ML19329A304
| ML19329A304 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 08/30/1977 |
| From: | Grimes B Office of Nuclear Reactor Regulation |
| To: | Goller K Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8001020877 | |
| Download: ML19329A304 (4) | |
Text
(.,4k/A.4/ 5
,gi c
i AUG 3 01977 I
I MEMORANDlM FOR: Karl R. Goller, Assistant Director for Operating Reactors, 1
Division of Operating Reactors l
?
FR0ll:
Brian K. Grimes, Chief. Environmental Evalution Branch, DDR StBJECT:
REVIEW OF " SAFETY ASSESSilENT OF STEAM GENERATOR TtBE LEAK-AGE EXPERIENCED AT THE OCOMEE NtELEAR STATION," AUGUST,1977 t
We have reviewed the draft report (marked proprietary) submitted by Duke Fwer in response to some of the staff's cuestions regarding the consecuences ar steam generator tube failures concurrent with the LOCA or the main steam line j
failure accidents.
i I
A major portion of the report deals with the systems' response to the ev9nts l
(pressure and temperature histories, etc). The correctness of these calcu-I lations would have to be ascertained by the Plant Systems and Reactor Safety i
Branches. Most of the licensee's calculations acree with the assumptions that I
we have previously nade for the case of the steam line failure accident. Ma.ior differences are that they assume operator action after 10 minutes (i.e., operator i
j switches off the Safe ty injection system and starts controlled cooldown at 100 F/hr), but the primary to secondary leak is not stopped within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />.
However, the primary system ternperature reaches 212 F after 63 ninutes and 93 minutes for the cases of 10 tube failures and 1 or 3 tube failures, respectively.
j They do not estimate any additional fuel clr.d failure as a result of the accident.
even for the case of 10 tube failures.
The report uses a new iodine spiking model for calculating the iodine releases, i
but it is barely explained. The nodel appears to be based on four spikes ob-served at the Oconee plants, but they are not compared to spikes observed at i
other plants nor is the probability of occurrence of a larcer spike at the Oconee units discussed. The expression given on page 12 for the reactor coolant activity as a function of time is erroneous.
It is our recommendation that they j
present their proposed iodine spiking model in a separate report which.could be
{
reviewed as.an independent effort.
I Finally, the results given on page 14 are based on the unjustified assumption i
that only 10% of the activity in the primary to secondary leakaoe is released to the environment. Everything else the same, but assuming that 100% of the activity is released to the environment, the results are 2110 C1, 2172 C1, and 1094 Ci for the cases of a steam line failure and 1, 3 and 10 tube failures, l
respectively. Such releases could lead to offsite exposures on the order of 250 rem thyroid for the Ocenee site. A larger fractional release over a two hcur period would not be unlikely for the system described.
i f
I.
f l
}
contact:
H. Fonteci lla L-l l
- "'c=*
--x28066 772210M4
(
ouna.us 7
.s.
m 3
NRC FORM SIS (9 76) NRCM 0240 W ua s. oovannusur eninvine orreces sere-eas.ead
.--877
o AUG 8 01977 K. Goller ;
I l
{
The licensee was asked to provide analyses of the probability of tube fail-ures following a LOCA and steam line failure accidents and of these accidents j
occurrir!g following shutdown because of identified tube leaks. Theybave not i
perfomed the former on the basis that the consecuences (considered bounded by their analysis) are sufficiently low not to warrant any additional effort.
The report does include an estimate of the probabilities of a stean line failure or LOCA during the shutdown period following detection of a leak.
A cursory review of their calculations show the probability of these sequences 4
of events to be reasonably low.
Enclosed is a list of questions which I suggest be addresseti to the licensee.
r I
Ortdnni Siped by Brian K. Grimes Brian K. Grimes, Chief Environmental Evalution Branch Division of Operating Reactors As stated DISTRIBUTION :
CC:
V. Stello Central Files.
O. Eisenhut EEB/D0' Reading OT BC's J. Guibe.t i
D. Bunch D'. Neighbors B. Grimes L. Barrett E. Adensam H. Fontecilla s
'r t
i 6
3
-N I
l i
l s
l l
l l
t l
}
orrie s >
EEB/OT/ DOR FE d DOR,,
L IW95tSc4}b -
E. AdeAsam BC, i
h771 -i 8/?fj/77 8/JJ/77
(
,, s I
wac romu sis <97s3 deu a24e
- ui
.ov e.....,,.,=,.. or ric a.. 7. -.. a L.
QUESTIONS ON DRAFT REPORT SAFETY ASSESSMENT OF STEAM GENL ATOR TUBE LEAKAGE EXPERIENCED AT THE OCONEE NUCLEAR STATION, AUGUST,1977 1.
It is stated that switching off the safety injection is conservative because it results in minimum dilution.
Explair, the effect of delay-ing this action. The concern is that continuation of the safety injection will keep the system press *e at a higher level and would result in higher releases, in spite of the increased dilution.
This appears to be particularly important for the cases of 1 and 3 tube failures for which the leak rate is calculated to be increasing at a high rate at the time that the safety injection is switched off.
The time for operator action should be considered as a variable over a range of values.
2.
The iodine spiking model presented in Appendix A needs to be discussed in more detail, preferably as a separate report.
Explain why the model proposed is considered to be conservative.
In particular, estimate the probability of a spike exceeding the model occurring at the Oconee plants.
Compare these spikes with those observed at other plants and explain differences in the phenomena causing the spike which allow other data to be disregarded. Present an analysis using a correlation derived from all spiking data available.
t
?
..~
2-3.
The expression given on page 12 to calculate the reactor coolant activity as a function of time appears to be incorrect.
Indicate how it was derived and assumptions made.
4.
The assumption is made that only 10% of the iodine contained in the primary to secondary leak is released to the environment.
j Explain where the remainder of the iodine is expected co be as a function of time, in view of the fact that the steam generator is assumed dry.
l
{
I i
l l
t p..
l^