ML20247B879
| ML20247B879 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 05/15/1989 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20247B857 | List: |
| References | |
| NUDOCS 8905240268 | |
| Download: ML20247B879 (6) | |
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SAFETY EVALUATION REPORT CONTROL. SYSTEM FAILURE. REANALYSIS.- LICENSE. CONDITION.4 ILLINDIS. POWER COMPANY l
CLINTON. POWER STATION DOCKET.NO. 50-461
1.0 INTRODUCTION
The Clinton Safety Evaluation Report (SER) outstanding issue number 15 deals with multiple control system failure resulting from high-energy line breaks, common power source failure or sensor malfunction. The staff concern was that the subject control system f ailure would result in more serious consequences than those analyzed in Chapter 15 of Clinton's FSAR. The staff requested that the applicant identify those sources, which provide power to two or more control systems and demonstrate that failures of these power sources will not result in consequences outside the bounds of the FSAR Chapter 15 analyses.
In addition, the applicant was asked to review the designs to determine whether harsh environments associated with high-energy line breaks (HELBs) might cause control system malfunctions resulting in consequences more severe than those dnalyzed in FSAR Chapter 15.
IP's response (analysis) did not consider the i
effects of all nonsafety-related control system failures for each FSAR Chapter i
15 event.
In response to the staff's request for aeditional information, the licensee proposed a complete re-review of the control system failure analysis and a submittal of " Qualitative Event Analysis" to address the staff's concerns and questions. The licensee's proposal was found acceptable in Section 7.7.3.1' of NUREG-0853, Supplement 6 (Reference 1) and was made a licensing condition for Clinton full power operation by 14RC letter to IP dated April 17, 1987 i
(Reference 2,'.
Ly letter dated November 18,1988(Reference 3),IPCOsubmitted the required analysis. The submittal consisted of a " Comminatory Qualitative 1
Event Ar.alysis," licensee's ansheer to the six NRC questions, and a proprietary l
quantitative analysis of a special transient event by General Electric.
The scope of the licensee's analysis was defined in letters dateo April 17, May 15 and July (16,'1986 (Rafs. 4-6),
Additional information was submitted on March 20, 1989 Ref.7). The worst case event ide.1tified is the loss of feedwater heating with turbine trip and main ste6m turbine bypass failure.
1 The submittal included a General Electric transient analysis (Pef. 8) which i
assemed a 1004 loss of feedwater temperature which showed no fuel damaDe.
However, actual Clinton Station operating experience showed that a feedweter t s perature drop greater than 0 0'F could occur.
The licensee analyses included the effect of a single active failure in a mitigating safety system to assure that a sufficient number of such systems will be available for accident mitigation.
In addition, the licensee N NOobk
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connitted to several improvements to minimize the probability of loss of feedwater heating and to instituting several operating procedure changes to either prevent or effectively mitigate feedwater losses.
2.0 REACTOR SYSTEMS EVALUATION The approach taken in the reanalysis was to attempt to identify the non-safety control systems which could af feet the reactor. All failure modes of these systems were identified and assessed for event sequences that may not be bounded by the existing FSAR Chapter 15 analysis. The worst case identified is the loss of feedwater heating with turbine trip and failure of the turbine bypass system. An analysis of this event by GE showed that fuel damage would not occur if the feedwater temperature decrease is limited to 100*F. However,
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Clinton has experienced a loss of feedwater heating with a temperature drop grcater than 100*F (Ref. 9).
The submitted study was carried out by QUADREX, a licensee consultant. The object of the analysis is to determine whether the consequences of multiple control system failures are bounded by the Clinton FSAR Chapter 15 events and whether the failures would have on adverse effect on the ability to achieve plant cold shutdown conditions. The methodology assumed that all combinations of non-safety related control system failures are considered likely to occur, regardless of power source, connon instrument sensor, or proximity to a high energy lir,e. The Chapter 15 events were not trodified, rather, they were considered initiating events that were examined for potential exacerbation by non-safety control system failures. However, systems comprised of structures alone or information systems that merely provide alarms, annunciations, or information to the control room operators were not considered.
