RS-07-086, Supplement to Request for Amendment to Technical Specification 3.3.1.1, Reactor Protection System (RPS) Instrumentation, Scram Discharge Volume Level Instrumentation Surveillance Requirements
| ML071580953 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 06/06/2007 |
| From: | Benyak D AmerGen Energy Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RS-07-086 | |
| Download: ML071580953 (10) | |
Text
AmerGen Energy Company, LLC wwwexeloncorp.com 4300 Winfield Road Warrenville, IL 6o555 RS-07-086 June 06, 2007 U. S. Nuclear Regulatory Commission ATTN : Document Control Desk Washington, D.C. 20555 Clinton Power Station, Unit 1 Facility Operating License No. NPF-62 NRC Docket No. 50-461
Subject:
Supplement to Request for Amendment to Technical Specification 3.3.1.1, "Reactor Protection System (RPS) Instrumentation," Scram Discharge Volume Level Instrumentation Surveillance Requirements erC en
,M
Reference:
Letter from Mr. T. S. O'Neill (AmerGen Energy Company, LLC) to U. S.
NRC, "Request for Amendment to Technical Specification 3.3.1.1,
'Reactor Protection System (RPS) Instrumentation,' Scram Discharge Volume Level Instrumentation Surveillance Requirements," dated January 26, 2007 In the referenced letter AmerGen Energy Company, LLC (AmerGen) requested a change to the Technical Specifications (TS) of Facility Operating License No. NPF-62 for Clinton Power Station (CPS), Unit 1. Specifically, the proposed change will revise TS 3.3.1.1, "Reactor Protection System (RPS) Instrumentation," Table 3.3.1.1-1, "Reactor Protection System Instrumentation," Function 8, "Scram Discharge Volume Water Level
- High," Item b, "Float Switch," by replacing Surveillance Requirement (SR) 3.3.1.1.9 with SR 3.3.1.1.12. This change will effectively revise the surveillance frequency for the scram discharge volume (SDV) level float switch from every 92 days to every 24 months.
This change is being requested to reduce personnel radiation exposure that is inherent in the current surveillance frequency that requires containment entry at power.
On April 3, 2007, representatives of AmerGen and the NRC participated in a conference call to discuss the proposed amendment request provided in the referenced letter. The NRC indicated that to complete its review of the proposed amendment request additional information is required. Specifically, the NRC requested an evaluation against Generic Letter 91-04, "Changes in Technical Specification Surveillance Intervals to Accommodate a 24-Month Fuel Cycle," Regulatory Guide 1.174, "An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to An Exelon Company 10 CFR 50.90
June 06, 2007 U. S. Nuclear Regulatory Commission Page 2 the Licensing Basis," and Regulatory Guide 1.177, "An Approach for Plant-Specific, Risk-Informed Decisionmaking : Technical Specifications." The attachment to this letter provides the requested additional information.
AmerGen has reviewed the information supporting a finding of no significant hazards consideration that was previously provided to the NRC in the referenced letter. The supplemental information provided in this submittal does not affect the bases for concluding that the proposed license amendment does not involve a significant hazards consideration. No new regulatory commitments are established by this submittal.
If you have any questions concerning this letter, please contact Mr. Timothy A. Byam at (630) 657-2804.
I declare under penalty of perjury that the foregoing is true and correct. Executed on the 6th day of June 2007.
Respectfully, Darin M. Benyak Director - Licensing and Regulatory Affairs AmerGen Energy Company, LLC Attachment :
Deterministic Evaluation in Support of Request for Amendment to Technical Specification 3.3.1.1, "Reactor Protection System (RPS)
Instrumentation," Scram Discharge Volume Level Instrumentation Surveillance Requirements
Generic Letter 91-04 ATTACHMENT Deterministic Evaluation in Support of Request for Amendment to Technical Specification 3.3.1.1, "Reactor Protection System (RPS) Instrumentation," Scram Discharge Volume Level Instrumentation Surveillance Requirements In Generic Letter (GL) 91-04, "Changes in Technical Specification Surveillance Intervals to Accommodate a 24-Month Fuel Cycle," (Reference 1) the NRC provided generic guidance for evaluating a 24 month surveillance test interval for Technical Specification (TS) Surveillance Requirements (SRs). As described in Reference 2, the proposed TS surveillance frequency change from quarterly to 24 months involves SR 3.3.1.1.9 that requires a Channel Functional Test (CFT) be performed on each of the Scram Discharge Volume (SDV) water level instrumentation channels every 92 days. The instrumentation tested as part of this SR are the float type level switches and, as noted in Reference 2, these float switches are mechanical devices that are not subject to instrument setpoint drift. GL 91-04 generally identifies surveillance changes in one of two categories. The categories are : (1) changes to surveillances other than channel calibrations, identified as "Non-Calibration Changes;" and (2) changes involving the channel calibration frequency identified as "Channel Calibration Changes." As noted above, the proposed change involves the surveillance frequency for the CFT on the SDV water level float type switches. The TS Bases defines a CFT as the injection of a simulated or actual signal into the channel as close as practicable to the sensor to verify operability of all devices in the channel required for channel operability. This surveillance requirement does not include a channel calibration that the TS Bases define as adjusting the channel output such that it responds within the necessary range and accuracy to known values of the parameter monitored. Therefore, the change proposed in Reference 2 constitutes a non-calibration change.
