ML18058B329
| ML18058B329 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 01/14/1993 |
| From: | Slade G CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9301190112 | |
| Download: ML18058B329 (13) | |
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consumers Power l'OWERIN&
MICHl&AN'S l'RO&RE55 Palisades Nuclear Plant:
27780 Blue Star Memorial Highway, Covert, Ml 49043 January 14, 1993 Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 GB Slade General Manager DOCKET 50-255 - LICENSE DPR PALISADES PLANT - TECHNICAL SPECIFICATIONS TABLE 4.2.2 - REQUEST FOR A TEMPORARY WAIVER OF COMPLIANCE Consumers.Power Company hereby requests a temporary waiver of compliance to extend the Technical Specifications surveillance (TS Table 4.2.2, Item 2) frequency requirements for control rod exercise testing, for two control rods, from every two weeks to once between now and the start of the next refueling outage.
This request addresses those items for consideration in Thomas E. Murley's February 22, 1990 memorandum for a temporary waiver of compliance.
Our Plant Review Committee has reviewed and approved this request.
The biweekly test frequency schedule for the control rod exercise test would require the test to be completed by 8:00 p.m. Friday, January 15, 1993.
This includes the allowable extension time per TS 4.0.2, of 25%.
Action to approve this temporary waiver of compliance request would help to limit the control rod seal leakage we are experiencing and help to prevent a future forced outage due to the leakage.
Your decision is requested by 6:00 p.m. Friday, January 15, 1993.
Your immediate attention to this request is appreciated.
><S~~-*-
Gerald B Slade General Manager CC Administrator, Region III, USNRC NRC Resident Inspector - Palisades Attachment 9301190112 930114 PDR ADOCK 05000255 P
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ATTACHMENT Consumers Power Company Palisades Plant Docket 50-255 TECHNICAL SPECIFICATION TABLE 4.2.2 REQUEST FOR TEMPORARY WAIVER OF COMPLIANCE January 14, 1993 11 Pages
- 1.
REQUIREMENTS FOR WHICH WAIVER IS REQUESTED Palisades Technical Specifications Table 4.2.2, "Minimum Frequencies for Equipment Tests", Item 2, requires partial movement of all control rods (Minimum of 6 inches) every two weeks.
A waiver of this requirement for selected control rods is requested as follows:
Reduce the Technical Specifications required surveillance test frequency for control rods 20 and 31 from every two weeks to once more between now and the start of the next refueling outage, which is currently scheduled to start June 4, 1993. The surveillance test will be conducted in March.
This waiver is requested to become effective prior to the next scheduled test at 2000 hours0.0231 days <br />0.556 hours <br />0.00331 weeks <br />7.61e-4 months <br /> on January 15, 1993 and remain effective until the 1993 refueling outage.
2a.
DESCRIPTION OF SITUATION Control rod drive biweekly testing is currently aggravating the leakage of least 2 control rod seals. Repeated testing of a leaking seal has been shown to shorten seal life and increase control rod seal leak rate, which can lead to forced shutdown due to excessive PCS leakage.
Technical Specification 3.10.4b permits plant operation with one inoperable control rod.
Technical Specification (TS) 3.10.4b states that:
A control rod is considered inoperable if it cannot be moved by its operator or if it cannot be tripped... If more than one control rod or part-length rod becomes misaligned or inoperable, the reactor shall be placed in the hot shutdown condition within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.
In conjunction with TS 3.10.4b, if a single control rod drive seal is leaking, it has been plant practice to declare that rod administratively inoperable.
While the rod remains functional and trippable in this condition, the inoperable designation allows that the biweekly surveillance of that rod not be performed.
This minimizes continued degradation of that rod's seal.
Since Technical Specifications will only permit one inoperable rod, this practice is not available to minimize degradation when two or more seals are leaking.
Presently two control rods (CRD 20 and CRD 31) are evidencing seal leakage.