In addition, systems whose failures would not affect reactor parameters or influence plant operation were eliminated from further analysis. Thus, the systems combinations examined whose failure could affect reactor parameters are:
loss of feedwater heating combined with non-safety related control system failures feedwater controller failure combined with non-safety related control system failures turbine pressure regulator failure combined with non-safety related control system failure safety / relief valve opening inadvertent RHR shutdown cooling operation generator load rejection with no turbine bypass combined with non-safety related control system failures turbine trip combined with non-safety related control system f ailures closure of main steam line isolation valves combined with non-safety related control system failures
l l,
loss of condenser vacuum combined with non-safety related control system failures feedwater line break combined with non-safety related control system failures loss of instrument air combined with non-safety related control system failures 1arge steam pipe break outside containment combined with non-safety related control systems failures loss of coolant accident inside containment combined with non-safety related control system failures, and main condenser offgas treatment system failure combined with non-safety related control system failures All of the 6bove cases were found to be bounded by the results of the relevant Chapter 15 analyses except for the loss of feedwater heating conibined with turbine trip and no turbine bypass. The licensee submitted a GE analysis which shows that for a 100*F loss of feedwater heating combined with turbine trip and failure of the turbine bypass system no fuel cladding damage is predicted. The peak pressure is estimated at 1,250 psia which is below the ASME Code Section III Service Level B design limit of 1,375 psia.
In addition, analysis reporting GE results show that for reactor operation at power levels lower than 95.6% of rated power, feedwater temperature reductions greater than 126 F will result in operation exceeding the MCPR safety limit, thus, can result into fuel damage (Ref.7). Therefore, because the Clinton system design is such that a greater than 100*F feedwater temperature drop can occur, the licensee committed to implement (prior to the second cycle start-up) the following changes to decrease the likelihood of loss of feedwater heating and increase the indicating range of feedwater temperature inputs to the main control room:
the licensee will institute operator procedures to shut the reactor down if feedwater heating delte-T approaches 100*F.
the 48V DC and the AC power supplies will be coordinated te improve circuitry reliability tne level trip setpoint for the extraction steam valves will b6 raised from 6.5 to 16.0 inches to allow level transients to be mitigated by automatic and operator actions prior to isoleting the extraction steam flow to the heater drains during power ascension the control valves in the heater drain system will be " toned" to ensure that their tru sient response is correctly adjusted, and the range of the feedwater temperature inputs to the main control room will be increased from a dif ference of about 115'F to about 250*F
We find the improvements in feedwater heating temperature monitoring, the improvements in the operation of extraction steam flow and the new operating procedures which instruct the operator to shut the reactor down if the feedwater temperature reduction is approaching 100"F to be acceptable.
3.0 INSTRUMENTATION AND CONTROL SYSTEMS. EVALUATION The " Comminatory Qualitative Event Analysis" postulated the possible f ailure modes of each nonsafety-related control system identified in Section 7.7 of the FSAR. The assumption was that all combinations of these nonsafety-related control system failures can occur to exacerbate the initiating event mechanisms identified in the FSAR Chapter 15, i.e., failure of common power bus, instrument sensor, or HELB. Each FSAR Chapter 15 event scenario was analyzed with this assumption to determine if the effects were beyond the bounds of the existing FSAR Chapter 15 analysis. The criteria for this determination were based on a
'" qualitative analysis" of how the nonsafety-related control system failures affect the reactor parameters. Those control systems whose failure would not affect reactor parameters were eliminated from further analysis. The following four control systems tailures were found to affect reactor parameters, initiate engineered safety feature systems or trip nonsafety-related equipment.
1.
Recirculation Flow Control 2.
Feedwater Control 3.
Pressure Regulator and Turbine-Generator Control 4.
Anticipated Transient-Without-Scram (ATWS) Control The staff requested the licensee to verify that all higher voltage power source failures were used in the analysis such that the loss of the higher voltage bus, as the common power source to various control systems, caused an event which was bounded by the existing analysis in Chapter 15 of the FSAR. The licensee was further requested to provide a positive statement regarding the requested analysis. The licensee's " Comminatory Qualitative Event Analyses" postulated failure of all nonsafety-related control systems regardless of the cause, i.e.,
failure or malfunction of its power sources or instrument power supplies. The effect of the failure of 120 volt AC to 6900 volt AC (including all intermediate AC voltages), and 125 volt DC, was included in the analysis.
In addition to this analysis, a review was made to assure that no safety-related equipment, instrument or control systems were supplied from nonsafety-related AC or DC buses. Based on this qualitative analysis, the licensee has provided a positive statement as required by the staff. The statement assures that the failure of electric power, leading to multiple control system failures, would not result ir, an event which was not bounded by the FSAR Chapter 15 analysis.
