ML20236X708
| ML20236X708 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 08/05/1998 |
| From: | Zinke G Maine Yankee |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GAZ-98-45, MN-98-55, NUDOCS 9808100196 | |
| Download: ML20236X708 (5) | |
Text
. _ _.. _
MaineVankee P.O. BOX 408
- WISCASSET, MAINE 04578 * (207) 882 6321 I
August 5,1998 MN-98-55 GAZ-98-45 l
UNITED STATES NUCLEAR REGULATORY COMMISSION Attention Document Control Desk Washington, DC 20555 l
References:
(a)
License No. DPR-36 (Docket No. 50-309).
1 (b)
Letter: M.J. Meisner to USNRC; Defueled Emergency Plan and 10CFR50.54(q)-
Exemption Raquest, MN-97-119, Dated November 6,1997.
(c)
Letter: G.A. Zinke to USNRC; Summary of Maine Yankee's Radiological Analyses Applicable to the Decommissioned Plant Condition
Subject:
. Summary of Maine Yankee's Bounding Radiological Analyses In Support of the Defueled Emergency Plan l
Gentlemen:
In Reference (b), Maine Yankee requested an exemption to 10CFR50.54(q) that would allow Maine Yankee to discontinue certain aspects of offsite emergency planning activities commensurate with the reduced risk to the public associated with the permanently shutdown and defueled status of the reactor and to reduce the scope of its onsite plan as indicated in Maine Yankee's Defusied Emergency Plan. In Referenco (c), Maire Yankee provided additional information conceming radiological analyses in support of the staff's review of the oxemp' on requests (Reference (b)).
l In response to a NRC verbal request for additional information, Maine Yankee is hereby providing further clarification of the bounding radiological analyses to demonstrate that the resulting offsite exposures are sufficiently low and below the EPA Protective Action Guides to allow discontinuance of certain aspects of emergency planning.
Very Truly Yours,'
George A. Zinke
/
Director, Nuclear Safety & Regulatory Affairs Il Attachment c:
Mr. H.J. Miller k\\o Mr. M.K. Webb Mr. M. Masnik Mr. M. Roberts Mr. P.J. Dostie Mr. U. Vanags 9809100196 980005 PDR ADOCK 05000309 F
MaineYankee l
I Attachment Letter MN 98 55 Summarv of Boundina Radiological Analysis in Suncort of Qefueled Emergency Plan l
In order to conclude that the Maine Yankee Defueled Emergency Plan will provide for the full capability to respond effectively to the spectrum of credible accidents, the bounding credible accidents must be defined and analyzed for their resulting consequences. In this summary, Maine Yankee defines the bounding credible accidents which remain as a result of the permanently shutdown and defueled status of the reactor. These accidents are categorized as the bounding radiological release and the bounding direct radiation (skyshine). The analysis for these accidents is described and the resulting consequences
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quantified. The resulting consequences are then compared to the Environmental Protection Agency's (EPA) Protective Action Guides (PAGs).
Boundina Radiological Release Accident l
The credible Maine Yankee accidents controlling the Exclusion Area Boundary (EAB) dose rates are the Fuel Handling Event, Radioactive Liquid Waste System Leaks and Failures, and the Low Level Waste Storage Building Accident. Each of these accidents, complete with descriptions of the key assumptions and methods of analysis, are discussed in the Maine Yankee DSAR and summarized in the letter, Maine I
Yankee to USNRC, dated July 9,1998 (MN-98-050).
i in assessing these bounding radiological accidents, as described in the Maine Yankee Defueled Safety Analysis Report (DSAR), the following results are summarized:
i l
l Licensing Basis Whole Body Thyroid Skin Organ TEDE8 Accident Deses8 Dosos*
, Dose:;8 Doses 8 Fuel Handling Event 6.12 31.7 0.405 i
Radioactive Liquid 230' 58' 52 l
Waste System Leaks and Failures Low Level Waste 7.08' 70.52' 262' 110 Storage Building (teen Accident lung)
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Notes:
l 1
Calculated for a 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> exposure duration at the EAB.