Of course, we have the option of shutting down the reactor to replace leaking seals, but this may not be the most prudent course of action.
Of the 33 CRD seals assembled in 1990 or later, two are showing evidence of leakage and some others are indicating a slightly higher temperature than the average.
Efforts are in progress to determine whether recently built seals are inherently prone to leakage.
If a generic concern exists with seal reliability, it would not be beneficial to replace leaking seals with others equally prone to leakage. This would potentially subject the plant to additional cooldown and heatup transients and it would not be consistent with maintaining radiation exposures ALARA.
2 During the CROM biweekly testing normally conducted on alternate Tuesdays during the day shift no leakage measurement for individual seals is possible. Combined leakage from all seals (collected in the seal leakoff header) can only be measured locally inside containment.
It is normally measured every Tuesday evening during the weekly containment entry.
The seal leakoff header flow is directed into the containment sump, so the combined seal leakoff flow rate can be approximated between measurements by observing the rate of sump level increase.
Individual CROM seal leakoff temperatures are available for review and trending on a chart recorder in the control room.
Typical leakoff temperatures are in a band of approximately 120-145°F.
The seal leakoff temperature of CRD-20 increased after testing on April 28, May 12, and May 26, 1992, the first three testing dates of the current fuel cycle. Seal leakoff header flow increased on those dates, but dropped on the weeks in between.
Leakoff temperature would drop on post-test days and then trend slowly upward until the next test, when another sharp increase would occur. After May 26, CRD-20 leakoff temperature generally remained above 200°F when withdrawn, so the rod was declared administratively inoperable in order to prevent further test-induced damage.
No other CRDMs exhibited signs of leakage at that time.
In spite of its leakage and regardless of its administrative designation, CRD-20 has remained fully functional and has tripped properly during all 5 plant trips since refueling.
The seal leakoff temperature indication for CRD-31 has operated intermittently during this fuel cycle. Its normal temperature of approximately 145°F rose to 165°F following December 1 testing, dropped afterward, and rose to 185°F after the December 15 test. The last recorded temperature prior to the December 29 test was 182°F on December 23. After that, indication was lost but when it returned about 6:00 pm December 29 (after testing), the indicated leakoff temperature was 215°F.
The current CRD-20 indicated leakoff temperature is also about 215°F.
Since both CRD-20 and CRD-31 exhibited leakage on December 15 and 29, CRD-31 was selected for testing and CRD-20 remained inoperable for three reasons:
Based upon prior trending of temperature and leak rate data we concluded that the CRD-20 leak rate exceeded that of CRD-31; CRD-20 was expected to degrade more rapidly than CRD-31 if tested; and it was theorized that exercising might flush the CRD-31 seal and reduce leakage.
Effect of Leakage on Tripping Ability of the CRDMs CROM seal leakage does not increase the likelihood of an untrippable control rod.
In order to do so, leakage would have to cause mechanical binding of the driveshaft between the lower clutch face and mechanical seal, because all components above the lower clutch face are disengaged from the driveshaft upon a trip, and normally wetted components inside the PCS boundary will not be mechanically bound by leakage effects.
Clutch:
In order to hinder trippability, the lower section must either fail to disengage or else jam between the shaft and some stationary component.
Plausible failure modes cause the clutch to disengage (thus causing a rod trip), not remain engaged.
Original clutches employed a splined sleeve which was prone to binding, but current clutches use a
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3 spring bellows and jaw faces which do not depend upon sliding action.
When electrical power is removed, the upper face springs away from the lower one, an action which is not prone to mechanical jamming.
Even if the vapor seal failed, leakage would not prevent rotation of a disengaged lower clutch element.
Bearings: There are three sets of ball bearings between the clutch and vapor seal.
To prevent a rod trip, one or more of these sets would have to bind sufficiently to resist dropping of a weight in excess of 200 pounds, or else degrade badly enough to allow gross driveshaft misalignment.
