l
VERMONT YANKEE NUCLEAR POWER CORPORATION l-Docket No. 50-271 BVY 99-85 l
l' I
Attachment 4 Vermont Yankee Nuclear Power Station l.
I
! Proposed Technical Specification Change No. 214 Turbine Control Valve and Turbine Stop Valve Closure Scram Bypass l . Retyped Technical Specification Pages L
l-1 l
L_
- VERMONT YANKEE NUCLEAR POWER CORPORATION BVY 99-85 / Attachment 4 / Page i Listina of Affected Technical Specifications Pages Replace the Vermont Yankee Nuclear Power Station Technical Specifications pages listed below with the revised pages. The revised pages contain vertical lines in the margin indicating the areas of change.
Remove Ln.sg1 10 10 17 17 24 24 30 30 31* 31*
32* 32*
- Due to the addition of a paragraph on page 30, the text overflow affects pages 31 and 32. The content of pages 31 and 32 is otherwise unchanged.
L
, , VYNPS i
l .,1 SAFETY LIMIT 2.1 LIMITING SAFETY SYSTEM SETTING D. Reactor low-low water level Emergency Core Cooling System l (ECCS) initiation shall be at l least 82.5 inches above the top l of the enriched fuel.
E. Turbine stop valve scram shall, when operating at greater than 30% of Rated Thermal Power, be less than or equal to 10% valve closure from full open.
F. Turbine control valve fast closure scram shall, when operating at greater than 30%
of Rated Thermal Power, trip upon actuation of the turbine control valve fast closure relay.
G. Main steam line isolation valve closure scram shall be less than or equal to 10% valve closure from full open.
H. Main steam line low pressure initiation of main steam line isolation valve closure shall ,
I be at least 600 psig.
l i
Amendment No. 48, 84 10
VYNPS BASES: 2.1 (Cont'd) metal-water reaction to less than 1%, to assure that core geometry remains I
intact.
The design of the ECCS components to meet the above criteria was dependent on three previously set parameters: the maximum break size, the low water level scram setpoint, and the ECCS initiation setpoint. To lower the ECCS initiation setpoint would now prevent the ECCS components from meeting their design criteria. To raise the ECCS initiation setpoint would be in a safe direction, but it would reduce the margin established to prevent actuation of the ECCS during normal operation or during normally expected transients.
E. Turbine Stop Valve Closure Scram Trip Setting The turbine stop valve closure scram trip anticipates the pressure, neutron flux and heat flux increase that could result from rapid closure of the turbine stop valves. With a scram trip setting of <10% of valve closure from full open, the resultant increase in surface heat flux is limited such that MCPR remains above the fuel cladding integrity safety limit even during the worst case transient that assumes the turbine bypass is closed. This scram signal may be bypassed at $30% of reactor Rated Thermal Power.
F. Turbine Control Valve Fast Closure' Scram The control valve fast closure scram is provided to limit the rapid increase in pressure and neutron flux resulting from fast closure of the turbine control valves due to a load rejection coincident with failure of the bypass system. This transient is less severe than the turbine stop valve closure with failure of the bypass valves and therefore adequate margin exists. This scram signal may be bypassed at $30% of reactor Rated Thermal Power.
G. Main Steam Line Isolation Valve Closure Scram The isolation valve closure _ scram anticipates the pressure and flux
, transients which occur during normal or inadvertent isolation valve closure.
l With the scram setpoint at 10% of valve closure, there is no increase in neutron flux.
H. Reactor Coolant Low Pressure Initiation of Main Steam Isolation Valve Closure-The low pressure isolation of the main steam lines at 800 psig is provided to give protection against rapid reactor depressurization and the resulting rapid cooldown of the. vessel. Advantage is taken of the scram feature which l occurs when the main steam line isolation valves are closed, to provide the reactor shutdown so that high power operation at low reactor pressure does not occur. Operation of the reactor at pressures lower than 800 psig
, requires that the reactor mode switch be in the startup position where l
protection of the fuel cladding integrity safety limit is provided by the '
Thus, the combination of main steam line low pressure isolation and isolation valve closure scram assures the availability of neutron scram protection over the entire range of applicability of the fuel cladding integrity safety limit.
l l
Amendment No. 14, G6, 44, 144 17
1 VYNPS TABLE 3.1.1 NOTES (Cont'd) l 9. Channel signals for the turbine control valve fast closure trip shall be I derived from the same event or events which cause the control valve fast closure.
