ML20214S898

Proposed Tech Specs Adding Action Statement to Allow Units to Remain at Power for Up to 72 H W/More than One full-length Rod Inoperable But Trippable

ML20214S898
Person / Time
Site:	Mcguire, Catawba, McGuire, 05000000
Issue date:	06/03/1987
From:	DUKE POWER CO.
To:
Shared Package
ML20214S895	List: ML20214S894 ML20214S898
References
TAC-65528, TAC-65529, TAC-65530, TAC-65531, NUDOCS 8706100041
Download: ML20214S898 (7)

Text

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REACTIVITY CONTROL SYSTEMS 3/4.1.3 MOVABLE CONTROL ASSEMBLIES GROUP HEIGHT LIMITING CONDITION FOR OPERATION All full-length shutdown and control rods shall be OPERABLE and 3.1.3.1 positioned within !12 steps (indicated position) of their group step counter demand position.

APPLICABILITY:

MODES la and 2*.

With one or more full-length rods inoperable due to being immovable ACTION:

as a result of excessive friction or mechanical interference or a.

known to be untrippable, determine that the SHUTDOWN MARGIN require-ment of Specification 3.1.1.1 is satisfied within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and be in HOT STANDBY within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.

_ c misaligned from the With more than one full-length rod i- ;

group step counter demand position by more than t12 steps (indicated b.

position), be in HOT STANOBY within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.

With one full-length rod trippable but incoerable due to causes other than addressed by ACTION a., above, or misaligned from its c.

group step counter demand height by more than 12 steps (indicated position), POWER OPERATION may continue provided that within 1 hour:

The rod is restored to OPERABLE status within the above alignment 1.

requirements, or The rod is declared inoperable and the remainder of the rods in 2.

the group with the inoperable rod are aligned to within 2 12 steps of the inoperable rod while maintaining the rod sequence and insertion limits of Figure 3.1-l Q THERMAL POWER level shall y

be restricted pursuance to Specification 3.1.3.6 during sucse-quent operation, or g

y g

g The rod is declared inocerable and tne SHUTDOWN MARGIN require-3.

POWER OPERATION ment of Specification 3.1.1.1 is satisfied.

may then continue provided that:

A reevaluation of each accident analysis of Table 3.1-1 is a) performed within 5 days; this reevaluation shall confirm that the previously analyzed results of thed accidents remain valid for the duration of operation under these conditions; The SHUTDOWN MARGIN requirement of Specification 3.1.1.1 is b) determined at least once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />; g62 PDR "See Special Test Exceptions Specifications 3.10.2 and 3.10.3.

FATAWRA - UNI 3/4 1-14

REACTIVITY CONTROL SYSTEMS.

LIMITING CONDITION FOR OPERATION ACTION (Continued)

A power distribution map is obtained from the movable c)

N incore detectors and F (Z) and F are verified to be g

aH within their limits within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />; and The THERMAL POWER level is reduced to less than or d) equal to 75% of RATED THERMAL POWER within the next hour and within the following 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> the High Neutron Flex Trip Setpoint is reduced to less than or equal to 85%

of RATED THERMAL POWER.

t SURVEILLANCE REQUIREMENTS The position of each full-length rod shall be determined to be 4.1.3.1.1 d positions witnin the group demand limit by verifying tne individual ro at least once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> except during time intervals when the Rod Position Deviation Monitor is inoperable, tnen verify the group positions at least ence per 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.

Each full-length rod not fully inserted in the core shall be 4.1.3.1.2 cetermined to be OPERABLE by movement of at least 10 steps in any one direction at least once per 31 days.

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d.

With more than oneirod trippable but inoperable due to causes other than addressed by ACTION a above, POWER OPERATION may continue provided that:

1.

Within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, the remainder of the rods in the bank (s) with the inoperable rods are aligned to within i 12 steps of the inoperable rods while maintaining the rod sequence and insertion The limits of Figure 3.1-la or Figure 3.1-lb, as applicable.