Reference 1 identifies three steps to evaluate non-calibration changes. Each of these steps is discussed below. The evaluations documented below are intended to confirm the effect on safety resulting from the proposed change is small and to confirm that the assumptions in the plant licensing basis is not invalidated on the basis of performing any surveillance at the bounding surveillance interval limit provided to accommodate a 24-month fuel cycle. In consideration of these confirmations, GL 91-04 provides that licensees need not quantify the effect of the change in surveillance intervals on the availability of individual systems or components.
STEP 1 :
Licensees should evaluate the effect on safety of the change in surveillance intervals to accommodate a 24 month fuel cycle. This evaluation should support a conclusion that the effect on safety is small.
EVALUATION.
As described in Reference 2, SDV water level is measured by two diverse methods.
The level in the SDV is measured by four float type level switches and four level transmitters with associated analog trip modules (ATMs) for a total of eight level signals.
The outputs of these devices are arranged so that there is a signal from a level switch and a transmitter to each trip logic division. One channel of each type of Scram Discharge Volume Water Level - High Function associated with each of the four trip logic divisions is required to be Operable to ensure that no single instrument failure will preclude a scram from this Function on a valid signal.
Page 1 of 8
ATTACHMENT In accordance with TS Table 3.3.1.1-1 Function 8, SR 3.3.1.1.9 and SR 3.3.1.1.10 are required to be completed for the transmitters. In addition, SR 3.3.1.1.9 is also required to be completed for the float switches. SR 3.3.1.1.9 requires that a CFT be performed on each required channel every 92 days. The CFT is performed to ensure that the entire channel will perform the intended function. SR 3.3.1.1.10 requires that the ATMs associated with the level transmitters be calibrated every 92 days to provide a check of the actual trip setpoints.
The non-calibration SR frequency requirement being changed (i.e., SR 3.3.1.1.9) has been evaluated with respect to the effect on plant safety. The methodology utilized to justify the conclusion that extending the testing interval has a minimal effect on safety was based on the fact that the function/feature is :
(2)
(3)
Deterministic Evaluation in Support of Request for Amendment to Technical Specification 3.3.1.1, "Reactor Protection System (RPS) Instrumentation," Scram Discharge Volume Level Instrumentation Surveillance Requirements Tested on a more frequent basis during the operating cycle by other plant programs ;
Designed to have redundant counterparts or be single failure proof; and Highly reliable.
Drift evaluations were not performed for the SDV float switches. The float switches that perform this function are mechanical devices that require mechanical adjustment only.
Drift is not applicable to these devices. These devices have proven to be reliable over time as described below.
The proposed change will revise the surveillance test interval associated with the CFT for the SDV float switches and does not revise the surveillance testing for the transmitters and associated ATMs. The transmitters will continue to be functionally tested every 92 days and the ATMs will be calibrated every 92 days. In addition to the surveillances performed every 92 days on the level transmitters and ATMs, a channel check is also performed every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />, in accordance with SR 3.3.1.1.1, to ensure that a gross failure of the instrumentation has not occurred.
Based on the above, it has been demonstrated that the SDV high water level function is measured by two diverse and redundant methods. The instrumentation that is designed to be redundant to the float switches is tested on more frequent basis (i.e., every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and 92 days) and will continue to be tested on the same frequency following the proposed change. Additional justification for extending the surveillance test interval is that this function, including the actuating logic, is designed to be single failure proof and, therefore, is highly reliable.
In summary, it has been concluded that the effect on safety from the change in surveillance interval from once every 92 days to once every 24 months, if any, is minimal.
ATTACHMENT Deterministic Evaluation in Support of Request for Amendment to Technical Specification 3.3.1.1, "Reactor Protection System (RPS) Instrumentation," Scram Discharge Volume Level Instrumentation Surveillance Requirements STEP 2:
Licensees should confirm that historical maintenance and surveillance data do not invalidate this conclusion.