The vapor seal protects the bearings from a corrosive atmosphere, and leakage limitations restrict the likelihood of vapor seal failure.
Leakage limitations are not changed by the proposed waiver.
In the past, even bearings filled with boric acid have performed properly.
There is no reason to believe that any currently installed bearings have been exposed to steam or boric acid.
Vapor Seal: This is an elastomeric cup seal with a metal backing ring.
The steam impingement washer protects it from erosion, and the vapor seal in turn protects drive components above from leakage. Operating pressure depends upon seal leakoff temperature as long as flashing occurs in the leakoff cavity. The elastomer is designed for high temperature operation, and there is no metal-to-metal contact between stationary and rotating parts. If the vapor seal were to fail, it would not itself prevent shaft rotation.
Steam Impingement Washer:
This thin stainless washer fits loosely around the driveshaft immediately below the vapor seal, at the top of the seal leakoff cavity. It cannot bind between the shaft and housing while remaining around the shaft, and plausible leaks will not break it.
Seal Assembly:
The rotating element is inside the PCS boundary, so leakage will not corrode or bind small internal parts. There is ample clearance between the stationary assembly and driveshaft. Shear forces will prevent binding at the seal boundary itself, as seal contact area is very small and materials were selected for low friction operation.
Leak-induced temperature increase can degrade the three static 0-rings, but this will not prevent rotation.
Driveshaft:
One end of the driveshaft is inside the PCS boundary, so component material was selected to withstand PCS effects. Driveshaft alignment is maintained by the three sets of ball bearings above the vapor seal.
We have concluded, based on the system design and acceptable performance of the refueling outage trip test, that the control rods are trippable and therefore, can meet their functional requirements.
2b.
NEED FOR PROMPT ACTION The combined CRDM seal leakoff flow through the leakoff header increased considerably during December, commencing shortly after December 1 testing.
On December 29, leak rate rose from about 870 mi; min a coup 1 e of hours prior to testing to 920 m~m~ eight hours after testing.
4 Approximately 600 m~m~ is attributed to CRD-20, based upon trending when CRD-31 temperature was near normal, and most of the balance to CRD-31.
Palisades Technical Specification 3.1.5b mandates shutdown when total identified PCS leakage equals 10 gpm (37,850 m~m~), or unidentified 1 eakage equals 1 gpm (3' 785 ml; min).
Gross control rod drive seal leakage eventually can cause the vapor seal to fail, allowing leakage to flash and escape the leakoff piping near the drive package. This leakage can eventually damage drive package internals, and contaminate the surrounding area.
To prevent these effects Palisades Off Normal Procedure ONP 23.1, Section 4.8, requires reactor shutdown when leakage is confirmed to be a CROM seal failure in excess of 2 gpm ( 7, 570 mi; min)
- This 1 eak rate is we 11 within the 1 eakoff header flow capacity, so the limitation effectively protects vapor seal integrity.
If compliance is not waived, biweekly testing of control rod(s) with leaking seals will continue.
The resulting accelerated seal degradation would be expected to result in forced shutdown within a matter of weeks due to excessive PCS leakage.
Delayed processing of this request would have the same effect as disapproval since biweekly testing must continue until relief is granted.
If reducing the surveillance testing interval of CRD-20 and CRD-31 is allowed, the rate of seal degradation will be reduced and may facilitate continued operation until the next scheduled refueling outage.
Excessive leakage may still force a maintenance outage prior to refueling, but it will occur later and allow more time for evaluation of a possible generic reliability problem and root cause before repairs are made.
2c.
DISCUSSION OF WHY SITUATION WAS UNAVOIDABLE It has long been recognized that there is a connection between biweekly CROM exercising and seal leakage.
For some time we have been investigating ways to justify a reduction in test frequency.
During the course of that investigation we became aware of an effort by the Combustion Engineering Owners Group to develop generic justification for reducing rod drive test frequency from biweekly to quarterly for CE plants with magnetic jack type control element drive mechanisms (CEDMs).