THERMAL POWER 1evel shall be restricted pursuant to Specification 3.1.3.6 during subsequent operation, and 2.

The inoperable rods are restored to OPERABLE status within 72 l

hours.

3/4 1-15 CATAW8A - UNITS 1 & 2

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REACTIVITY CONTROL SYSTEMS

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3/4.1.3 MOVABLE CONTROL ASSEMBLIES GROUP HEIGHT LIMITING CONDITION FOR OPERATION

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3.1.3.1 All full-leagth shutdown and control rods shall be OPERABLE and positioned within i 12 steps (indicated position) of their group step counter demand position.

APPLICABILITY:

MODES 1* and 2*.

ACTION:

a.

With one or more full-length rcds inoperable due to being immovable as a result of excessive friction or mechanical interference or known to be 7ntrippable, determine that the SHUTOOWN MARGIN require-ment of Specification 3.1.1.1 is satisfied within I hour and be in HOT STANOBY within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.

b.

With more than one full-length rod ' ; :

1'_ _. misaligned from the group step counter demand position by more than 2 12 steps (indicated:

position), be in HOT STANDBY wi_ thin 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.

c.

With one full-length rod trippable but inoperable due to causes other than addressed by ACTION a., above, or misaligned from its group step counter demand height by more than i 12 steps (indicated k

position), POWER OPERATION may continue provided that within 1 hcur:

1.

The rod is restored to OPERABLE status within the cbove alignment requirements, or 2.

The rod is declared inoperable and the remainder of the rods in the group with the inoperaDie rod are aligned to within t 12 steps of the inoperable rod while maintaining the rod sequence and insertion limits of Figure / 3.1-1 c " i l 2-The THERMAL POWER level shall be restricted pursuant to Specification 3.1.3.6 during subsequent operation, or 3.

The rod is declared inoperable and the SHUTCOWN MARGIN requirement of Specification 3.1.1.1 is satisfied.

POWER 4

OPERATION may then continue provided that:

a)

A reevaluation of each accident analysis of Table 3.1-1 is perfc.med within 5 days; this reevaluation shall confirm that the previously analyzed results of these accidents remain valid for the duration of operation under these conditions; b)

The SHUTDOWN MARGIN requirement of Specification 3.1.1.1 is determined at least once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />; ISee Special Test Exceptions 3.10.2 and 3.10.3.

McGUIRE - UNITS 1 and 2 3/4 1-14

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REACTIVITY CONTROL SYSTEMS ACTION (Continued)

A power distribution map is obtai'ned frcm the movable c) incore detectors and F (Z) and F are verified to be g

within their limits within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />; and The THERMAL POWER level is reduced to less than or d) equal to 75% of RATED THERMAL POWER within the next hour and within the following 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> the High Neutron Flux Trip Setpoint is reduced to less than or equal to 85%

of RATED THERMAL POWER.

SURVEILLANCE REQUIREMENTS

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The position of each full-length rod shall be determined to be 4.1.3.1.1 within the group demand limit by verifying the individual rod positions at least once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> except during time intervals when the Rod Position Deviation Monitor is inoperable, then verify the group positions at least once per a hours.

Each full-length rod not fully inserted in the core shall be 4.1.3.1.2 determined to be OPERABLE by movement of at least 10 steps in any one direction at least once per 31 days.

full-lenM

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With more than one rod trippable but inoperable due to causes other d.

i than addressed by ACTION a ab1ve, POWER OPERATION may contirue n

provided that:

Within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, the remainder of the rods in the bank (s) with

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1 1.

the inoperable rods are aligned to within i 12 steps of the inoperable rods while maintaining the rod sequence and insertion

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The limits of Figure 3.1-1/,r " e- _ :- _

-3 THERMAL PCWER level shall be restricted pursuant to Specification 3.1.3.6 during subsequent operation, and The inoperable rods are restored to OPERABLE status within 72 2.

hours.