EVALUATION:
The surveillance test history of the affected SR has been evaluated. This evaluation consisted of a review of available surveillance test results, condition reports entered into the corrective action program, and associated maintenance records for the last 12 quarters of operation. With the extension of the testing frequency to 24 months, there will be a longer period between each surveillance performance. If a failure that results in the loss of the associated function should occur during the operating cycle that would only be detected by the performance of the quarterly TS SR, then the increase in the surveillance testing interval might result in a decrease in the associated function's availability. Therefore, this review of surveillance test history was conducted to assess the potential for impact on availability of these components during the extended surveillance interval.
This review supported a determination as to whether the as-found condition of the affected instrumentation trip settings were ever found to be less conservative than the Allowable Value specified for TS Table 3.3.1.1-1 Function 8.b. For Function 8.b, SDV water level is measured by four float switches (1C11-NO13A through D). To satisfy SR 3.3.1.1.9, CPS procedures 9431.22, "SDV High Water Level Float Switch C11-N013A (B, C, D) Channel Calibration," and 9531.22, "SDV High Water Level Float Switch C11-N013A, (B, C, D) Channel Functional," are performed. These surveillances have routinely shown that the as-found condition of the instruments has not required readjustment. The review of surveillance test results from the past 12 quarters indicated that the as-found condition of the four float switches have been found to be within the acceptance criteria specified in the surveillance test procedures. The review of associated maintenance history also indicated that there has been no maintenance performed on these switches that would invalidate these conclusions.
This review of surveillance test history validated the conclusion that the impact, if any, on system availability will be minimal as a result of the change to a 24-month testing frequency.
STEP 3:
Licensees should confirm that the performance of surveillances at the bounding surveillance interval limit provided to accommodate a 24-month fuel cycle would not invalidate any assumption in the plant licensing basis.
EVALUATION.
As part of the evaluation of the affected SR, the impact of the change against the assumptions in the CPS licensing basis was reviewed. The SDV receives water displaced by the motion of the control rod drive (CRD) pistons during a reactor scram.
Should this volume fill to a point where there is insufficient volume to accept the displaced water, control rod insertion would be hindered. Therefore, a reactor scram is initiated when the remaining free volume is still sufficient to accommodate the water from a full core scram. However, even though the two types of Scram Discharge Volume Page 3 of 8
Regulatory Guides 1.174 and 1.177 ATTACHMENT Deterministic Evaluation in Support of Request for Amendment to Technical Specification 3.3.1.1, "Reactor Protection System (RPS) Instrumentation," Scram Discharge Volume Level Instrumentation Surveillance Requirements Water Level - High Functions are an input to the RPS logic, no credit is taken for a scram initiated from these Functions for any of the design basis accidents or transients analyzed in the CPS Updated Safety Analysis Report (USAR). Therefore, it was confirmed that the proposed change does not invalidate any assumption in the plant licensing basis.
GL 91-04 Evaluation Conclusion :
The above qualitative evaluation is provided for the proposed change, and concludes that the effect on plant safety is small, that the change does not invalidate any assumption in the plant licensing basis, and that the impact, if any, on system availability is minimal from the proposed change to a 24-month testing frequency. These conclusions have been validated by a review of the surveillance test history at CPS as discussed above.
Regulatory Guide (RG) 1.174, "An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis," (Reference
- 3) and RG 1.177, "An Approach for Plant-Specific, Risk-Informed Decisionmaking :
Technical Specifications," (Reference 4) describes an acceptable method for assessing the nature and impact of licensing basis changes when these changes, including TS changes, are supported by risk information. These two RGs identify the five critical principles that any risk-informed TS change is expected to meet. Each of these principles is identified below with an evaluation of the proposed change in Reference 2 against these principles.
1.
The proposed change meets the current regulations unless it is explicitly related to a requested exemption or rule change.
EVALUATION.
The proposed change provided in Reference 2 is consistent with the current regulations.
10 CFR 50.36, "Technical specifications," provides the content required in a licensee's TS. Specifically, 10 CFR 50.36(c)(3) requires that the TS include surveillance requirements. NRC regulations do not, however, specify the required surveillance test interval for any given SR. Since the proposed change results in an extension of the surveillance test interval for the SDV float switch CFT there is no impact to current regulations. As stated in Attachment 1 to Reference 2, the proposed SR frequency change continues to support the requirements of 10 CFR 50.36(c)(3) to assure that the necessary quality of systems and components is maintained, that facility operation will be within safety limits, and that the limiting conditions for operation are met. AmerGen has determined that the proposed change does not require any exemptions or relief from regulatory requirements, other than a change to the Technical Specifications, and does not affect conformance with any General Design Criteria (GDC) differently than described in the CPS USAR.
