ML20210R621
| ML20210R621 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 08/15/1986 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20210R494 | List: |
| References | |
| NUDOCS 8702170458 | |
| Download: ML20210R621 (12) | |
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oam UNITEdSTATES 8
NUCLEAR REGULATORY COMMISSION o
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,I WASHINGTON, D. C. 20585 6
SAFETY EVALUATION RY THE OFFICE OF NitCLEAR REACTOR Rent!LATION SUPPORTING A DEMONSTRATION TEST OF A FINE MOTION CONTROL D0D DRIVE COWOUWEALTH EDIS0N LASALLE COUNTY STATION llNIT 2 DOCKET NO. 50-374 1.0 INTRODi!CTION By letter of February 25, 1986, Comonwealth Edison, the licensee for LaSalle Unit 2, requested a review and approval of a General Electric Topical Report, "LaSalle (fnit 2 Fine Motion Control Rod Drive Denonstration Test Description" NEDO,31130, dated December 1985. The proposed test will consist of replacino an existing peripheral lockino "
piston control rod drive (LPCRD) module with a Fine Motion. Control Rod Drive (FMCRD) module for approximately one plant fuel cycle (18 months 1 The purpose of the test is to demonstrate the capability of the FMCRD module in a reactor environment. At the end of the test period, the FMCR0 will be removed for inspection and the plant will be restored to its pretest configuration.
Fundamentally, the LPCRD differs from the FMCRD by utilizing:
(a) hydraulic action for nomal drive motion; (b) an external scram discharge forscrammotion;and(c)scramcapabilitywithreactorpressureasa backup to the scram accumulators. The FMCRD nomal control rod drive motion is accomplished through an electrically powered AC motor. A 8702170450 870209 PDR ADOCK 05000374 P
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2 ball-nut assembly transintes the motor's shaft rotation to lingar motion.
Resting on the ball-nut assembly is a hollow piston which is coupled to the control rod. The translational motion of the hall-nut assembly lifts the resting hollow piston when rod insertion is desired. For rod withdrawal, the ball-nut is retracted. This allows the restino hollow piston-to withdraw by its own weight. An unweighing detection assembly will detect the loss of weight due to a stuck control rod and enforce a withdrawal block sianal. Upon receipt of a scram signal, high pressure water from the FMCRD scram accumulator lifts the hollow piston away from the ball-nut assenhly and rapidly inserts the hollow piston and coupled control rod. Water in the control rod drive is discharoed into the reactor vessel. After scram completion, latches hold the control rod in
' place at the full-in position. A drive-in sional is also received by the drive motor upon receipt of a scram signal and within 2 minutes of scram initiation the ball-nut assembly cars in the latches and completes the motion to full insertion if the hydraulic pressure does not fully insert the rod.
2.0 EVALUATinN The sub.iect GE Topical Pecort and the licensee's follow-up letters of Pay 12 and June 11, 1986, have been reviewed. The basis for our evaluation has been an audit review, usina the Standard Review Pl'an (SRP) 4.6 to assess compliance with the following:
600 13 - as related to instrumentation and control Section 4.5 of the topical report indicates that interconnections between the new FMCRD and existing plant systems and equipment have been minimized and are configured to assure that any potential fault within the FMCR0 or its
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interconnections with their protective functions:
Si a._
Power to the FPCPD is provided from a power distribution pade').,
u Circuit breakers and fuses provide protection.
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b.
The FMCRD receives a rod withdrawal block signal from the Reactor Manual Control System (RMCS). Relay coil to contact isola, tion N'
provides fault propacation protection.
- x c.
The FMCPD receives scram initiation signals from the Reactor ProtectionSysten(RPS).
Relay coil to contact isolation provides protection.
.y d.
The FMCRD scram solenoid valves receive electrical power from the RPS.
In-line fuses and conduit provide protection.
In addition to the above interconnections the topical report indicates that the following reconfigurations or procedural chances are~ required in order to accormodate the replacement of the LPCRD with an FMCRD..
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a.
Since the position indicatino probe is removed with the LPCRD, there will be no input to the plant's normal rod position information system. The rod position display will show the removed LPCRD to have a default indication. The new FMCRD rod will have its position indicated over 100 percent of its ranne of movement at the FMCRD operation panel.