The CE designed plants with magnetic jack CEDMs are vulnerable to dropping rods during the exercise test and therefore, in large part this was the reason for the frequency reduction.
In August, CPCo submitted a purchase order to ABB-Combustion Engineering to develop a report to apply to the Palisades rack-and-pinion type drives, and to also develop a safety evaluation for a Technical Specifications Amendment request. The draft of this Palisades-specific report was sent to CPCo in December, less than a week after CRD-31 began to exhibit leakage.
CPCo is currently reviewing that draft report. Following resolution of CPCo comments and receipt of the final report we will submit a proposed Technical Specifications change to adopt a quarterly rod testing surveillance frequency.
Concern about a potentially generic seal performance problem did not arise until after the CRD-31 temperature increase on December 1 when it
5 was recognized that both the leaking seals were some of the more recent to be rebuilt.
The seal for CRD-20 was assembled in 1990 and that of CRD-31 in 1992.
On January 7 and 11, Consumers Power and ABB-CE (on January 7) inspected several previously removed CRD se.al assemblies which have been assembled from the same and earlier lots of materials. This group included one assembly which was rebuilt in 1990 and was hotter than normal when it was removed as part of an ongoing seal housing replacement project which was unrelated to seal leakage.
The preliminary results of the inspection do not indicate an inherent problem with the seals that were inspected, however, our investigation is continuing to evaluate generic implications and look for a root cause.
- 3.
COMPENSATORY ACTIONS TO BE TAKEN No specific compensatory measures are necessary outside the proposed surveillance for CRD-20 and CRD-31 that will occur in March.
That test is fully adequate to assure operability of control rods in lieu of biweekly testing.
It is not our intent to continue operating once seal leakage becomes excessive. If a TWOC is approved, CPCo will maintain the requirement of Palisades Off Normal Procedure ONP 23.1, Section 4.8, to shut down the reactor if combined seal leakoff exceeds 2 GPM.
Until a Technical Specifications Amendment is approved for a quarterly rod testing frequency, biweekly testing will continue for CRDs other than CRD-20 and CRD-31.
CRDs 20 and 31 will be tested once more between now and the start of the next refueling outage, currently scheduled to start June 4, 1993.
This test will occur in March.
No other CRD will be declared administratively inoperable due to increased seal leakage to avoid biweekly testing. If other rods exhibit significant seal leakage or must be declared inoperable due to seal leakage, the NRC will be promptly notified to discuss the applicability of this Waiver.
- 4.
PRELIMINARY EVALUATION OF SAFETY SIGNIFICANCE AND POTENTIAL CONSEQUENCES IF REQUEST IS GRANTED The Technical Specifications Bases do not explicitly define the purpose for biweekly control rod surveillance testing.
We believe the primary basis for the biweekly surveillance is to verify that each rod is moveable (i.e., not mechanically bound) and therefore the test provides some measure of increased confidence that it is trippable. This interpretation is consistent with the basis for comparable surveillance requirement SR 3.1.5.5 in the Restructured Standard Technical Specifications (RSTS) for Combustion Engineering plants, NUREG 1432.
The surveillance frequency for RSTS Surveillance 3.1.5.5 is quarterly.
The Bases for SR 3.1.5.5 also indicates that other information is available and other surveillances are performed which add to the determination of operability of a control rod.
The FSAR is of limited value in trying to define the purpose of the biweekly test. The updated FSAR, Section 7.6.1.3, is the most relevant to the topic but it only addresses rod position indication.
The existing reference in TS Table 4.2.2 to Section 7.4.1.3, of the original FSAR also
6 only addresses rod position indication.
(Original Section 7.4.1.3 became 7.6.1.3 in the updated FSAR.)
FSAR Subsection 7.6.1.3 discusses primary and secondary control rod position indication systems.
During biweekly testing, the primary system displays individual rod position to the operator, who verifies operability by ensuring that the 4 11 deviation annunciator initiates and clears.
