ML20058F543
| ML20058F543 | |
| Person / Time | |
|---|---|
| Site: | Crystal River  |
| Issue date: | 07/15/1982 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20058F533 | List: |
| References | |
| TAC-48126, NUDOCS 8207300558 | |
| Download: ML20058F543 (9) | |
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g UNITED STATES g
3e g
NUCLEAR REGULATORY COMMISSION g
E WASHINGTON, D. C. 20555 t
SAFETY EVALUATION BY THE OFFICE OF fiUCLEAR REACTOR REGULATION SUPPORTING AMENDf'ENT NO. -55 TO FACILITY OPERATIflG LICENSE NO. DPR' 72 FLORIDA POWER CORPORATION, ET AL CRYSTAL RIVER UNIT NO. 3 NUCLEAR GENERATING PLANT DOCKET N0. 50-302 Introduction Amendment No. 41 to Facility Operating License No. DPR-72 (Reference 1) authorized Florida Power Corporation (the licensee or FPC) to operate Crystal River Unit No. 3 (CR-3) at a power level of 2544 MWt, increased from the previously authorized level of 2452 FMt. As part of the review of this increased power request, the NRC determined that the time response of the previous flux-to-flow monitoring instrumentation was too slow to avoid violating the Departure from Nucleate Boiling Ratio (DNBR) criterion during certain postulated loss-of-flow transients.
The licensee installed a pump power monitoring (PM) instrumentation system which could detect loss of p(ower to more than one reactor coolant pump (RCP) on a much faster basis 620 ms vs.1400 ns).
Since then, plant operation has been interrupted several times due to spurious operation of the RCPPMs.
To resolve the spurious trip problem, the licensee proposed increasing the response time of the RCPPMs by 100 to 150 msec.
By telephor.e the evening of March 3,1982, and confirmed by letter dated March 4,1982, the licensee requested authorization to operate the CR-3 plant at no more than 75% of full power with response times greater than those in the Technical Specifica-tions (TSs) until they could justify a proposed new response time.
The authorization was granted on March 3,1982. By letter dated March 9, 1982, the licensee provided adequate justification for a proposed new response time for the RCPPMs. On March 9,1982, we authorized operation at 100% power with the RCPPM response time increased from <0.47 seconds to <0.56 seconds.
On March 26,1982, CR-3 was again tripped by its RCPPMs.
Increasing the response time to 560 msec did not resolve the spurious trip problem. Therefore, in a letter dated April 1,1912, the licensee proposed operating at less than 100%, power with the RCPPMs bypssed until they could establish the cause of the PM trips and implement a fix. They further stated that they expected to be able to justify operation at 90% of full power with the RCPPMs bypassed. However, until they could provide the justification, they would limit reactor power to 75%
of full power.
On April 1,1982, we authorized operation at 75% of full power with bypassed.
RCPPMs until. operation at 90.4% full power (2300 Mit) could be justified.
Subsequently, by letter dated April 6,1982, the licensee provided the neces-sary justification for operation of CR-3 at '?300 MWt (90.4% of full power),
and we approved operation at 90.4% full powe, sith the RCPPMs bypassed.
By letter dated April 9,1982, the licen.:ee requested approval for operation at 75% of 2300 MWt for three RCPs with & prooMs bypassed. Subsequently, by letter dated April 30, 1982, the licensee..... 6ted a TS c' s request supplementing the information provided on April 1 and A'r7 6.
- However, r207300558 820715 PDR ADOCK 05000302 P
\\
1 CR-3 :
neither the April 9,1982.or April 30,1982 submittals co. ntained luitable
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.j analyses related.to plant operhtion.with only three RCPs in operation. -
Discussion & Evaluation 4
1.
Operation at 75% and 90.4% Power With The RCPPMs Bypassed (a)
Discussion i
The licensee initially indicated that for the present core operation at about 90% of full power with the RCPPMs bypassed, the flux-to-flow trip is adequate to prevent violating the DriBR limit.
However, since they did not provide justification for this power, operation was limited to 75% of full power.
