ML20217C912
| ML20217C912 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 10/12/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20217C908 | List: |
| References | |
| NUDOCS 9910140092 | |
| Download: ML20217C912 (8) | |
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p t UNITED STATES g g ~[ NUCLEAR REGULATORY COMMISSION y.....)
WASHINGTON, D.C. 30se64001 I
SAFETY EVALUATION REPORT OFFICE OF NUCLEAR REACTOR REGULATION
' REQUEST TO AMEND DEFINITION OF CORE ALTERATION COMMONWEALTH EDISON COMPANY LASAI I F COUNTY STATION. UNITS 1 AND 2
'1 INTRODUCTION in accordance with 10 CFR 50.90,' Commonwealth Edison Company (ComEu) submitted an application on August 13,1999, to amend the facility operating licenses NPF-11 and NPF-18 for the LaSalle County Stations (LaSalle) Units 1 and 2. The amendment request se,eks to adopt the core alteration definition of Section 1.0 of the standard technical specification (STS) by eliminating neutron monitors and control rod movement from the definition of core alteration under certain special conditions.
Comed is scheduled to convert the technical specifications (TSs) for LaSalle Units 1 and 2 to j the STS within a year. However, the licensee seeks to adopt the STS core alteration definition i in order to perform maintenance on the control rod drive systems and replace the nuclear i instrumentation in the upcoming refueling for Unit 1. According to the licensee, the current TS !
definition of core alteration will hamper the licensee's ability to conduct the necessary )
maintenance, without increasing the safety of the refueling activities. . j i
in response to a telephone discussion with the staff, the licensee supplemented the initial !
amendment request on August 27,1999 -(see Reference 2). The letter presents additional clarification of the proposed refueling practices and discusses the licensee's interpretation of the requirements and restrictions of the facilities' TSs.
. 2 EVALUATION 2.1 Proposeo Channes i
Table 1.0 (below) presents the requirements in the current LaSalle TSs for both units and defines core alteration as specified in the STS. The current LaSalle TSs define core alteration to include the addition, relocation, or menment of fuel, sources, incore instrumentation, or i reactivity controls within the pressure vessel with the vessel head removed. The STS l exempts neutron instrumentation and control rods from the definition of core alteration under l certain conditions. 1 9910140092 991012 i PDR ADOCK 05000373 P PDR i
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' TABLE 1.0 Core Alteration Definition TS CURRENT, STS CORE ALTERATION LASALLE ' UNITS 1 AND 2 CORE DEFINITION ALTERATION CEFINITION (NUREG 1433/1434) 1.1 DEFINITION CORE ALTERATION shall be the CORE ALTERATION shall be the addition, removal, relocation or movement of any fuel, sources, or movement of fuel, sources, incore reactivity control components, CORE instruments or reactivity controls within the reactor vessel with the ALTERATION: within the reactor pressure vessel vessel head removed and fuelin with the vessel head removed the vessel. The following and fuelin the vessel. exceptions are not considered to be CORE ALTERATIONS:
Suspension of CORE ALTERATIONS shall not preclude a. Movement of source range completion of the movement of a monitors, local power range component to a safe conservative monitors, intermediate range position. monitors, traversing incore probes, or special movable detectors (including undervessel replacement); and
- b. Control rod movement, provided there are no fuel g assemblies in the associated core cell.
In addition, some LCOs had footnotes that exempted the movement of neutron monitoring and control rod movement using the normal control red drive systems. The revised definition of core alteration formalizes the qualifying comments ar,d the footnotes are no longer needed. The licensee proposes that the following footnotes be revised or deleted:
e Delete the footnote in LCO 3.1.1," Shutdown Margin." The footnote qualifies core alteration, stating, "except movement of IRMs, SRMs or special movable detectors."
o Modify LCO 3.1.3.2, " Control Rod Maximum Scram insertion Times." The footnote currently states in reference to core alteration, "except movement of SRM, IRM or special movable detectors or normal control rod movement." The licensee proposes to revise the footnote to state, "except normal control rod movement."
e Delete the footnote at the bottom of page 3/4 3-4, which states except movement of IRM, SRM, or special movable detectors, or replacement of LPRM strings provided SRM l
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' 3-instrumentation is operable per Specification 3.8.2..." The footno.e refers to Action 9 of
. Table 3.3.1-1, " Reactor Protection System instrumentation."
e' LCO 3.9.2, " Instrumentation," suspends core alteration in its action statement. The licensee proposes to delete that corresponding footnote, which states, "except movement of IRMs, SRMs, or special movable detectors."
o' The licensee proposes to delete the footnote that refers to the action statement in LCO 3.9.5, " Communication." The footnote states, "except movement of incore instrumentation and control rods with their normal drive system."
