ML17202U736
| ML17202U736 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 06/15/1990 |
| From: | Murley T Office of Nuclear Reactor Regulation |
| To: | Kovach T COMMONWEALTH EDISON CO. |
| Shared Package | |
| ML17202U737 | List: |
| References | |
| GL-89-16, TAC-74863, TAC-74864, NUDOCS 9007120089 | |
| Download: ML17202U736 (4) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 Docket Nos. 50-237 and 50-249 Mr. Thomas J. Kovach Nuclear Licensing Manager June 15, 1990 Commonwealth Edison Company - Suite 300 OPUS West I II 1400 OPUS Place Downers Grove, Illinois 60515
Dear Mr. Kovach:
SUBJECT:
STAFF'S BACKFIT ANALYSES FOR DRESDEN NUCLEAR POWER STATION UNITS 2 AND 3 REGARDING INSTALLATION OF A HARDENED WETWELL VENT (GENERIC LETTER 89-16} (TAC NOS. 74863 AND 74864}
In.SECY 89-017, "Mark I Containment Performance Improvement Program," of January 23, 1984, the staff.demonstrated that hardened wetwell venting capabilities at Mark I containments would prevent majority of severe accident sequences involving loss of decay heat removal capability (TW sequences} from resulting in core melt.
The staff also demonstrated that venting through a hardened vent ~ath from suppression pool airspace would significantly mitigate the risks to public health and safety, because substantial amounts of fission products released by core melt would be trapped in the suppression pool and would not be available for release to the environment.
Some benefits are also expected because of the prevention of severe accident sequences other than TW sequences from resulting in core melt. Based on'. the analyses in SECY 89-017, the staff informed the Conunission that the generic installation of hardened vent capabilities at Mark I containments would provide significant added benefits resulting from a reduction of severe accident risks to public health and safety.
On July 11, 1989, the Conunission responded to the staff reconunendations in SECY 89-017 and directed the staff to implement, *on a generic.basis, the installation.of hardened vent capabilities at boiling water reactors (BWRs}
with Mark I containments. Accordingly, on September 1, 1989 the staff issued Generic Letter 89-16 (GL 89-16}.
In that letter the staff urged the ~ffected licensees to voluntarily install hardened vent capabilities at their Mark I containments using the provisions of the Conunission's rules in 10 CFR 50.59. If the licensees chose not to install the hardened vent capability on a voluntary basis, the staff requested in GL 89-16 that the licensees provide their plant~sp~cific estimates of costs of installation of hardened vent capabilities. The licensees were.informed that the staff would use the cost data to perform plant-specific backfit analyses, and to determine if hardened vent installations could be imposed as backfits in accordance with the Conunission's backfit rule in 10 CFR 50.109.
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Mr. Thomas June 15, 1990 By letter of October 30, 1989, you responded to GL 89-16 indicating that you had decided not to commit to install hardened vent capabilities on a voluntary basis.
You also provided the staff with plant-specific cost
- estimates for modifications at Dresden Nuclear Power Station (Dresden),
Units 2 and 3.
Following the receipt of your October 30, 1989 letter, the staff initiated plant-specific backfit analyses for Dresden Units 2 and 3.
In its analyses, the staff used the plant-specific cost estimates that you provided.
The staff estimated the benefits of venting by determining the reductions in core damage frequencies (CDFs) for only the TW sequences.
The benefits were calculated by using the results of the probabilistic risk assessments (PRAs) for BWRs with Mark I containments and isolation condenser syst.ems (ICS') similar to Dresden Units 2 and 3.
The staff then adjusted the analyses to account for recent advances in the PRA methodology (NUREG-1150).
The results of the staff's analyses showed that for TW sequences alone the overall CDF for each of the Dresden Units 2 and 3 can be reduced by 1.4 E-5 per reactor year. The credit for the operation of the ICS was included in the analyses.
The analyses were~
adjusted to account for the power levels of Dre~den Units 2 and 3, and the.
density of population surrounding the Dresden site. The staff has calculated that for TW sequences alrine, the operation of vent would avert the expected radiological exposure to public by 50.2 man-rem per reactor year. Using 20 years of rem~ining plant life for Dresden.Unit 2, and 21 years for Dresden*
Unit 3 and plant-specific modification costs, the staff has estimated an averted radiological po~ulation exposu~e of 1005 man-rem per million dollars for Unit 2 and 1055 man-rem per million dollars for Unit 3.
The preceding results of the staff analyses demonstrate that hardened vent capabilities would provide significant benefits in the expected reduction in radiological exposure,risks posed by TW sequences.
The staff has also calculated the other averted costs that would*be associated with severe accidents. involving TW sequences to clean the site surroundings and to replace the lost power.
Assuming that the modification costs would be offset by the averted costs of cleaning the site surroundings and replacing power, the staff estimates that.1266 man-rem will be averted per million dollars for Dresden Uriit 2, and 1333 man-rem will 'be averted per million dollars for Dresden Unit 3.
The staff ha~ considered but not quantified the reduction in risks posed by (1) severe accidents other than TW sequences, and (2) scrubbing of the fission products in the suppression pool for accident sequences that result in significant damage to the core. These benefits provide added incentives for installation of a ha.rdened vent capability at Dresden Units 2 and 3.
Based on the preceding quantitative and qualitative discussions, the staff believes that there will be a substantial additional increase in protection public health and safety if a hardened vent capability is imp_lemented at Dresden Units 2 and 3. Therefore, the staff has concluded that the backfit is justified for Dresden*units 2 and 3. Copies of the staff's supporting analyses for Dresden Unit 2 (Enclosure 1) and Dresden Unit 3 (Enclosure 2) are enclosed for your information.
Mr. Thomas June 15, 1990 In light of the staff's backfit analyses, the staff urges that you reconsider your decision and commit to install a hardened vent capability at Dresden Units 2 and 3.
You are requested to inform the staff of your intent within 30 days of receipt of this letter.
You may implement your commitment under the provisions of the Commission's rules in 10 CFR 50.59, provided that the modifications are in place by January 1993.
In the absence of such a commitment, the staff intends to pursue the imposition of this backfit under the provisions of the Commission's backfit rule in 10 CFR 50.109.
Sincerely, Original signed by Thomas E. Murley, Director Office of Nu.clear Reactor Regulation
Enclosures:
- 1. Plant-Specific Backfit Analyses for
. *Dresden 2 2~* Plant-Specific Backfit Analysis for Dresden 3.
cc w/enclosures:
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Mr. Thomas J. Kovach-Commonwealth Edison Company_
cc:
Michael I. Miller, Esq.
Sidley and Austin One First National Plaza Chicago, Illinois 60690 Mr. J. Eenigenburg Plant Superintendent Dresden Nuclear Power Station Rural Route n Morris, Illinois 60450 U. S. Nuclear Regulatory Conmission Resident Inspectors Office Dresden Station
- Rural Route #1 Morris, Illinois 60450 Chairman Board*of Supervisors of Grundy County Grundy County Courthouse Morris, Illinois 60450 _
Regional Administrator, -.
Nuclear Regulatory Commission, Region III 799 Roosevelt Road, Bldg. #4 Glen Ellyn, Illinois 60137 I 11 inoi s Department of Nuclear_ Safety Office of Nuclear.Facility Safety 1035 Outer Park Drive Springfield, Illinois 62704
-Robert Neumann Office of Public Counsel State of Illinois Center 100 W. Randolph Suite 11-300 Chicago, Illinois 60601 Dresden Nuclear Power Station Unit Nos. 2 and 3