In the conclusion section of their "Conbinatory Qualitative Event Analysis" of the hansafety-related control systems failure, IP provided the following statement.
A further conclusion of this analysis is that multiple failures of nonsafety-related control systems at CPS do not impact the capability of safety-related systems, as required by NRC IE Notice 79-22.
Furthermore, loss of electrical power to instrumentation and control systems does not affect the ability to achieve a colo shutdown condition, as required by NRC IE Bulletin 79-27.
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The staff does not agree with this conclusion due to the following reasons.
l 1.
IP's analysis of the nonsafety-related control system failure to I
determine if the consequences of these failures were within those analyzed in the FSAR Chapter 15 has no correlation with IE Bulletin 79-27 concerns.
i This Bulletin required licensees to review the effects of loss of power to each Class IE and non-Class IE bus supplying power to plant instrumentation and controls, and on the operator capability to achieve a safe- (cold) shutdown condition using plant operating procedures following the power loss.
2.
IP's analysis is comminatory qualitative which does not actually fail a bus to determine components, controls and instrumentation lost due to the bus failure. Rather all nonsafety-related control systems are failed regardless'of the power supply. An analysis for IE Bulletin 79-27 concerns is a quantitative analysis where the affect of loss of each component, control and instrumentation supplied by a failed bus is evaluated.
This discrepancy was discussed with the licensee in a telecon and it was agreed to consider the subject statement void.
4.0 CONCLUSION
We have reviewed the Illinois Power submittal providing information supporting deletion of license condition 4 for the Clinton Power Station. License condition 4 regards multiple non-safety control system failures, resulting from incividual high energy line brakes. Analyses showed that the only case which is more severe than existing chapter 15 events is the loss of feedwater heating with turbine trip and no turbine bypass. Analyses further indicated that loss of feedwater heating up to 100*F with turbine trip end bypass failure is acceptable. The licensee committed to hardware and procedural changes which will minimize the probability for loss of feedwater heating and procedures instructing the operator to shut the reactor down in the event the feedwater heating temperature loss is approaching 100*F. Given that the loss of feedwater heating is a gradual and detecteble change, operator action based on protedures is accoptable.
Based cn the above evaluation, the staff concludes that the licensee's
" Comminatory Qualitative Event Analysis" adequately addresses the staff's concerns regarding less of electric power to the ronsafety-related control systems. The analysis has followed the guidelines provided in the steff's request for additional information and methodology approved in NUREG-0853, Supplement 6, and is, therefore acceptable.
5.0 REFERENCE $
1.
HUREG-0853, Supplerrent 6, " Safety Evaluation Report Relsted to the Operation of Clinton Power Station, Unit No. 1," July 1986 2.
Letter from Gary H. Holahan, NRC to Frank A. Spangenberg, Illinois Power Company, dated April 17, 1987
3.
Letter from D. L. Holtzscher, Illinois Power Company to USNRC "Clinton Power Station, License Condition 4, Control System failures," dated November 18. 1988.
4.
Letter form F. A. Spangenberg, Illir.ois Power Company to W. B.
Butler, NRC, *Clinton Power Station Response to Request for Additional Information Related to Control Systems Failure," dated April 17, 1986.
5.
Letter f rom F. A. Spangenberg, Illinois Power Company to W. R.
Butler, NRC, "Clinton Power Station Control Systems failure Analysis SER Outstanding Licensing Issue #15," cated May 15, 1986.
6.
Letter from F. A. Spangenberg, Illinois Power Company to W. R. Butler, NRC, "Clinton Power Station, Control System Failure Reanalysis SER Outstanding Licensing ~ Issue #15," dated July 15, 1986.
7.
Letter from D. L. Holtzscher, Illinois Power Company to USNRC, "Clinton Power Station License Condition 2.C(4), Control System Failure," dated March 20, 1989.
8.
EAS-18-0388, "Special Transient Event Analysis to Support Control System Thilure Analysis for Clinton Power Station" by S. Wolf and A. Horna, GE huclear Energy, dated March 1988.
9.
LER 88-25, " Loss of Feedwater Heating System Transient Outside Design Basis Due to Inappropriate Level Controller Setting," by R. D.
Freeman, dated July 28, 1988.
Dated:
May 15, 1989 l
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