ML20059M851
| ML20059M851 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 10/02/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20059M847 | List: |
| References | |
| NUDOCS 9010050327 | |
| Download: ML20059M851 (5) | |
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION
$UPPORTING AMENDMENT NO.113 TO PROVISIONAL OPERATING LICENSE NO. DPR-19 AND_ AMENDMENT NO.109 70 FACILITY OPERATING LICENSE NO. DPR-25 i
COMMONWEALTH EDISON COMPANY DRESDEN NUCLEAR POWER STATION, UNITS 2 AND 3
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DOCKET N05. 50-237 AND 50-249
1.0 INTRODUCTION
J In July of 1984 the Code of Federal Regulations was amended to include Section 10 CFR $0.62, " Requirements for Reduction of Risk from Anticipated Transients Without Scram (ATWS) Events for Light Water Cooled Nuclear Power Plants." An ATWS is an expected operational transient which is accompanied i
by a failure of the Reactor Protection System (RPS) to shutdown the reactor.
In summary, the ATWS rule required the following elements for boiling water reactors such as Dresden:
1.
A recirculation Pump Trip (RPT) system that automatically trips the recirculation pumps under an ATWS condition.
2.
A Standby Liquid Control system (SLCS) with a minimum flow capacity and boron content equivalent in control capacity to 86 gallons per minute of 13 weight percent sodium pentaborate solution.
In May of 1989, this requirement was amended to clarify the assumed isotopic enrichment of Boron-10 (natural) and assumed vessel size (251 inch diameter) for these flow rate and concentration values and to acknowledge the use of equivalent values.
3.
An Alternate Rod Insertion (ARI) system that is diverse from the RPS and has redundant scram air header pressure exhaust valves.
CommonwealthEdisonCompany(Ceco)participatedintheBWROwnersGroup (BWROG) development of the licensing topical report that addressed the ATWS rule (Licensing Topical Report, Anticipated Transients Without Scram -
Response to NRC ATWS Rule 10 CFR 50.62, General Electric Company NEDE-31096-P, December 1985). The staff subsequently issued a safety evaluation report (Letter, G. Lainas to T. A. Pickens (BWROG), Acceptance for Reference of LTR-31096-P, October 21,1986) which defined the basis for NRC's acceptance of the GE licensing topical report (LTR).
In a letter dated September 30, 1987, Ceco endorsed the GE LTR.
Subsequently, modifications were implemented at Dresden that satisfied the ATWS rule.
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In a letter dated September 29, 1989 and supplemented in a letter dated February 1,1990, Ceco proposed to amend the Dresden Technical Specifications (TS) for Dresden Units 2 and 3 to reflect the completion of modifications to the SLCS and the addition of the ATWS RPT. ARI requirements were not proposeo by Ceco since the BWROG and staff have nat, as yet determined the need.
The February 1,1990 submittal provided additional,information and did not j
alter the proposed action noticed in the Federal Register on November 15, 1989 and did not affect the initial determination.
2.0 EVALUATION i
2.1 StandbyLiquidControlSystem(SLCS)
Ceco has proposed changes to SLCS TS that are consistent with the require-ments of the ATWS Rule 10 CFR 50.62.
These proposed TS changes reflect completed modifications to the SLCS which: 1)increasetheconcentrationof sodium pentaborate in the SLCS tank to 14 weight percent in conjunction with
'he capability to operate both SLCS pumps simultaneously at a total combined flow rate of 80 gpm; 2) establish a minimum deliverable sodium pentaborate decahydrate solution volume of 3329 gallons; 3) establish a minimum volume of 3605 gallons of sodium pentaborato decahydrate in the tank to assure the minimum deliverable volume and concentration; 4) permit the manual testing of the system (except explosive valves and pump solution) to demonstrate the pump suction line is not plugged; 5) increase the relief valve pressure setting range by 55 psig; and 6) raise the solution saturation temperature from 59'F to 62'F.
The stiff has reviewed the TS changes proposed by Ceco for t5e SLCS for t-l Dresder Units 2 and 3 against the requirements of the ATWS rule 10 CFR 50.62 and cont.luded the following.
I Increasing the SLCS sodium pentaborate concentre. ion to 14 weight percent in g
conjunction with a flow rate of 80 gpm provides a boron content equivalent l
in control capacity to 86 gpm of 13 weight percent sodium pentaborate.
This l
1s in compliance with 10 CFR 50.62 and is, therefore, acceptable.
Ceco's proposal to change the TS required liquid poison tank volume to a minimum 3329 deliverable gallons is acceptable because, with an increased solution concentration of 14%, 3329 gallons will provide the equivalent amount of poison and shutdown mergin as required by 10 CFR 50.62.
Establishing a minimum poison tank volume of 3605 gallons of sodium pentaborate decahydrate solution in the TS to account for the tank volume below the pump suction assures that the 3329 gallons of poison required is deliverable and is, therefore, acceptable.
Specifying the minimum solution concentration and minimum gallons of solution in the tank eliminates the need for the existing Figure 3.4.1 which provides a Boron Concentration versus Solution Volume Curve and is, therefore, acceptable.
Additionally, the proposed surveillance to manually initiate the system once per operating cycle to demonstrate flow path integrity utilizing a single pump instead of hth pumps simultaneously is acceptable. This is based upon l
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, CECO's performance of initial two pump tests, correlation of single pum data to the initial two pump data, and subsequent comparison of periodic sin le pump test data with previous results and to initial test data for verif cation of systems capability.
Increasing the poison solution temperature from 59'F to 62*F to assure the increased concentration of sodium pentaborate will remain in solution is acceptable.
