SEPA Issues Variation Notice to
Rosyth Royal Dockyard
Issued on 22 December 1997 - Ref 46/97

SEPA has issued a variation notice to Rosyth Royal Dockyard which changes the limits in the Company's authorisation to dispose of liquid radioactive waste by pipeline into the Firth of Forth. The changes take effect from 19 December 1997.

The variation notice has halved the maximum allowable discharge of cobalt-60 and, at the same time, increased the limit on the radiologically less significant radionuclide tritium by a factor of four. The radiological differences between the two radionuclides are such that the overall effect of this change is to reduce the maximum possible dose received by the most affected members of the public by 50%.

The variation notice also imposes additional reporting requirements on the Company in the event of accidental discharges or the discovery of unusual environmental monitoring results.

SEPA believes that this change demonstrates its commitment to a downward trend in permitted discharges of radioactive materials to the environment (the cobalt-60 limit has already been reduced by SEPA in April 1996 from 55GBq/year to 10GBq/year). The increase in tritium has only been permitted after assessment of the environmental consequences of the release, both by the Company and independently by SEPA, and after consultation with various public bodies, the Secretary of State for Scotland and the Nuclear Installations Inspectorate.

ENDS

Note to Editors

1. Discharges of radioactive waste into the environment are regulated under powers of the Radioactive Substances Act 1993. No person may discharge radioactive waste without an authorisation granted by the enforcing authority (SEPA in Scotland) under Section 13 of RSA 93.

2. The two radionuclides referred to in the press release are quite different in nature:

Cobalt-60 is a relatively energetic gamma ray emitter whereas tritium is a weak beta emitter. The radiological significance of these two radionuclides can be expressed in terms of the damage done per unit intake. Although these effects can be measured in many different ways, one common approach, based on dose received by ingestion, indicates that cobalt-60 is 190 times more potent than tritium.

Cobalt-60 and tritium are formed in nuclear reactors on board submarines. Tritium is also produced naturally.

The radiation produced by tritium does not give rise to a radiation dose unless ingested. The radiation from cobalt-60 is more penetrative and can give rise to a radiation dose following ingestion or proximity.

3. As well as the difference in radiological effect, the two radionuclides behave quite differently in the environment. Tritium becomes rapidly dispersed and diluted to near background levels in the large volume of water in the Firth of Forth, whereas the cobalt-60 tends to be absorbed onto silt particles, and can therefore be found in sediments. It is this behaviour coupled with both the pathways by which people might come into contact with these substances and the radiological effects that accounts for the large difference in radiological significance.

4. It must be stressed that even though cobalt-60 is the most radiologically significant radionuclide in Rosyth effluent, the environmental and radiological impact of discharges of this radionuclide from Rosyth are extremely small.

SEPA Press Office contacts

Press Officer: Maggie Hamilton. Tel: 01786 457724 Mobile 0370 686073
Head of Public Affairs: Monica Straughan. Tel: 01786 457723 Mobile 0421 942498

SEPA Head Office, Erskine Court, The Castle Business Park, STIRLING FK9 4TR
Tel: 01786 457700 Fax: 01786 448040

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© SEPA 1997