ML20057D995
| ML20057D995 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 09/30/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20057D992 | List: |
| References | |
| NUDOCS 9310070050 | |
| Download: ML20057D995 (5) | |
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WASHINGTON, D.C. 2056& 0001 x.w.... j SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION OF A RE0 VEST FOR EXEMPTION FROM CERTAIN 10 CFR PART 50 REQUIREMENTS FOR EMERGENCY PLANNING FOR PORTLAND GENERAL ELECTRIC COMPANY TROJAN NUCLEAR PLANT DOCKET NO. 50-344
1.0 INTRODUCTION
By letter dated March 9,1993, the Portland General Electric Company (PGE, or the licensee) submitted a request for exemption from certain 10 CFR Part 50 requirements for emergency planning for the Trojan Nuclear Plant (Trojan). On September 8, 1993, the NRC staff (or the staff) and PGE held a telephone conversation to discuss this exemption request. As a result of this conversation the licensee submitted, by letter dated September 14, 1993, a revision to their March 9, 1993 exemption request.
The September 14, 1993 submittal modified the March 9, 1993 exemption request by retaining certain commitments to met requirements in Sections 10 CFR 50.47 and 10 CFR 50, Appendix E, Paragraph IV originally requested for exemption but that were still considered by the staff to remain applicable to Trojan.
On November 9, 1993, the Trojan plant ceased power operations. By letter dated January 27, 1993, PGE informed the staff of the decision by PGE to cease operations at Trojan on a permanent basis.
Further, by letter dated February 2,1993, PGE informed the Commission that the Trojan reactor had been permanently shut down and defueled, with the nuclear fuel placed in the spent fuel pool. Additionally, by letter dated February 17, 1993, PGE certified that fuel would not be moved back into the containment building at Trojan without prior NRC approval. On March 24, 1993, the Commission issued an order confirming the licensee commitment not to move new or spent fuel into the reactor building without prior written NRC approval.
On May 5, 1993, the Commission issued Amendment No. 190 for Facility Operating License No. NPF-1 amending the operating license to a possession-only license for Trojan.
In a letter dated May 18, 1993, the NRC staff informed the licensee that the staff had determined that the most significant potential accident associated with -a permanently defueled and shut down reactor involves the spent fuel stored onsite. The postulated accident sequence involves the complete or partial loss of water from a spent fuel pool containing recently offloaded fuel. This beyond design basis accident sequence could result in a zirconio, fuel cladding fire that could propagate through the spent fuel storage pool and result in significant offsite consequences. Although such an accident i-beyond the design basis, it could be considered within the spectrum of 9310o70050 930930 PDR ADOCK 05000344 j
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- accidents that could require continuance of the offsite emergency plan. A description of the accident sequence and estimates of impact are contained in NUREG-1353, and the behavior of the spent fuel during heatup is described in NUREG/CR-0649. Consideration of this accident scenario is limited to the period of time that the spent fuel is thermodynamically capable of a cladding fire. Over time, decay of short half-life radionuclides reduces the potential for a cladding fire. Af ter about one to three years, depending on the fuel burnup and the spent fuel storage configuration, the spent fuel is thermodynamically incapable of causing a cladding fire.
The staff expressed concern that the fuel removed from the Trojan reactor, which shut down on November 9, 1993, and stored in the high density racks of the Trojan spent fuel pool, posed a risk to the public that would justify the continuation of the offsite emergency plan. The staff requested, in the May 18, 1993 letter to the licensee, that the licensee consider this accident scenario and provide an analysis of site specific considerations that would support their position that continuance of offsite emergency planning was not necessary.
The licensee responded in a letter dated June 17, 1993, and concluded that the possibility of the proposed scenario is sufficiently beyond that of a design basis event such that offsite emergency preparedness is not warranted. Based on existing models the licensee also concluded that at one year after shut down of the reactor, assuming no active ventilation, the fuel in the pool would not reach the rapid oxidation point until more than two days after the loss of all water from the pool.
