ML20126F906
| ML20126F906 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 12/23/1992 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20126F901 | List: |
| References | |
| NUDOCS 9212310194 | |
| Download: ML20126F906 (8) | |
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SAFETY EVALUATION BY THE OFFICE OF NVCLEAR REACTOR REGULATION RELATED TO AMENDMENT NQ.167 TO FAcIllTY OPERATING LICENSE NO. DPR-65 NORTHEAST NUCLEAR ENERGY COMPANV, IllE C0f(NECTICVT LIGHT AND POWER COMPANY THE WESTERN MASSACHUSETTS ELECTRIC COMPANY MILLSTONE NUCJ, EAR POWER STATION._ UNIT NO. 2 DOCKET NO. 50-33fi
1.0 INTRODUCTION
By letter dated October 28, 1992, as supplemented November 20, 1992, and December 4,1992, Northeast Nuclear Energy Company (the licensee) submitted an application for amendment of the operating license for Unit 2 at the Millstone Nuclear Power Station (Ref. 1).
The proposed amendment would change the technical specifications to permit the licensee to modify instrumentation and-adjust setpoints to provide additional assurance that a main steam line break accident would not cause pressure and temperature in containment to exceed values for containment design and equipment qualification.
2.0 BACKGROUNQ in 1979, the licensee analyzed the main steam line break (MSLB) accident to demonstrate that the containment would withstand an MSLB accident. The-analysis assumed that the reactor was at hot zero power, that the break was double-ended and was located between the steam generator and the inboard main steam' isolation valve (MSIV), and that an emergency diesel generator failed to operate resulting in failure of one of two containment spray pumps and two of four containment air recirculation fans.
The analysis demonstrated that the pressure and temperature in containment would be less than the design pressure and temperature for the containment.
On February 8,1980, the staff issued Bulletin 80-04, ' Analysis of a PWR Main Steam Line Break with Continued Feedwater Addition." The bulletin. requested that licensees review their analyses of the MSLB to determine whether continuation of main feedwater, auxiliary feedwater, or condensate flow would adversely affect pressure in containment.
The staff, with assistance from Franklin Research Center, reviewed the licensee's response _and concluded that there is no aotential for overpressurizing containment because the reactor would be at Tot zero-power, the main feedwater would be isolated from the 9212310194 921223 PDR ADOCK 05000336 P
. steam generators, and the initiation of auxiliary feedwater flow to the affected steam generator would be delayed.
The staff concluded that the licensee's response was acceptable (Ref. 2).
On October 18, 1991, while the unit was operating at full power, and during planning for replacement of the steam generators, the licensee determined that the existing MSLB accident analysis was no+ conservative with respect to containment response.
The licensee notified the NRC and reduced reactor power to 3% (Ref. 3).
These actions were based on an analysis by the -licensee that assumed that an MSLB occurs while the reactor is operating at full power, that one of two main feedwater regulating valves fails to close automatically, and that an operator closes the valve after 10 minutes (Ref. 4). The licensee stated that the analysis indicated that pressure and temperature in the containment would reach 92 psig and 427'F because of the flow of feedwater to the containment through the failed main steam line.
The design pressure and temperature for the containment are 54 psig and 289'F (Ref. 3).
The licensee prepared a justification for continued operation (Ref 4) and the unit was returned to power.
Initially, the licensee stationed a dedicated operator at the controls for the main feedwater block valves with instructions to close them if the reactor shut down automatically.
Later, the licensee modified the main feedwater block valves to close automatically on a
-containment isolation signal and thus precluded the need for a dedicated operator.
On Argust 4, 1992, the licensee found two more conditions which would cause pressure and temperature to exceed the design values for the containment during an MSLB accident. One of the conditions was failure of the feedwater regulating bypass valve to stop the flow of feedwater to a steam generator, lhe other was failure of the vital buses to fast transfer to the reserve station services transformer.
If this occurred, power would not be available to close the feedwater regulating valves and start the containment pressure control systems until the emergency diesel generators started and loaded (Ref 4).
To provide permanent solutions to these problems, the licensee modified the facility as permitted by 10 CFR 50.59, proposed changes to the technical specifications as described in their application dated October 28,1992 for amendment to the operating license, and provided additional information to support their application on November 20 and December 4, 1992 (Ref. 5 and 6).
3.0 CHANGES TO THE FACILITY L
3.1 Engineered Safety features Actuation. System l-l
. Prior to modification of the engineered safety features actuation system, a main steam isolation signal was generated when the output of two of four steam generator pressure channels dropped to the low pressure setpoint. The system l
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. was modified to connect four containment pressure channels to the system.