2.2 Licensee's' Justification According to Comed, the purpose of the proposed changes is to allow the maintenance and replacement of control rod drive systems and nuclear instrumentation without these activities being designated as core alterations, while fuel is in the vessel. Under the current TS definition.
the maintenance of the control rod drives or the nuclear instrumentation activities would be considered core alteration, when fuel is in the reactor vessel. The proposed definition of core alteration in the STS will exempt the movement of the nuclear instrumentations from the definition of the core alterations. It will also exempt the maintenance of control rod drives (CRDs) from the definition if all fuel assemblies are removed from the control cell selected for maintenance. The licensee reports that if the STS definition of core alteration is adopted, it expects to gain appreciable savings in the outage critical path.
The licensee pointed out that the proposed core alteration definition is identical to the improved standard technical specification (ISTS) as documented in NUREG 1433, Revision 1. The proposed STS definition limits the core alteration to the movement of only those components that can affect core reactivity, primarily fuel assemblies and control rods adjacent to loaded fuel assemblies. The licensee outlined the TS LCOs that will remain in effect and will provide the necessary reactivity controls and monitoring.
e TS Section 3/4.1.1, " Shutdown Margin," requires the shutdown margin (SDM) to be maintained, and core alteration must be suspended if the SDM requirement cannot be met.
e Neutron monitoring and manual scram functions must be maintained at all times as required by TS Section 3/4.3.1, " Reactor Protection System Instrumentation."
Otherwise, core alteration must be suspended except for movement of source range monitors. Section 3.9.2, " Instrumentation,", requires two SRMS to be operable out of four SRMs available. One SRM must be located in the quadrant in which core alteration is taking place, and another one must be located in an adjacent quadrant.
e TS Section 3.9.1, " Reactor Mode Switch," requires the reactor mode switch to be operable and locked in the shutdown or the refuel position. If the mode switch is in the refuel position, core alteration should not be performed unless the refuel position interlocks are operable. Core alteration must be suspended if the mode switch conditions cannot be met or the refueling interlocks are inoperable.
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e TS Section 3.9.3, " Control Rod Position," requires all control rods to be inserted during core alteration, except for control rods removed in accordance with TS 3.9.10.1, " Single Control Rod Removal," and TS 3.9.10.2, " Control Rod Removal."
e TS Section 3.9.5, " Communication," requires that direct communication be maintained between the control room and the refueling platform personnel during core alterations, except for movement of incore instrumentation and normal drive system control rod movements.
e - TS Section 3.9.10.1 and TS Section 3.9.10.2 stipulate in part, that the required number of source range monitors (SRMs) be operable and that the SDM be maintained. The LCOs place additional restrictions before a single or multiple CR can be removed or withdrawn.-
The licensee stated that the TS sections listed will ensure that maintenance or repair of the control rods or control rod drive systems is performed under conditions that limit the probability of lnadvertent criticality. The movement of the neutron monitoring fission chambers does not significantly affect core reactivity. Movement or removal of a control rod in a defueled cell will not be considered a core alteration, since the movement or removal does not impact core reactivity. Direct communication will be maintained between the control room and the refueling platform; therefore, the command and control functions associated with refueling will not change.
The licensee concluded that the proposed change will not affect the shutdown margin, the core monitoring, and the reactor protection system operability.
Comed generally performed full core offloads as part of its refueling activities; however, in October 1999, for the Unit 1 refueling, the licensee intends to perform a core shuffle. In the August 27,1999 ( Referance 2), supplement to the amendment request, the licensee outlined the refueling process. Tne licensee will initially shuffle fuel to align the core to support the open reactor pressure vesis: (RPV) work window. All the control rod blade replacement and swaps, control rod drive m Aintenance and nuclear instrumentation will be done during the open RPV work window. After the maintenance work is completed, all control rods are inserted to the full-in position, and all instrumentation is restored, the licensee will initiate the final phase of the fuel shuffle. The supplement reiterated that with multiple control rods removed or withdrawn, Comed will not conduct or perform any fuel movements. -
2.3 Staffs Evaluation The definition of core alteration in the STS provides the flexibility to perform neutron instrumentation and control rod blade or drive maintenance. In addition, the TSs for both units of LaSalle have adopted footnotes that exempt movement of neutron monitors from the core alteration definition, and the proposed changes will formalize the array of footnotes now available in the TSs of both units.
