ML20079D683
| ML20079D683 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 07/10/1991 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20079D682 | List: |
| References | |
| NUDOCS 9107240054 | |
| Download: ML20079D683 (6) | |
Text
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D,0,C,K,E,T, p,0._50 -2 78 1.0 J NT,R0 DUCTION Fy letter dated June 14, 1901, the Philadelphia Electric Company, Public Service Electric & Cas Company, Delmarva Power and Light Company and Atlantic City Electric Company (the licensees) submitted e request for a temporary change to the Peach Bottom Atomic Power Station, Unit No. 3, Technical Specifications (TS). The requested change would permit operation of the facility with control rod 38-23 uncoupled for the remainder of operating Cycle 8.
The change to TS 3.3.B.1 would not require that the compensatory measures of the action statement be initiated for control rod 38-23 because it is not coupled. Also, repositioning of the control rod to its proposed step 46 position would be allowed when the reactor power was above 10% of rated power.
The surveillance requirements of TS 4.3.B.1 would include additional monitoring during the repositioning evolution.
In this regard neutron monitoring by means of either the local Power Range lionitor (LPRM) or Transversing Incore Probe (TIP) Systems would be used to verify the control rod movement.
The control rod 38-23 was identified as being uncoupled during an attempt to withdraw it to the fully withdrawn position during the weekly control rod drive (CRD) exercise required by TS 4.3.A.2.a.
The uncoupling was detected by noting that from rod position 48 the rod could be moved into the overtravel position. The overtravel feature provides a positive check as only uncoupled drives may reach this position. The licensee made several unsuccessful attempts to recouple by giving notch insert signals from position 48 to 46 using normal drive pressure per the " Control Rod Uncoupled Procedure." The licensee also observed that the rod could be inserted to position 00 without difficulty and would w thdraw normally and settle to any position from 00 to i
46 without incident.
Because the control rod to drive coupling cannot be confirmed, the licensee assumed that the rod was uncoupled. TS 3.3.B.1 requires that an uncoupled rod be inserted and the control rod directional control valves be disarmed electrically. Along with CRD 38-23, the three rods symmetric to it were also inserted to preserve operational symmetry.
9107240054 910710 DR ADOCK 050 7
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General Electric (GE) Company has analyzed the problem for the licensee and concluded that the most likely cause of control rod uncoupling is that the uncoupling rod was incorrectly installed in one of the spud flow holes instead of the spud center bole.
It is postulated that as the rod was withdrawn, the cocked unctupling rod contacted the top flange of the inner filter.
As the rod and index tube continued to move downward, the lock plug spr4ngs became fully con > pressed and forced the uncoupling rod to yield or become jammed in the spud flow hole. The inertia of the index tube may have caused the index tube to uncouple and move downward into the overtravel position. Analysis of possible deformation within the coupling assenbly does not point out any adverse scram performance. Although scram loading may cause further damage as discussed in section 2, the ability of the rod to be inserted in a scram action does not appear to be affected.
The proposed T5 changes are intended to allow withdrawal of control rod 38-23 to position 46 for the remainder of fuel Cycle 8, which should be completed before October 30, 1991.
The three synnetric partner rods could thus also be withdrawn. This will eliminate a power derating of approximately 4% of rated power. The unit refueling outage is currently scheduled to begin on September 7, 1991.
The basis for verification of rod movement during the withdrawal to position 46 would be through the use of neutron monitoring with either LpRM or TIP systen.
2.0 EVALUATION Licensee attempts to verify coupling integrity of rod 38-23 were unsuccessful, and, therefore, it must be assumed that the control rod and drive are uncoupled. The primary concern for control rod coupling integrity is its impact on the potential increase in the probability of a control rod drop accident (CFDA) as analyzed in the FSAR. Additionally, control rod coupling integrity ensures that indicated-control rod position is indicative of actual control rod position. The uncoupled rod condition also raises an operational concern for equiament damage due to scram loading. The rod could separate from the CFD during tie deceleration phase of the scram stroke which could result in increased loads on the affected parts.