2 All units are in millirem at the EAB.
l The bounding radiological release accident at Maine Yankee, with respect to the TEDE dose consequences at the EAB, is that associated with the Low Level Waste Storage Building Accident. This accident involves the dropping of a highly loaded spent resin liner within the building, resulting in the liner failure, spillage of the spent resin, and the release of a fraction of the radioisotopic contents as a cloud to i
the environment. The contents of this cloud form the basis for determining the radiological source term at t'le site boundary.
The key analysis assumptions for this incident are as follows:
1.
The liner is loaded with spent resin at the allowable Department of Transportation Low Specific I
Activity (LSA) limits per 40 CFR 173.403, except for the isotopes of l*, l' ', and Co" 2.
The amount of 1 'is assumed to be equivaient to 0.08 Curies per cubic meter, which is in excess of 12 the limits allowed by 10CFR 61 LLW burial criteria.
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i Mainekkee Attachment Letter MN-98 55
- 3. The amount of l* is assumed to be 800 Curies in the liner.
4.
The amount of Co" is assumed to be 1,627 Curies in the liner.
5.
The liner contains 148 cubic feet of spent dewatered resin at 40 lbs/ cubic feet.
6.
One percent of the activity of the liner non-mechanistically forms an acmni 7.
Ten percent of the aerosol is non-mechanistically released outside the LLWSts; acung as a " puff" release, dispersed over an arc of 225 degrees at 700 meters.
These assumptions are conservative for many reasons. The quantity of resin normally used to fill a liner is about 90 cubic feet rather than 148 cubic feet as assumed in this analysis. The values for aerosol and release percentages are taken from those associated with a fire, even though a fire is not credible due to the extremely low fire loading in the LLWSB, due to the relatively non-fiammable nature of resins themselves and due to the lack of an ignition source (Maine Yankee does not use heating methods to c:ewater resins.) Finally, the values for release percentages were derived for a transportation accident which is open to the environment and therefore do not credit any mitigation from the Low Level Waste Storage Building itself. These aerosol and release percentage values are taken from Sandia Report SAND 87-2808 "The Potential Consequences and Risks of Highway Accidents involving Gamma-Emitting Low Specific Activity (LSA) Waste", August 1988.
l The calculation of the doses at the exclusion area boundary was performed in accordance with the NRC Regulatory Guide 1.109, Appendix C, using the code ATMODOS.
l The EPA Protective Action Guidelines (PAGs) set a lower limit of 1000 millirem. The Maine Yankee
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maximum TEDE dose are approximately one tenth of the EPA PAGs. Therefore, Protective Action Guideline dose criterion is not approached for the bounding credible radiological release accident at Maine Yankee.
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l Bounding Skysh]ne Radiological ADalysis For the purposes of establishing the bounding radiological dose at the site boundary due to skyshine, Maine Yankee considers the partial loss of water inventory from the spent fuel pool as the bounding credible accident. defining event. This event, as described below, and as described in section 5 of the Maine Yankee DSAR, is considered to be beyond design basis.
l The scenario associated with this transient is composed of an inadvertent syphoning of the spent fuel pool water as initiated through the breakage of a cooling line at a lower elevation. The existing syphon break in the cooling line is assumed to fait, resulting in the immediate (approximately 2-3 hours) lowering of the pool water leve! to the bottom of the cooling water inlet piping (31.5 foot elevation), a loss of approximately l
147,500 gallons. This loss corresponds to a decrease in water level of approximately 12.5 feet of level from the spent fuel pool. Operator actions through the time required to drain this amount of fluid are l
neglected. The water level in the spent fuel pool stabilizes at the 31.5 foot elevation and, since the cooling suction has been uncovered, the cooling system is assumed to fail and the water in the spent fuel pool begins to heat up. Operator actions are neglected during the time required for the water to reach boi'ing (approximately 39 hours4.513889e-4 days <br />0.0108 hours <br />6.448413e-5 weeks <br />1.48395e-5 months <br /> with a July 1,1998, decay heat level). The loss in the spent fuel pool water level l
due to boiioff is calculated to be 1.27 feet per day with a calculated boiloff rate of 10.06 gallons per minute.
l The spent fuel pool is assumed to boil at this rate for the following 4 days before recovery actions are effective in increasing the water level to the point of reinitiating the cooling system.