These channels generate a main steam isolation signal when the outputs of two of the channels exceed the high pressure setpoint.
3.2 Main feedwater System Prior to modification of the control circuitry for the main feedwater system, single main steam isolation signals were connected to the pumps, the block valves, the regulating valves, and the bypass regulating valves for the main feedwater system.
Redundant main steam isolation signals were added to each of these components.
Redundant main steam isolation signals were also added to the pump discharge valves which isolate main and main bypass feedwater on closure.
In addition, the source of control power for the main feedwater regulating valves was changed from normal power to vital power with battery backup.
3.3 Emergency Diesel Generators (EDGs)
Prior to modification of the control circuitry for the EDGs, the diesel engines started automatically only on initiation of a loss of normal power signal.
The control circuitry has been modified to add automatic starting on initiation of a safety injection actuation signal (SIAS).
4.0 PROPOSED CHAf1GES TO THE TECHf41 CAL SPECIFICAll(Lilji 4.1 Isolation of the Main Steam System An existing limiting condition for operation (LCO) requires that three of four steam generator pressure channels be operable when the reactor is in modes 1, 2, or 3 and that a main steam isolation signal be initiated when any two of th? channel outputs reach the cetpoint. The proposed change to the technical specifications would add an LCO setting forth similar requirements for the containment pressure channels.
The proposed change wculd also include an LC0 requiring that the setpoint for these channels be < 4.75 psig and the allowable value be < 5.20 psig, in addition, the proposed change to the technical specifications would require the same periodic surveillance for the containment pressure instrumentation which is now required for the steam generator pressure instrumentation.
4.2 1 solation of the Main Feedwater System for main feedwater isolation from a steam generation low pressure signal, an existing LC0 requires that the response time, including signal generation and valve closure, be < 60 sec.
The proposed change to the technical specifica-tions would require that the response time be < 14 sec.
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. 4.3 Actuation of the Containment Spray System Existing LCOs require that the containment spray system actuate automatically when containment pressure is < 27 psig with an allowable value that is < 27.45
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psig and a response time that is < 35.6 sec with or without normal poweiF available.
The proposed change 16 the technical specifications would reduce the actuation setpoint to 5 9.48 and the allowable value to $ 10.11 psig, further, the proposed changes to the technical specifications would reduce the containment spray response time from $ 35.6 see to $ 16 see with normal power available.
4.4 Actuation of the Containment Air Recirculation System Existing LCOs for the response time of the containment air recirculation system to a high containment pressure sigi,a1 or a low pressurizer pressure are
< 31 see with or without normal power available.
The proposed change to the Technical specifications would change this value to < 15 sec with normal power available and to $ 26 see without normal power available.
4.5 Actuation of the Charging Pumps and the Safety injection System Existing LCOs for the response time of the charging pumps to a low pressurizer pressure signal or a high containment pressure signal is < 40 see with or without normal power available. The proposed changes to lhe technical specification would change the response time to $ 35 see with or without normal power available.
Existing LCOs the response time of the high and low pressure safety injection systems to a low pressurizer pressure signal or a high containment pressure signal are < 30 sec and < 50 sec respectively without normal power available.
The proposed changes to The technical specification would change the response times to $ 25 sec and $ 45 sec.
4.6 Actuation of the Enclosure Building Filtration System Existing LCOs for the response time of the enclosure building filtration system to a high containment pressure signal or a low pressurizer pressure signal is < 50 sec with or without normal power available.
The proposed changes to the technical specification would change the response time to < 45 see with or without normal power available.
4.7 Startup of the EDGs Existing LCOs require that the EDGs achieve > 97 percent of rated voltage in
< 20 sec.
The proposed change to the technical specifications would reduce That value to $ 15 sec.
- 4.
5.0 LyALUATIQB 5.1 Containment and Safety-related Equipment if an MSLB accident were to occur, two main steam isolation signals would be initiated.
Each signal would demand closure of the MSIVs the main feodwater regulation and block valves, and the main feedwater bypass regulation valve in one train of the steam generation system, if the accident were to occur at full power and if a main steam isolation signal were not generated for-the steam generator with the f ailed steam line, then feedwater would flow to the containment through the broken steam line until the main feedwater was isolated.
If an operator were to fail to isolate main feedwater promptly, pressure and tem)erature in containment would exceed the design values.
To assure that t11s does r9t occur, the licensee provided redundant main steam isolation signals to both main feedwater trains.
