ML17334A618
| ML17334A618 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 01/02/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML17334A617 | List: |
| References | |
| NUDOCS 9801200132 | |
| Download: ML17334A618 (7) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON> D.C. 2055&0001 FE E
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By letter dated October 8, 1997, and supplemented October 21, 1997, the Indiana Michigan Power Company (the licensee) requested amendments to the Technical Specifications appended to Facility Operating License Nos. DPR-58 and DPR-74 for the Donald C. Cook Nuclear Plant, Units 1 and 2. The proposed amendments would increase both the minimum required ice mass per ice basket and the total minimum required ice mass, and change the basis for the technical specification.
The licensee's letter of October 8, 1997, contained a proprietary submittal from a licensee contractor.
The licensee's letter of October 21, 1997, contained the identical technical specification proposal and a non-proprietary version of the contractor's information. Therefore, the letter of October 21, 1997, did not change the staffs no significant hazards considerations determination as set forth in the Federal Register notice dated October 22, 1997 (62 FR 54863).
- 2. ~c During a loss-of-coolant accident (LOCA), water from several sources (e.g., refueling water storage tank (RWST), reactor coolant system (RCS), accumulators, and melted ice) collects in the lower regions of the containment, part of which acts as a sump (i.e., recirculation sump) for the recirculation ofwater through the safety injection and containment spray systems.
As the accident progresses, the RWST, the initial source ofwater for the emergency core cooling (ECCS) and containment spray systems, empties and the water that has accumulated in the lower regions of the containment is used as the source ofwater for the recirculation phase of safety injection and containment spray. The water inventory in the recirculation sump must be sufficient to provide adequate net positive suction head to the pumps, and to prevent vortexing in the recirculation sump. As described in the Bases section 3/4.5.5, "Refueling Water Storage Tank," of the Cook Technical Specifications, the water volume of the RWST is sufficient to support post-accident recirculation flow in containment.
Thus, with regard to water inventory in PDR ADQCK 050003 P
PDR the recirculation sump, the accident analysis considers water only from the RWST and does not take credit for the other water sources described above.
As part of an NRC Architect Engineer design inspection conducted at the D.C. Cook facility during the period from August 4 through September 12, 1997, a plant-specific issue was raised (designated as URI 50-315,316/97-201-06) indicating that under certain loss-of-coolant accident (LOCA) scenarios, the volume ofwater in the ECCS sump may not be sufficient to support operation of the ECCS and containment spray pumps in the recirculation phase of a LOCA.
The inspection report stated that this was because the licensee could not confirm adequate communication between the active and inactive sumps within the containment and that water was being removed over time from the active sump to the inactive sump by the containment spray system.
The inactive sump is an annular space under the ice condenser bays extending 300 degrees around the containment and bounded by the crane wall and the containment wall.
In order to correct this situation, the licensee proposed to take credit for the additional water sources resulting from ice melt, leakage from the RCS, and accumulator inventory.
In order to gain sufficient margin, the licensee determined that the amount of ice specified in the technical specifications must be increased.
The licensee performed an analysis pursuant to 10 CFR 50.59 to determine ifthe proposed changes to the facilityas described in its Updated Safety Analysis Report would involve a change to a technical specification or result in an unreviewed safety question.
The licensee determined that taking credit for these additional water sources was a reduction in the margin of safety as defined in the bases of a technical specification and, therefore, resulted in an unreviewed safety question.
By letter dated October 8, 1997, and supplemented on October 21, 1997, the licensee proposed to amend the technical specifications for D.C. Cook, Units 1 and 2, to increase the minimum required mass of ice per ice basket and the total minimum required ice mass in the ice condenser.
In addition, the licensee proposed a change to Bases section 3/4.5.5 of the technical specifications to reflect the fact that the water from the melted ice, the RCS, and the accumulators would be used in the calculation of the water level in the containment during the recirculation phase of a LOCA. As described above, staff approval of this section of the technical specifications Bases would resolve the unreviewed safety question.
Specifically, the licensee proposed to revise the technical specifications for both units as follows:
3/4.6.5 Each ice basket must have at least 1333 pounds of ice.
The current required minimum amount of ice is 1220 pounds.
3/4.6.5 The minimum total ice condenser ice weight at a 95% level of confidence shall not be less than 2,590,000 pounds.
The current required minimum ice weight is 2,371,450 pounds.
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leases 3/4.6.5 The minimum weight per basket contains a 5% allowance for ice loss through sublimation.
The current allowance is 10%.
Bases 3/4.5.5 This basis was revised to state that: when combined with water from melted ice, the RCS, and the accumulators, sufficient water is available within the containment to permit recirculation cooling flowto the core.
The current basis discusses only the water inventory of the refueling water storage tank. As stated above, the licensee considers this change to be an unreviewed safety question.