Subsequently, FPC submitted a summary of a Babcock & Wilcox Company (B&W) analysis of the four pump loss of coolant flow without taking credit for the RCPPM.
This analysis relied on the flux / flow trip and shows that i
the minimum DilBR is 1.43 for a four pump loss of flow initiated from 2300 fNt (90.4% of full power).
l (b)
Evaluation The effect of bypassing the RCPPM trip can be balanced by reducing reactor power. Operation at 75% of full power with the RCPPMs bypassed is acceptable i
since the existing flux / flow trip setpoint and response times adequately compensate for operation without the RCPPMs at this power level.
The analysis of the four pump loss of flow at 90.4% full power was done with i
the same codes, methods and correlation as previously used in CR-3 licensing analyses. The analyses indicate that the minimum DriBR would be 1.43 which is above the DitBR limit of 1.35.
The analyses therefore demonstrate acceptable results.
B&W was contacted to assure that the analyses had been performed in conformance with B&W quality assurance procedures.
Technical aspects of the analyses -
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l were also discussed to assure that the results were reasonable and consis-l tent with previous analyses.
Sufficient analyses or discussions relative to three pum'p operation were not
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included in the licensee's submittal.
Based on the results of the analyses submittal by FPC, we conclude that a l
four pump loss of coolant flow event initiated at 2300 MWt (90.4% of ful'
- power) would not exceed the applicable regulatory limits, therdfore approval of the proposed TS, as it relates to four pump operation with RCPPMs bypassed,~
will riot result i'n an undue risk to the health and safety of Lthe puti1~ic.~ The
~ 'r6)osed changes relited to three pump operation are not acceptable since the ~
p licensee did not provide suitable analyses to justify the proposed changes.
2.
RCPPMs Response Times l
(a) Discussion The RCPPMs protect against a multiple-pump loss-of-flow transient by tripping the reactor early enough to prevent exceeding the DriBR criterion of 1.30
CR-3 minimum. This is accomplished by causing control rod insertion (scram) to start within 620 ms of the occurrence of improper pump power conditions.
When the original authorization for the RCPPN was issued, the time response was allocated as:
240 ms for the sensor channel (sensor elements, watt transducer, bistable, and output relay); 150 ms for the Reactor Protection System (RPS) (logic, etc.); 80 ms for Control Rod Drive (CRD) breakers; 90 ms allocated for uncertainty (margin); and 60 ms for release of the control rods (roller nuts from lead screws).
Subsequently, the licensee's request (Reference 2) for TS changes stated that "Recent revisions of the RPS instrumentation delay times are the result of an instrument error analysis by B&W." Accordingly, a later amendment (Reference
- 3) showed the response time for the RCPPMs to be 470 ms. When the intentional time delay (100-150 ms) was added, attaining the 470 ms limit became questionable.
At the same time, the question arose about the adequacy of the time response tests being conducted to demonstrate compliance with the facility TSs. The tests did not conform in an obvious way to the definition of RPS response times in that the sensor elements and the " watt transducers" were not being tested. The licensee contended that use of manufacturer's data was sufficient.
(b) Evaluation The original design allocations of response times were listed above.
The crucial point of these values is that the plant transient analysis was run under the assumption of a 620 ms delay to the start of negative reactivity insertion (red motion). While the 620 ms assumption remains valid, several factors have been considered and are discussed below.
1.
Optical isolators were installed between the'RCPPM output relays and the RPS to prevent 6.9 kv from being applied to the RPS by certain postulated failures.
The design allocation of response time was 150 ms.
The original design allocation of 240 ms for the sensor channel was refined as follows:
16 ms for the sensor elements (current transformers and potential transformers);
72 ms for the watt transducer, bistable, and output relay; and 150 ms for the optical isolator.
2.
The design allocation for the RPS (logics, etc.) was revised from 150 ms to 131 ms. The basis for this revision is extensive testing associated with equipment qualification programs and is documented in B&W Topical Report BAW-1003.
This revision increased the " dedicated margin" for uncertainty from 90 ms to 109 ms.
3.