3/4 1-15 McGUIRE - UNITS 1 and 2

1 INSERT FOR BASES 3/4.1.3 - MOVABLE CONTROL ASSEMBLIES For Specification 3.1.3.1 ACTIONS c. and d.,

it is incumbent upon the plant personnel to verify the crippability of the inoperable control rod (s). This may be by verification of a control system failure, usually electrical in nature, or that the failure is associated with the control rod stepping mechanism.

During performance of the Control Rod Movement periodic test (Specification 4.1.3.1.2), there have been some " Control Malfunctions" that prohibited a control rod bank or group from moving when selected, as evidenced by the demand counters and DRPI.

In all cases, then the control malfunctions were corrected, the rods moved freely (no excessive friction or mechanical interference) and were trippable.

This surveillance test is an indirect method of verifying the control rods are not immovable or untrippable.

It is highly unlikely that a complete control rod bank or bank group is immovable or untrippable.

Past surveillance and operating history provide evidence of "trippability".

7 Based on the above information, during performance of the rod movement test, if a complete control rod bank or group fails to move when selected and can be attributed to a " Control Malfunction", the control rods can be considered

" Operable" and plant operation may continue while ACTIONS c. and d. are taken.

If one or more control rods fail to move during testing (not a complete bank or group and cannot be contributed to a " Control Malfunction"), the affected control rod (s) shall be declared " Inoperable" and ACTION a. taken.

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Reference:

E letter dated December 21, 1984, NS-NRC-84-2990, E. P. Rahe to Dr. C.

O. Thomas) i i

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u REACTIVITY CONTROL SYSTEMS BASES BORATION SYSTEMS (Continued)

The boron capability required below 200 F is sufficient to provide a SHUTDOWN MARGIN of 1% dalta k/k after xenon decay and cooldown from 200 F to 140 F.

This condition requires either 2000 gallons of 7000 ppm borated water from the boric acid storage tanks or 10,000 gallons of 2000 ppm borated water from the refueling water storage tank.

The contained water volume limits inclade allowance for water not available because of discharge line location and other physical characteristics.

The limits on contained water volume and boron cancentration of the RWST also ensure a pH value of between 8.5 and 10.5 for the solution recirculated within containment after a LOCA.

This pH band minimizes the evolution of iodine ano minimizes the effect of chloride and caustic stress corrosion on mechanical systems and components.

The OPERAEILITY of one Boron Injection System during REFUELING ensures that this system is available for reactivity control while in MODE 6.

3/4.1.3 MOVA8LE CONTROL ASSEMBLIES The specifications of this section ensure that:

(1) acceptable power distribution limits are maintained, (2) the minimum SHUTOOWN MARGIN is maintained, and (3) the potential effects of rod misalignment on associated accident analyses are limited. OPERABILITY of the control rod position indicators is required to determine control rod positions and thereby ensure compliance with the control rod alignment and insertion limits.

The ACTION statements which permit limited variaufons from the basic requirements are accumpanied by additional restrictions which ensure that the original design criteria are met. Misalignment of a rod requires measurement of peaking factors and a restriction in THERMAL POWER.

These restrictions En provide assurance of fuel rod integrity during continued operation.

dddition, those safety analyses affected by a misaligned Tod are reevaluated to confirm that the results remain valid during future operation.

The maximum rod drop time restriction is consistent with the assumed rod l

Measurement with T greater than or drop time used in the safety analyses.

equalto551*Fandwithallreactorcoolantpumpsoperatindnsuresthatthe l

measured drop times will be representative of insertion times experienced during a Reactor trip at operating conditions.

Control rod positions and OPERABILITY of the rod position indicators are y

required to be verified on a nominal basis of once per 12 hcurs with more p

frequent verifications required if an automatic monitoring channel is f[r These verification frequencies are adequate for assuring that the inoperable.

applicable LCO's are satisfied.

