ML19309A580
| ML19309A580 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 03/01/1980 |
| From: | Novak T, Rubin M Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| NUDOCS 8003310453 | |
| Download: ML19309A580 (4) | |
Text
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,... -. x UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION z.
BEFORE THE ATOMIC S AFETY AND LICENSING BOARD In the Matter of
)
Sacramento Municipal Utility District
)
(Rancho Seco Nuclear f
Docket No. 50-3L2 (SP)
Generating Station
)
NRC STAFF TESTIMONY OF MARK P. RUBIN AND THOMAS M. NOVAK REGARDING THE DESIGN BASIS FOR RANCHO SECO SAFETY SYSTEMS (CEC C0"TE".TIOWS 1-1 and 1-12)
Q.1 Pleas
- state your name and positi0n with the NRC.
A.
My name is Mark P. Ruoin. I am an employee of the U.S. Nuclear Regulatory Commission assigned to the Reactor Systems Branch, Division of Systems Safety, Office of Nuclear Reactor Regulation. However, from June through December, 1979, I was assigned to the Bulletins and Orders Task Force, Office of Nuclear Reactor Regulation.
My name is Thomas M. Novak. I am an employee of the U.S. Nuclear Regulatory Commission assigned to the Reactor Systems Branch, Division of Systems Safety, Office of Nuclear Reactor Regulation. However, f rom June through December, 1979, I was assigned as the Cecuty Director of the Bulletins and Orders Task Force, Office of Nuclear Reactor Regulation.
Q !
Have you prepared a statement of professional qualifications?
Yes, A copy of our statements is att ted to this testimony.
s..
l l
Q.3 Please state the nature of the resconsibilities that you have had with respect to the Rancho Seco Nuclear Generating Station.
A.
The accident at Three Mile Island Unit 2 (TMI-2) on March 28, 1979 involved a feedwater transient coucLed with a small break in the reactor coolant i
system. Because of the resulting severity of the ensuing events and the 8093310 Uh T ill ! U K N M -
. potential generic aspects of the accident on other reactors, the NRC staff initiated prom:t action to:
(L) assure that other reactor Licensees, particularly those plants such as sancho Seco which have a snitiar design to TMI-2, took the necessary actions to suestantially reduce the likelihood of future TMI-2-type events trem occurring, and (2) start comprehensive investigations into the potential generic imolications of this accident on other operating plants. To accomclish some of this work, the Bulletins and Orders Task Force (S&OTF) was established within the Office of Nuclear Regulator Regualtion (NRR) in May 1979. The B&OTF was responsible for reviewing and directing the TMI-2-related staff activities associated with Loss of feedwater transients and smaLL breakloss-of-coolant accidents (LOCAs) for aLL operating plants to asssure their continued safe operation.
The initial priority of the B&OTF was placed on evaluating the actions taken by the B&W operating plant Licensees in resconse to the Confirnatory Shutdown Orders issued in May 1979. We were assigned to the Task Force in mid-June 1979. Upon assuming those positions, we participated in the final preparation of the Staff. Safety Evaluation which documented our evaluation of SMUD's compliance with the immediate requirements of the May 7, 1979 Order. On the basis of this report, issued on June 27, 1979, the Rancho Seco Facility was authorized to return to power operation.
Q.4*
What it the purpose of your testimony?
A.
The purpose of our testimony is to rescend to California Energy Commission Issues 1-1 and 1-12 which read:
1-1 "Descite the modifications and actions of suoparagraphs (a) througn (e) of Sections IV of the Commission's Order, wiLL reliance uoon the High Pressure Injection System to mitigate pressure and volume control sensitivities in the Rancho Seco Primary system result in increased challenges to safety systems beyond the original design and Licensing basis of the facility?"
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- F' o o N gA li AJ o
=
,-.. 1-12 "Despite or because of the modifications and actions of Subparagrachs (a) througn (e) of Section IV of the Ccomission's Order of May 7,
, iLL Rancho Seco excerience an increase in reactor trips resulting w
from feedwater transients that wiLL increase challenges to safety systems beyond the original design and Licensing basis of the facility?"
Q.5 Have the actions of the May 7 Order resulted in increased challenges to safety systems, an increased numcer of reactor trips, or an increased actuation of the high pressure injecticn system?
A.
Probably yes.
G.6 If so, describe the nature of that increase.
A.
A review of the coerating history of S8'd plants indicates the cresence of some reactor trips and actuations of the reactor protection system which probably would not have occurred prior to the modifications of the May 7 l
Order. Therefore, the evidence does succort the hypothesis that the frequency of reactor trics and safety system actuation has increased.
This effect accears to largely be due to the lowered hign pressure reactor trip set coint and anticicatory trip system. A study submitted by the Midland plant reports that while the trip frequency has increased, there is not an excessive increase. The limited data base shows the trip frequency increased from 0.56 to 0.65 cer month. This is in agreem.ent with staff observations; however, i* should be noted that the staff has not performed a detailed statistical stuoy of post-TMI trip frequency and post-TMI operating ex=erience is Limited, so it is not possible to arrive at definitive findings.
Since there has been an increase in reactor trips, an increase in HPI actuation is also likely.
l Q.7 If an increase in challenges to the safety system, and increase in number l
of high pressure injection actuations and reactor trips has taken place, i
are these events beyond the original design and Licensing basis of the l
facility?
A.
No.
1 D"D R O Tyn 1k m
i Of 3
1
g-24-Q.3 If not, provide the basis for that answer.
A.
Plant, events such as reactor tries, high pressure injection initiation, and other safety system resconses are of interest inasmuch as they subject the reactor coolant pressure boundary to various levels of thermal stress.
During a reactor tric, or safety injection oceration, temperature changes take place in the reactor coolant pressure boundary. Due to material procerties of the ciping system and other structures, these temperature changes cause thermal stresses to occur. During the course of the Rancho Seco design, certain criteria were established for the allowable number of clant transients whi:n would result in thermal cycles and stress on the reactor coolant 3ressure boundary. These criteria are detailed in oesign information sucolied to the Rancho Sece ocerating staff. These reports describe how many transients of each category are allowed for in the basic plant design and include such clant responses as reactor tric and high pressure safety injection.
i An increased number of reactor tries, high pressure injection, or other safety system injection is acceptable to the staff, as long as the design criteria in regard to thermal stress cycling are not violated. At present, none of the thermal cycle limits have been accroached. During the course of plant oceraticn, all events and ocerating conditions are monitored and recorded to assure than an accurate account is being maintained regarding the thermal cycling and stresses to which Rancho Seco has been subjected. If at some time in the future the acclicant believes that the limits for thermal cycles and stress for any events (including trips and safety 3ystem actuation) will be exceeded, it is expected to notify the staff. At that time, before any limits are exceeded, the staff will l
determine what additional analysis or plant modifications are recuired to assure that continued coeration will not violate the plant's design basis.
In addition to the safety concern on thermal stress, a concern may exist that the increased challenges to the safety systems may degrade their performance and reduce the availability of these systems. This concern l
is considered since these safety systems are subjected to periodic testing ano maintenance to assure that they are cacacLe of cerforming their functicn l
when required.
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