The top secondary position indication reed switch causes the red "fully withdrawn" light on the CRD mimic panel to extinguish and relight.
Lower reed switches are not cycled during biweekly testing.
Other Updated FSAR sections were also reviewed for pertinent information and none was found.
Summaries of selected sections are provided below:
Section 7.2.3.10 refers to manual reactor trip by de-energizing CRD clutches. Biweekly testing does not de-energize clutches and hence does not fully test the trip function either electrically or mechanically.
FSAR Section 7.5.1.1 addresses reactivity control.
With respect to control rod operation, it states, "Any individual control rod may be positioned manually if required.
The regulating and shutdown control rods are inserted by gravity action (backed up by control rod rundown) on the receipt of a reactor trip signal." Biweekly testing demonstrates only that control rods may be manually inserted 6 inches, at which point they are not yet inserting any negative reactivity. Therefore the test does not demonstrate ability to control reactivity.
Full manual and trip insertion are verified during refueling and cold shutdown testing. The parenthetical reference to rundown backup is not confirmed directly by biweekly testing, because control rods are neither tripped nor driven to the trip position.
The proposed waiver does not affect ability to shut down the reactor by boration.
FSAR Table 7-1, "Reactor Protective System Relays", footnote (a) states, "The control rods receive a "rods in" signal following a reactor trip which causes any rod with a "stuck" clutch to be driven to the bottom of the core." As noted above, biweekly testing does not confirm directly the rod rundown feature.
FSAR Subsection 7.5.3.1 discusses control rod rundown, group insertion and withdrawal, and out-of-sequence issues.
Biweekly testing operates rods individually, so this subsection does not apply.
A complete electronic FSAR search for "control rod" references revealed no other discussion relevant to the purpose of the biweekly rod testing and the assessment of possible risk associated with reduction of CRDM exercise test frequency.
Summary of Known CRDM Failure Events Review of control rod events at Palisades and Fort Calhoun (the only other plant with Palisades-style CRDMs) back to 1971 has shown no instances in which biweekly testing detected untrippable rods.
Fort Calhoun data was obtained from NPRDS and was not verified with OPPD.
Inability to drive rods via the rod rundown feature was discovered in some cases, generally caused by brake, drive motor, or relay contactor failure.
Such occurrences could have prevented control rod rundown capability, but since affected components were all above the clutches,
7 the ability to trip the control rod was not affected.
The review also indicated that there were 33 instances of untrippable or sticking control rods (of which 22 were attributable to three common failure modes which have since been resolved).
Of these, 4 were discovered prior to initial ctiticality, 29 during tests other than biweekly exercising, 2 during scrams, and 2 by failure to withdraw during startup, but none by biweekly testing (some of the occurrences fit in multiple categories). There were 2 other events in which trippability was not ascertainable from records reviewed, but neither occurred during biweekly testing.
Possible Negative Consequences of Reducing Test Frequency for Leaking CRDMs It has been concluded that there will be no significant negative consequences from a reduction of the exercise test frequency for the two control rods exhibiting seal leakage.
Some impacts that are possible and a brief summary of why they are not safety-significant are provided below:
A.
Drive package damage induced by vapor seal failure might not be identified as quickly if rod motion is attempted on a less frequent basis rather than biweekly.
- 1.
Drive package damage is only possible if substantial seal leakage exists and the vapor seal has failed. Technical Specifications and procedural restrictions for the total permissible PCS leakage and seal leakoff header flow will not be relaxed, so vapor seal damage will still not be expected as a consequence of seal leakage.
- 2.
The relaxed test frequency will reduce the rate of mechanical seal deterioration so the likelihood of a challenge to vapor seal integrity may even be reduced.
B.
Detection of mechanical binding which made a rod untrippable might not be identified for a longer interval than the current two weeks.
- 1.
Mechanisms which could cause mechanical binding of a rod during plant operation should be detected during refueling shutdown.
