ML20083Q482

Proposed Tech Specs Re Limiting Safety Sys Setting,Average Power Range Monitor Flux Scram Trip Setting & Reactor Protection Sys Instrument Requirements

ML20083Q482
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	02/22/1983
From:	VERMONT YANKEE NUCLEAR POWER CORP.
To:
Shared Package
ML20083Q466	List: ML20083Q463 ML20083Q482
References
NUDOCS 8302250407
Download: ML20083Q482 (7)

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EO' M VYNPS Du o us 00 I

1.1 SAFETY LIMIT h!O 2.1. LIMITING SAFETY SYSTEM SETTING'

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O UHD OtJ cuo For the purpose of performing special

.uOU stability testing' when the mode switch is QNM

, in the RUN position, the APRM flux scram trip setting shall be:

S$ 0.66W + 85%

a For no combination of loop recirculation flow rete.and core thermal power shall the APRM flux scram. trip setting be

. allowed to exceed 120% of rated thermal i power.

During operation under the provisions of :

2.1.A.I.b, the special MAPLHGR limits of-3.11.A shall apply and such operation shall be limited . to the duration of . pump 4

trip and stability. tests. Adjustmente

for the ratio of MFLPD to FRP greater than 1.0 are not required while conducting special testing under this provision.

c. Flux Scram ' Trip Setting - (Refuel or Startup and Hot Standby Mode)

When the reactor mode switch ~is in the REFUEL or STARTUP position,' average power range monitor (APRM) scram shall be set down to less than or equal to 15% of rated neutron flux (except as allowed by Note 13 of Table 3.1.1). The IRM flux scram. setting shall be ' set at less than j or equal to 120/125 of full scale.

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j- _APRM Flux Scram Trip Setting (Run Mode)

_The scram trip setting must be adjusted to ensure that the LHGR transient peak is not increased for any combination of MFLPD and reactor core thermal povar. LIf the scram requires. a change due .te an abnormal peaking condition, it will be accomplished by. increasing the APRM gain by the ratio in Specification 2.1.A.I.a. thus assuring _a reactor scram at

j. Icwer than design overpower conditions.

V j Analyses of.the limiting transients show that no scram adjustment is required to assure fuel ~ cladding integrity when i

the transient is initiated f rom the operating limit MCPR (Specification 3.11C).

i Flux Scram Trip Setting'(Refuel or Startup and Hot Standby Mode)

! For operation in the startup mode while the reactor is at low pressure, the reduced APRM scran setting to 15% of rated power provides adequate thermal margin between the setpoint and the safety limit, 25% of the rated. (During an outage

when it is necessary to check refuel' interlocks, the mode switch must be moved to the startup position. - Since the' APRM reduced scram may be inoperable at that time-due to the disconnection of the LPRMs, it uis required that the IRM l scram and the SRM scram in noncoincidence be in effect. This will ensure that adequate thermal margin is maintained-l between the setpoint and the safety limit.) The margin.is adequate to accommodate anticipated maneuvers associated with station startup. Effects of increasing pressure at zero or low void content are minor, cold water from sources available during startup is not much colder than that already in the system, temperature coefficients are small, and l control rod patterns are constrained to be uniform by operating procedures backed up by the rod worth minimizer.

Worth of individual rods is very low in a uniform rod pattern. ,Thus, of all possible sources of reactivity input, j uniform control rod withdrawal is the most probable cause of significant power rise. Because the flux distribution I associated with uniform rod withdrawals does not involve high local peaks, and because several rods must be moved to

change power by a significant percentage of rated power, the rate of power rise is very slow. Generally, the heat

flux is in near equilibrium with the fission rate. -In an assumed uniform rod withdrawal approach to the scram' level,

the rate of power rise is no more than 5% of rated power per minute, and the APRM system would be more than adequate to assure a scram before the power could exceed the safety limit. The _ reduced APRM scram remains active until the node switch is plac'.d in the RUN position. This switch can occur when reactor pressure is greater than 850 psig. ,

The IRM system consists of 6 chambers, 3 in each of the reactor protection system logic channels. The IRM is a 5-decade instrument which covers the range of power level between that covered by the SRM and the APRM. The 5 decades i are covered by the IRM by means of a range switch and the 5 decades are. broken down into 10 ranges, each being one-half of a decade in size. The IRM scram trip setting of 120/125 of full scale is active in each range of the i IRM. For example, if the instrument were on range 1, the scram setting would be a 120/125 of full scale for that range; likewise, if the instrument were on range 5, the ' scram would be 120/125 of full scale on that range. Thus, as the IRM is ranged up to accommodate the increase in power level, the scram trip setting is also ranged up.- The most significant sources of reactivity change during the power increase are due to control rod withdrawal. For in-sequence control rod withdrawal, the rate of change of power is slow enough due to the physical limitation of withdrawing control rods, that heat flux is in equilibrium with the neutron flux and an IRM scram would result in a reactor

shutdown well before any-safety limit is. exceeded.