For scram surveillance, a reed switch on the FMCRD will provide position indication.
b; Using one of eicht bypass switches, the removed LPCRD will be bypassed from the Rod Sequence Control System (RSCS) rod pattern control logic. The removed LPCRD will also be programed out of the
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6 rod worth riinimizer. This will free the FMCRD rod from banked 3-position withdrawal sequence and notch movement restrictions.
Because thdse restrictions are only required durino O to 20 percent reactor power level for postulated rod drop accidents, the FPCRD (by t
administrative control) will not be moved until reactor power is creater than 25 percent and a rod pattern has been established.
c.
The remotely operated directional control' valves flocated in the Hydraulic Control Unit (HCU)) associated with the removed LPCRD serve no practical function for the FMCRD. As a matter of cood practice tiiey will be hydraulically isolated throuch the closure of manual maintenance valves. Since there are not two isolation valves in series, isolation does not meet the sinole failure criterion with respect to inadvertent operator action to initiate movement.of the renoved LPCRD. However, the licensee has stated that fluid flow resistance of this circuit, even with open maintenance valves, will he relatively hich with regard to other parallel flow paths. Thus, if an operator inadvertently initiates movement of the removed LPCRD
!i via movement of the' directional control valves, there will be no 0
adverse effect on the FMCRD or on the scram function of other control I
y rods. Since there are no unacceptable consequences associated with bg -
this operator error, we conclude that this aspect, of the design is
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acceptable.
d.
The refueling interlocks system will not receive a " rod-in" signal
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from the new FMCPD and will, therefore, not allow refueling bridge 6'
movement or withdrawal of any rod.
In order to allow refuelino o
bridge movement and withdrawal of rods, the full-in signal to the p
refuelino interlocks from the FMCRD will be simulated (,iumpered). A
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special administrative procedure is to ensure that the FMCR0 rod is i.
full-in before the signal is simulated. Procedures will specify that,
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the full-in signal can be simulated only if the refueling bridge movement or control rod withdrawal it necessary.
Procedures will 4
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6 also require disconnectinn of power to the FMCRD electric motor before the full-in sianal is simulated.
B6 sed on information presented in the topical report the staff agrees with the licensee that the above identified interconnections and reconfigurations include sufficient protection to assure that any electrical fault in the FPCRD module and its supporting equipment will not propaoate back into the rest of the plant equipment to which it is directly or indirectly connected.
In addition to the above identified interconnections, the staff reviewed the proposed FMCRD design for the existence of other possible interconnections. As a result of this review, the staff detemined that cables connecting the FPCRD with its local control panel (shown on Figure 2 of the topical report) pass through the containment structure and are, thus, indirectly interconnected.
Failure of these cables may affect the integrity of the containment structure. This indirect interconnection and the protection afforded containment was pursued with the licensee. By telecon on April 9, 1986, the licensee indicated that power and instrumentation / control cables for the FMCRD pass throuah two electrical containment penetrations.
Power cables (rated at 17 amps continuous) will
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have 2-12 amp fuses per phase for protection.
Instrumentation / control cables (rated at 2 amps continuous) will have 4-1.6 amp fuses per circuit for protection. Based on the April 9,1986 telecon and information i
I presented in the topical report, the staff concludes that all interconnections have been. identified and that adequate protection and/or isolation has been afforded safety systems, comoonents, and structures.
GDC 23 - as related to failing in a safe state f
i The licensee indicates that replacement of the LPCRD at a peripheral core locationwithaFMCRDdoesjnotaffectthefail-safefeatureofthereactor protection system. lipon the loss of external electrical power or scram
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6 air header pressure, the scram pilot valve on the new FMCRD Hyaraulic Control Unit (FCU) will automatically actuate and a scram will. result.
Similarly, the scram pilot valves of each of the other LPCRD HCU's will automatically open the scram inlet and outlet valves leading to scram of the LPCPD's. Each HCU is a separate and indenendent unit, designed to maintain the fail-safe feature of the reactor protection system. The staff considers this acceptable. The licensee has also considered the followino sinole failure:
A rupture upstrean of the nozzle connection to the FMCRD piston unit.
In this case, a reversed reactor coolant flow (small break LOCA) is prevented by ball checks within the piston unit. The staff considers this acceptable.
A rupture unstrean of the " excess flow check valve" in the suction to the added booster pump for the FMCPD. This break could affect the remaining 184 LPCRDs. The licensee states that each LPCRD is hydraulically " operated" by an independent HCil.