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MaineYankee Attachment Letter MN G8-55 The inherent significant conservatism in this scenario are listed as:
1.
The syphon break in the cooling lines is required to fail. This passive break consist of a section of piping designed to introduce air into the cooling piping to terminate loss of water from the spent fuel pool. Syphon breaks are present in each of the cooling water intet and outlet piping lines.
2.
All pool monitoring instrumentation notifying the operations staff is assumed to fail in such a manner so as to not provide indication of a problem in the spent fuel pool.
3.
All fuel building radiation monitoring instrumentation is assumed to fail.
4.
The operations staff is cssumed not to notice 147,500 gallons of water in the fuel building or spilling to the outside.
5.
The total amount of time that the operators are assumed not to react to this event is at least 41 hours4.74537e-4 days <br />0.0114 hours <br />6.779101e-5 weeks <br />1.56005e-5 months <br />.
6.
The recovery actions are assumed to take place during the following four days; however, these actions are not assumed to be effective until the fourth day.
7.
No credit is taken for the shielding of the fuel building walls, roof, or structure.
Additionally, no credit is taken for the shielding of the fuel structure or self-shielding capabilities.
The analysis was based on the use of the ORIGEN-2, ELISA, DIDOS-IV, RADFLEX and SKY computer codes, along with other pertinent information with respect to the homogenization of the fuel assemblies and the fuel racks.
l The radio logical doses assucisted with this sconcric a,c divisible into two classifications: those accociat9d with the vaporization of the liquid from the spent fuel pool and those directly attributable to the skyshine from the loss of water shielding.
For the first, the projected radiological dose consequences at the Exclusion Area Boundary (EAB) to the 4
whole body are 1.12 x 10 rem / hour. Given that the transient duration is no greater than 140 hours0.00162 days <br />0.0389 hours <br />2.314815e-4 weeks <br />5.327e-5 months <br />, the total whole body dose at the EAB is 0.16 mrem. This value is so small as to be neglected without consequence.
l The second contributor to the projected radiological dose consequences is derived from the skyshine dose rates at a lowered level in the spent fuel pool. Assuming the drop in level from the 31.5 foot elevation to 26.4 feet (a boil off time of 4 days, resultir:g in a water level of approximately 5 feet above the spent fuel), the maximum skyshine dose rate at the EAB is 7.6 x 10 Rad /hr. For the four day duration of l
this transient, the collective dose from the skyshine is 0.48 mrad.
The calculation of the skyshine dose rates assumed that the spent fuel pool was completely full of the
" worst case" fuel assemblies, a total of 2679 discharged assemblies with a one year resident decay time in the spent fuel pool. The total number of assemblies in the spent fuel pool at Maine Yankee is 1434. Of these assemb!ies, approximately 15% have resided in the spent fue! pool with at least 1.5 years of decay with the remainder of the spent fuel considerably longer, ranging from 2.5 to 24 years of decay.
Given the magnitude of these collective doses, and the substantial conservatism in the calculation of the doses, the total effective dose equivalent for this transient is estimated to be well within the value of 10 mrem and is therefore approximately 2 orders of magnitude below the EPA Protective Action Guidelines.
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MaineYankee Attachment Letter MN-98-55 The radiological dose at the EAB, as determined from this beyond design basis transient, are conservatively assessed to be a very small fraction of the EPA PAGs.
Conclusion Maine Yankee's calculations show that the doses resulting from these bounding credible accidents are signiocantly below the EPA PAG's. Therefore, under the gerieral guidelines defining emergency classifications in NUREG-0654/ FEMA-REP-1, Revision 1, " Criteria for Preparation and Evaluation of Radiological Emergency Response Plans and Procedures in Support of Nuclear Power Plants," dated November 1980, for an accident of this nature, the level of severity would not reach a point where offsite protective actions would be warranted.
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