ML20076K737
| ML20076K737 | |
| Person / Time | |
|---|---|
| Site: | Pilgrim |
| Issue date: | 09/12/1983 |
| From: | BOSTON EDISON CO. |
| To: | |
| Shared Package | |
| ML20076K736 | List: |
| References | |
| NUDOCS 8309150250 | |
| Download: ML20076K737 (6) | |
Text
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T Attachment Proposed Change to Control Rod Drive Weekly Surveillance Technical Specifications Proposed Change The proposed change involves Pilgrim Nuclear Power Station Technical Specifica-tions, Appendix A, Section 4.3, Reactivity Control and its associated bases.
Specifically, the proposed change is shown on attached Technical Specification Pages 80, 88, and 89 and is described below.
1.
Technical Specification 4.3. A.2 currently states, in part, "Each partially or fully withdrawn operable control rod shall be exercised one notch at least once each week."
It is proposed that this sentence he changed to read "Each partially or fully withdrawn operable control rod shall be exercised at least once each week."
2.
The bases for Technical Specification 4.3.A.2 currently state the following, in part.
Also if damage within the control rod drive mechanism and in particular, cracks in drive internal housings, cannot be ruled out, then
'eneric problem affecting a number of drives cannot be ruled out. Circumferen-tial cracks resulting from stress assisted intergranular corrosion have occurred in the collet housing of drives at several BWRs. This type of cracking could occur in a number of drives and if the cracks propagated until severance of the collet housing occurred, scram could be prevented in the affected rods. Limiting the period of operation with a poten-tially severed collet housing and requiring increased surveillance after detecting one stuck rod will assure that the reactor will not be operated with a large number of rods with failed collet housings.
It is proposed that the above section be deleted and replaced with the followi ng.
Each partially or fully withdrawn operable control rod shall be exercised at least once each week based on the following requirements:
a) The control rod drive mechanisms shall be monitored for potential circumferential cracking of tho collet housing resulting from inter-granular stress corrosion cracking. This is a potential generic problem that could affect a number of control rod drives, resulting in a loss of scram capability in the affected rods.
b) The control rod drive mechanisms shall be monitored to demonstrate both the movement of the control rod under control rod drive water pressure and the mechanical integrity of the collet fingers.
c) The crevices under the control rod drive piston seals shall be flushed weekly to minimize the corrosion of the nitrided surfaces.
8309150250 830912 PDR ADOCK 05000293 P
These requirements are satisfied by a weekly control rod exercise con-sisting of a one notch insertion, or, as a minimum, a partial insert to an intermediate position indication (e.g., Position 46 to 45) and a settle back to the original notch. This partial insert exercise cannot begin at control rod Position 48 because the control rod does not latch at this position.
As additional protection against operating the reactor with a large num-ber of control rods with failed collet housings, control rod surveillance is increased with a potentially severed collet housing and the period of operation is limited to 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />.
Reason for Change Several control rod drive mechanisms at Pilgrim have recently had some degrada-tion of the stop piston and collet piston seals. This degradation affects the ability to withdraw these control rods, but does not affect their scram capa-bility. Although it is not a safety concern, this seal degradation has created difficulty in returning these few problem control rods to their original position after the successful completion of the weekly surveillance test required by Technical Specification 4.3. A.2.
Often, power reductions have been necessary to complete the control rod manipulations needed to return a control rod to its original position. This technical specification change would decrease the number of power reductions needed by allowing weekly control rod exercise to be per-formed without requiring a full notch insertion.
Safety Considerations This change does not present an unreviewed safety question as defined in 10CFR 50.59.
It has been reviewed and approved by the Operations Review Committee and reviewed by the Nuclear Safety Review and Audit Committee.
Significant Hazards Considerations It has been determined that the amendment request involves no significant hazards consideration. Under the NRC's regulations in 10CFR50.92, this means that opera-tion of the Pilgrim Nuclear Power Station in accordance with the proposed amend-ment would not (1) involve a significant increase in the probability or conse-quences of an accident previously evaluated; or (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.
The NRC has provided guidance concerning the application of standards for deter-mining whether license amendments involve significant hazards considerations by providing certain examples (48 FR 14870). One example of an amendment that is considered not likely to involve a significant hazards consideration is "...(iv)
A relief granted upon demonstration of acceptable operation from an operating restriction that was imposed because acceptable operation was not yet demon-strated." Although the proposed partial insert surveillance test for control rod drives is not in itself an operating restriction, the present full notch insert surveillance test can create operating restrictions in the form of power reduc-tions to restore the control rod to its original position.
It has been determined
that the proposed partial insert surveillance test is an acceptable alternative to the present test because it fulfills the requirements of the present weekly test:
(a) The control rod drive mechanisms shall be monitored for potential circum-ferential cracking of the collet housing resulting from intergranular stress corrosion cracking.
(b) The control rod drive mechanisms shall be monitored to demonstrate both the movement of the control rod under control rod drive water pressure and the mechanical integrity of the collet fingers.
(c) The crevices under the control rod drive piston seals shall be flushed weekly to minimize the corrosion of the nitrided surfaces.