In the event of a postulated piping rupture upstream of the " excess flow check valve,"
the decreased charging water header pressure would be annunciated in the control room.
Scram pressure would be maintained for all HCll's by way of a charging water check valve.
If the accumulator pressure decreases below the set point, this will also be' annunciated in the control room.
Furthermore, the FNCR0 HCtl is equipped with two valves
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for isolating the postutated leakage. Since each HCll operates independently, rod insertion or scram performance of the remaining rod would not be connromised. The staff considers this acceptable.
A purge line pipe break or an orifice failure. The licensee indicates that "purpe" water fnr the FMCRD utilizes the existing "cooline" water piping from the replaced LPCRD. No additional piping is introduced requiring consideration of a pipe crack or break. The purging function for the FMCRD is to be achieved through the W
7 introduction of an orificed wedge into the existing coolipg water isolation valve. Failure of this orifice could lead to undercooling of the LPCRDs ad.iacent to it. Persistent undercooling is to be annunciated in the control roon as a hich drive temperature. The licensee indicates that (1) given the annunciation of the hiah drive temperature, the FMCRD could be isolated manually, and proper cooling would then be restored to the remaining CRD's and (2) operatino a drive at temperature in excess of 250*F will not compromise the capability of rod insertion or scram performance. However, our review has determined that a sinole active failure can defeat the high ter.perature alarm in the control room. Therefore, no operator action can be credited for isolation of the break.
In addition, no test data have been provided to support the claim that operating a drive at temperature exceedino 250* F will not endanger the, capability of rod insertion or scram performance. Therefore, this issue is not fully resolved.
The staff has concluded that the pipe break or failure in the purge.
line to the FMCRD is a ceneric concern which is independent of the FMCRD installation. Therefore, it will not be considered as an issue in this review and the staff considers the FMCRD substitution for LPCRD to be accentable. However, the staff intends to pursue this concern as a ceneric issue relating to GE RWR CRD designs and will prioritize it for future resolution.
GDC 26 - as related to redundancy The LaSalle Unit 2 has two independent reactivity control systems utilizing different principles:
a)
The normal method of reactivity control employing control rod assemblies.
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A. standby liouid control system (SLCS) containing neutron 6 absorbing sodium pentaborate solution as an independent backup systelm.
These systens have been previously reviewed and found to be acceptable.
Another area considered in.the FMCRD review is functional testina. The licensee indicates that the testing of the FMCRD In-plant Test Program will be conducted in two phases. Durino phase one, after installation of the eouipment and FMCRD, the post-installation electrical system check and the FMCR0 system preoperation test will be performed. During phase two, after the power reaches 25% durine the startup, the FMCRD operational test will be performed. There is no specific FMCRD test required after ~the startup tests, and the FMCRD will perform the identical function reovired of the replaced LPCRD during the entire second fuel cycle.
The licensee also states that since the FNCRD will be treated as a special
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demonstration, special test exceptions will be reauested to exempt it from the existing plant Technical Specification.
This is acceptable.
However, the Technical Specification exception must be sub.iect to staff review prior to FMCRD installation.
ADC 28 - as related to reactivity limits The FMCRD rod in laSalle will have a normal control blade and be located on the core periphery. With that location it has intrinsically low
. reactivity effects compared to other control rods (more centrally located). That is, reactivity changes caused by or influenced by the FMCRD, and in particular those chances related to transient or accident events, are expected to be small compared to those which could be produced by other rods. Thus, it should provide reactivity perturbation effects which are small compared to those assumed in normally analyzed conditions and events involving rod movements. Reactivity changes are relatively small either for the movement of the FMCRD rod itself or for the interactive effect of movement of other rods with the FMCRD rod in an l
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erroneous (axial) position.
(Noticeable interactive effects s$ould not extend significantly beyond adjacent rods, which are not nomally high I
worth rods.) Thus, even when onstulating independent or concomitant misoperation of the FMCRD, results of the usually analyzed transient or accident events (and control rod related parameters such as shutdown naroin and scram worth) may be expected to bound the postulated misoperation. There are several reactor conditions or events which are relevant to postulated misoperation of the FMCRD rod. These are (1) scram reactivity worth, (?) shutdown maroin, (3) low power rod withdrawal error (RWE), (4) full power RWE, (5) rod drop accident (RDA). The role of FMCRD rod in these areas is discussed as follows:
a.
