IR 05000454/1990008
| ML20043B418 | |
| Person / Time | |
|---|---|
| Site: | Byron  |
| Issue date: | 05/23/1990 |
| From: | Phillips M, Rescheke P NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | |
| Shared Package | |
| ML20043B417 | List: |
| References | |
| 50-454-90-08, 50-454-90-8, 50-455-90-07, 50-455-90-7, NUDOCS 9005300005 | |
| Download: ML20043B418 (5) | |
Text
g?
'
+
..
.. '.
[i'-
k[t
...
- .
U.S. NUCLEAR REGULATORY COMMISSION
,
REGION 111
-
-Report No. 50-454/90008(DRS);50-455/90007(DRS)
Docket Hos. 50-454;.50-455'
qL
. Licensee: Commonwealth Edison Company k
..
..
P Post Office Box 767 i
Chicago, IL 60690
<
-Facility Name: Byron Nuclear Power Station - Units 1 & 2 Inspection At:' Byron, IL-61010-9750 Inspection Conducted:
February 15 through May 9,1990 Inspector:
.0,001/
LOG [
'N ()T,0 9h Peggy R~.dRascheske Date'
"
<
Approved By-k F# L
Monts P. Phillips,-Chief Date Operational Programs Section
' Inspection Summary I1nspection~on February 15 through May 9, 1990 (Reports No. 50-454/90008(DRS);
50-455/90007(DRS)).
Areas Inspected:
Special safety inspection focusing on problems encountered
- by -?.he licensee during the UnitL2 startups attempted on November 20,-1989, and February 11, 1990. The inspection was conducted to follow the licensee's investigation of the two events, and to evaluate the adequacy of the t
, licensee's engineering,) administrative controls, and corrective-actions
'
(IP 90712, 93702, 61707.
Results: The licensee suspended both reactor startups when unexpected
' differences between the estimated (actual) and predicted critical conditions-were discovered. The safety significance of the two events was considered minor, since the approach to critical was conducted in a controlled manner, and no-safety limits were approached. The licensee's investigation was extensive and thorough, ond an understanding of the issues was evident.
Corrective actions
- taken or planned should be effective in preventing further problems in this area.
No violations were identified during the inspection. One previously identified
-
open item for tracking the resolution of these events is considered closed
-(455/89024-01(DRP)).
9005300005 900524 PDR ADOCK 05000454 Q
,
-. _ _ _ _ _ _, _ _ -. _. _ _ - - _ - _ - - - _ -. - _ - - _ - - _ - - - - -.. - - -. _
,. - _
%,;
-. -
I'
REPORT DETAILS 1.
Persons Contacted
-
R. Pleniewicz, Station Manager-J. Bowers, Safety Assessment Engineer D.'R. Brindle, Operations Engineer R. F. Choinard, Regulatory Assurance W. J. Dean, bafety Assessment Engineer D. M. Farr, Station Nuclear Engineer
.
W. E. Grundmann, Nuclear Quality Programs Engineer T. K. Higgins, Assistant Superintendent - Operations G. W. Stauffer, Assistant Technical Staff Supervisor R. C. Ward, Technical Superintendent E. M. Zittle, Regulatory Assurance
,U S. NRC
W.J. Kropp, Senior Resident inspector All of the above persons attended the exit meeting held on May 9, 1990.
Other persons were contacted during the course of the inspection, including members of Corporate Nuclear Fuel Services.
2.
Introduction The inspection focused on the problems encountered by the licensee during the Unit 2 startups attempted on November 20, 1989, and February 11,
.1990.
Both reactor startups were suspended'when unexpected differences between the (actual) estimated critical condition (ECC) based on the 8-fold count rate and the predicted critical condition were discovered.
The inspection was conducted to follow the licensee's investigation of the two events, and to evaluate the adequacy -of. the licensee's
"
engineering, administrative controls, and corrective actions. The inspector reviewed numerous documents during the course of the e
inspection, and held discussions with the licensee's plant staff as well as corporate engineering. The following paragraphs discuss the events, the actions taken by the licensee, and the conclusions resulting from the inspection.
3..
Events On November 20, 1989, the licensee was attempting to bring Unit 2 to critical when it appeared, based on the 8-fold count rate, that a large deviation existed between the ECC and what was predicted.
Prior to reaching critical, the licensee inserted the control rods and started boration. The Technical Specification limit on ECC deviations was
-
m
'
w
~. -.
.
.f 1000 pcm and the licensee administrative limit was 500 pcm. The licensee's review concluded that the misprediction was approximately 900 pcm. _The Referen;e Reactivity Data (RRD) used to predict the ECC was based on the point the reactor was shutdown, namely November 13, 1989.
Prior to this shutdown, the unit had been load following, and the reactor was not at_ equilibrium conditions. The licensee determined that about 420 pcm of_the misprediction was attributed to the choice of the_RRD
.statepoint. The remaining 480 pcm difference was unaccounted for, but was within the administrative guidelines. On November 21, 1989, with additional administrative controls, Unit 2 was successfully started up.
