ML20010E596

Forwards Comments on NUREG/CR-1659,Vol 4, Reactor Safety Study Methodology Applications Program:Grand Gulf 1 BWR Power Plant. Insufficient Info Provided to Adequately Review Sequence Evaluations

ML20010E596
Person / Time
Site:	Grand Gulf
Issue date:	09/03/1981
From:	Dale L MISSISSIPPI POWER & LIGHT CO.
To:	Rowsome F NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES)
References
RTR-NUREG-CR-1659 AECM-81-346, NUDOCS 8109080021
Download: ML20010E596 (3)

Text

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MISSISSIPPI POWER & LIGHT COMPANY Helping Build Alississippi EdMnMidd5 P. O. B O X 1640, J AC K S O N, MIS SIS SIP PI 39205 NUCLE AR PRoOUCT1oN DEPARTMENT September 3, 1961

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,t f Mr. Frank Rowsome , Acting Chief C ' /n Reactor Risk Branch .

5 Division of Risk Assessment S A I' Of fice of Research ~

[/ 9 S[p O'f fggI U. S. Nuclear Regulatory Cornission --

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Washington, D. C. 20555 ,C\ kgeth%,

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Dear Mr. Rowsome :

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SUBJECT:

Grand Gulf huclear Sta' tion Units 1 and 2 Docket Nos. 50-416 and 50-417 File 0260/L-860.0/16686/L-953.0 RSSMAP Study AECM-81/346 Mississippi Power & Light Company has reviewed Volume 4 of NUREG/CR-1659

" Reactor Safety Study Methodology Applications Program: Grand Gulf #1 BWR Power Plant" and prepared the attached comments for your consideration.

Very r uly yours, L. F. Dale Manager of Nuclear Services SHH/JDR:dn Attachment cc: Mr. N. L. Stampley Mr. R. B. McGehee Mr. T. B. Conner Mr. G. B. Taylor Mr. Victor Stello, Jr., Director gl Of fice of Inspection & Enforcement U. S. Nuclear Regulatory Commission J Washington, D. D 20*T5 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D. C. 20555 8109080021 810903 PDR ADOCK 05000416 A PDR Member Middle South Utilities System

Attachment to AECM-81/346 Comments on Volume 4 of NUREG/CR-1659 RSSHAP: Grand Gulf General Comments:

1. In many instances, insufficient information is provided to adequately review sequence evaluations. For example, for some cases the cut sets presented represent less than 25% of the failure probability.

2. A containment failure pressure of twice design was assumed. Analyses done in support of the Grand Gulf H2 control system design have shown that the failure pressure would be a factor of 3 to 4 times design. In many sequences this would significantly impact the time to core melt and thus the recovery factor.

3. Pressure / temperature curves for many aequences were not provided. Therefore, a complete review was not possible. In at least one instance (sequence TPQE),

the curves presented contradicted assumptions made (see specific comments on TyPQE).

4. Although noted in the report, it is misleading to present results for Grand Gulf and try to compare them to WASH 1400 when different assumptions were used. In particular, the assumptions for the TPQE sequence regarding the PCS will make a difference of one order of magnitude.

5. No credit in the report was given to recovery of the diesels. Recovery of of f site power was included and credit for hardware repair was given in some cases. WASH 1400 uses a value of 0.1 for failure to recover diesels in the long term. This could make a difference of an order ci magnitude in many cut sets.

6. Resut;s presented in Appendix C show a spiks in the fraction of cladding reacted (FCR) at the time of core slump. There is no physical basis for this model. It arbitrarily increases the noount of hydrogen in the atmosphere at the time a burn is assumed. Jote that all sequences resulting in an H2 burn will be changed significantly by the proposed hydrogen ignition system.)

Comments on Specific Accident Sequences:

TPQI - It is nct credible to believe that the operators would stand by and watch the containment fail due to overpressurization over a 28 hour3.240741e-4 days <br />0.00778 hours <br />4.62963e-5 weeks <br />1.0654e-5 months <br /> period (or longer). Numerous options are available to the operator to prevent over-pressure from breaching the containment. Among these are:

o Drywell air coolers could be made available in chis time to remove heat. The fans can be manually loaded on the diesel anu tooling water is supplied by the plant service water system.

r o Containment air coolers may be available for the T 23 PQI sequence (they are powered by of fsite power). Cooling water is supplied by the plant chilled water system.

o In the long term, numerous options are open to the operators to supply additional water to the suppression teol-The dominant cut set in the TyPQI sequence involves loss of all power.

However, a recovery factor of 0.23 is applied. Thisfrctorisapparentlyggsed on a time period of 28 hours3.240741e-4 days <br />0.00778 hours <br />4.62963e-5 weeks <br />1.0654e-5 months <br /> and a mean time to repair of 19 hours2.199074e-4 days <br />0.00528 hours <br />3.141534e-5 weeks <br />7.2295e-6 months <br /> (R = e- /19).

In fact, this value is applicable to hardware failures but not to diesel recovery.

WASH-1400 assumed a value of 0.1 for failure of long term recovery diesels. This factor should be used in place of the 0.23 in the dominant cut set and in addition to the 0.23 in the other cut sets in which both diesel failure and hardware failures are considered.

T1 PQE - This sequence assumes the manual initiation of ADS is required for LPCI operation. In fact, as shown in Figure C-9 of this report, at 70 ml.a. (the onset of core melt) the system pressure is well below the set point for LPCI and the head available via the condensate booster pumps. Consideration of automatic operation of LPCI would significantly reduce core melt probabilities.

T PQE - Again it was assumed that automatic ADS does not occur but no RCS 23 pressures are provided in the report to demonstrate that manual ADS operation is required.

SI - No recovery factor is included despite the fact that this is apparently a long term event (no time scales or heat up curves were included in the report).

TQW - As described earlier for sequences TPQI, recovery of diesel failures was not properly considered. This could reduce individual cut set frequencies by factors of 2 to 10. Also, as mentioned earlier, the containment failure pressure is quite pessimistic. Finally, although a conservative recovery factor is included, it only covers repair times for failed hardware. No recovery is considered for alternate actions by operators (i.e. , initiating air coolers, supplying additions cooling water, etc.). It is totally unreasonab?.e not to assume some corrective actions by the operators during the minimum of 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> of the pressure rise.

T23C - The assumption of containment failure ignores alternate containment cooling options (e.g. air coolers). It also ignores the fact that for some initiating transients it may be possible to continue plant operations at a 30%

power level.

Ti QUV - Manual ADS actuation is assumed to be required although no analysis to support this assmnption is provided. As noted earlier (sequence TPQE), this assumption may not be justified. Also, as decribed earlier, recovery from diesci failure has not been properly considered.

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