IR 05000010/1977019
| ML19340A763 | |
| Person / Time | |
|---|---|
| Site: | Dresden, Quad Cities  |
| Issue date: | 07/18/1977 |
| From: | Creswell J, Little W NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | |
| Shared Package | |
| ML19340A762 | List: |
| References | |
| 50-010-77-19, 50-10-77-19, 50-237-77-17, 50-249-77-17, 50-254-77-20, 50-265-77-21, NUDOCS 8009030802 | |
| Download: ML19340A763 (6) | |
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U.S. NUCLEAR REGULATORY COMMISSION
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0FFICE OF INSPECTION AND ENFORCEMENT
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REGION III
i Report No. 50-010/77-19, 50-237/77-17, 50-249/77-17, 50-254/77-20,-50-265/77-21
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Docket No. 50-0!0,50-237,50-249,50-254,50-265 License No. DPR-2, 19, 25, 29, 30 Licensee: Commonwealth Edison Company P. O. Box 767 Chicago, IL 60690
Facility Name:
Dresden Nuclear Power Station, Units 1, 2, and 3 Quad-Cities Nuclear Power Station, Units 1 and 2 Inspection At:
Dresden Nuclear Power Site, Morris, IL Quad-Cities Nuclear Power Site, Cordova, IL
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j Inspection Conducted: June 30, 1977
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j/ 7 Inspectors:
J. S. Creswell 7-1 #/
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date signed
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W. S. Little
n,9 v,f-Approved By: W h
C ef 7 /8
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j Nuclear Support Section date signed
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Inspection Summary Inspection on-June 30, 1977, (Report No. 50-010/77-19, 50-237/77-17, 50-249/77-17, 50-254/77-20,- 50-265/77-21)
j Areas Inspected:
Special inspection of calculations associated with short periods' that occurred December 28, 1976, at Dresden, Unit 2 and
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May 4, 1977, at Quad-Cities, Unit.l.
The inspection involved eight i
inspector-hours at ~ he Com.wsnwealth Edison Corporate Offices by two t
l NRC inspectors.
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'Results:
Inspection of the calculatione performed pertaining to the j
short period events revealed no items of noncompliance.
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DETAILS
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1.
Persons Contacted
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- L. Butterfield, Supervisor, Nuclear Reactor Division I
. *H. Ma cin, Supervisor, Large BWR Croup
- D.
Pallatta, Nuclear Engineer
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- Denotes those present in the exit interview.
2.
Licensee Rod Worth Calculation Method The licensee uses the codes TRIBIG and XENOBIG to perform rod worth calculations. TRIBIG and XENOBIG were developed from the FLARC code and XEN0 BIG includes a treatment of time varying Xenon concentration.
f For 7 x 7 assemblics ENDF-B cross section data is flux weighted
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by the LOCALUX code which contains the MUFT and THERMOS codes,
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three group data from LOCALUX is fed into 2D-PDQ which modgls
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assembly geometry in a 49 x 49 node calculation. K and M i
data are output from 2D-PDQ as a function of control exposure
and voids. K and h for 8 x 8 assemblies are supplied to the licensee by the reactor vendor. This data is then input into
the TRIBIG or XENO3IC codes to determine an eigenvalue for a given set of core conditions including control rod position.
3.
Corporate Office Analvsis of Fast Period Event at Dresden, Unit 2
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As a result of the event which occurred on December 28, 1976, personnel in the corporate office core analysis of rod worths
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experienced during the event. This analysis was sert to the site personnel on March 4,1977. The following assun otions
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were'made in that analysis:
t a.
The scram preceeding the short period event occurred from 95% power at an equilibrium Xenon condition..
b.
A time period of nine hours elapsed between the scram and-the event. This time period was devided into three, three
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hour periods for the purpose of the Xenon concentration calculations.
c.
Calculational parameters were based on a core temperature
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of approximately 550*F rather than the actual'338*F condition during the event.
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Results of the calculations showed the rod associated
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with the short period trip, J-2, to have a worth of 0.2% AK when withdrawn from position 04 to 06.
This
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i worth was stated to be roughly equivalent to a ten i
second period when calculated from generic B vs T tables. The licensee also calculated a worth of rod J-2 associated'with rod movement from position O'O to
position 08.