McGUIRE - UNITS 1 and 2 B 3/4 1-3

REACTIVITY CCNTROL SYSTEMS 4

SASES i

MOVABLE CONTROL ASSEMBLIES (Continued)

The ACTICN statements which permit limited variations from the basic i

J requirements are accompanied by additional restrictions whicn ensure tnat tne original design critaria are met.

Misalignment of a rod reauires measurement cf peaking factors and a restriction in THERMAL POWER.

These restrictions cro-4 vide assurance of fuel rod integrity during continued operation.

In addition, those safety analyses affected by a misaligned rod are reevaluated to confirm i

tnat the results remain valid during future operation.

i The maximum rod droo time restriction is consistent with the assumed rod drop time used in the safety analyses.

Measurement with T,yg greater than or ecual to 551*F and with all reactor coolant pumos operating ensures that the measured drop times will be representative of insertion times excerlenced during a Reactor trip at operating conditions.

Control rod positions and OPERABILITY of the rod position indicators are equired to be verified on a nominal basis of once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> with more fra.-

auent verifications required if an automatic monitoring channel is inoceraole.

These verification frequencies are adequate for assuring that the aoplicaDie LCOs are satisfied.

IASERT i

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CATAWBA - UNITS 1 & 2 8 3/4 1-4

Westinghouse Water Reactor

$Q Electric Corporation..

Divisions

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NS-NRC-84-2990 December 21, 1984 5

Dr. Cecil O. Ihmas, Branch Chier i

Standardization ar.d Special Projects Branch Office of Nuclear Reactor Regulation l

U.S. Nuclear Regulatory Comission Washington, D.C.

20555

Dear Dr. Thomas:

Attached please find a Westinghouse recomended revision to Specification 3/4.1.3 Movable Control Assemblies and its associated Bases. This revision is the result of efforts made to address multiple imovable, but trippable, control rods. These efforts were made due to several occurrences at different j

plants with a Westinghouse NSSS where a group or several groups of control rods became imovable by a rod control systen failure. Under these conditions the 9

control rods would not step in or out, but would drop if a rwactor trip was l

iritiated.

The Technical Specifications as currently provided in NU3D~r-0452 KEV. 4 do not recognize the fact that in this situation the control reds would still perform their safety function and because more than one control rod is imovable the plant is forced to repair the failure or be in Hot Shutdwn in six hours. An action this drastic is trinecessary as noted by Westinghouse verbally in recent discussions with members of the staff.

It should be noted that the suggested revisions have been discussed in detail with Mr. M. S. Dunenfeld of the Cere Performance Branch.

It is our understanding that he is in general agreer.ent with the proposed changes based upon our sutrr.ittal cf additional infomation concerning rod control systen organization, failure, and troubleshooting. The requested infonnation is provided as Attachment C.

ammme M

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i Dr. C. O. Thomas Page 'No It is our beliefh. hat the proposed changes to this specification adequately address the safety requirements with regards to imovable and misaligned centrol mds.

It would be appreciated if you would review the attached and consider its inclusion in all Westinghouse NSSS plant Technical Specifications (if so requested by the plants) and any future revisions to NUREG-0452. If you have any questicms concerning the above or the attached please contact either Mr. W. L. Luce, Manager, Licensing Initiatives (412/37b4793) or Mr. c. R.

Tuley (412/37b4172).

Very truly yours, h-M CLw 6..W g+

'uclear Safety Department P. Rahe, Jr., Manager CRT/kk Attacinents

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cc: D. S. Brin'can M. S. Dunenfeld

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ATTACHMENT A RFACTTVITY CO TRM. SYSTFMS t/4.1.1 MOVABLE CCBITROL ASSEMBLIES g

CROUP M?TCMT LTWlTTNG CO!DTTTON FOR OPFRitTON f

3.1 3 1 All shutdown and control rods, which are inserted in the core, shall be OPERABLE and positioned within a 12 steps (indicated position) of their group step counter danand posit 1on.