Neutron monitoring does not directly affect reactivity of the core; however, it provides the necessary monitoring that mitigates reactivity changes while in the refueling mode. LCO 3.9.2 of the LaSalle TSs requires two neutron monitors to be operable during core alteration when fuel
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i is in the core. The LCO also requires removal of the RPS "s,horting links" preceding and during )
any control rod withdrawal. The removal of the RPS " shorting links" allow a scram to be initiated from the SRM readings. Therefore, in accordance with the revised definition of core alteration, neutron monitoring and RPS functions are adequate.
In the STS definition, movement of control rods in a control cells containing fuel assemblies will be considered core alterations. The STS definition will, however, exempt movement of control
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rods in defueled cells, because with the removal of the fuel bundles, the control cell itself does not contribute to the core reactivity and can be considered a " water hole." Therefore, the exclusion of th' CR withdrawal / removal from a defueled cell in the definition of core alteration is acceptable.
LCO 3.1.1 requires the SDM to be maintained at all times. Comed has the capability to determine. the SDM for all of the intermediate steps and this will provide the ability to ensure that the SDM is not reduced in a more reactive intermediate configuration. The SDM, however, is based on the assumption that a single control rod of the highest worth is withdrawn. The SDM, thus, implicitly assumes that the refueling equipment interiocks are operable and prevents the ,
withdrawal of a second control rod or the loading of an uncontrolled fuel cell. l l
The refueling equipment interlocks receive signals from the (1) all-rods-in position indication (for fullinsertion of all CR); (2) the loading of the main hoist (indicative of fuel bundle motion); and (3) the ' position of the refueling platform (over the core or not). If a CR is not in its full-in position, the refueling interlocks disarm the refueling equipment when loading a fuel assembly. If the main hoist is loaded with fuel and located over the core, the equipment refueling interlocks insert ;
a CR withdrawal block to prevent inadvertent withdrawal during fuel loading. However, under the multiple CR LCO, the refueling equipment interlocks are defeated in order to allow multiple CR l withdrawal for maintenance. The LCO institutes a number of restrictions, including removal of fuel from the control cell prior to CR withdrawal or removal. If fuel is loaded while multiple j control rods are withdrawn or removed for maintenance, the potential increases for loading an !
uncontrolled fuel cell or an inadvertent CR withdrawal. Administrative procedures provide the i necessary controls for these situations instead of the built-in refueling equipment interlocks.
if, inadvertently, a second CR is withdrawn or loading of uncontrolled fuel cell occurs then maintaining SDM does not guarantee adequate protection against criticality.
The proposed definition of core alteration is identical to the STS definition; however, the requirements in the TSs for both units are not identical nor do they necessarily parallel the requirements in the STS. Specifically, the special operation LCO 3.10.6 for the STS and LCO 3.9.10.2 for LaSalle Units 1 and 2 differ significantly.
LCO 3.10.6 of the STS pwmits maintenance of multiple control rods or the associated control rod drives provided that (1) the four fuel assemblies are removed from the fuel cell selected for maintenance; (2) all other core cells containing one or more fuel assemblies are fully inserted
' and (3) the fuel assemblies are loaded in an cpproved spiral reload scheme. In order to
withdraw / remove more than one CR with fuel in the core, the special LCO suspends the following: (1) LCO 3.9.3, " Control Rod Position;" (2) LCO 3.9.4, " Control Rod Position Indication" and (3) LCO 3.9.5, " Control Rod OPERABILITY-Refueling." For the STS, LCO 3.9.3 requires all CRs to be fully inserted when loading fuel into the core. LCO 3.9.4 requires, in part, that the one control rod " full-in" positioh indication channel for each CR be operable or that fuel movement to be suspend. The full-in indications provide the input signal for the all-rods-in refueling interlocks in LCO 3.9.1. " Control Rod Operability," LCO 3.9.5, requires each withdrawn CR to be operable.
The LaSalle multiple CR L CQ 3.9.10.2 bypasses the one-rod-out interlock LCO 3.9.1.