- 10. Turbine stop valve closure and turbine control valve fast closue scram signals may be bypassed at $30% of reactor Rated Thermal Power.
- 11. The IRM scram is bypassed when the APRMs are on scale and the mode switch is in the run position.
- 12. While performing refuel interlock checks which require the mode switch to be in Startup, the reduced APRM high flux scram need not be operable l provided:
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l
- a. The following trip functions are operable:
- 1. Mode switch in shutdown, l 2. Manual scram,
- 5. Scram discharge volume high water level, and;
- b. No more than two (2) control rods withdrawn. The two (2) control rods that can be withdrawn cannot be faced adjacent or diagonally adjacent.
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l Amendment No. 44, 33, 44, 3B, GO 24
VYMPS
- BASES ': 3.1 (Cont'd)
The Control Rod Drive Scram System is designed so that all of the water l that is discharged from the reactor by the scram can be accommodated in the i discharge piping. This discharge piping is divided into two sections. One l section services the control rod drives on the north side of the reactor, l the other serves the control rod drives of the south side. A part of the l+ piping in each section is an instrument volume which accommodates in excess
- of 21 gallons of water and is at the low point in the piping. No credit l was taken for this volume in the design of the discharge piping as concerns i the amount of water which must be accommodated during a scram. During
- normal operation, the discharge volume is empty; however, should it fill l with water, the water discharged to the piping from the reactor could not l be accommodated, which would result in slow scram times or partial or no control rod insertion. To preclude this occurrence, level instrumentation has been provided for the instrument volume which scram the reactor when the volume of water reaches 21 gallons. As indicated above, there is sufficient volume in the piping to accommodate the scram without impairment of the scram times or amount of insertion of the control rods. This function shuts the reactor down while sufficient volume remains to accommodate the discharged watur, and precludes the situation in which a L
scram would'be required but not be able to perform its function adequately.
The present design of the Scram Discharge System is in concert with the BWR Owner's Group criteria, which have previously been endorsed by the NRC in their generic " Safety Evaluation Report (SER) for Scram Discharge Systems",
l dated December 1, 1980.
l Loss of condenser vacuum occurs when the condenser can no longer handle the heat input. Loss of condenser vacuum initiates a closure of the turbine L stop valves and turbine bypass valves which eliminates the heat input to the condenser. Closure of the tur,bine ,stop and bypass valves causes a pressure transient, neutron flux rise,.and an increase in surface heat flux. To prevent the clad safety limit from being exceeded if this occurs, a reactor scram occurs on turbine stop valve closure. The turbine stop valve closure scram function alone is adequate to prevent the clad safety limit from being exceeded in the event of a turbine trip transient without bypass.
- Turbine stop valve (TSV) closure and turbine control valve (TCV) fast l closure scram signals may be, bypassed at $30% of reactor Rated Thermal Power since, at low thermal power levels, the margins to fuel thermal-hydraulic limits and reactor primary coolant boundary pressure limits are large and an immediate scram is not necessary. This bypass function is normally accomplished automatically by pressure switches sensing turbine first stage pressure. The turbine first stage pressure setpoint l controlling the bypass of the scram signals on TCV fast closure and TSV ;
closure is derived from. analysis of reactor pressurization transients. !
Certain operational factors, such as turbine bypass valves open, can influence the relationship between turbine first stage pressure and reactor Rated Thermal Power. However, above 30% of reactor Rated Thermal Power, these scram functions must be enabled.
High radiation levels in the main steam line tunnel above that due to the normal nitrogen and oxygen radioactivity is an indication of leaking fuel.
