ML072330293
| ML072330293 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 07/31/2007 |
| From: | John Hughey Plant Licensing Branch III-2 |
| To: | |
| Hughey J, NRR/DORL, 301-415-3204 | |
| Shared Package | |
| ML072330272 | List: |
| References | |
| TAC MD3717, TAC MD3718, TAC MD4837 | |
| Download: ML072330293 (2) | |
Text
DRAFT REQUEST FOR ADDITIONAL INFORMATION MILLSTONE POWER STATION, UNIT 2 (TAC No. MD4837)
SMALL BREAK LOSS-OF-COOLANT-ACCIDENT QUESTIONS (Page 1 of 2)
A. OVERALL APPLICABILITY TO MILLSTONE, UNIT 2 QUESTION #1.
To show that the referenced generically approved SBLOCA analysis methodology applies specifically to the Millstone-2 plant, provide a statement that Dominion Nuclear Connecticut and its vendor have ongoing processes which assure that the ranges and values of the input parameters for the Millstone-2 SBLOCA analysis bound the ranges and values of the as-operated plant parameters. Furthermore, if the Millstone-2 plant-specific analyses are based on the model and or analyses of any other plant, then justify that the model or analyses apply to Millstone-2. (e.g. if the other design has a different vessel internals design the model wouldnt apply to Millstone-2.)
B. APPLICATION OF THE SBLOCA MODEL AND ANALYSES RESULTS Because the February 20, 2007, Millstone Power Station Unit 2 Proposed Revision to Technical Specification 3/4.5.2..., and figures and tables presenting Millstone-2 small break LOCA analyses results presented in the Millstone 2 FSAR do not discuss a mixed core, the NRC staff assumes that the small break analyses results referred to in the February 20, 2007, submittal are for one fuel type rather than a mixed core of different types.
In reviewing the latest SBLOCA analysis for Millstone 2, it appears that the most limiting break size may not have been evaluated. A break size of 0.08 ft2 CLB is identified as the worst case. However, at 2000 sec, the SIT's inject a very small amount of liquid to turn over the PCT near 2000F. It is possible that a break size between 0.06 and 0.08 ft2 exists that does not actuate the SITs. Note that the break sizes and PCTs near the 0.08 ft2 break are:
break size, ft2 PCT, F 0.06 1782 0.08 1941 0.10 1808 There may also be a peak between 0.08 and 0.1 ft2 as well as between 0.06 and 0.08 ft2 for the case when the SITs do not inject.
The Millstone Unit SBLOCA analysis identifies the worst small break as the 0.08 ft2 cold leg break at the reactor coolant discharge. Since the SITs do not actuate for the 0.06 ft2 break, but momentarily actuate to terminate the clad temperature rise for the 0.08 ft2 break, the limiting break may not have been identified and, as such, the limiting nature of the 0.08 ft2 may not have been established. The limiting break for this class of CE plants is typically the largest break size that does not actuate SITs.
DRAFT REQUEST FOR ADDITIONAL INFORMATION MILLSTONE POWER STATION, UNIT 2 (TAC No. MD4837)
SMALL BREAK LOSS-OF-COOLANT-ACCIDENT QUESTIONS (Page 2 of 2)
QUESTION #2.
Millstone 2 FSAR Table 14.6.5.2-6 provides the results of small break LOCA analyses results for break sizes 0.05 ft2, 0.06 ft2, 0.08 ft2, 0.10 ft2, 0.12 ft2, and 0.15 ft2. A plot of these points (PCT vs. break size) strongly indicates that the limiting PCT occurs between 0.06 ft2 and 0.08 ft2. Additional analyses are required to support identification of the limiting break.
The NRC staff has a similar concern that there may be a more limiting break size between 0.08 ft2 and 0.10 ft2. To address this concern, provide a SBLOCA analysis for a 0.09 ft2 break.
(Note: In a letter to NEI dated November 8, 1999, Gary M. Holahan, reiterated the NRC position that total oxidation encompasses accident and pre-accident oxidation. This position continues to apply. Therefore, in response to QUESTION 2, provide total oxidation for the other (non-FTI) fuel, including pre-accident oxidation, plus LOCA cladding outside oxidation, plus cladding inside oxidation.)
QUESTION #3.
Please confirm and also explain why the charging pumps are no longer needed to maintain PCTs below 2200 F for small breaks for Millstone Unit 2, since previous analyses at 2700 Mwt have required the additional injection from these pumps.
QUESTION #4.
Please also provide the axial power shape used in the analyses.