The licensee looked at six potential initiating events for the instantaneous loss of water from the spent fuel pool. Based on the comparison of the probability of occurrence of the potential initiating events, the licensee concluded that seismic induced structural failure of the spent fuel pool was the event of greatest concern.
In order to assess the potential seismic induced structural failure of the Trojan spent fuel pool the licensee performed a seismic evaluation and a probabilistic assessment to determine the bounding probability of structural failure of the Trojan spent fuel pool. The Trojan spent fuel pool structure was evaluated for ground motions that would result from the occurrence of a conservatively postulated Seismic Margin Earthquake (SME) that would result in a peak horizontal acceleration at Trojan of 0.38g. The structural analysis of the spent fuel pool, performed by the licensee, determined that the spent fuel pool has a seismic margin of 5.3 times the SME demand. The peak horizontal ground acceleration required to exceed the spent fuel pool margin is 5.3 times the peak horizontal ground acceleration for the SME or 2.0g.
The probability of earthquake ground accelerations on the order of 2.0g for the SME is considered extremely remote.
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. Based on.thd structural analysis and the seismic margin evaluation, the licensee concluded.that the possibility of the proposed scenario in which there is an-instantaneous loss of water in the spent fuel pool is sufficiently.
beyond a design basis event that offsite emergency preparedness planning is not warranted.
The NRC staff conducted a review of the licensee submittal dated June 17, 1993, and determined that the use of the SME with a peak horizontal 1
acceleration of 0.38g is appropriate for the Trojan site. The staff compared the seismic loads with the shear wall strength and found that the Trojan spent fuel pool would maintain its structural-integrity for a SME of 0.38g with a margin of approximately 2.8.
The licensee calculated the margin'to be 5.3 using their shear wall capacity.
In either case, the evaluation demonstrated that the Trojan spent fuel pool is_ expected to resist the effect_of a SME of 0.389 with adequate margin.
Furthermore, the staff concluded that because of an adequate margin, the Trojan spent fuel pool is expected to maintain structural integrity even for a RLE with a peak horizontal acceleration of 0.5g.
The staff also evaluated the licensee analysis of the time 'to onset and likelihood of rapid oxidation of the cladding should an instantaneous loss of water in the spent fuel pool occur.
The licensee evaluation was based on approximate models developed earlier by the NRC and contained in the NUREG documents referenced above. The staff concluded that the licensee estimate is reasonable that, with the current level of decay heat, there would be-many hours (on the order of two days at the one year anniversary of shut down) available for mitigative activities before the onset of rapid cladding oxidation following the instantaneous loss of water from the Trojan spent fu.el pool. The licensee has implemented procedures that would provide cooling water to the spent fuel pool from a variety of sources to preclude the gradual
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heat up of the spent fuel if the instantaneous loss of cooling water from the pool were assumed to occur.
The staff has concluded that there is an extremely low likelihood of a complete or partial loss.of water'from the Trojan spent fuel pool.
Furthermore, the staff has also determined that in view of the low likelihood of the event and the time elapsed (almost one year) since shut down of the facility, and the configuration of the fuel in the pool, there would be
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sufficient time after a postulated instantaneous loss of coolant and before
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the initiation of a cladding fire for the licensee to implement actions to preclude a cladding fire. The length of time available also provides confidence that additional offsite measures could be taken without pre-planning if required.
PGE has proposed that the degree of emergency planning and preparedness necessary-to' provide adequate protection of the public health and safety from a permanently shut down and defueled reactor is significantly less than th_at required for an operating facility.
Pursuant to Title 10 of the Code of Federal Regulations, Part 50.12, PGE is requesting exemption from certain -
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4 sections of 10 CFR 50.47, " Emergency Plans," and 10 CFR 50, Appendix E, Paragraph IV, " Content of Emergency Plans." The requested exemption addressed two areas:
(1) the discontinuance of the need for offsite planning, and (2) the reduced onsite planning needs of the Trojan Permanently Defueled Emergency Plan.