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APPLICABILITh HDDES 18 AND 2*.

EIEMa With one or more rods inoperable due to being immovable as a result of 4

s.

excessive friction or mechanical interference or known to be untrippable, determine that the SIUTDOWN MARGIN requirement of Specification 31.1.1 is satisfied within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and be in HOT STANDBY 4

j witnin 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.

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i b.

With one red trippable but inoperable due to causes other than addressed by ACTION a above, or misaligned from its group step counter deand height by mete than a 12 steps (indicated position), POWER OPERATION may continue provided that within one hour either:

1 i

1.

The rod is restored to OPERABLE status witr.in the above alignment requirements, or 2.

The rod is declared inoperable and the reminder of the rods in the group with the inoperable rvd are aligned to within a 12 steps of the inoperable red while maintaining the rod sequence and insertion limits of Figure 31-1. The THERMAL POWER level shall be restricted pursuant to Specification 3 1 3.6 during subsequent operation, or 3.

The rod is declared inoperable and the SHUTDOWN MARGIN requirement of Specification 31.1.1 is satisfied. POWER i

OPERATION may than continue provided that:

l a)

A reevaluation of each accident analysis of Table 31-) is performed within 5 days; this reevaluation shall confirm that the previously analyzed results of these accidents rer.ain valid for the duration of operation tmder these conditions.

b)

A power distribution map s obtained from the novable incore limits within 70(hours.

detectors and F Z) and H are verified to be within their i

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• See Special Test Exceptions 3.10.2 and 310 3 i

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q c)

The THERFA POWER level is reduced to less than Cr equal to i :

755 of RATED THERPE POWER witnin the next hour and within the following 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> the high neutron flux trip setpoint is reduced to less than or equal to 855 of RATBD THERHAL P;r,,

c.

With more than one rod trippable but inoperable due to causes other i

than add' essed by ACTION a above, POWER OPERATION may continue r

providedFthat:

1.

Within one hour, the remainder of the mda in the bank (s) with the inoperable rods are aligned to within g 12 steps of the inoperable rods while maintaining the rod sequence and insertion limits of Figure 3.1-1.

The THERMAL POWER level shall be restricted pursuant to Specification 3.13 6 during subsequent operation, and 2.

The inoperable rods are restored to OPERABLE status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.

i d.

With more than one rod misaligned from it's group step counter demand height by more than A 12 steps (indicated position), be in HOT STANDBY within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.

RJnvrit f act arourpsmTs 4.1 3 1.1 The position of each rod shall be determined to be within the group demand limit by verifying the individual red positions at least once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> except during time intervals when the Rod Position Deviation Monitor is inoperable, tnen verify the group positions at least once per 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.

i 4.1 3 1.2 Each red not fully inserted in the core shall be determined to be 1

OPERABLE by moveent of at least 10 steps in any one direction at least once per 31 days.

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TABLE 31-1

,1cc7pp;T tyttvert FEUIPTNS PI:Vit UATTOM IN TME n'n T OF AN IN'PEPART r Ron

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Rod Cluster Control Assembly Insertion Characteristics Rod Cluster Control Assembly Misalignment Loss of Reactor Coolant From Small Ruptured Pipes Or From Cracks In large Pipes i

Which Actuates the Emergency Core Cooling System Sin 61e Rod Cluster Control Assembly Withdrawal At Full Power Major Reactor Coolant System Pipe Ruptures (Less of Coolant Accident)

Major Secondary System Pipe Rupture Rupture of A Control Rod Drive Mechanism Housing (Rod Cluster Control Assembly Ejection) e

,,n.+

--e.----,--c

ATT C c!!NT B E

l 1/ 4.1.1 Mavahi e cn trol Amma~hliam i

The specifications of this section are necessary to ensure that the following requirments are a$ at all times during nomal N loop or S1 loop operation.