Misalignments or intrusion of foreign material would be expected to occur during refueling, not operation.
The Technical Specifications required rod drop timing testing following refueling would detect binding from these causes.
This test requirement remains unaffected by this Waiver request.
- 2.
Since the test under discussion only moves each rod approximately 6 inches, it will only detect mechanical binding in this small range of rod positions. Detection of mechanical binding outside this range (full rod travel is approximately 132 inches) would probably not be identifiable. This surveillance during operation, then, contributes little to the assurance that mechanical binding does not exist.
C.
Inability to drive or run down a control rod due to an electrical failure might not be identified for a longer interval than the current two weeks.
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- 1.
The tripping ability would not be affected by electrical control system malfunctions except in the highly unlikely case in which a clutch fails to de-energize. This case would not be detectable during the biweekly surveillance either.
- 2.
Rod rundown as an alternative to trip is not a required function since there is no credit taken for rod rundown in the analysis of any FSAR Chapter 14 accident.
Even though not required, rundown capability verification for non-leaking CROMs will be no different than it is currently.
- 3.
Review of Palisades and Fort Calhoun control rod drive failures revealed 35 which were or possibly were discovered during biweekly CROM testing.
None of the 35 events involved untrippable control rods.
Of the 35 events, 29 were due to brake wear or failure, electrical relay or contactor failure, loosened setscrews, or electrical damage resulting from severe CROM seal leakage.
All of these 29 occurrences are the possible results of CROM cycling and would be less likely to occur if rods were exercised less often.
Two leakage events occurred when CROM leakage rose until vapor seals failed and allowed boric acid into drive packages; this may have been hastened by biweekly testing of leaking seals.
- 0.
Postponement of a forced outage might result in simultaneous gross leakage from numerous unrepaired CROM seals, possibly escalating to a LOCA.
- 1.
Palisades' experience over twenty years of operation with this type of seal shows that catastrophic failure due to seal erosion does not occur.
The seal leakage experienced currently results in progressive degradation over time.
Exercising the rods such as for a biweekly surveillance accelerates the rate of this degradation.
- 2.
The largest documented leak rate from a single seal failure was an estimated 28 gpm for a seal which was destroyed by a loose setscrew, not progressive erosion.
Seal maintenance procedures were modified to prevent future setscrew loosening. Twenty-eight gpm far exceeds shutdown leakage limits but is only a fraction of PCS makeup capability.
- 3.
The possibility that multiple CROM seals could simultaneously fail catastrophically due to this waiver and give a leak rate high enough to exceed makeup capability (i.e., become a LOCA) is judged to be nonexistent.
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- 5.
JUSTIFICATION FOR EXPECTED DURATION OF WAIVER If the waiver is granted, continuing seal degradation and the likelihood of a forced plant outage will be minimized.
It is requested that the waiver be effective until the 1993 refueling outage or until issuance of a Technical Specifications Amendment which reduces the test frequency of all rods (whichever is sooner).
CPCo is preparing a Technical Specifications Change Request to revise the test frequency for all control rods from biweekly to quarterly during operation. The consultant's analysis which will provide in part the basis for this change is in draft form and being technically reviewed.
It is expected that this report will be finalized by early February, and the Technical Specification Change Request should be submitted to the NRC shortly thereafter.
Ongoing efforts to identify and respond to the cause of leakage should also be completed by the end of the refueling outage.
It is not desirable from a time, prudency, or dose standpoint to rush into a quicker program or to schedule an otherwise unnecessary maintenance outage prior to refueling.
In view of the minor safety significance of the request, we believe this time period is reasonable.
- 6.
BASIS FOR CONCLUSION THAT GRANTING THE REQUEST WOULD NOT INVOLVE SIGNIFICANT HAZARDS CONSIDERATIONS A.