The staff reviewed the acceptance criteria for onsite emergency plans for operating nuclear power reactors, taking into consideration the current permanently shut down status and inherently low risk of the Trojan plant, as described in the following sections of this evaluation. The acceptance criteria include the planning standards of 10 CFR 50.47(b), the requirements of Appendix E to 10 CFR Part 50, the guidance criteria of NUREG-0654/
FEMA-REP-1, " Criteria for the Preparation and Evaluation of Radiological Emergency Response Plans and Preparedness in Support of Nuclear Power Plants,"
dated November 1980, and the guidance contained in NUMARC/NESP-007,
" Methodology for Development of Emergency Action Levels," dated January 1992.
For any potential offsite impacts, the staff reviewed the Permanently Defueled Emergency Plan using the standards of 10 CFR 50.47(d), which state the requirements for a license authorizing fuel loading and low power testing only.
The standards of 10 CFR 50.47(d) recognize the lower risk associated with low power operation and are considered by the staff to be generally appropriate for reviewing the offsite aspects of the PGE exemption request.
The potential for emergency events to occur and their possible consequences are discussed in the " Summary of the Permanently Defueled Safety Analysis" submitted with the Permanently Defueled Emergency Plan by the licensee on March 9, 1993.
All of the irradiated fuel has been removed from the reactor vessel and is being stored in the spent fuel pool. The radioactive source terms for an accidental release have been greatly reduced by radioactive decay.
Based on the analysis of credible events at Trojan, the licensee states, in the Permanently Defueled Emergency Plan, that there are no postulated accidents which could result in the release of radioactive materials to the environment in quantities which would require protective actions for the public.
Therefore, the licensee proposes to delete offsite emergency response capabilities and requests an exemption from certain requirements of 10 CFR 50.47 and 10 CFR 50, Appendix E.
2.0 STAFF EVALUATION OF 0FFSITE RADIOLOGICAL CONSE0VENCES The NRC staff independently evaluated the offsite radiological consequences of the credible design basis accidents for Trojan in its defueled state. The most limiting design basis accident with regards to the severity of its consequences is a fuel handling accident where a fuel assembly was dropped.
The staff analysis indicates that doses at the exclusion area boundary would be a small fraction of the Environmental Protective Agency (EPA) Protective Action Guides (PAGs). The licensee calculated doses at the exclusion area boundary for the whole body, the thyroid, and the skin were also a small fraction of the EPA PAGs.
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. 3.0 STAFF EVALUATION OF 10 CFR PART 50 EXEMPTIONS The staff reviewed the licensee request for exemption from certain sections of 10 CFR 50.47 and Appendix E of 10 CFR 50, as stated in the March 9, 1993, submittal.
Based on the staff review of the initial licensee submittal, a telephone conversation was held on September 8, 1993, to discuss portions of the regulations which the licensee had requested exemption from which the staff believed should be retained. As a result of this discussion the licensee submitted, by letter dated September 14, 1993, a revision to their exemption request which included the portions of the regulations (primarily those related to notifications of local and state government authorities),
which the staff indicated should be retained.
4.0 CONCLUSION
S The proposed exemption as revised has been reviewed by the staff against the criteria included in 10 CFR 50.47(b), Appendix E to 10 CFR 50, NUREG-0654/
FEMA-REP-1, Revision 1, and NUMARC/NESP-007, Revision 2.
The staff review took into consideration the shutdown and defueled status of the facility, the configuration of the stored fuel and the length of time since power operation.
Based on our independent review of the Trojan analysis, the staff concurs with the licensee accident analysis and concludes that there is no design basis or beyond design basis accident at Trojan, in its defueled condition, at this point in time, which warrants continuation of offsite emergency planning measures.
Therefore, the staff concludes that Trojan in its shut down and defueled condition may discontinue offsite emergency preparedness activities and reduce the scope of onsite planning as the licensee has proposed.
Based on our review of design basis and beyond design basis events at Trojan, in its permanently shut down status, the staff concludes that the licensee request for an exemption from offsite emergency preparedness requirements of 10 CFR Part 50 is acceptable in view of the greatly reduced offsite radiological risk associated with the current plant status.
Principal Contributors: Daniel M. Barss Michael T. Masnik Date:
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