The difference between the actual and predicted ECC was about 480-pcm.
.
The RRD point was taken at a stable power history on November 11, 1989.
On february 11, 1990, the licensee suspended a reactor startup prior to criticality when it appeared that the ECC had been mispredicted.
Based on the 8-fold count rate, the ECC deviation was determined to be approximately 820 pcm. Core life was about 10900 MWD /MTU, which was between the middle-of-1ife (MOL) and end-of-life (E6L) burnup specific-rod worth curves used in the ECC calculation. The licensee concluded that the use of E0L data (instead of M0L or interpolation between M0L and EOL) contributed about 400-450 pcm to the misprediction. A portion of
the remaining'400 pcm difference was attributed to the questionable
"
choice of the boron sample used. On February 12, 1990, Unit 2 was successfully started up, with about a 250 pcm difference between the actual and predicted critical condition. A different RRD boron concentration was used and burnup-specific rod worths were generated for the ECC
- prediction.
4.
Licensee Investigation and Action The licensee's immediate action in both events was to suspend the startup and evaluate the problem. Following the November startup attempt, the licensee initiated an investigation and a reactivity management task force was formed. -An action plan was drafted to resolve issues in four areas; conduct of startups, procedures used during startup, determination of the root cause of the anomaly, and training. Approximately 50 action items were generated requiring resolution by either plant staff or corporate engineering (Nuclear Fuel Services, NFS).
Following the February ECC misprediction, the task force actions were extended to also resolve this event.
NFS was tasked to evaluate the events and determine the root causes.
Utilizing new 3-dimensional design methods to verify the current 2-dimensional code used at Byron, NFS concluded that reduced power operation contributed very little to the events and that there was no design deficiency in the current methodology. Ail differences seen between the two methods were expected. A portion of the 480 pcm deviation unaccounted for in the November startup attempt, was determined to be due to inaccuracies in power defect modeling and boron concentration.
"
p:m x
m
,
,
gy c W
.
4,h m t 7
,
fim,
,
U x
,
b
'
t E
_Burnup specific rod'worthjcurves were generated following the February.
'
'
P tstartup attempt. NFS determined that using the MOL-curves would have led
~
'
)to a closer ECC; however, a simple interpolation between the MOL~~and EOL curves would have given results almost identical-to the burnup spt.cific'
,
b t
data gener.ated.- It was 'noted that Dyron-procedures had not provided'for:
f, jinterpolating between rod worth curves, whereas,5NFS had assumed that this
>
option was :available when they had generated the cycle' specific set:of y
,
,
- cu rve s. -
,
k LThe fo11'owing briefly. summarizes the more significant actions which the
'
~
W[j licensee has taken or proposed to resolve the deficiencies identified during>the investigation of the.two events.
,
Ja.
' Review and revision of startup and ECC_ procedures to clarify and add-t guidance. The_ licensee planned to add guidance to the applicable-D
,
procedures for determining reference reactivity data points using
'
steady state _ conditions, and for interpolating between rod worth
[
curves.
Fl b.
"onsnunications. The licensee planned to enhance communications
.
between NFS and plant engineering to ensure understanding of i
curvebook information and how it is used. Technical exchange-meetings.between NFS and the Ceco PWR stations regarding reactivity =
l management.and nuclear / reactor engineering have been initiated, c.
Training. LThe licensee planned to revise and enhance the~ station
.
nuclear: engineer:(SNE) training program,'and include simulation
F
. training on reactor startups.~-The qualifications and duties of a-
?,
SNE would also be redefined,
'
Computer codes. A new on-line core monitoring system has or will-d, c
be installed a_t the Ceco PWR stations.
Implementation of this system will improve the accuracy 'of ECC' calculations. especially.
'du' ring' load following and reduced power operation.
Further, future 3-dimensional. reload design' methods will improve the accuracy of u
core'modeling.
'
. 5.
Conclusions
,
' The licensee's-inraediate actions to suspend the startups was conservativ~e.
.The safety significance of the~ two events was considered minor, since the C
approach to. reactor critical was conducted in a controlled manner.and no safety limits were approached. The licensee's investigation was extensive and thorough, and understanding of the issues was evident. Corrective p
' actions ltaken or planned should be effective in preventing further
problems in this area.
e s-
.
i
,
bra
..
.. --
.
. _... - - -. - -....
. - -
.
-
- ';..
- o
.
,,
?..
No violations were identified during the inspection. One previously identified open item tracking the resolution of'these events is p;
considered closed (455/09024-01(DRP)).
6.
Exit Meeting The-inspector met with the licensee representatives (denoted in Paragraph 1) on May 9, 1990. The-inspector summarized the scope and findings of the inspection, and the licensee acknowledged the statements made by the inspector. The inspector also discussed the likely informational content of the inspection report with regard to documents
.
or. processes reviewed by the inspector during the-inspection, and the licensee did not identify any such documents / processes as proprietary.
5