The licensee has also provided redundant main steam isolation signals to the main feedwater pump discharge valves which previously did not receive a main steam isolation signal.
Further, the licensee has modified the engineered safety features actuation system to generate main steam isolation signals on high containment pressure as well as low steam generator pressure.
To reduce the challenge to containment, the licensee will assure that:
(a) the feedwater isolation response time is reduced by a factor of 4.2, (b) containment gauge pressure at which containment spray is initiated is reduced by a factor of 2.7 and (c) the EDGs are started 5 sec earlier.
With these changes assumed to be in place, the licensee analyzed the MSLB accident with various single failures.
For the cases analyzed, the maximum peak pressure in the containment was 53.7 psig and the maximum peak temporal and spatial temperature in the containment atmosphere was 425.4*F (Ref. 6).
Because of the difference in masses and thermal capacities of the containment atmosphere and the components and materials contiguous with the containment atmosphere, it would cool rapidly after the discharge of feedwater and steam is sto) ped, and components and materials contiguous with the containment atmospiere would heat up slowly. With the containment atmosphere at saturation, the expected temperature and pressure are estimated to be 285'F (Ref 3) and 38.5 psig.
The safety-related equipment in containment is environmentally qualified for temperatures up to 289'F.
Containment response and Equipment Qualification issues will be evaluated in response to a separate submittal.
The staff also looked at the potential for the changes to the facility and the-proposed changes to the technical specifications to increase.the probability of other accidents which were previously evaluated and the probability of a malfunction of equipment important to safety..The licensee-indicated that the probability of occurrence of loss of load and an MSIV closure type of event could be'affected (Ref. 1).
Since the high containment pressure signal is-two out of four logic, the impact on the probability of an inadvertent MSIV closure is negligible. Also, since the probability of an inadvertent main steam isolation or an SIAS signal is not signi_ficantly increased by the-proposed plant changes, therefore, any resultant damage to or wear of
, equipment important to safety, actuated by these signals, would not be significantly affected.
The staff has evaluated the licensee's assessment and finds that there will be no significant change in the probability of an accident previously evaluated or the probability of occurrence of a malfunction of equipment affected by the proposed plant changes.
The staff concludes that the changes to the facility and the pro)osed changes to the technical specifications will provide assurance t1at challenges to containment and qualification of equipment within containment will not exceed design values for pressure and temperature.
5.2 Core The licensee has provided its assessment of the effect of the proposed changes described in Sections 3.0 and 4.0 of this evaluation on the core response to an MSLB or a loss-of-coolant accident (LOCA) (Ref. 6).
For the HSLB, the following cases were analyzed:
(a) hot zero power (HZP) with normal power-available, (b) HZP without normal power available, (c) hot full power (ilFP) with normal power available, and (d) HFP without normal power available.
The licensee concluded that the proposed changes that could impact the MSLB cases are beneficial and, thus, the existing analysis in the docket remains bounding.
For the LOCA analysis, the licensee has evaluated the effect of each of the proposed changes on the small break and large break LOCAs and has concluded that those changes are either bounded by-the assumptions used in the existing analysis or cause only a negligible effect to the existing analysis, i
The staff has evaluated the licensee's assessment and finds that the LOCA analysis of record is not affected by the proposed plant changes and does not require reanalysis.
5.3 EDGs The original design for the EDGs included a requirement to start automatically on either an SIAS or loss of normal power (LNP) signal.
The EDG start time was 20 seconds. On an SIAS signal the EDGs start automatically and run but would not load until an LNP signal was received.
The licensee determined that if the EDGs operated unloaded, this could cause undesirable conditions and could render the EDGs inoperable and unavailable. As a result the licensee elected to modify EDG initiation logic to remove the starting of the EDGs on the SIAS signal. The starting of the EDG on a LNP signal was not changed.
After the MSLB was reanalyzed, the licensee determined that the EDG start time should be reduced by 5 seconds and that the EDGs should start on an SIAS signal allowing an earlier response time for the containment spray and containment air recirculation systems.
To meet the MSLB reanalysis, the licensee has proposed to start the EDGs on an SIAS signal per the original design.
The licensee has reevaluated the EDG actuation on an SIAS signal and has concluded that operation of an EDG unloaded will not adversely affect the reliability or availability of the EDG.