Due to some operaticnal problems, the operating voltage of the isolators had to be increased. Type testing of the isolators at the new operating voltage shows that at an artient temperature of 65*F the isolators responded in 106 ms or less. At higher temperatures the response is faster. The ambient temperature for this installation is maintained at 74 + 2*F.
Therefore, use of 106 ms includes some conservatism and provides an additional margin of 44 ms, over the 150 ms design allocation.
CR-3 4 When the spurious trips became a problem, the licensee decided to use part of the " dedicated margin" (153 ms) in the form of an intentional time delay.
The outpt.t relay was removed and an Agastat 0.1-3 minute time delay relay was installed.
(The removal of the output relay represents a response time savings of 5-11 ms).
The time delay relays were set for a 0.1 sec.
delay, with a design allocation of 150 ms uximum.
Testing showed that the values were 85-139 ms.
While this repeatability is not trivial, it remains within the 150 ms allocation.
5.
The 620 ms value used for the transient analysis does not directly equate to the response time requirements in the TSs because the end-points are dif-ferent.
The 620 ms includes 60 ms for release of the roller nuts from the lead screws of the CRD mechanisms.
The TS definition of end-point is the opening of the control rod breakers. The original 620 ms value less 60 ms is the 560 ms value which is the value proposed for the TSs.
(A similar 60 ms reduction in the allowed response times for other instrumentation shown in TS Table 3.3-2 is also proposed.
Our understanding is that all instrumen-tation. meet these revised values.)
The licensee has stated that the start-point for rod drop time measurements is the opening of the CRD breakers.
Therefore, the time for the roller nuts to release the control rod before rod motion actually starts is in fact included in the rod drop test.
6.
If the 560 ms response time value is further reduced by the original design allocation of 90 ms for " dedicated margin" for uncertainty, we arrive at the present TS value of 470 ms. The appropriateness of such an approach is questionable. The licensee has stated that proposing a TS limit of 0.470 seconds was an error on their part.
We have completed a best-estimate of the present response time of the RCPPM i
instrumentation.
The licensee has conducted certain limited response time measurements on the installed equipment.
Measurements have been made from the output of the watt transducer to the output of the contact monitor of the RPS, yielding a wo'rst-case value of 136 ms. This measurement included
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the bistable and the original output relay. Additionally, this measurement used the output of the RPS contact monitor as its end-point, which is a slight overlap of the RPS measurements.
Therefore, we can reasonably sub-tract 6 ms for the output. relay that has been removed, and another'6 ms for the overlap, to yield a value of 124 ms.
The newly-installed time delay relays have been measured separately, yielding a worst case value of 139 ms.
.The RPS and CRD breaker together have been measured, yielding a worst case value of 104 ms.
Recently obtained test data indicates that a value for the watt transducer itself (not including the bistable and output relay) is 22 ms.
Baseo upon manufacturer's calculations, B&W is recommending that the sensor elements be assigned a response time of 16 ms, Collecting these i
l values:
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CR-3 a.
sensor elements 16 ms b.
watt transducer 22 ms c.
RCPPM measurement 124 ms d.
time delay measurements 139 ms e.
RPS measurements 104 ms 405 ms The 405 ms best-estimate value is compared to the design limit of 560 ms, and indicates a substantial actual margin of over 15'~ ins.
Further, based upon 0
engineering judgment, we do not believe that even ultra-conservative estimates for uncertainty and for drift over the next 12-18 months could cause the actual response to exceed the 560 ms limit.
Additionally, the licensee has agreed that, at the next plant shutdown of significant duration (i.e., 4 weeks or longer) that occurs after the develop-ment of appropriate test methods and procedures (expected to be completed in June 1982), complete response time measurements of at least one RCPPM channel will be made, that include the sensor elements and run to the opening of the CRD breakers. The licensee has stated that the capability already exists to measure the response time of the channel from the output of the sensors. The licensee is concerned that in-place testing of the se,nsor elements may hot be feasible.
If this is the case, they have furtrier committed to provide, for~
our review and approval, an acceptable alternative.
If these actual measure
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ments yield results no longer than 560 ms, we could conclude that the system is acceptable.