The change in surveillance frequency for CRDs-20 and 31 would not involve a significant increase in the probability or consequences of an accident previously evaluated, for the following reasons:
The intent of the biweekly control rod exercise surveillance test is to detect control rods that are stuck and demonstrate that control rods can move freely over a small range of movement (minimum of 6 inches).
The current Palisades surveillance frequency of every two weeks was apparently based on engineering judgement. Operating experience has demonstrated that this surveillance is not a principal method for detecting stuck control rods.
The ability to trip the control rods, i.e., the operability of the rods, is not affected by decreasing the surveillance frequency.
Operability (trippability) of the rods is demonstrated by the refueling outage surveillance test. Further evidence this cycle has been the five reactor trips that have occurred in which all control rods including CRD-20 (which has evidenced leakage since April 1992) have tripped. Reactivity control, therefore, through control rod tripping or through boration is not affected by this change in the surveillance frequency.
The FSAR reactivity events consider that the most reactive control rod remains fully withdrawn from the core during a reactor trip. Because the trippability of the control rods are not degraded by this surveillance frequency changes the
consequences of these reactivity events have not been increased.
The control rod rundown feature, which is not required to mitigate an accident, will also not be degraded by the change in surveillance frequency.
Control rod indication would not be affected by the change.
Additionally the mechanical or electrical reliability of the control rods would not be degraded by the change in frequency of the surveillance for the leaking control rods. Therefore, combined with the ability of the control rods to remain trippable (operable), the probability of occurrence of an accident previously evaluated has not been increased.
10 The effect of CROM seal leakage on CROM components has been reviewed to determine if trippability of the control rods is affected. That review of the components (described in section 2a above) leads to the conclusion that seal leakage will not affect the trippability of the control rods.
B.
The change in surveillance frequency for the leaking control rods would not alter the equipment design or operation and therefore, the change does not create the possibility of a new or different kind of accident from any previously evaluated.
C.
Biweekly testing of the control rods over the 20 years of Palisades operating history has not shown any instance where control rods have not been trippable.
The control rods were demonstrated trippable (operable) by the control rod drop timing test during the last refueling outage and by their successful operation during the five reactor trips since refueling. Therefore, even with the presumed most reactive rod being stuck during an FSAR reactivity event, there is not a reduction in the margin of safety with respect to limiting reactivity additions during any of these FSAR events.
- 7.
BASIS FOR CONCLUSION THAT GRANTING THE REQUEST WOULD NOT INVOLVE IRREVERSIBLE ENVIRONMENTAL CONSEQUENCES A.
Approval of the waiver would not result in a significant change in the types or a significant increase in the amounts of any effluents that may be released offsite.
- 1.
The CRDMs are located inside containment, and all leakage is processed by the radwaste system.
- 2.
The radwaste system is not altered in any way.
- 3.
The effluent type is unchanged.
- 4.
Limitations on effluent flow rate are not changed, so the radwaste system will not be challenged any more than at present.
B.
Approval of the waiver would not result in a significant increase in cumulative or occupational radiation exposure.
11
- 1.
The Waiver will reduce the rate of CRDM seal degradation and resultant PCS leakage.
It should add as much as a few months of life to seals whose leakage is detected early.
- 2.
The Waiver will reduce the likelihood of a forced outage and its resultant employee exposure.
- 3.
If a forced outage is still required, it will be later and provide more time for advance planning.
- 4.
Reduced seal degradation can result in less exposure to persons who must enter the containment building during power operation.
- 5.
Reduced seal damage will cut exposure to maintenance personnel repairing seal assemblies.
Based on the above considerations, the proposed waiver does not involve any irreversible environmental considerations. Since the proposed waiver does not involve any significant increase in the amounts of any effluents or increase in cumulative or occupational exposure 10CFR51.22 has been satisfied.
CONFIRMATION OF PRC REVIEW AND RECOMMENDATION FOR APPROVAL The Plant Review Committee reviewed this request in meetings on January 11 and 14, 1993 and found it acceptable.