The reactivity associated with this movement was 0.8% 06K.
Results of code. determined eigenvalues for the positions of rod J-2 are given i
below:
Position Eigenvalue Worth
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0.97721 0.97801 >>
0.1% 41K
0.2% d1K
0.97996 >
0.5% 2kK
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0.98462 I
l It should be noted that at position 04 the code
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eigenvalue was calculated to be 0.97801 which is
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approximately 2.2% from indicated criticality while
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under the same conditions the reactor was on a measured
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period of 150 seconds.
i On April 20, 1977, a new analysis was sent to the personnel at the site. The new analysis included a study of the sensitivity of modeling cssumptions and a comparison with a period measurement for a similar condition.
Sensitivity studies revealed that the most significant
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changes in rod worths were due to the number and duration of time steps for Xenon distributions and concentrations (5% increase) and the number of source iterations taken to produce will behaved convergence characteristic (8% increase).
The comparison with a well defined period measurement was made with a period determined during the 2nd criticality on December 28, 1976, during a recovery l
from the IRM high flun scram. A period of 8.6 seconds
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was measured following the withdrawal'of G-2 from
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position'04 and 06.
The new analysis increased the worth of rod J-2
@ osition 04 to 06) from 0.203% 26 K to 0.24% 45 K.
The corresponding period derived f rom generic /2 vs T
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tables was five seconds. Calculated and measured
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i parameters are presented in tabular form below:
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i Rod Measured Excess Control Position Period Reactivity %
Eigenvalue
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G-2
8.6 sec 0.244 0.97999 G-2
550 sec 0.012 0.97804 J-2
150 sec 0.038 0.97828 J-2
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0.226 0.98045
As can been seen from the above data there is a considerable dif ference in the multiplication f actor for the conditions predicted from period measurement and conditions predicated by the computer calculation.
For example, with control rod G-2 at position 06 the multiplication factor is 1.00224 as determined from period measurement whereas the computer eigenvalue is 0.97999. It can been seen that this is over 2%
difference between measurement and predication. The licensee attributes this difference to errors in 41 K correction as a function of power level and lack of correction for moderator temperature effects.
4.
Corporate Office Analysis of Fast Period Events at Ouad-C#. ties
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On May 8, 1977, the licensee reported that they had experienced
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periods less than five seconds during shutdown margin testing which took place on May 4 and 7, 1977. The prelininary analysis of the periods was performed by plant personnel based on limited rod worth data. On June 15, 1977, the licensee supplied to the commission an update report to Reportable Occurrence Report No.
RO 50-254/77-23 which included an analysis of the periods based on computer calculations performed in the corporate of fices.
The licensee utilized the code TRIBIG to perform the calculations.
For these calculations the licensee used data based on hot core conditions (a' 550*F) and approximam<d the terperature effee'
" r cold conditions. This approximation was done by gene,
.od worth data for control rod H-9.
Hot conditions
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and compa-ing those results to " cold" (ae100*F) results obtained from the reactor vendor for control rod H-9.
The comparison was used to obtain a relationship of approximately 62% of " hot" rod worths for " cold" rod worths. This f actor was applied to all rod worths calculated. Hot and cold rod worths that were calculated are shown in Figure 1.
The report concluded that a period of less that five seconds
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had occurred on May 4,1977, but had not occurred on May 7, 1977.
5.
Manacement Discussions Discussions were held with the licensee represcatatives noted in Paragraph 1.
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Items discussed were:
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a.
Analysis performed concerning the short period events and limitations regarding effects of temperature on the calculations, b.
The need for rod worth analysis concerning the rod drop accident when shutdown margin demonstrations are planned.
c.
The lack of comparitive data for the face adjacent shutdown m rgin demonstration performed at Quad-Cities, Unit 1.
d.
The need for analysis of two " worst case" rods associated with the two rsJ maintenance shutdown margin demonstrations.
e.
The need for a timely response in furnishing the plaats shutdown margin data when events such as inoperable control rods require a shudown margin analysis.
f.
The need for a timely offsite review of physics test results when the offsite raview is required.
g.
The fact that the licensee sas generating their own control rod withdrawal sequences for up to 50% control density.
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Attachcent: Figure 1, Rod Worth Curve for Rod H-9 with Rod H-8 Withdrawn
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