While this best-estimate of RCPPM response time (being based upon limited testing and original manufacturer's data) may be sufficient for justifying y
return.to full power and continued operation until the next refueling, it is not a sufficient basis for operation over the remaining plant lifetime, 30 years or more.
The licensee has agreed to periodic testing of the response time of one complete RCPPM channel (i.e., including the sensor elements) per pump and RPS at each refueling outage to demonstrate that the required 560 ms limit is maintained.
For purposes of this evaluation, the TS limit is:
l RCPPM channels
. < 0.560 sec.
(including RPS to CRD breakers open)
Anticipating that the actual measurements will be performed in parts, we are basing the 560 ms limit on:
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sensor elements 1 0.030 sec.
-< 0.325 sec.
RCPPM channel (exclusive of sensor elements, but to RPS contact monitor operating)
RPS (including CRD breaker opening) s 0.211 sec.
total (includes 6 ms overlap)
$ 0.566 sec.
CR-3.
We are assigning a conservative response time of'30 ms to the sensor el emer.ts.
Such conce; vatism is necessary sir re:
rio resp:ve tima 'esting has been conducted, the manufacturer's calculations show quite a varia-bility (3.7 - 14.8 ms), the current being measured in this application is that of a highly inductive load, and the manufacturer has not certified the response time of the sensors. The licensee has agreed to obtain appro-priate type test data for the sensor elements within six months. When this data is provided, we can reconsider the present 30 ms assignment.
The question has been raised of using the " staggered test basis" for response time testing of the RCPPM instrumentation.
The question is com-pounded by misleading entries for the RCPPMs (Item 14) in TS Table 3.3-1.
Overall, the function of the RCPPM instrumentation is to provide a trip signal upon loss of power to multiple pumps.
Therefore, the power to each RCP must be monitored.
If each RCP had a single PM ch'annel, the safety function could be accomplished, but the degree of redundancy would be zero.
If each.RCP had two monitoring channels, the degree of redundancy would be 1; in TS language, the number of redundant channels, N, would be 2.
At this plant, since each RCP has two RCPPM channels, N is 2.
Therefore, at least one of the two redundant channels for each of the four RCPs must be tested for response time at each refueling outage (i.e., every 18 months).
Accordingly, each channel will be retested on intervals of 3 years.
- Further, considering the equipment involved for this particular instrumentation, a 3-year test interval is the maximum allowable at this time.
In order to avoid future confusion, the licensee has agreed to the folicwing-clarification to TS Table 3.3-1 regarding the RCPPMs (Item 14):
a.
The Total Number of Channels 2 per pump b.
Channels to Trip 1 from 2 or more pumps c.
Min. Channels Operable 2 per pump d.
Action Statement 3 is deleted from Item 14 e.
A New Action Statement 25 is added for Item 14, which reads as follows:
"With the number of" channels operable one less 'than the required Minimum
'Chan.:els Operable requi'rement, plant operation 'may continue until the'neit required Channel Functional Test provided the irioperable channel is plhied in the tripped conditiori within' 4 houfs."
Additionally, we are concerned that drift in the time delay relays may accumulate between tests.
To allay this concern, the licensee has agreed l
to test all the time delay relays at each refueling not only to assure that their "as found" responses are within the 150 ms allocation, but also to readjust each relay as close as practical back to the nominal 100 ms value.
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Based upon the cdnsiderations described above, we conclude that the basis of the current plant transient analysis will remain valid for the longer tem.
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CR-3 The licensee believes that the cause of the spurious trippir.g of the RCPFM instrumentation is an electrical power transient occurring on the 6.9 kv station distribution system, causing the sensor elements to trip the channels.
The 6.9 kv is obtained from the station main generator via the auxiliary trans former.
Considering the RCPPM setpoints of 70% power and the time responses involved, we find it difficult to understand that the main generator is producing such electrical transients. The licensee thinks the transient originates on the electric grid and is being fed back into the
, station distribution system.
The licensee stated that the non-self-powering elements of the RCPPM channels are powered from the Class lE Vital Buses.