The licensee has proposed procedural changes to assure that withdrawal and operation with an uncoupled rod 38-23 will not pose a significant CRDA concern for the remainder of the fuel Cycle 8.
The rod will remain inserted and not be withdrawn at reactor power levels less than 10 perc.nt.
During the withdrawal sequence above 10 percent, neutron flux infarmation in the vicinity of the rod will be monitored to verify that the contrcl rod blade tracks with the drive movement. This will ensure that the rod is not sticking and separatid from the CRD.
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. An analysis performed by GE for the licensee shows that, for the fuel cycle under consideration, the consequences of a CRDA at power levels above 10 percent of rated thermal power are negligible and that no constraints on contial rod sequences are required.
Below 10 percent of rated power, the uncoupled control rod will be fully inserted.
Above ten percent power, the compensatory actions ensure that the Fod Block Monitor mitigates the consequences of a Pod Withdrawal error.
The licensee's proposed changes provide an additional n.easure to minimize the possibility of a CRDA by requiring the use of neutron instrumentation (LPRii or 71p) to verify rod position during repositioning of the uncoupled rod. This is addressed in proposed change 4.3.B.I.d.
The GE analysis also addressed the possibility of equipment darnage from scram loadings. l'echanism damage could occur during the deceleration phase of the
-scram stroke.
The uncoupled rod would continue to move upward and the velocity limiter would strine the bottom of the fuel support casting.
Analysis shows that in this scenario, damage might occur to the velocity -
limiter or, upon rebound, to the spud and the lock plug.
However, there is insufficient energy to dislodge the fuel support and fuel.
CE has provided recommended operating strategies to minimize possible scram load problems.
The recommended operation with rod 38-23 withdrawal limited to notch position 46 minimizes the scram loadings on the spud and socket. To minimize the forces on the rod, scram of the rod should not occur under cold depressurized conditions.
Scram testing of the rod should be avoided to prevent the potential for mechanical damage.
If a scram test is required for the rod during the cycle, it should be conducted from the lowest achievable fully withdrawn position.
The weekly tests of rod movement required by the TS will continue, thus assuring rod movement capability.
GE has evaluated the effect of the control rod coupling integrity on scram performance. The scram and insertion performance were not considered to be degraded nor would other reactivity control functions be adversely affected.-
Since the rod will be operated at a slightly inserted position for full withdrawal, it should have slightly better scram reactivity insertion characteristics.
It is, therefore, reasonable to conclude that operation with rod 38-23 fully withdrawn will not lead to any condition adverse to reactor safety.
The TS changes accompanying this mode of operation consist of changes to Sections 3.3.B.1 and 4.3.B.1.
The Change to section 3.3.B.1 specifies that, for' the remainder of Cycle 8, if coupling cannot be achieved, rod 38-23 may be withdrawn when rated thermal power is greater or equal to 10 percent under certain conditions. These conditions are that no other uncoupled rods are withdrawn and rod 38-23 may not be withdrawn past notch position 46. The
-change to Section 4.3.B.1 requires the use of neutron instrumentation (LPRM or TIP) to verify that rod 38-23 followed the CDR during repositioning.
If the blade cannot be verified to have followed to its final position, then the rod shall be conoletely inserted and the directional control valves electrically disarmed. TTese TS changes adequately implement the required changes in rod operation and are acceptable.
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-4 The staff has reviewed the licensee's proposed Technical Specification changes for operation of control rod 38-23 for the remainder of Cycle 8 at peach Bottom, Unit 3, and the safety evaluation prepared by General Electric.
Based on this review, we conclude that the proposed changes satisfy staff positions and requirements in these areas. Operation with control rod 38-23 withdrawn
-under the guidance of the proposed procedures and Technical Specifications is acceptable.
