ML20216F492

Correction to Safety Evaluation Re Revised SG Tube Rapture Analysis

ML20216F492
Person / Time
Site:	Byron, Braidwood
Issue date:	03/11/1998
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20216C605	List: ML20216C600 ML20216F492
References
NUDOCS 9803180413
Download: ML20216F492 (3)

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5-Additionally, a number of single failures were evaluated to determine the most limiting failures.

The failures considered included the failure of an atmospheric dump valve (ADV), the failure of an MSIV [ main steam isolation valve], and the failure of AFW control va ve opened or closed.

The most limiting single failure for the margin to overfill cases for both the OSG and RSG cases was the failure of an ADV to open in one of the intact SGs.' This reduces the SG cooling available to the operators and slows the cooldown process. The limiting single failure for the offsite dose cases is the failure of an ADV in the open position in the faulted SG. This maximizes the amount of the release to the environment and the offsite doses.

A number of cases were run to determine the most limiting set of conditions. The analysis was run for both the OSGs and RSGs. The analysis was run assuming the reactor tripped on low RCS pressure and on overtemperature delta-temperature (OTDT). For the low pressurizer pressure case a runback of 30 percent was assumed and for the OTDT case a runback to 95 l percent was assumed. These assumptions are conservative and maximize secondary inventory because it delays the reactor trip and causes an increased SG level at lower turt>ine loads. The analysis was run with single failures to minimize the margin-to-overfill and to maxim;ze the dose consequences. The results indicate that for the OSG cases the low pressure case resulted in a margin to overfill of 290 ft8 , and 293 ft3 for the OTDT case. For the RSGs the margin to SG overfillis 226 ft 3for the low pressurizer case and 60 ft3for the OTDT case.

The smallest margin to overfill for all the calculated results is 60 ft8 . Relative to the size of the SGs, this is not a significant amount of margin and it is a reduction from the original analysis.

However, the conservatisms described in the analysis assumptions and initial conditions have Justified that a margin of 60 ft8is acceptable.-

2.2.3 Summary The staff has reviewed the licensee submittal relating to the SGTR and found that the analysis presented is performed using an approved methodology with appropriately conservative inputs and assumptions. The use of the updated version of RETRAN is consistent with the original use of RETRAN and the approved SGTR methodology. An appropriate number of cases were evaluated and the results presented are acceptable for licensing applications. There is acceptable margin to SG overfill, and the use of this analysis for input into the dose consequence analysis is also acceptable. As a result, based on the above discussion, the staff finds the revised analysis acceptable.

2.3 Radiolooical Analysis 2.3.1Backaround The change in SG design affects the manner in which the reactor responds in the event of certain accidents. This change in response can impact the radiological releases, thus affecting offsite and onsite radiological doses.

2.3.2 Evaluation

. The staff evaluated the consequences of a postulated SGTR accident. Two cases were analyzed. One case involved a pre-existing iodine spike and the other case, an accident-it.itiated spike. For the pre-existing spike case, the reactor coolant iodine activity level of dose equivalent '8'l [ iodine-31) was assumed to be at the full power level of 60 pCi/gm of dose 9803180413 900311 PDR ADOCK 05000454 P PDR -

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TABLE 1 Staff Assumptions Used for Steam Generator Tube Rupture Accident Evaluation i

l Steam and H2O Releases from Faulted SG 0-120 minutes 1.18E5 l Steam Release from Intact SGs (Ibs) 0 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> 4.10E5 2-8 hours 9.49ES )

616 hours0.00713 days <br />0.171 hours <br />0.00102 weeks <br />2.34388e-4 months <br /> 6.77E5 16-24 hours 5.81E5 24-32 hours 5.22E5 32-40 hours 4.82E5 l Primary to Secondary Leak Rate 150 (9Pd/SG) l Flashing Fraction Variable with respect to time. Provided in Comed letter dated 11/3/97.

Scrubbing Fraction 0 Primary Bypass Fraction for intact 0 l SGs Duration of Plant Cooldown (hrs) 40 Primary coolant concentration of 60 pCilg of dose equivalent *l Pre-existina Spike Value (uCi/a)

• l = 46.2 is2 1 = 51.7

'88 1 = 73.9 1% *l = 11.1

• l = 40.6 Volume and mass of primary coolant and secondary coolant Primary Coolant Volume (ft') 12,062 @S86.2 'F I Primary Coolant Temperature ( F) 586.2 T1-1

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l TABLE 2 l

l Potential Consequences of a Steam Generator Tube Rupture Accident f

BYRON BRAIDWOOD l r.an LP2 can LP2 l l .

l Thyroid Dose ]

Coincident Spike 1) 4.9 0.23 5.5 0.79 l' l Pre-existing Spike 2) 24.7 0.85 28.0 2.9 Whole-Body Dose Coincident Spike 3) <1 <1 <1 <1 l Pre-existing Spike 4) <1 <1 <1 <1 Control Room Dose 5) THYROID WHOLE BODY THYROID WHOLE BODY Coincident Spike 0.15 <1 .11 <1 l Pre-Existing Spike 0.55 <1 0.41 <1 r

l 1) Acceptance Criterion is 30 rem

l. 2) Acceptance Criterion is 300 rem

3) Acceptance Criterion is 2.5 rem

4) Acceptance Criterion is 25 rem l l 5) Acceptance Criterion are 5 rem ~whole body and 30 rem thyroid. j i

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