Althouah the FMCRD will scram on sinnal, the scran function (reactivity insertion versus tine) used in transient analysis was assume that it does not. The maximum worth adjacent rod was also assumed not to scran. This will he a minor modification to the nomal scram function, but the transient responses are not significantly affected. However, since the FMCRD is assumed not to operate, it will not he necessary to declare the FMCRD inoperable if excessive scram times are observed.
b.
The core design for the FFCRD rod cycle is such that shutdown requirements (at least 0.38% Ak suberitical, cold, xenon free at maximum reactivity time in cycle) will be met with both the FMCRD rod and stronnest additional rod withdrawn. Thus, normal shutdown requirements can be met without considering the (axial) position of the FMCRD rod. This will also apply durino refueling.
c.
Calculations of the FMCRD rod reactivity worth in the startuo and low power rance indicate worths (for various relevant rod patterns) less than 0.5% Ak. This is a reasonable and expected upper value for this range and is an acceptable workino value. A low power RWE for the FMCRD rod with this reactivity potential would be well under
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6 acceptable fuel temperature rise limits for the event. Generic low power RWE analyses have'been performed by GE using rods worth 2.51 4k giving peak fuel enthalpy results of about 60 cal /gm, well under assumed damage limits of 170 cal /gm. At 0.5%4k the FMCRD rod would likely not reach pronpt critical and would produce peak enthalpies well within the generic analyses, d.
In the power rance, peripheral rod worths are sufficiently low and associated initial minimum critical power ratios (MCPP) sufficiently high that full power RWE events do not approach MCPP limits even without rod block constraints. There are no rod block monitor (RW) requirements for these rods. Thus, the FMCRD rod does not provide a unique problem in this area, and if erroneously withdrawn would not produce an event exceeding MCPR limits. The perturbation effect of mispositioning of the FMCRD rod on a RWE of the ad.facent rod would be minor and would not significantly affect the RBM limit of the event.
e.
The FMCRD is designed to provide a signal if the blade and drive become separated, thus making an RDA more unlikely. Moreover, rod l
withdrawal procedures are such that, althounh not controlled by the
" rod pattern control systems," the FMCRD rod will be treated as an inoperable rod in the Banked Position Withdrawal Sequence and will not be withdrawn until power is above 25 percent (and inserted before going below 25 percent), and thus will not be subject to an RDA in, the low power reoion.
(The RDA is of no consequence above 25 percent power.) However, if an RDA is assumed to occur for the FMCRD rod, the low maximum worth of the rod, 0.5% ak, assures that a low peak enthalpy (less than 100 cal /gm) would result, well under the criterion of 280 cal /cm.
Furthermore, a mispositioned FMCRD rod would not affect nearby rods sufficiently to exceed the normally analyzed PDA event. Thus, the FMCRD rod does not affect the RDA analysis.
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4 11 It is thus concluded that postulated erroneous operation of thk FMCRD rod does not lead to reactivity effects which approach or are beyond the results normally determined for centrol rod related reactor states, transients or accidents,.nor make a significant reactivity event more likely.
3.0 CONCLUSION
P.ased nn the review discussed in Section 2.0 of tbis SER, the staff concludes that the topical report provides an acceptable basis for the installation and demonstration of the FMCRD for one operating cycle.
In addition, the staff requires that Drfor to FMCRD installation the Tech-nical Specifications exceptions be reviewed. With regard to the postulater' FMCRD purge line failure and a hiah drive temperature, the staff.will generically pursue the issue with the reactor vendor, General El'ectric Company.
The staff has cencluded, based on the censiderations discussed above, that: (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (2)
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such activities will be conducted in compliance with the Comission's reaulations and the issuance of this amendment will not be inimical to the i
comon defense and security nor to the health and safety of the public.
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4 AMENDMENT NO. 30TO FACILITY OPERATING LICENSE NO. NPF LA SALLE, UNIT 2 DISTRIBUTION:
-DocketlNo.;50-374?*
NRC PDR Local PDR PRC System NSIC BWD-3 r/f ABournia (?)
EHylton EAdensam Attorney, OELD Chiles RDiggs JPartlow BGrimes EJordan LHarmon TBarnhart (di FEltawila Mary Johns, RIII EButcher