ATTACHMENT Deterministic Evaluation in Support of Request for Amendment to Technical Specification 3.3.1.1, "Reactor Protection System (RPS) Instrumentation," Scram Discharge Volume Level Instrumentation Surveillance Requirements Applicable regulatory requirements will continue to be met, adequate defense-in-depth will be maintained, sufficient safety margins will be maintained, and any increase in plant risk is very small and consistent with the NRC "Safety Goals for the Operations of Nuclear Power Plants ; Policy Statement," Federal Register, Vol.51, p.30028 (51 FR 30028), August 4, 1986, as interpreted by References 3 and 4. The proposed changes as documented in Reference 2 were submitted in accordance with 10 CFR 50.90, "Application for amendment of license or construction permit." In addition, AmerGen has confirmed that the proposed changes do not involve a discrepancy with any of the CPS license conditions.
- 2.
The proposed change is consistent with the defense-in-depth philosophy.
EVALUATION.
As stated above, the level in the SDV is measured by four float type level switches and four level transmitters with associated ATMs for a total of eight level signals. The proposed change does not revise the surveillance testing for the transmitters and associated ATMs. The transmitters will continue to be functionally tested every 92 days and the ATMs will be calibrated every 92 days. In addition to the functional test, a channel check is performed on the transmitters every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. This frequency of testing ensures that a major portion of the circuitry is operating properly and will detect significant failures within the instrument loop. System redundancy, independence, and diversity are maintained commensurate with the expected frequency, consequences of challenges to the system, and uncertainties.
Diversity of SDV level measurement instrumentation will be maintained and therefore, defenses against potential common cause failures are preserved. This diversity also ensures that the potential for the introduction of new common cause failure mechanisms is not an issue resulting from the proposed change. There is no degradation of the independence of barriers introduced by the proposed change and the existing defenses against human error are preserved.
The risk analysis performed and documented in Attachment 4 to Reference 2 demonstrated that the proposed change results in a very small increase in core damage frequency and containment failure frequency. When this very small risk change is considered, in addition to the diverse SDV level instrumentation, it is clear that a reasonable balance is preserved among prevention of core damage, prevention of containment failure, and consequence mitigation.
The proposed change does not involve a change in the SDV level instrumentation design. The proposed change simply revises the surveillance frequency for the SDV level float switch CFT from every 92 days to every 24 months. Therefore, there is no reliance on programmatic activities to compensate for weaknesses in plant design.
- 3.
The proposed change maintains sufficient safety margins.
EVALUATION.
ATTACHMENT Deterministic Evaluation in Support of Request for Amendment to Technical Specification 3.3.1.1, "Reactor Protection System (RPS) Instrumentation," Scram Discharge Volume Level Instrumentation Surveillance Requirements As stated in the No Significant Hazards Consideration Determination evaluation provided in Attachment 1 to Reference 2, margins of safety are established in the design of components, the configuration of components to meet certain performance parameters, and in the establishment of setpoints to initiate alarms or actions. The proposed TS change involves a change in the surveillance frequency for the SDV water level float switch CFT. There is no change in the design of the affected systems, no alteration of the setpoints at which alarms or actions are initiated, and no change in plant configuration from original design. Since no credit is taken for a scram initiated from the SDV Water Level - High Functions for any of the design basis accidents or transients analyzed in the CPS USAR, the proposed change does not impact the condition or performance of structures, systems, and components relied upon for accident mitigation.
The proposed TS change does not result in any hardware changes or in any changes to the analytical limits assumed in accident analyses. All applicable codes and standards continue to be met following the proposed change. Existing operating margin between plant conditions and actual plant setpoints is not reduced due to these changes. The proposed change does not impact any safety analysis assumptions or results.
AmerGen has conducted a risk assessment (Reference 2) to determine the impact of a change to the SDV water level instrument CFT surveillance frequency from the current once every 92 days to once every 24 months for the risk measures of Core Damage Frequency (CDF) and Large Early Release Frequency (LERF). This assessment indicated that the proposed CPS surveillance frequency extension has a very small change in risk to the public and is an acceptable plant change from a risk perspective.
As documented in the TS 3.3.1.1 Bases, even though the two types of SDV water level-high functions provide input to the Reactor Protection System (RPS) logic, no credit is taken for a scram initiated from these functions for any of the design basis accidents or transients analyzed in the USAR. Therefore, safety analysis acceptance criteria in the USAR continue to be met. The proposed surveillance test interval change does not adversely affect any assumptions or inputs to the safety analysis.