This information does not agree well with the NRC Safety ~ Evaluation (SE) (Reference 1) which originally approved the RCPPMs. The concern in the SE was that certain postulated failure mechanisms (for example, a seismic event) might cause the RCPPMs not to pmduce an output trip signal. While there may have been some mis-understanding on the original desfgn, the licensee agrees that these postulated failure mechanisms must be addressed. It was therefore agreed that the existing high-level RCP power trip would be required for safety purposes.
The licensee has pmposed a revised page in the Basis of the TSs to make the reason for this requirement explicit. We believe that having " required" high-level and low-level trips as part of the RCPPMs provides adequate protection to assure that an output trip signal will not be prevented when needed.
We do not believe that the licensee has to date adequately investigated the spurious trips to determine the cause(s). We suggested that voltage recording instruments on the sources of power may be diagnostically necessary.
The licensec has agreed to refine the raw data presently available and to further investigate the apparent electric power transients.
I Based upon our review of the information provided by the licensee and the reactor vendor, we find that:
i (1) The response time of the RCPPMs (through opening of the CRD breakers) is required to be < 0.560 seconds for the current plant transient analysis to
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. remain valid.
(2) The addition of an intentional time delay (set to a nominal 100 ms value) is acceptable as long as the 560 ms overall response is maintained.
(3) The best-estimate of the response time for the RCPPM system is edequate for return to full power operation and continued operation to the next scheduled refueling outage. The licensee has agreed to response-time test at least one complete RCPPM channel at the first appropriate outage prior to the refueling outage.
(4) The licensee has committed to response time testing one complete RCPPM system (including sensor elements) for each pump at the next refueling, and each refueling thereafter on a staggered test basis.
This will pro-vide adequate assurance that the response time will be acceptable on a continuing basis over the rest of the plant lifetime.
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.CR-3 (5)
The high-level (pump overpower) trip is required for safety in order to assure that the protective action will occur under certain instrumen-tation failure conditions.
(6) The licensee is continuing to investigate the spurious tripping to determine the cause(s) of the apparent electrical power transients.
Based upon these findings and upon the actions agreed to by the licensee as discussed in this evaluation, we conclude that the RCPPM instrumentation will provide adequate protection for plant operation at 100% of the authorized 2544 power level.
Environmental Consideration We have determined that the amendment does not authorize a change in effluent types or total amounts nor an increase in power level and will not result in any significant environmental impact. Having made this determination, we have further concluded that the amendment involves an action which is insignificant from the standpoint of environmental impact and, pursuant to 10 CFR 551.5(d)(4), that an environmental impact statement, or negative declaration and environ-mental impact appraisal need not be prepared in connection with the issuance of this amendment.
Conclusion We have concluded, based on the considerations discussed above, that:
(1) because the amendment does not involve a significant increase in the probability or consequences of an accident previously evaluated, does not create the possibility of an accident of a type different from any evaluated previously, and does not involve a significant reduction in a margin of safety, the amendment does not involve a significant hazards consideration, (2) there is reasonable assurance that the health and safety of the public will not be endangered by operation in.the proposed manner, and (3) 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 t'o the health and safety of the public.
.e
CR-3 Refe rences 1.
Letter, J. Stolz (NRC) to J. Hancock (FPC), dated July 21, 1981, 2.
Letter, P. Baynard (FPC) to Director, Office of Nuclear Reactor Regulation, NRC, dated November 16, 1981.
3.
Letter, J. Stolz (NRC) to J. Hancock (FPC), dated December 4,1981.
4.
Letter, D. Rainey (Babcock & Wilcox) to D. O'Shea (FPC), dated July 17, 1981.
5.
Letter, D. Mardis (FPC) to H. Denton (NRC), dated March 4,1982.
6.
Letter, K. Wazowicz (General Electric) to S. Ulm (FPC), dated March 5,1982.
7.
Letter, J. Castanes (Babcock & Wilcox) to P. Baynard (FPC), dated March 5, 1982.
8.
Letter, D. Mardis (FPC) to H. Denton (NRC), dated March 9, 1982.
Da ted: July 15,1982 The following NRC personnel have contributed to this Safety Evaluation:
f J. T. Beard, Gary Holahan and Sydney Miner.
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