Revised surveillance requirements were also proposed to increase the allowable TS setpoint band for the system pressure relief valves from the current range of 1400 - 1490 psig, to a band of 1455 - 1545 psig because of increased pump discharge pressure during two pump operation. Accordingly, the allowable system pressure relief valve setsoints have been increased by approximately 55 psig and we find this accepta>1e.
New and revised TS bases were proposed to reflect the above changes which we find acceptable.
2.2 Recirculation Pump Trip (RPT)
TS changes proposed by Ceco that reflect the installation of the RPT system have been reviewed by the staff against the requirements of the ATWS N1e (10CFR50.62). Ceco's proposed changes include the incorporation of nigh reactor pressure and low-low reactor water level instrumentation that initiates recirculation pump trip and the associated operability and surveillance requirements into the TS. The RPT on low-low reactor level h6; an associated nine second time delay to lessen the severity of a postulated design basis Loss-of-Coolant Accident. To prevent spurious ATWS initiation a two-out-of-two taken once logic is employed.
Since tho Dresden RPT system was modeled after the Monticello design which the staff approved in its safety evaluation report dated October 21, 1986, as previously mentioned, the incorporation of the low-low reactor water inel trip and high reactor pressure into the TS for the instrumentation that initiates RPT is acceptable.
However, the staff, during its review of Ceco's submittal, identified two issues related to the RPT that required additional information.
The first issue is related to the ATWS RPT high pressure setpoint of 1240 psig which is considerably higher than the General Electric STS value of 1120 psig.
In its February 1,1990 response, CECO cited a General Electric Analysis (MSIV Closure Event with ATWS/RPT and ARI for Dresden Units 2 and 3 and Quad Cities Units 1 and 2, NSE-45-0880, August 1980) and stated that this higher setpoint is designed to avoid ATWS RPT initiation during design basis pressurization transients, such as Load Rejection Without Bypass. ATWS RPT initiation during these pressurization transients is undesirable since it will increase the severity of the event. This adverse impact is of particular concern since a non-ATWS pressurization transient is considerably more likely to occur than a pressurization event with failure to scram.
4 e With the proposed setpoint, the only non ATWS pressurization transient that would result in an ATWS RPT initiation is the closure of all Main Steam Isola-tion Yalves (MSIV) with a failure of direct scram on MSIV position. This I
transient scenerio does not credit the electromatic relief valves and assumes i
that the terminating scram signal is generated by high neutron flux. Although ATWS RPT initiation will cause the peak vessel pressure for this event to increase, margin to the ASME oversressure limit of 1375 psig is maintained.
1 CECO has stated that this margin las been and will continue to be, verified for each new reload core design specifically including the effects of the ATWS RPT.
Although the proposed setpoint increases the peak pressure during a limiting ATWS event (compared to ATWS peak pressure with the GE STS value) it still remains below the ASME Service Level C over)ressurization limit of 1500 psig based on the General Electric analysis. T1e higher RPT setpoint used at the Dresden and Quad Cities units produces acceptable ATWS peak pressures primarily due to the larger total capacity of the 13 relief and safety valves compared to BWRs of similar vintage, which typically have fewer valves and lower overall capacity.
The staff has determined, based on:
- 1) the results of the General Electric i
analysis; 2) the larger relief and safety valve capacity at Dresden compared to sin.Ilar BWRs; 3) the desirability)of avoiding ATWS RPT during i
design basis pressurization transients; and 4 the peak pressure during a limiting ATWS event remaining below the ASME Service Level C overpressuri-zation limit of 1500 psig, that Ceco's high pressure setpoint of 1240 psig for ATWS RPT is acceptable.
The second issue is related to the proposed test and calibration frequencies for the RPT system. The surveillance frequencies specified in the proposed TS utilize the currently applied intervals for Dresden 2 and 3 (i.e., functional checks quarterly and instrument checks daily). This is in l
contrast to the GE STS surveillance frequencies which have a functional j.
check monthly and an instrument check shiftly.
The )roposed frequencies, supported by General Electric recommendations, are tie surveillance frequen-7 cies that have been in place at Dresden since the installation of the ATWS RPT. CECO has reviewed the surveillance records going back to 1981 which j
showed that there were no instances where the initiation setpoints have drifted beyond the proposed values. A review of Quad Cities surveillances also showed similar results, with minimal or no adjustments needed over the past two years. This represents 22 reactor years of operation with no appreciable instrument drift. Based on the surveillance history, the staff has determined that the surveillance frequencies proposed by CECO are acceptable.
On the basis of the review of the information provided by Ceco, the staff has determined that the )roposed addition of TS and TS bases for ATWS RPT are acceptable and satisfy tie requirements of the ATWS Rule 10 CFR 50.62.
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3.0 ENVIRONMENTAL CONSIDERATION
These amendments involve changes to a requirement with respect to the instal-
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lation or use of a facility co:nponent located within the restricted area as q
defined in 10 CFR Part 20 and changes surveillance requirements. The staff 1
has detemined that the amendments involve 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 Commissip has previously I
issued a proposed finding that these amendments involve no significant hazards consideration and there has been no public coment on such finding.
Accordingly, these amendments meet the eligibility criteria for categorical exclusionsetforthin10CFR51.22(c)(9). Pursuant to 10 CFR 51.22(b) no environmental impact statement nor environmental assessment need be prepared in connection with the issuance of these amendments, j
4.0 CONCLUSION
The staff has concluded, based on the considerations discussed above that: (1)thereisreasonableassurancethatthehealthandsafetyofthe public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in conpliance with the Commission's regula-tions, and (3) the issuance of these amendments will not be inimical to the common defense and security nor to the health and safety of the public, i
Principal Contributor:
Byron Siegel/NRR/PDll!-2 Dated:
October 2,1990
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