By observing that me RCCAs are positioned above their respective insertion limits during cormal operation, i

i 1.

At any time in life for Mode 1 and 2 operation, the minimm 51UTDOWN MARGIN I

will be maintained. For operational modes 3, 4, 5, and 6, the reactivity l

condition consistent with other specifications will be maintained with all i

RCCAs fully inserted by ubserving that the boron concentration is always greater than an appropriate minima value.

2.

During nomal operation the enthalpy rise hot channel factor, F4H' Will D' maintained within acceptable limits.

j 3.

The consequences of an ejected RCCA accident will be restricted below the limiting consequences referred to in the ejected rod analysis.

4.

The core can be made suberitical by the required shutdown margin with one i

RCCA stuck. In the event of an RCCA ejection, the core can be ande subcritical with two RCCAs stuck, where one of the RCCAs is assmed to be the worst ejected rod control assembly.

5. The trip reactivity assmed in the accident analysis will be available.

I 6.

Dropping an RCCA into the core or statically misaligning an RCCA during normal operation will not violate the themal design basis with respect to j

DNBR.

7 The econtrciled withdrawal of an RCCA will result in consequences no more severe than presented in the accident analysis.

8.

The mcontrolled withdrawal of a control assembly bank will not result in a peak power density that exceeds the center line melting criterion.

i OPERABILITY of the control rod position indicator channels (LCO 313 2) is l.

required to detemine control rod positions and thereby er.sure con:pliance with the control red alignment.

j OPERABILITY of the demand position indication system (LCO 313 2) is required to determine bank deand positions and thereby ensure compliance with the insertion limits.

The ACTION statements which permit limited variations from the basic i

requirenents are accompanied by additions 1 restrictions which ensure that some of the originsi criteria are met. Hisalignment of a rod requires measurement of peaking factors or a restriction in THERMAL POWER, either of these l

i restrictions provide assurance of fuel rod integrity during continued operation j

provided no further abnormal condition develops.

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For Specification 3.1.31 ACTIONS b and e it is incabent upon the plant to verify the trippability of the inoperable control rod (s). This may be by l

verification of a control system failure, usually electrical in nature, or that the failure is associated with the control rod stepping mechanism. In the

cvent tae plant is unable to verif,' tne roc (s) trippability, it must be assumes to be mtrippable and thus fall under tne require ents of ACTION A.

Assumir.; a controlled shutcown from 1001 RATED TriEPp.AL POWER, this allows approximately four hours for this verification.

The maximun rod drop time permitted by (LCO 31.3.4) is consistent with the assumed rod drop time used in the accident analyses. Measurement with 7 a

350 degrees-F ang,with all reactor coolant punps operating ensures that yj, measured drop times will be representative of insertion times experienced during a reactor trip at operating conditions.

Bank decand positions and OPERASILITY of the red position indicators are required to be verified on a nominal basis of once per 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> with more fraquent verifications required if an automatic monitoring channel is inoperable. These verification frequencies are adequate for assuring that the applicable LCO's are satisfied.

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i ATTACHMENT C 1

Arranneent of Meehani mmt he Westinghouse NSSS design for four, three, and two loop plants uses fif ty-three, forty-eight and twenty-nine full length rod drive mechanims arranged into banks and groups as shown in Figure 1.

A group consists of two or more mechanisms that are electrically paralleled to step simultaneously. A bank of mechanisms consists of two groups that are mwed in staggered fashion such that the groups are always within one step of each other. Part length rods have j

either been rammed or locked out in all Westinghouse NSSS plants. The arrangement includes two or four shutdown banks, A and 8 or A, B,.C and D; and i

four Control Banks A, B, C and D.

Control banks are awed in overlap in the follcuing withdrawal sequence: When Control Bank A reaches a predetemined height in the top half of the core, Control Bank B starts to awe out with A.

Control Bank A stops at the top of the core and Bank B continues stil it reaches a predetemined height in the top half of the core when Control Bank C starts to mwe out with B.

