ML20248D013
| ML20248D013 | |
| Person / Time | |
|---|---|
| Site: | Perry  |
| Issue date: | 09/22/1989 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20248D003 | List: |
| References | |
| NUDOCS 8910040095 | |
| Download: ML20248D013 (7) | |
Text
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NUCLEAR REGULATORY COMMISSION
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\\..... pf SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT'NO. 25~
TO FACILITY OPERATING LICENSE NO. NPF-58 THE CLEVELAND ELECTRIC ILLUMINATING COMPANY, ET AL.
PERRY NUCLEAR POWER PLANT, UNIT NO. 1 DOCKET NO. 50-440
1.0 INTRODUCTION
By letter dated August ~23, 1989 from A. Kaplan, Cleveland Electric 111umi-nating Company (CEI), to the NRC (Ref. 1), CEI proposed Technical Specifi-cation.(TS) changes for the Perry) Nuclear Power Plant (Perry) relating to the Traversing In-Core Probe (TIP system. The' changes would be to Technical Specification TS 3.3.7.7 and related Bases. The primary change would be an addition (paragraph b.) to the TS Limiting Condition for Operation (LCO) which would permit, with one or more TIP measurement locations (channels) inoperable, data to be substituted for these channels from operable channels (neutronically) symmetric to the inoperable channels.
(There are minor changes combining the current LC0 paragraphs
- a. and b. and adding the footnote of Applicability paragraph b. to paragrapha.) The LCO addition would also require (1) the reactor to be operated in a type A control rod. pattern,(diagonally) symmetric measurement providing an octant symmetric core symmetry and a resulting cross-core channel pattern, and (2) the total core TIP uncertainty for the cycle to have been measured to be less than 8.7 percent (standard deviation) as used in the General Electric safety analysis.
The proposed change has been requested because there are currently several channels in one of the five TIP units in which a TIP measurement cannot be made. The reactor must be shut down to gain access to the drywell for repair work on the TIP unit. The current TS 3.3.7.7 requires that all channels be operable for the TIP system to be operable for required periodic power distri-bution measurements. Thus the reactor would have to be shut down soon for the repair. The proposed TS change is intended to avoid such a shutdown now, and in the future, when suitable backup information is available.
Following the submittal and the initial NRC staff review, there were several telephone conversations between CEI and the staff about the need for restrictions in the number of substitutions permitted. As a result of these discussions and with the licensee's agreement, the staff denies the original application as submitted and has modified the proposed LCO paragraph b. restricting the number of channels for which data could be substituted to a maximum of ten.
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. 2.0 EVALUATION The TIP sy(LPRM and APRM) and to supply detailed axial power distributionste monitors information for the analysis of core operating conditions and the approach to limits. During normal operation with a symmetric control rod pattern, the core power distribution is correspondingly symmetric, and symmetric TIP measurement channels provide similar information to within statistical differences which are accounted for in safety analyses and measured in the course of' cycle startup tests.
It is normal, approved practice to translate by symmetric transfers the information from measured locations to unmeasured locations when calculating, via the measurements and the process computer, the core power distribution. Under these normal operating circumstances it_would be acceptable to similarly supply data from' operating symmetric channels to
. replace inoperable channel information. No significant loss of accuracy would likely be involved.
However, inoperable channels do decrease the information supplied by the measurement system, and if abnormal power distributions developed, excessive substitution might make them more difficult to recognize. Perry has 41 TIP channels, and unrestricted synnetric substitution would permit, in theory, as much as 44 percent of the TIP information to be missing. This might not be unreasonable in a normal neutronic configuration, but is undesirable for abnormal situations.
Limiting inoperability for Perry to 10 channels means that 75 percent of the channels are available. The NRC staff advocates maintenance of as close to 100 percent operability of the instrumentation system as possible. This is necessary to be able to identify and evaluate possible power distribution or reactivity anomalies which might occur. The 75 percent operability requirement was chosen to allow a reasonable amount of failures in the system, but to encourage licensees to strive for as near to 100 percent as possible.
TS changes to reduce the number further might result in a lack of incentive to keep the system operating as close to 100 percent as possible. This could result in an unacceptably degraded ability to detect anomalous conditions in the core.
This position has not been explicitly stated in previous Boiling Water Reactor (BWR) reviews of TIP operability restrictions but it has been in many staff reviewsforPressurizedWaterReactors(PWR's),. The BWR and PWR incore systems are not exactly analogous, but they are sufficiently similar in application that it is reasonable to adopt a similar limit for power distribution measurement i
operability. The evaluations in previous BWR reviews (for Washington Nuclear 2 l
and LaSalle 1 and 2) have been compatible with this position.