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TABLE 3.1.1 REACTOR PROTECTION SYSTEM (SCRAM) INSTRUMENT REQUIREMENTS

-Modes in Which -

Functions Must be Minimus Number Required Conditions When Operating Operating Instrument Minimum Conditions For Refuel Startup Run Channels Per Operation Are Not I

Trip Function Trip Settings (1) -(13) Trip System (2) Satisfied (3)- [

1 i X X X 1 A -

1. Mode Switch l in Shutdown

$ 2. Manual Scram X X X 1 A

3. IRM .

High Flux X X X(11) 2 A

-< 120/125 A INOP X X X(11) 2 l

4. APRM High Flux < 0.66W+54%(4) X 2 A or B '

l (flow bias) 2 'A

High Flux < 15% X X

! (reduced) ,l .

j INOP X 2(5) A or B

. Downscale > 2/125 X~ 2 A or B

5. High Reactor <_ 1055 psig X X X 2 A Pressure

6. High Drywell < 2.5 psig X X X 2 A Pressure X X 2 A

7. Reactor Low (6) >_ 127.0 inches X Water Level

8. Scram Discharge <_ 2 A 24 gallons X X X Volume High Level 19

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• TABLE 3.1.1 NOTES 1.. When the reactor is subcritical and the. reactor water temperature is less than 2120F,'only the following~ trip functions need to be operable:

a) mode switch in shutdown b) manual scram c) high flux IRM or high flux SRM in coincidence f' d) scram discharge volume high water level .l.

2. Whenever an instrument system is found to be inoperable, the instrument system output relay shall be tripped immediately. Except for MSIV & Turbine Stop Valve Position,- this action'shall result in tripping the trip.

system.

3. When the requirements in the column " Minimum Number of Operating Instrument Channels Per Trip System" cannot be met for one system, that system shall be tripped. If the . requirements cannot be met for both trip systems, -the appropriate actions listed below shall be taken:

I a) Initiate insertion of operable rods and complete insertion of all operable rods within four hours.

Reduce power level to IRM range and place mode switch in the "Startup/ Hot Standby" position within eight

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b) hours, i c) Reduce turbine lead and close main steam line isolation valves within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />. ,

d) Reduce reactor. power to less than 30% of rated within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />.

4 "W" is percent rated drive flow where 100% rated-drive flow is that flow equivalent to 48 x 106 lbs/hr core flow.

5. To be considered operable an APRM must have at least 2 LPRM inputs per level and at least a total of 13 LPRM inputs, except that channels A, C, D, and F may lose all LPRM inputs from the companion APRM Cabinet plus one additional LPRM input and still be considered operable.

6. The top of the enriched fuel has. been designated as 0 inches and provides common reference level for all vessel .

j water level instrumentation. -

7. Channel shared by the Reactor Protection and Primary Containment Isolation Systems.

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. 8 An alarm setting of 1.5 times normal background at rated power shall be established to alert the operator to abnormal radiation levels in primary coolant.

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i i 9. . Channel signals for the turbine control valve fast closure trip shall be derived from the same event or events which cause the control valve fast closure.

10 A turbine stop valve closure and generator load rejection bypass is permitted when the first stage turbine pressure is less than 30% of normal (220 psta).

11. The IRM scram is bypassed when the APRMs are on scale and the mode switch is in the run position.

l 12. For special stability tests, the APRM flux scram shall be < 0.66W + 85% for the duration of testing.

Adjustments for the ratio of MFLPD to FRP greater than 1.0 are not required while conducting special tests.

y 13. While performing refuel interlock checks which rquire the mode switch to be in Startup, the reduced APRM high

flux scram need not be operable provided:

a. The following trip functions are operable:

1. Mode switch in shutdown,

2. Manual scram

3. High flux IRM scram i 4. High flux SRM scram in noncoincidence,

5. Scram discharge volume high water level, and; l b. No more than two (2) control rods are withdrawn. The two (2) control rods that can be withdrawn cannot be j faced adjacent or diagonally adjacent.

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i VYNPS 3.1 (cont'd)

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 i monitors to 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 scraming at this setting, the resultant transient is inaignificant.

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 1short 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 from 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 socitoring protection against excessive power levels. In the power range, the normal APRM . system provides required protection. Thus, t

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 type have occurred and whether the particular function involved is still operable or capable of meeting the single f ailure 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,

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3.1 (Continued) i 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 j continued operation with scrr.m functions which may Se 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 i subsystems are found to be operable. The conditions under which the bypass is permitted require an immediate determination that the particular function is operable. Hewever, during the time a bypass is applied, the l.

i function will not meet the single failure criteria; therefore, it is prudent to limit the. time the bypass is in l effect by requiring that surveillance testing proceed on a continuous basis and that the bypass be removed as

soon as testing is completed.

l Sluggish indicator response during the perturbation test will be indicative of a plugged instrument line or I

closed instrument valves. Testing immediately af ter functional testing will assure the operability of the instrument lines. This test assuren 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.

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