AECM-81-336, Forwards Amended & Expanded Rept Which Supersedes 810619 Rept Describing Hydrogen Control Measures Being Implemented. Description of Integrated Scenario Outlined
| ML20010E089 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 08/31/1981 |
| From: | Dale L MISSISSIPPI POWER & LIGHT CO. |
| To: | Tedesco R Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20010E090 | List: |
| References | |
| AECM-81-336, NUDOCS 8109030063 | |
| Download: ML20010E089 (4) | |
Text
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ss Mr. Robert L. Tedesco H "LI'02 g
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,7 U. S. Nuclear Regulatory Commission Washington, D. C. 20555 4
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Dear Mr. Tedesco:
I
SUBJECT:
Grand Gulf Nuclear Station Units 1 and 2 Docket Nos. 50-416 and 50-417 File 0262/0755/1-860.0 Hydrogen Control AECM-81/336 On June 19, 1981, in letter AECM-81/221, Mississippi Power & Light Company (!T&L) transmitted a report describing and evaluating the hydrogen control measures being implemented at the Grand Gulf Nuclear Station (GGNS).
The attached report consis*s of an amended and expanded submittal which supercedes the June 19 rc ) ort.
The changes fall into three categories:
1.
Two additional bounding cases have been added bringing the total number of containment response cases analyzed in the report to six; 2.
Cas concentrations (of hydrogen, oxygen, nitrogen, and steam) in each volume (drywell, wetwell, an.1 containment) have been provided for each of the six cases; 3.
Minor typographical errors and deletions in the June 19 report 1
have been corrected.
l Changes in the text have been delineated by change bars in the right hand margin.
In addition, each page is dated either 6/81 for pages which contain i
no new material or corrections or 8/81 for pages which do contain new l
information or corrections.
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8109030063 810831 PDR ADOCK 05000416 A
PDR Member Middle South Utilities System
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MISSISSIPPI POWER & LIGHT COMPANY AECM-81/336 Page 2 The two new bounding cases (Cases 5 and 6) described in detail in Appendix D of the attached report are very conservative cases in which it is assumed that containment spray is not available. Case 5 also assumes that there is no ignition in the wetwell leading to global burns in the containment.
Such an analysis appropriately models a situation where there is cxygen depletion in the wetwell (although the gas concentration information supplied does not support such a hypothesis).
The results of these cases along with the results of the first four cases demonstrate that containment integrity is not threatened by the hydrogen release associated with the postulated occurrence of a 75% clad water reaction when the CGNS Hydrogen Ignition System (HIS) is used for miti-gation of the event.
As described in the status report submitted by letter AECM-81/298 on August 18, 1981, substantial additional work is underway in a variety of areas to resolve further concerns related to hydrogen control at GGNS.
In particular, a commitment was made to complete the action items listed in Sections 1.0, 3.0, 4.5, 6.1, 7.0, 8.1, 9.0, and 10.0 of the attachment to the August 16 e.t.doa ieport and submit information to the Nuclear Regulatory Commission (NRC) ducing the week of September 28, 1981. All efforts are being made to expedit, this work to allow submittal no later than September 11, 1981.
In the case of action item 7.0 on containment ultimate capacity, most, if not all, of the information has already been provided in responses to informal questions on this subject.
In addition, the response to action iteu 6.1 on cross-sectional flow areas is in the final stages of preparation, and, if possible, will be submitted no later than September 4, 1981.
i To the extent possible, the remaining action items which were scheduled for submittal in October and December 1981 will also be expedited. An updated schedule will be provided by Septenber 30, 1981.
A commitment was also uade in letter AECM-81/298 to provide a description l
of the GGNS integrated scenario bo be used as a base case for further containment response analysis. The integrated scenario which is described i
l below is fundamentally similar to the stuck open relief valve cases l
previously submitted, particularly Case 3.
Based on evaluation of the l
analyses done to date, a review of the GGNS Emergency Procedures, and l
concerns raised by the NRC during informal conversations, the assumptions i
have been modified to represent a consistent integrated scenaric:
1.
The burn parameters (representing realistic values based on the recommendation of MP&L consultants) are:
a.
ignition at 8 volume % of hyd. xfn b.
burnup of 85% of hydrogen in the volume or until only 5 volume % of oxygen remains c.
propagation of burns to adjoining volumes if they contain at least 8 volume % of hydrogen d.
flame speed of 6 fps l
I
l MISSISSIPPI POWER & LIGHT COMPANY AECM-81/336 Poge 3 2.
The initiating event is a transient followed by a stuck open relief valvo (SORV) and an inability to maintain water level in the reactor.
This is believed to be one of the more probabic scenarios for hydrogen generation.
3.
The igniters (91S) and drywell purge (CCCS) are initiated 20 minutes into the scenario.
In fact, the CGNS Energency Procedures are being 4
changed to incorporate a requirement for initiation of the HIS and CGCS based on water level in the reactor.
For computational case (since CLASIX-3 does not track reactor water level), it is assuned that this occurs at 20 minutes.
This is also consistent with taking no credit tor operator action for the first 20 minutes of an accident.
4.
Prior to generation of hydrogen, at least seven but no more than nine safety relief valves will be open.
In the event that reactor water level cannot be maintained above the core midplane, the GGNS Emergency Procedures call for the operator to open either seven or eight safety relief valves depending on the details of the specific event.
This provides additional cooling due to increased steam flow over the uncovered f uel and extends the length of time bef ore f uel damage.
If the SORV was not one of valves opened by the operator, there could then be as many as nine valves open.
These valves are distributed around the suppression pool and yield an approximately uniform distri-bution of hydrogen into the suppression pool.
5.
Following the first hydrogen burn, it is assumed
- t. hat one train of containment spray is operating. Current CGNS Emergency Procedures call for manual actuation of containment spray if containment tem pe ra ture reaches 185 F.
This will occur at the first hydrogen b: rn.
The Emergency Procedures are being modified so that once containment spray is actuated, it will be left on as long as the HIS is energized.
Only one train is assumed to be available for conservatism.
In addition, if Residual Heat Removal System (RHR) trains A and B were both available, this assumption allows for the possibility that it might be desirable to l
use one of the trains for Low Pressure Core Injection.
[
l Yours truly,
%. f 42 F. Dale
/
Manager of Nuclear Services SHH/JDR:sh Attachment ec:
(See Next Page)
i MISSISSIPPI POWER & LIGHT COMPANY AECM-81/336 Page 4 cc:
Mr. N. L. Stampley Mr. G. B. Taylor Mr. T. B. Conner Mr. Victor Stelle, Jr., Director Of fice of Inspection 6 Enforcement U. S. Nuclear Regulatory Commission Washington, D. C. 20555 i
i l
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