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. A restriction to 10 channels would permit Perry to lose one of the 5 tip units and 2 or 3 other channels before reaching the limit. Based on past experience, this should be sufficient to keep shutdowns from TIP inoperability to an extremely low level. Perry intends to repair the present TIP problem at the first opportunity arising from a shutdown for other causes. This should always be the intent with failures in this system.
With regard to the other restrictions of the new paragraph b., (1) Perry will be op(erated with a type A control rod pattern and thus have the required symetry, and 2) the Perry TIP symmetry pair variations have been measured during the current cycle startup tests and the results fall well within the required limits. The " total core TIP uncertainty" referred to in the TS includes both the measured pair variations (consisting of both detector geomatry and neutronic noise components) and standard components for LPRM correction uncertainty (3.4%) and analytical model uncertainty (4.6%) as discussed in Reference 2.
The total uncertainty for "TIP readings" used in the GE safety limit analysis is 8.7 percent (see Table 4-1 of Reference 3), so that the required measured TIP uncertainty is 6.6 percent. For this cycle for Perry this has been measured to be 1.7 percent. This low value is to be expected since Perry is using, gamma detectors (rather than fission detectors) and detector geometry uncertainty components are expected to be very small.
Finally, it is noted that the proposed modification to the paragraph structure of the LC0 and the addition of the footnote to Applicability paragraph a.
and the additions to Bases 3/4.3.7.7 are all compatible with the primary changes and are acceptable.
As discussed above, unlimited substitution for inoperable TIP channels would be unacceptable. Therefore, the proposed TS changes have been modified to be in accord with acceptable restrictions in channel substitution, and operations will be within the other limits in the specification on control rod symmetry and TIP uncertainty. Based on the above, the staff finds the proposed changes, as modified, to be acceptable.
3.0 EXIGENT CIRCUMSTANCES
CEI first discovered a problem on Friday, August 11, 1989, while taking TIP traces with the B TIP Unit. A trace for TIP channel B2 could not be taken due to mechanical interference within the indexing mechanism for the B unit. The indexing mechanism for each TIP unit selects the channel (or LPRM location) to be accessed by the TIP detector probe. This mechanical interference in the indexing mechanism prevented the B TIP detector probe from physically passing from the indexing machine into the guide tube resulting in that channel on the B TIP unit being inaccessible. Subsequently, three other LPRM locations (channels) on the B unit could not be accessed due to this interference.
However, two of these channels (locations) can be accessed by other TIP units which allows flux measurements to be made at these locations. Therefore, currently two channels cannot be accessed by a TIP Unit.
- The TIP indexing mechanisms are located within the drywell and are therefore
. inaccessible during power operation. Even at reduced power levels, of the drywell cannot be performed (only permitted in Modes 4 and 5) purgings and 1
therefore direct access to the TIP machines by drywell entry is severely j
limited due to temperature and health physics concerns. Attem)ts are continuing to.be made, by various means, to remotely advance tie sprocket wheel to correctly position the indexing mechanism and therefore allow passage 1
of the TIP detector. The exact problem within the B machine's indexing mechanism cannot be determined until a drywell entry can be made, since troubleshooting attempts from outside the drywell to date have proven unsuccessful.
As originally issued, the TS state that the TIP system shall be operable with i
five detectors and support equipment to enable mapping the core, and all 5 3
detectors are required to be capable of calibration at a connon location. At the present time, four channels (including the common channel) cannot be accessed by the B TIP machine. Therefore, without approval of this revision to Technical. Specification 3.3.7.7 the TIP system will be considered inoperable when it is next necessary to recalibrates the LPRM detectors. The next calibration of the LPRM's is required to be performed within 1000 mwd /t of the last calibration date. This next calibration is estimated to be due on September 18, 1989 (assuming full power operation). The late date takino into account the 25 percent permissible extension of the surveillance interval is September 29, 1989.
Without approval of this Technical Specification change, Perry will be forced to shut down when the next surveillance for calibrating the LPRM's comes due in late September.
CEI could not have foreseen this problem with the TIP system as TIP calibrations can only be performed at an appreciable flux level (after entry into Mode 1) and no problems with the indexing mechanism were identified during prior testing of the system.
Prior to and during plant startup following the recent refuel outage, the TIP probes were driven through each of the indexing mechanisms under both cold and hot conditions. Three successful full core TIP traverses were performed during the current operating cycle prior to this failure. CEI therefore could not have reasonably submitted their request in a more timely manner.
An exigent TS change has been requested since a full 30-day Federal Register notice period may not be possible before shutdown of the plant is required.
To provide a full 30-day notice, the amendment would not be able to be issued prior to close of business on September 29, 1989. This might not allow suf-ficient time to complete the surveillance before plant shutdown is required.