This sequence continues stil all rods are withdrawn. The insertion sequence is the opposite of the withdrawal sequence.

Main Contral Roem Contrain Controls for the Rod Control Systen located in the main control room are listed in Figure 2.

The I> Hold-out lever is a joy stick used for manual rod motion and is located on the main control toard. Also on the main control board is a 1

Bank Selector Siritch with eight positions. In the manual position, control l

banks are mwed in overlap with the ImHold-out lever. Control banks are a w ed J

in overlap by the automatic Tavg control system with the switch in the auto j

position. Six additional positions are provided for individual bank mwement.

Step counters, one for each group, are located on the main control board to display demand rod position. A Rod Position Indication Systen, not connected to i

the Rod Control Statem, is used to display actual red position and is taed in conjuncticn with the step counters to detemine deviation between demand and actual position.

i Ir>0ut lights shew the request for rod motion frtzn either the In-Hold-out lever j

i or the Automatic Tavg Control Systen. A startup pushbutton is provided to reset the step comters and all internal systen counters such as the bank overlap l

comter en startup. An alenn reset pushbutton, resets internal system failure detectors and alarms which include a seal in feature. Lift coil disconnect switches, one for each mechanian, are provided behind the main control board to l

allow retrieval of a dropped rod.

l l

T,to annunciators are located on the control board; an urgent and non-urgent slann. The u sent slann indicates that a control system failure has occurred that would affect the ability of the control systen to awe reds. A nor> urgent alarm indicates failures of one or more redundant power supplies that feed the system printed circuit cards.

1 i

i s

m Basic "htrist:r EL-idge Cc : rel Ci uit Bree thyristers feming a half wave phase contec11ed bridge supply current to four mechanism coils, either lif t, movable or staticnary gripper coils as shown in Figure 3 Current feedback signels from shmts in series wLth each coil are used to regulate the current comanded by a slave cycler locatS in the system logic cabinet.

Pm er cmbinot Pewer cireu4ts 4

Five thyristor br'idges fem one system power cabinet as shown in Figure 4 Bree, four, or five power cabinets are used in the system. De power cabinet basically amplifies low level comand signals from a slave cycler in the logic cabinet. One power cabinet drives three groups of four medanisms and is capable of moving one group while holding the other two in position. The selection as to which group is to move is made with multiplexing thyristors, one for each group of movable coils and one for each lift coil. The lift coil t

f multiplexing thyristors also serve as lift disconnect maitches for retrieving a dropped rod.

Syntam Bleek Diarram the power cabinets are supplied with power from two motor generator sets nomally operating in parallel through two reactor trip breakers in series as shown in Figure 5.

The logic cabinet includes a pulser, master cycler, bank overlap mit, and four slave cyclers. The pulser determines the speed of red motim as directed by the reactor Tavg control system when automatic operation -

is selected or by a potentometer located in the Tavg control system when manual operatim is selected. The master cycler directs pulses from the palser alternately to the slave cyclers for the two groups in a bank. Selection of which bank or banks are to move is made by the bank overlap mit and master i

cycler. The slave cycler sequences the mechanism coils through one step, either in or out for each "go" pulse from the master cycler. A DC hold cabinet is provided to hold rods and allcw replacement of printed circuit cards in the power cabinet while the plant is in operation.

Failure Detectim and Alams A rod control urgent alarm is actuated by five failure detectors in each power cabinet or by three failure detectors in the logic as shown in Figure 6.

An urgent alam stops automatic rod motion and pemits manual movement of a selected bank if the logic cabinet and the two power cabinets associated with the selected bank are not in urgent alam.

Detectim of a failure by a failure detector results in the folicWing indications:

A failure detector lamp, one for each type of failure, located on the edge a.

of a printed circuit card in the failed cabinet, is energized.

b.

A red urgent failure lamp on the front of the failed cabinet is energized.

c.

