ML19317G084
| ML19317G084 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 05/07/1975 |
| From: | Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| Shared Package | |
| ML19317G075 | List: |
| References | |
| NUDOCS 8002210776 | |
| Download: ML19317G084 (3) | |
Text
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SACRAMENTO MUNICIPAL UTILITY DISTRICT C 1708 59th Street. Box 15830. Sacramento. California 95813:(916)452 3211 May 7, 1975 Director Division of Reactor Licensing U.S. Nuclear Regulatory Commission IJashington, D.C.
20545 Re: Operating License DPR-54 Docket No. 50-312 Rancho Seco Nuclear Generating Station Unit No. One Abnormal Occurrence No. 75-8
Dear Sir:
ll As defined by Proposed Amendment No. 30 to Technical' Speciffcations for the Rancho Seco Nuclear Generating S'tation, Section 6.9.1 and Regulatory Guide 1.16, Rev. 3, Section C,2.a.(1), we are reporting the following Abnormal Occurrence as A0 75-3 (m
)
On April 29, 1975 Babcock and tiilcox Company informed SMUD that during a review of the Reactor Protection System (RPS) setpoints for Rancho Seco v
Unit No. One, an error was found in the positive imbalance portion of the trip envelope as defined in Technical Specification 2.3 for flux / imbalance /
flow. The calculations were being reviewed to deternine consistent setpoints for a RPS-II module to be placed in service at the Rancho Seco site.
This situation existed as the result of misreading one point of'the
/
" offset versus power" limits during the conversion of the," core axial offset" to " core axial imbalance". Thus, the corrected positive imbalance limit (with the appropriate instrumentation and calibration errors included) now falls inside the positive imbalance, limiting safety system settings presently defined in the Rancho Seco Technical Specifications.
The portion of the protection envelope affected protects the unit against steady state positive imbalance conditions which could result in y_
centerline fuel melting.
At the time B&'i notified SMUD of this situation they provided a recommended set of interim settings for the RPS which significantly restricted allowable positive imbalance. They have now provided the final set of corrected settings for the positive imbalance portion of the flux / imbalance /
flow trip envelope. The following table shows the original settings as given in FSAR Table 7.1-3 and modified by the " interim" and " final" corrected values.
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l May 7, 1975 Director Division of Reactor Licensing Parameter Boundary Values FSAR Interim Final M
+0.906 No C,hange No Change 7
M
-1.230
-2.85
-2.03 2
B
-40.0%
No Change No Change 1
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B
-17.1%
No Change No Change j
2 a,
B
+7.74%
.No Change No Change 3
B
+40.0%
+20.0%
+25.0%
4 s
As can be seen above. the interim flux / imbalance / flow envelope represents the most restrictive RPS settings. The Operational Power Imbalance envelope de--
fined in Technical Specification Figure 3.5.2-2 lies entirely within the interim-RPS settings. During.the extensive power escalation' test program and normal operation to date, the core has never been operated with positive imbalances exceeding the " Operational Power" envelope.
In fact, the largest positive,
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imbalance observed was as a result of the return to power done for the " Pseudo Dasign Transient" and is fully reported in our " Performance Report" of '
March 1975. That.value was slightly less than +10% Imbalance at 82% full During steady state power the imbalance follows inserted controlling power.
rod group position, giving nominal values of 0 to -5% Imbalance.
[
. In summary, B&W informed SMUD of the error in the Rancho Seco Tech-nical Specifications limiting safety system settings immediately upon deter-mination that an error did exist.
"A very conservative interim positive im-balance limit was recommended to SMUD and installed in the RPS that same day,
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af ter review and administrative approvals had been obtained. Upon formal receipt of the " final" settings SMUD will install them in the RPS,-after At i
again reviewing and obtaining'the necessary administrative approvals.
no time during the operation and testing of Rancho Seco Unit No. One has the positive imbalance Operational Limit been exceeded; thus, even the
" interim" settings have never been reached.
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Director May.7, 1975 l-Division of Reactors Licensing 3
I There~was no reactor transient associated with this occurrence.
Respectfully, i
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.' 'Mattimoe Assistant General Manager and Chief Engineer r,F i-cc:
R. H. Engelken, Region V h
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