The staff met twice with the licensee at public meetings on September 23, 1997, and October 9, 1997 to discuss the licensee's proposal and the supporting analyses.
The staff has reviewed the licensee's proposal.
Our evaluation is provided below.
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The licensee used the MAAP4 computer code to demonstrate that sufficient water inventory
- would be available in the active containment sump in order to support continued recirculation pump flowfor both the ECCS and containment spray pumps.
However, MAAP4 has not been reviewed and approved by the NRC for licensing calculations.
In order to verify that there is adequate assurance that the water level in the containment sump willbe sufficient to satisfy the vortexing limit, the staff requested Science Engineering Associates, Inc. (SEA), to perform confirmatory calculations of the ice melt rate and the sump water level in the D.C. Cook plant.
SEA performed its calculations using the MELCOR/CONTAINcomputer code.
MELCOR/CONTAINwas developed by the NRC, in part, to provide a means of independently verifying design-basis containment calculations performed by licensees.
MELCOR/CONTAINis a versatile code that is actively used and maintained by the NRC and has been successfully validated against numerous experiments.
Because this code was specifically developed for independent verification, the staff considers it an appropriate verification tool for this application.
The staff depended on data provided by the licensee for several important portions of the calculation.
For example, the geometry of the containment (distances, areas, and volumes) were taken from the licensee's data.
Break flowmass and energy calculations were the results of NOTRUMP (a Westinghouse proprietary computer code) calculations and MAAP4 calculations provided by the licensee.
Although using the licensee's data for these important parameters decreased the extent to which the calculations were independently verified, the staff was nevertheless able to examine the validity of the licensee's calculations in considerable detail.
The licensee's analysis considered both large-and small-break LOCAs. The critical factor is to maintain the sump recirculation water level above elevation 602 feet 10 inches.
According to the licensee, tests performed in 1977 demonstrated that a minimum level of 602 feet.10 inches
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prevents pump vortexing at maximum safeguards flow. The limiting case was the 2-inch double-ended guillotine break of the RCS in the inactive sump. This small break minimized RCS flowto the sump and, at the same time, maintained RCS pressure sufficiently high to prevent accumulator flow into the RCS.
Finally, flowout of the sump was maximized by assuming both trains of containment spray were operating.
Using these conservative assumptions, SEA's calculations demonstrated that the sump level during recirculation flow would be maintained above the minimum level of 602 feet 10 inches.
The staff also examined the licensee's revised allowance for sublimation of ice. The licensee's October 8, 1997, submittal provided data on ice bed sublimation rates for Unit 1 and Unit 2 for a period of 13 years.
The licensee stated that the average measured change in ice mass over an 18-month period was 2.31% for Unit 1 and 2.68% for Unit 2. Although there is considerable variability in the data provided by the licensee for both units, the staff considers the conservatism in the ice weight (a 95% confidence level is required by the technical specifications on measurements of the ice weight) to be sufficient. Since the data for approximately 12 years on each unit demonstrates a mean of less than 5%, the staff finds the licensee's proposal to reduce the sublimation factor to 5% to be acceptable.
4.0 ~UM~Y Based on staff calculations using the MELCOR/CONTAINcomputer code, using some data provided by the licensee but using independent models for some key assumptions, the staff finds that the licensee's proposal to credit ice melting in determining the water inventory available to the ECCS and containment spray pumps is acceptable.
In particular, the licensee's proposed change to the technical specifications to increase the minimum required total ice weight to 2,590,000 pounds and the minimum required weight of ice per basket to 1333 pounds, with a sublimation uncertainty of 5%, is acceptable.
On Bases page 3/4 5-3 for Unit 2, the wording "the limits of RWST...." has been corrected to read "the limits on RWST...." The staff has also corrected a typographical error in the Unit 2 Bases section 3/4.5.5 (page B 3/4 5-3) introduced in Amendment No. 199. The licensee's May 26, 1995, application requested an RWST water temperature of 70 'F for both units; however, when Unit 2 page B 34/5-3 was issued on March 13, 1997, the value was inadvertently left as 80;F. The value has been corrected to read 70 'F.
5.0 ST S
T T In accordance with the Commission's regulations, the Michigan State officialwas notified ofthe proposed issuance of the amendments.
The State official had no comments.
6.0 ENVI 0 E
LC These amendments change requirements with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. The staff has determined 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
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Commission has previously issued a proposed finding that the amendments involve no significant hazards consideration and there has been no public comment on such finding (62 FR 54863). Accordingly, the amendments meet the eligibilitycriteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.
7.0 The staff has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and safety of the public willnot be endangered by operation in the proposed manner, (2) such activities willbe conducted in compliance with the Commission's regulations, and (3) the issuance of the amendments willnot be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor: Richard Lobel, NRR Date:
JBO~ 2, 19ge
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