A " Rod control Urgent Failure" annmeistor in the control roca is actuated.

A non-urgent alam indicates failure of one of a raaber of redundant power supplies and does not affect the operation of the systen.

I

Effect er Me:Pr.ir Me:P2:r.ical Fail.:re en Cer.~:1 Siste-The Rod Control System operates ind2 pendently of the red drive medianims, Nothing has been included in the syste, either by design or iradvertently, to allow it to see movement of the mechanin medanical parts, the drive shaft, or rod control clusters. This has been verified many times during factory check out of completed systems where the test loads consist only of simulated mechania coils with iron pipes in the center to approximate the magnetic properties of the coils. Checkout of the Rod Control syste at the site is generally perforted during the Hot Functional Test when no reactor core, rods, or drive shafts are in place but only the mechanisn coils are connected. In the factory tests and Hot Functional checkout, the systems operate nomally without alarms.

Hen.t to Di stirmH sh Between rentrol Syste and Feehani e Prehl e=

Based on the previous discussion, a Rod Control System Urgent Alann must be the result of a control syste failure and cannot be related to an inoperable rod or rods. There are failures that do not result in an urgent alarm that could prevent one or more rods from moving. In this case, the proble can be traced to either the control system or me&ania by acr11toring the medanim coil currents with a voltneter, oscilloscope, or recorder. Built-in test points are located in the power cabinets for this purpose. If the control system will not vary the currents to the mechanim coils, the proble Euah be in the control system and not the mechanims. If the control system varies currents to the coils, then the me&anian may be suspect. Grossly abnomal currents would indicate control system prebles and mildly abnormal currents would indicate medanin problems. Recordings of the currents would have to be studied in this event. Figure 7 stamarizes this identification process.

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MAIN CONTROL ROOM CONTROLS Y

o IN-HOLD-0UT LEVEL o

BANK SELECTOR SWITCH MANUAL AUTO SHUTDOWN BANK A. B CONTROL BANK A. 8. C. D o

STEP COUNTERS SHOW DEKAND POSITION o

IN-0UT LIGHTS i

o STARTUP PUSHBUTTON i

o ALARM RESET PUSHBUTTON o

LIFT COIL DISCONNECT SWITCNES o

ANNUNCIATORS ROD CONTROL URGENT ALARM ROD CONTROL NON-URGENT ALARM FIGURE 2

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URGENT ALARM - POWER CABINET o ? REGULATION FAILURE o

PHASE FAILURE o

LOGIC ERROR o

MULTIPLEXING ERROR o

CARD MIS $1NG URGENT ALARA - LOGIC CABINET o

SLAVE CYCLER RECEIVES A GD PULSE DURING A STEP.

o OSCILLATOR FAILURE c.

CARD MISSING URGENT ALARM EFFECT ON SYSTEM o

AUTOMATIC ROD MOVEMENT IS STOPPED o

MANUAL MOVEMENT OF SELECTED BANK IS PERMITTED IF LOGIC CABINET AND POWER CABINET ARE NOT IN URGENT

, ALARM NON-URGENT ALARM - LOGIC OR POWER CABINET o

REDUNDANT POWER SUPPLY FAILURE FIGURE 6

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' HOW TO DISTINGUISH BETWEEN CONYROL SYSTEM i

AND MECHANISM PROBLEMS o URGENT ALARM - MUST BE CONTROL SYSTEM FAILURE o NO URGENT ALARM. ONE OR MO,RE RODS WON'T MOVE MONITOR COIL CURRENTS CONTROL SYSTEM WON'T VARY CURRENTS +

PROBLEM MUST BE IN CONTROL SYSTEM CONTROL SYSTEM VARIES CURRENT TO COILS NORMALLY + SUSPECT MECHANISM CURRENTS ABNORMAL GROSSLY ABNORMAL + $USPECT CONTROL SYSTEM MILDLY ABNORMAL + SUSPECT MECHANISM FIGURE 7

- _ -.