CEI has committed to fix the inoperable TIP machine prior to plant startup, should an unscheduled plant shutdown occur prior to the overdue date of the LPRM calibration surveillance.
l The staff.has reviewed the circumstances described above with respect to the proposed TS change and agrees that the amendment is necessary for continued operation and.that failure to act on the request in a timely manner would require CEI to unnecessarily shut down the unit. The staff has concluded that these circumstances could not have reasonably been avoided and, therefore, valid exigentcircumstancesexist,asdefinedby.10CFR50.91(a)(6).
4.0 FINAL NO SIGNIFICANT HAZARDS CONSIDERATION
DETERMINATION The Comission has provided standards.for determining whether a significant
' hazards consideration exists as stated in 10 CFR 50.92. A proposed amendment-to an operating license for. a facility involves no significant hazards consider-ations if operation of the facility in accordance with a proposed amendment would not: (1) involve a significant increase in the probability or consequences 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 licensees ~ have provided an analysis of their proposed amendment request in relation to the above standards and have concluded that it involves no significant:
hazards considerations. The Comission also has made a final determination that the amendment request involves no significant hazards considerations, based on the above standards and the following considerations:
1.
The core monitoring methodology is based on symmetry of rod patterns and fuel loading. This is not chan order of symmetry (octant symmetry)ged, but extended to use a higher which exists with " type A" sequence rod patterns.
This change does not change the fundamental process involved in calibratingneutroninstrumentation(LPRM's),butrequiresthatonly the equipment associated with the TIP channels necessary for recalibrating LPRM's and for' core monitoring functions be operable.
The use of symetric detectors to provide substitute data for inaccessible TIP channels does not compromise the ability of the process computer to accurately represent the spatial gama flux distribution of,the reactor core.
This proposed change does not alter the basic method used to calculate power and exposure distributions and fuel thermal limits.
The existing method for calculating core power and exposure distributions and fuel thermal limits includes provisions for monitoring the gamma flux distribution with mirror or rotational symmetry. This proposed change includes provisions for using octant symmetry, which is both mirror and rotationally symmetrical.
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> :This proposed change does not alter the basic method used to determine the appropriate constants-with which to relate the readings of LPRM's-to those of-the TIP's or the basic method used to determine substitute values to be used by the process. computer for LPRM's which have failed. The proposed change specifies the use of TIP data which is equivalent to that which would normally be used.
The calibration of LPRM's using symmetric string base distributions
. provide LPRM data within the normal uncertainty expected for calibrations with all five machines operable. Consequently,.this condition will not adversely. affect core thermal limit calculations.
This proposed change does not alter the function, performance or operation of.any safety system or safety-related equipment..The restriction to."A" control rod sequences and the limitation on total TIP uncertainty ensures the readings from symmetric channels are equivalent.
Therefore, this proposed change.does not involve a.significant; increase in the probability or consequences of an accident previously evaluated.
2.
The substitution of data into inaccessible TIP channels has no effect on any accident initiator, therefore this proposed change does not create the possibility of a new or different kind of accident from any accident previously evaluated.
3.
This proposed _ change does not involve a significant reduction in a margin of safety because the implementation is restricted by the LCO to type A symmetric control rod patterns, and then only when the total TIP uncertainty has been demonstrated previously in the cycle to be within the value assumed in the General Electric reload licensing topical report - GESTAR II (8.7 percent). Additionally, the maximum number of inoperable channels has been limited to ten.
Based upon the above considerations, the staff concludes that the amendment meets the three criteria of 10 CFR 10.92. Therefore, the staff has made a final determination that the proposed amendment does not involve significant hazards considerations.
5.0 STATE CONSULTATION
The staff made a good-faith effort to consult with the state of Ohio by l
telephone on September 14, 1989. The state offered no comments on this amendment.
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. 6.0 ENVIRONMENTAL CONSIG5 RATION This amendment involves a change to a requirement with respect to the instal-lation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 or a change to a surveillance requirement. The 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 Connission has previously issued a proposed finding that this amendment involves no significant hazards consideration and there has been no public connent on such finding. Accordingly, this amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuantto10CFR51.22(b),noenvironmental impact statement or environmental assessment need be prepared in connection with the issuance of this amendment.
7.0 CONCLUSION
The staff has concluded, baseo on the considerations discussed above, that:
(1) there is reasonable assurance that the health and safety of the public will not be endange:ed by operation in the proposed manner, and (2) such activities will be conducted in compliance with the Commission's regulations and the issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public.
8.0 REFERENCES
1.
Letter and attachments from A. Kaplan, CEI, to the NRC, dated August 23, 1989, " Exigent Technical Specification Change Request - Traversing In-Core Probe System."
2.
NED0-20340, " Process Computer Performance Evaluation Accuracy," June 1974.
3.
GESTAR II, NEDE-24011-P-A-9, " General Electric Standard Application for Reactor Fuel," November 1988.
Principal Contributors:
T. Colburn H. Richings Dated:
September 22, 1989
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