3.0 EX1GENTCIR,C,UESyNCES The Connission's regulation,10 CFR 50.91, provides special exceptions for issuance of amendments when the usual 30-day public notice period cannot be met. One type of special exception is an exigency. An exigency is a case in which the staff and the licensee need to act quickly and time does not permit the Commission to publish a Federal Register notice allowing 30 days for prior public concent, and the Commission also determines that the amendment involves no significant hazards considerations.
In this instance, peach Bottom, Unit 3 is operating in a four percent derated condition during a period of extremely high electrical demand.
The Unit 3 derate is a result of the current Technical Specification requirement to insert the uncoupled rod into the core and the requirement to fully insert three synnetric control rods to prevent flux tilting in the core. The result of operating with four control rods inserted is a reduction of maximum output power of approximately four percent. The high electrical demand during the sunner months requires maximum grid generating capability.
The cost of replacement power to the licensee during the suncer months is also extremely high. The licensee applied for this amendment change and requested that it be processed in an exigent manner.
The staff finds that the licensee did not deliberately or negligently cause the exigent situation to come into being.
Failure of the Concission to act on the licensee's request would result in loss of generating capability to the grid during a period of high demand and a very high cost to the licensee for replacement power.
4.0 FINAL NO SIGNIFICANT_ HAZARD CONSIDERATION DETERMINATION The Commission has provided standards for determining whether a significant hazards consideration exists (10 CFR 50.92(c)). A proposed amendment to an operating license for a facility involves no significant hazards consideration if-operation of the facility in accordance with proposed the amendment would not:
(1) involve a significant increase in the probability or consequences of an accident previously evaluated; (2) create the possibility of a new or different kind of accident from any accident previously evaluated; or (3) involve a significant reduction in a margin of safety.
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s The licensee has analyzed the proposed anendment to determine if a significant hazard consideration exists:
The proposed araendnent to Technical Specifications Sections 3.3.B.1 and 4,3.B.1 for Peach Bottom Unit 3; (1) does not involve a significant increase in the probability or consequences of an accident previously evaluated. This amendment incorporates compensatory actions in the Technical Specifications to assure that even with an uncoupled rod, the rod position is known, that no other uncoupled rods are withdrawn and that scram performance remains intact.
(2) does not create the possibility of a new or different kind of accident from any previously evaluated. The compensatory measures included in the Technical Specification changes assure that no new or different kind of accident is possible.
(3) does not involve a significant reduction in the margin of safety as
' - the limiting event is the [ control rod drop accident] CRDA and all fuel limits stipulated in that analysis will be met when the compensatory measures included in the Technical Speci'ication changes are inplemented.
Based on the above considerations, including the staff's safety evaluation, the staff concludes that the an.endment meets the standards set forth in 10 CFR 50.92 for a no significant hazards determination. Therefore, the staff has made a final determination that the proposed amendment involves no significant hazards consideration.
5.0 STATE CONSULTATION
in accordance with the Commission's regulations, the Pennsylvania State official was notified of the proposed issuance of the amendment. The State official had no comments.
6.0 ENVIR0tiMENTAL CONSIDERATION The amendment changes a requirement with respect to installation-cr use of a f acility component located within the restricted area as defined in 10 CFR Part 20. The NRC staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the anendment involves no significant hazards consideration, and there has been no public comment on such finding. Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth ir,10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
-0 7.0. CONCLUSION The Consission has co<icluded, bascd on the considerations discussed above, that because tFe requested changes do not involve a significant increase in the probability or consequences of an accident previously evaluated, do not cr-v.e the possibility of an accident Of-a type 'lifferent from any evaluated previously, and do not involve a signi'
.....t reducti e in a margin of safety, the amendments do not involve a significant hazards consideration that:
(1) there is reasonable assurance that the heal ' and safety of the public will not be endangered by operation in the proposed u,onner, (?) such activit'ies will be conducted in conpliance with the Conmission's regulations, and (3) the issuance of the--amendment will not be inimical to the-coneon defense and security or to the health and safety of the public.
. Principal Contributors:
J. Shea P. Milano Date:
July 10, 1991 a.
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