Boston Edison has received concurrence from the vendor that the proposed partial insert surveillance test is an acceptable alternative to the present full notch insert surveillance test. Because the test requirements are fulfilled, the pro-posed change does not increase the probability or consequences of an accident previously evaluated and does not significantly reduce the existing safety margin.
i In addition, the proposed change only reduces the extent of control rod movement from the present full notch insertion and thus does not create the possibility of a new or different kind of accident from any accident previously evaluated.
Schedule of Change This change will be put into effect upon Boston Edison's receipt of approval by the Commission.
Fee Determination Pursuant to 10CFR170.12, Boston Edison proposes that this is a Class III change.
)
LIMITING CONDITION FOR OPERATION SURVEILLANCE REQUIREMENT 3.3 REACTIVITY CONTROL 4.3 REACTIVITY CONTROL Applicabili,ty:
Applicability:
Applies to the operational status Applies to the surveillance require-of the control rod system, ments of the control rod system.
Objective:
Objective:
To assure the ability of the con-To verify the ability of the control trol rod system to control reac-rod system to control reactivity, tivity.
Specification:
Specification:
A.
Reactivity Limitations A.
Reactivity Limitations 1.
Reactivity margin - core 1.
Reactivity margin - core loading loading The core loading shall be Sufficient control rods shall limited to that which can be withdrawn following a re-be made subcritical in the fueling outage when core most reactive condition alterations were performed during the operating cycle to demonstrate with a margin with the strongest operable of 0.25 percent ak that the control rod in its full out core can be made subcritical position and all other at any time in the subsequent operable rods fully in-fuel cycle with the strongest serted.
operable control rod fully withdrawn and all other oper-able rods fully inserted.
2.
Reactivity margin - inoper-2.
Reactivity margin - inoper-able control rods able control rods a.
Control rod drives Each partially or fully with-which cannot be moved drawn operable control rod with co1 trol rod drive shall be exercised at least l
pressure shall be con-once each week. This test sidered inoperable.
If shall be performed at least a partially or fully once per 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> in the withdrawn control rod event power operation is con-drive cannot be moved tinuing with three or more with drive or scram inoperable control rods or pressure the reactor in the event power operation shall be brought to a is continuing with one fully shutdown condition with-or partially withdrawn rod in 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> unless which cannot be moved and investigation demon-for which control rod drive strates that the cause mechanism damage has not been of the failure is not ruled out. The surveillance due to a failed control need not be completed within rod drive mechanism 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> if the number of collet housing.
inoperable rods has Amendment No.
80
3.3 and 4.3 BASES:
2.
Reactivity margin - inoperable control rods.
Specification 3.3.A.2 requires that a rod be taken out of service if it cannot be moved with drive pressure.
If the rod is fully inserted and then disarmed electrically *, it is in a safe position of maximum con-tribution to shutdown reactivity.
If it is disarmed electrically in a non-fully inserted position, that position shall be consistent with the shutdown reactivity limitation stated in Specification 3.3. A.1.
This assures that the core can be shutdown at all times with the remaining control rods assuming the strongest operable control rod does not insert. An allowable pattern for control rods valved out of service, which shall meet this Specification, will be determined and made available to the operator. The number of rods permitted to be inoperable could be many more than the eight allowed by the Specification, particularly late in the operation cycle; however, the occurrence of more than eight could be indicative of a generic control rod drive problem and the reactor will be shut down.
Each partially or fully withdrawn operable control rod shall be exercised at least once each week based on the following requirements:
a) The control rod drive mechanisms shall be monitored for potential cir-cumferential cracking of the collet housing resulting from inter-granular stress corrosion cracking. This is a potential generic problem that could affect a number of control rod drives, resulting in a loss of scram capability in the affected rods, b) The control rod drive mechanisms shall be monitored to demonstrate both the movement of the control rod under control rod drive water pressure and the mechanical integrity of the collet fingers, c) The crevices under the control rod drive piston seals shall be flushed weekly to minimize the corrosion on the nitrided surfaces.
These requirements are satisfied by a weekly control rod exercise consist-ing of a one notch insertion, or, as a minimum, a partial insert to an intermediate position indication (e.g., position 46 to 45) and a settle back to the original notch. This partial insert exercise cannot begin at control rod Position 48 because the control rod does not latch at this position.
As additional protection against operating the reactor with a large number of control rods with failed collet housings, control rod surveillance is increased with a-potentially severed collet housing and the period of operation is limited to 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />.
- To disarm the drive electrically, four amphenol type plug connectors are removed from the drive insert and withdrawal solenoids rendering the rod incapable of withdrawal. This procedure is equivalent to valving out of the drive and is preferred because, in this condition, drive water cools and minimizes crud accumulation in the drive. Electrical disarming does not eliminate position indication.
Amendment No.
88
B. Control Rod Withdrawal 1.
Control rod dropout accidents as discussed in the FSAR can lead to signifi-cant core damage.
If coupling integrity is maintained, the possibility of a rod dropout accident is eliminated. The overtravel position feature provides a positive check as only uncoupled drives may reach this position.
Neutron instrumentation response to rod movement provides a verification that the rod is following its drive. Absence of such response to drive movement could indicate an uncoupled condition.
2.
The control rod housing support restricts the outward movement of a control rod to less than 3 inches in the extremely remote event of a housing fail-ure. The amount of reactivity which could be added by this small amount of rod withdrawal, which is less than a normal single withdrawal increment, will not contribute to any damage to the primary coolant system. The design Amendment No.
89
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