A scram is initiated whenever such radiation level exceeds three times normal background. The purpose of this scram is to reduce the source of such radiation to the extent necessary to prevent release of radioactive materials to the turbine. An alarm is initiated whenever the radiation level exceeds 1.5 times normal background to alert the operator to possible serious radioactivity spikes due to abnormal core behavior. The air
! ejector off-gas monitors serve to back up.the main steam line monitors to l Amendment No M , M 30 1
L-- _~
1 VYNPS BASES: 3.1 (Cont'd) provide further assurance against release of radioactive materials to site environs by isolating the main condenser off-gas line to the main stack.
The main steam line isolation valve closure scram is set to scram when the
-isolation valves are 10 percent closed from full open in 3-out-of-4 lines.
This scram anticipates the pressure and flux transient, which would occur when the valves close. By scramming at this setting, the resultant transient is insignificant.
A reactor mode switch is provided which actuates or bypasses the various scram functions appropriate to the particular plant operating status.
The manual scram function is active in all modes, thus providing for manual means of rapidly inserting control rods during all. modes of reactor operation.
The IRM system provides protection against short reactor periods and, in conjunction with the reduced APRM system provides protection against excessive power levels in the startup and intermediate power ranges. A source range monitor (SRM) system is also provided to supply additional neutron level information during startup and can provide scram function with selected shorting links removed during refueling. Thus, the IRM and the. reduced APRM are normally required in the startup mode and may be required in the refuel mode. 'During some refueling activities which require the mode switch in startup; it is allowable to disconnect the LPRMs to protect them froa damage during under vessel work. In lieu of the protection provided by the reduced APRM scram, both the IRM scram and the SRM scram in noncoincidence are used to provide neutron monitoring protection against excessive power levels. In the power range, the normal APRM system provides required protection. Thus, the IRM system and 15%
APRM scram are not required in the run mode. The requirement that the IRMs be inserted in the core until the APRMs read at least 2/125 of full scale assures that there is proper overlap in the neutron monitoring systems.
If an unsafe failure is detected during surveillance testing, it is desirable to determine as soon as possible if other failures of a similar i type have occurred and whether the particular function involved is still operable or capable of meeting the single failure criteria. To meet the requirements of Table 3.1.1, it is necessary that all instrument channels in one trip system be operable to permit testing in the other trip system.
.Thus, when failures are detected in the first trip system tested, they would have to be repaired before testing of the other system could begin.
In the majority of cases, repairs or replacement can be accomplished quickly. If repair or replacement cannot be completed in a reasonable time, operation could continue with one tripped system until the surveillance testing deadline.
The requirement to have all scram functions, except those listed in Table 3.1.1, operable in the " Refuel" mode is to assure that shifting to this mode during reactor operation does not diminish the need for the reactor protection' system.
The ability to bypass one instrument channel when necessary to complete surveillance testing will preclude continued operation with scram functions which may be either unable to meet the single failure criteria or completely inoperable. It also eliminates the need for an unnecessary shutdown if the remaining channels and subsystems are found to be operable.
Amendment No. 31, 78 31
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\
VYNPS BASES: 3.1 .(Cont'd)
The conditions under which the bypass is permitted require an immediate determination that the particular function is operable. However, during the time a bypass is applied, the function will not meet the single failure criteria; therefore, it is prudent to limit the time the bypass is in effect by requiring that surveillance testing proceed on a continuous basis and that the bypass be removed as soon as testing is completed.
Sluggish indicator response during the perturbation test will be indicative of a plugged instrument line or closed instrument valves. Testing immediately after functional testing will assure the operability of the instrument. lines. This test assures the operability of the reactor pressure sensors as well as the reactor level sensors since both parameters are monitored through the same instrument lines.
The independence of the safety system circuitry is determined by operation of the scram test switch. Operation of this switch during the refueling outage and following maintenance on these circuits will assure their continued independence.
The calibration frequency, using the TIP system, specified for the LPRMs will provide assurance that the LPRM input to the APRM system will be corrected on a timely basis for LPRM detector depletion characteristics.
32