An EDG start on an SIAS signal without loss of normal power would require the
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. manufacturer it would not cause any adverse oEDG t e and according to the licensee has implemented procedures from th r undesirable condition.
is operated under no-load or light load conditie manufacturer that afte The be run at > 75 percent load 2076 KW) for at least 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> before shutdowno I
This will addition, firevent fouling or(other damage to the diesel ge the licensee will test the SIAS signal prio committed to propose an additional change to the te h ir to operation In include a surveillance requirement for the SIAS c n cal specifications to signal every 18 months.
Additionally, the licensee has also evaluat dstart w e
capability.
specifications to include the 15 second start timeTherefore requirements.
o the technical as part of the surveillance The staff finds the licensee's proposed cha to reduce the start time for the EDGs by 5 snges to start on an SIAS h] ATE COU1VLLA.llDE econds to be acceptable.
6.0 in accordance with the Commission's regulatio of ficial was notified of the proposed issuance o,f ththe Connecticut St ns official had no comments.
e amendment.
The State 7.0
[lillROMilallQU11DIMUDB Pursuant to 10 CFR 51.21, 51.32, and 51 35 LEsteral Register on December 23 finding of no significant impac upon the environmental assessmen,t 1992 (57 FR 61101).e ared and published in the Accordingly based human environment.of the amendment will not have a s,ignificant effect on the quality of the 8.0
[QE Ulll0S The Commission has concluded, based on the consid that:
public w(ill not be endangered by operation in the p1) activities will be conducted in compliance with th and safety of the and (3 roposed manner
- 2) such defense) and security or to the health and safety the issuance of the amendment will not be ini ie Commission's r,eg(ula m cal to the common of the public.
. EDG to run unloaded for a short period of time and according to the manufacturer it would not cause any adverse or undesirable condition.
The licensee has implemented procedures from the manufacturer that after the EDG is operated under no-load or light load conditions the diesel generator.shall be run at > 75 percent load (2076 KW) for at least:2 hours before shutdrwn.
This will jirevent fouling or other damage to the diesel generator.
In addition, the licensee will test the SIAS signal prior to operation and has committed to propose an additional change to thc technical specifications to l
include a surveillance requirement for the SIAS signal every 18 months.
Additionally, the licensee has also evaluated the capability of the EDG to start within 15 seconds and concluded that the EDG has the necessary capability.
Therefore, the licensee proposed the change to the technical specifications to include the 15 second start time as part of the surveillanca requirements.
The staff finds the licensee's proposed changes to start on an SIAS signal and to reduce the start time for the EDGs by 5 seconds to be acceptable.
6.0 STATE CONSULTATION
in accordance with the Commission's regulations, the Connecticut State official was notified of the proposed issuance of the amendment.
The State official had no comments.
7.0 ENVIRONMENTAL CONSIDERATION
Pursuant to 10 CFR 51.21, 51.32, and 51.35, an environmental assessment and finding of no significant impact have been prepared and published in the Federal Reaister on December 23, 1992 (57 FR 61101). Accordingly, based upon the environmental assessment, the staff has determined that the issuance of the amendment will not have a significant effect on the quality of the human environment.
8.0 CONCLV510N The Commission has-concluded, based on the considerations discussed above, that:- (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common 1
defense and security or to the health and safety of the public.
e..
9.0 REFERENCES
i (1) Northeast Nuclear Energy Company, letter to NRC, Docket 50-336, " Proposed Revision to Technical Specifications Main Steam Line Break Design Limits," dated October 28, 1992.
(2) HRC, letter to Northeast Nuclear Energy Company, Docket _50-336,
" Resolution of Main Steam Line Break with Continued Feedwater Addition Event for Millstone Nuclear Power Station, Unit No. 2," dated October 7, 1982.
(3) Northeast Nuclear Energy Company, Docket 50-336, Licensee Event Report 91-010-02, dated September 2, 1992.
(4) Northeast Nuclear Energy Company, " Millstone Unit No. 2, Justification for Continued Operation #2-91-1, Main Steam Line Break Inside Containment," to be implemented 10/21/91.
Docketed on November 24, 1992.
(5) Northeast Nuclear Energy Company, letter to NRC, Docket 50-336, " Proposed Revision to Technical Specifications, Main Steam Line Break Design Limits, Response to Request for Additional Information," dated November 20, 1992.
(6) Northeast Nuclear Energy Company, letter to NRC, Docket 50-336, " Proposed Revision to Technical Specifications, Main Steam Line Break Design Limits, Response to Request for Additional Information," dated December 4, 1992.
Principal Contributors:
R. Woodruff C. Liang C. Thomas S. Mazumdar Date:
-December 23, 1992