Therefore, based on the above, it has been demonstrated that the proposed change maintains sufficient safety margin.
- 4.
When proposed changes result in an increase in core damage frequency or risk, the increases should be small and consistent with the intent of the Commission's Safety Goal Policy Statement.
EVALUATION.
The risk-acceptance guidelines are based on the principles and expectations for risk-informed regulation. As documented in Reference 2, the proposed change was evaluated to determine that any increase in CDF or LERF is small and consistent with Page 6 of 8
Deterministic Evaluation in Support of Request for Amendment to Technical Specification 3.3.1.1, "Reactor Protection System (RPS) Instrumentation," Scram Discharge Volume Level Instrumentation Surveillance Requirements the NRC Safety Goal Policy Statement, USNRC, "Use of Probabilistic Risk Assessment Methods in Nuclear Activities : Final Policy Statement," Federal Register, Volume 60, p.42622, August 16, 1995.
The results of the quantification of the SDV level instrumentation impact on the CPS risk profile are as follows.
This risk assessment estimated the increase in CDF and LERF due to the proposed change to extend the current 3-month surveillance interval for the SDV water level instruments to a 24-month interval. The changes in CDF and LERF are as follows.
ACDF = 6.0E-9/yr ALERF = 1.2E-9/yr ATTACHMENT These quantitative risk results fall into the Reference 3 Region III risk category (i.e.,
"very small" risk impact) with significant margin. Therefore, the proposed change is acceptable from a risk perspective without the need for special compensatory actions. A detailed summary of this assessment is provided in Attachment 4 to Reference 2.
- 5.
The impact of the proposed change should be monitored using performance measurement strategies.
EVALUATION.
In accordance with NUMARC 93-01, "Industry Guideline for Monitoring the Effectiveness of Maintenance at Nuclear Power Plants," the reliability of the SDV water level float switches are monitored to demonstrate that their performance is adequate. The reliability of the affected float switches is monitored under the CPS Maintenance Rule program.
If the pre-established reliability performance criterion is exceeded for the SDV float switches, consideration must be given to 10 CFR 50.65, "Requirements for monitoring the effectiveness of maintenance at nuclear power plants," paragraph (a)(1) actions, including increased management attention and goal setting in order to restore their performance (i.e., reliability) to an acceptable level. The performance criteria are risk based and, therefore, are a means to manage the overall risk profile of the plant. An accumulation of large core damage probabilities over time is precluded by the performance criteria.
As described above, monitoring and periodically evaluating the actual SDV water level float switch reliability will assess the effect of the proposed extension of the surveillance test interval on plant performance in relationship to the Maintenance Rule goals. To Page 7 of 8 Risk Metric Quarterly Test Interval Base 24-Month Test Interval LAR Change RPS Unavailability due to SDV High Level 4.166E-8 9.129E-8 4.96E-8 Core Damage Frequency CDF 6.466E-6/ r 6.472E-6/ r 6.0E-9/ r LLarge Early Release Frequency (LERF) 1.564E-7/yr 1.576E-7/yr 1.2E-9/yr
ATTACHMENT Deterministic Evaluation in Support of Request for Amendment to Technical Specification 3.3.1.1, "Reactor Protection System (RPS) Instrumentation," Scram Discharge Volume Level Instrumentation Surveillance Requirements ensure the proposed change does not degrade operational safety over time, the Maintenance Rule program will identify and correct adverse trends.
If AmerGen concludes that the performance or condition of the float switches affected by the proposed change does not meet established performance criteria, appropriate corrective action will be taken, in accordance with the Maintenance Rule.
RGs 1.174 and 1.177 Evaluation Conclusion :
As shown above, AmerGen has demonstrated that the proposed change to the CPS SDV water level float switch CFT surveillance test interval satisfies the five principles of RG 1.174 and that the proposed change is acceptable.
References 1.
Generic Letter (GL) 91-04, "Changes in Technical Specification Surveillance Intervals to Accommodate a 24-Month Fuel Cycle," dated April 2, 1991
- 2.
Letter from Mr. T. S. O'Neill (AmerGen Energy Company, LLC) to U. S. NRC, "Request for Amendment to Technical Specification 3.3.1.1, "Reactor Protection System (RPS) Instrumentation," Scram Discharge Volume Level Instrumentation Surveillance Requirements," dated January 26, 2007
- 3.
Regulatory Guide 1.174, "An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis,"
Revision 1, dated November 2002
- 4.
Regulatory Guide 1.177, "An Approach for Plant-Specific Risk-Informed Decisionmaking : Technical Specifications," dated August 1998