LCO 3.9.3 requires all CRs except for one to be inserted, and a footnote suspends this LCO when CRs are removed in accordance with LCO 3.9.10.1 and LCO 3.9.10.2. Note that the corresponding STS LCO requires all CRs to be inserted.
Therefore, the STS and the LaSalle TSs all suspend the built -in, refueling, one-rod-out interlocks and the requirement to have all CRs inserted before loading fuel. During the development of the STS, only approved spiral reload schemes were authorized under the multiple CR withdrawal LCO. The objective of the spiral reload sequence is to minimize the reactivity addition. Moreover, reactor vessel work can be conducted with all fuel removed from the core, including multiple CR maintenance.
The LaSalle TSs though, permit both fuel shuffle and spiral reload under the multiple CR LCO 3.9.10.2. Fuel shuffle while multiple CRs or their associated drives are withdrawn / removed or disarmed has not been evaluated to determine if it represents increased risk for inadvertent criticality, in discussions with the staff, the licensee stated that fuel shuffle will not be conducted while multiple control rods are withdrawn or removed for maintenance. The August 27,1999, supplement states that "during both the initial and final shuffles, all rods will be in compliance with the TS for control rod position (i.e., TS Section 3.9.3," Control Rod Position") that requires all control rods to be fully inserted, with the exception that one rod is permitted to be withdrawn as permitted by the mode switch refueling interlock." However, there is a footnote in LCO 3.9.3,
" Control Rod Position," which states, "except control rods removed par specification 3.9.10.1 or 3.9.10.2." The licensee, therefore, committed to perform the fuel shuffle while operating under LCO 3.9.10.2, without complying with or invoking the footnote. The supplement also states that "during the open vessel work window with multiple control rods removed or withdrawn, Comed
. will not perform any fuel movement within the RPV." 1 The staff reviewed the licensee's proposal to adopt the STS definition of core alteration for LaSalle, Units 1 ad 2. However, the staff finds the multiple control rod LCO of the STS and the j
- TSs, for both units of LaSalle, differ significantly. Since Comed is scheduled to convert to the j
- STS within a year, it is acceptable for LaSalle to adopt only a portion of the affected STS {
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. LCOs. Also according to Comed, the plant procedures prohibit fuel movement unless all CRs except one are inserted, and the staff believes that this commitment should be incorporated into a license condition for both units at LaSalle. The LaSalle County Station, Units 1 and 2, should be prohibited from moving any fuel within the reactor vessel when more than one control rod is ,
not fully inserted during refueling in Mode 5. 1 i
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,. . The staff has also reviewed the LCOs the licensee proposed to modify. The staff finds the proposed changes in LCOs 3.1.1,3.1.3.2,3.8.2,3.9.2, and 3.9.5 acceptable. The footnotes '
. are no longer applicable and the STS definition formalizes the content of these footnotes.
3 CONCLUSIONS l
' The staff has reviewed the licensee's request to amend LaSalle County Station, Units 1 and 2 facility licenses. Comed proposes to adopt the standard technical specification core alteration !
definition. The staff accepts the licensee's amendment request; however, the TSs for both !
units of LaSalle differ significantly from the STS,"Special Operation, Multiple Control Rod," l LCO 3.10.6. The STS restricts fuelloading sequence under the multiple CR LCO to an 1 approved spiral reload in order to minimize core reactivity with multiple CRs withdrawn. The multiple CR withdrawal LCO requires that all the fuel assemblies be removed before withdrawing or removing the CR. ,
1 Comed is scheduled to convert both units of LaSalle within a year; therefore, the staff believes )
that the following condition should be included in the license for both Units:
. "The .LaSalle County Station, Units 1 and 2 are prohibited from moving any fuel within the reactor vessel when more than one CR is not fully inserted in the core during refueling in Mode 5."
On the basis of its review, the staff approves the amendment request as stated and concludes that:
. (1)' There is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner; j l
(2) Such activities will be conducted in compliance with the Commission's regulations; and (3) The issuance of the amendment will not be inimical to the common defense and security or to the health and safety to the public:
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e 4 REFERENCES
- 1. Commonwealth Edison Company, Request for a Change to Technical Specification,
" Core Alterations." LaSalle County Station, Units 1 and 2, August 13,1999.
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- 2. Letter from J. A. Benjamin, Commonwealth Edisen Company. " Supplemental Information i' Related to Request for a change to Technical Specifications, Core Alteration", .
August 13,1999.
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